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exhaust gases in coolant


winterset

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I have never opened up my coolant system on my N*, but I have seen several people have issues with overheating.

Seems the statementis "super heated" gases enter the coolant and cause the engine too overheat.

My statement and suggestion are as follows:

Is it just a tiny leak that is causing a small amount of air into the block when it is not pressurized enough to keep exhaust air from entering the coolant system. In other words - the car is cool, and exhaust gas enters the block, and reaches the top of the thermostat where (it being closed because it's cold), does not allow it to exit. As such, because of the air pocket, the thermostat never opens. - If that's what is happening, it's a shame that because the equivalent of possibly one cup of air, it will cause a motor to overheat.

Seems thermostats don't have a bleed hole to purge out that little bit of air that will allow the thermostat to open once it reaches it's operating temperature. What finally happens is that the engine legitamely overheats spewing either hot or cool coolant out of the everflow tank - and onto the street.

Seems a solution will be to drill a 1/8 bleed hole in the thermostat housing that will allow the air bubble to travel out of the block up to the top of the radiator and as the system gets pressurized, these tiny exhaust bubbles will just exit & cause no harm. - even at the worst case, and the exhaust leak continues, the air will continually get purged. What is required is that the thermostat stayes immersed in coolant, so it keeps the enine at a constant temperature. (getting the air out also allows more coolant to flow in keeping the block uniformly cooled).

Aluminum unlike a steel block has an expansion rate 4-5X that of steel at 200 degrees, and increases as the temperature increases. Because of the air, the cars temperature gauge may also be reporting the incorrect temp for some time, allowing the block and gaskets to expand and contract more than designed.

Not sure if anyone ever tried to drill a 1/8 hole in their thermostat to allow the air to purge. Of course this will not solve anything if oil & coolant are mixing.

I'm open to comments - even someone telling me it's nonsense!!

Edited by winterset
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I believe that your interpretation of the mechanism of overheating is accurate for some instances of overheating in the early and middle stages of head gasket failure. The overheating that mimics a plugged bypass are an example, where air or cool water at the thermostat prevents the heated water from reaching the thermostat. The classic first-overheat instance where a highway passing maneuver is followed about 30 seconds later by a temperature spike is an obvious example. The bubble might need to be large enough to unload the water pump to cause this.

I do believe that a small air relief hole in the thermostat would help. I don't recall whether mine has one or not, but I do believe that there is one, and it has a tiny check valve in it. Drilling another hole would help pass a steam pocket.

The problem is that this treats the symptom. Once you start having head leakage, it will get slowly worse until the car becomes un-driveable. Reducing the overheating might or might not slow the process; the torque-and-twist head bolts on the Northstar stretch as the block expands and after cooling down everything is back as it was, so I'm not sure that overheating accelerates the process, unless the head gasket does *not* expand with overheating or some other mechanism is in play. The head leakage itself becomes the eroding force that makes the head gasket leakage increase over time.

I was told my my mechanic who first verified my head leakage with a pressure test that I could drive it for another year; he was unaware of my daily high-speed commutes that were nearly impossible by then. In such cases drilling a hole in the thermostat might help to postpone the repair until you could schedule it at your convenience - if you don't need the car for high-speed highway use.

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Thanks Jim for contributing. I guess the question now is if the thermostat already has a bypass hole? (although I don't believe this is done anymore) Yes, air pumping into coolant is definately an issue that will eventually need to be delt with, and anyone that uses their N* on high speed runs should beware. I was thinking of this possible solution more for someone that has the car for short local trips etc. I would say that if you have a car where the temperature spikes then resumes on acceleration, the HG is definately getting stressed, and will eventually leak oil, coolant, and gases everywhere.

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Drilling a hole in the thermostat is not going to help the situation. The system has a purge line that purges any air from the system. This is the first thing to check if the car is overheating.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Is it located before or after the thermostat. I'm not sure how the N* cools. - or even how a purge line works.

I am saying the air needs to get past the thermostat and flow to the highest point (radiator cap), where after approx 16 psi, the cap will release the excess pressure (and release the air). the water pump will suck the water in from the bottom hose & cool the engine, so the excess air on top will not affect cooling.

If someeone with a minor leaking HG, will the purge line expell the air on it's own, or would the bolt need to be opened manually?

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Is it located before or after the thermostat. I'm not sure how the N* cools. - or even how a purge line works.

I am saying the air needs to get past the thermostat and flow to the highest point (radiator cap), where after approx 16 psi, the cap will release the excess pressure (and release the air). the water pump will suck the water in from the bottom hose & cool the engine, so the excess air on top will not affect cooling.

If someeone with a minor leaking HG, will the purge line expell the air on it's own, or would the bolt need to be opened manually?

It will expel the air on its own - the surge tank cap is the highest point in the system and the purge line leads to the top of the surge tank. A minor headgasket leak will cause swings in the temp gage but it will not overheat. When it gets bad enough, it will overheat due to the exhaust gasses superheating the coolant.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I can see this working and will have more info to do this being that I am (Lucky?) to have a car in this situation. Very early stages of a hg. Went an hour each way on highway to the city and back did not over heat. Preashure test and eghaust gasses in coolant show hg. Other very random spikes in water temp due to thermostat staying closed. For the first time when it overheated knowing more about the system I wfelt the hoses. Hose going into thermostat was cold along with that side of the radiator. The other hose leaving the engine was very hot with the coolant boiling. The 2 hoses ging in and out of heater core were very cool (Explains the no heat comming from vents) The heat was on and was blowing hot ahead of time.

This was after pulling a hill and water level was a little low for a couple days. You see when the thermostat finally opens up the heater hoses get hot along with the hose going into the thermostat and that side of the radiator due to the water leaving the engine and circulating through the rad. Heat vents blow hot in the car and as soon as that happens I know i am good to go no matter if I am on a hill pushing it or not the temp will go down to 12 O-clock. WHen I get some time from putting the midget together I will get around to taking the thermostat back out and drilling a hole in it. Or maby drill a hole in the old one I still have that I will check if it works. The new one didn't seem t make a difference.

Just got a laser temp gun so I will record more quantitative info for everyone. I am in no way saying I am not going to fix the head gasket just want to make the wait till spring a little more comfortable.

Edited by sprinter10
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The problem is not the presence of air in the system but the exhaust gasses superheating the coolant resulting in overheating. Drilling a hole in the thermostat will not solve that.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Thanks KHE. Sprinter, It would be great if you do have an opportunity to try this out. Not sure how easy it is to change the Thermostat on a N*. Seems for the N*, GM did put the provision to automatically bleed air from the system. - & I understand it was not the intention to have it bleed exhaust gases. I am still hopeing someone can tell us if the OEM thermostat does have that bleeder hole in it. Since the N* is not a conventional engine I am not sure this will still work. If the air gets past the thermostat, will it get to the surge tank thru the bleeder, or will it float up and cause an air bubble in the radiator?

Again, I don't want to question anyones knowledge, just looking to possibly have an option for someone to get a little bit more out of their car and/or prevent a catastrophic failure on a weak HG.

BTW, I now have Verizon Wireless 4G/LTE as my mobile internet provider & I love it. Much better than 3G/EVDO!!

Today is my first time using it for caddyinfo.com

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There is a small spring loaded valve designed into the OEM thermostat. All bets are off the table if a generic aftermarket thermostat is involved.

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Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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There's another interesting phenomenon that we need to understand that is happening with early HG failures. The HG leakage generates a pocket of gas that is mostly steam. When it is big enough to unload the water pump before it is bled off into the surge tank, we see a temperature spike. This may or may not generate more steam that blows out coolant, but when the thermostat does open the steam pocket goes into the radiator - where the stem condenses back to water. This causes a contraction of the coolant volume.

Possible results of this are reduction of the cold water back into the block and heads, which would extend the temperature spike if the water pump was still unloaded, or suddenly terminate the temperature spike if the water pump was engaged. If the volume of the steam pocket exceeded the reserve volume of the surge tank, coolant would be lost in the incident. This pretty much describes the early symptoms of HG failure.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Looking at the picture of the thermostat I see the hole and reamember the one I got from advance having it too it has a stopper maby check valve? When egine is running it looks like it won't blead the air out because the preashure of the water will be up agaist the stopper from the water pump but if you shut the engine off the air could possibly then bleed out through the hole. I wonder wheather that should be up down left right etc when placed in the car. I thought this when I was putting my thermostat in but didn't do anything about it. As for changing the thermostat it is not to bad. Air box, airfilter, upper and lower plastic splash gaurds on car. then just remove 2 screws and the hose.

35457_473821089241_637739241_5575548_5370195_n.jpg

Here is a bad picture of where the thermostat is located. It is on the inlet side of the cooling system on the engine.

As for what causes the engine to overheat when a bad HG is present There are prob. different ways for different conditions. As for me sofar mine is deff due to the thermostat sticking closed no if and or buts. When it opens I can do a wot run when I am shure the heads are pushing a ton of gas out the HG but it won't over heat until temp fully drops and thermostat closes again. After it is closed then the cycle of an air pocket building up there and not letting it open can happen again. If that makes any sense. Its hard to fully explain my experiences over the computer.

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Looking at the picture of the thermostat I see the hole and reamember the one I got from advance having it too it has a stopper maby check valve? When egine is running it looks like it won't blead the air out because the preashure of the water will be up agaist the stopper from the water pump but if you shut the engine off the air could possibly then bleed out through the hole. I wonder wheather that should be up down left right etc when placed in the car. I thought this when I was putting my thermostat in but didn't do anything about it. As for changing the thermostat it is not to bad. Air box, airfilter, upper and lower plastic splash gaurds on car. then just remove 2 screws and the hose.

35457_473821089241_637739241_5575548_5370195_n.jpg

Here is a bad picture of where the thermostat is located. It is on the inlet side of the cooling system on the engine.

As for what causes the engine to overheat when a bad HG is present There are prob. different ways for different conditions. As for me sofar mine is deff due to the thermostat sticking closed no if and or buts. When it opens I can do a wot run when I am shure the heads are pushing a ton of gas out the HG but it won't over heat until temp fully drops and thermostat closes again. After it is closed then the cycle of an air pocket building up there and not letting it open can happen again. If that makes any sense. Its hard to fully explain my experiences over the computer.

I completely understand what you are saying. so when the car cools, any air trapped under the stat will escape out the relaxed tstat bleed valve & then out to the purge tank. So the first cycle that the stat closes to warm the block again is when the air will form under the stat, but because the way the "unpressure bleed only" valve on the stat works, it will not open again because of the pressure. If it were just an unconditional hole, the air will always be allowed to escape out the purge valve, and the stat will always be able to get the actual temp of the coolant, and open so it will not overheat. also it will always allow the air to escape out to the purge tank. Also what you are saying is that if you run the car really hard that the stat has to stay open to keep the engine cool, the air will always have a way out of the block to the purge tank.

The small hole will of course slow down the warm up time on the car a little, but if it helps the overheating it'll be worth it. I can't imagine it having too much of an impact on warmup time, or preventing the car from reaching normal operating temperature.

Again, because of the air, I wouldn't believe the temp reading on the dash is accurate. there are probably hot spots that if we know the real temp, we'd feel ill. so many are thinking the car is running at 220 or so, but because of air, the stat opens up a little later where portions of the heads could be much hotter. The self purging system bleeds out the air, so it does not build up over time & explode out. - this can also kind of hide a minor leaking HG.

I can only believe that these hot spots caused by unknown air pockets over time can definately stretch an aluminum block & heads, and stretch the bolts, and eventually completely blow the head gaskets on an engine that can otherwise process a little exhaust air in the coolant. Again, I'll go out on a limb and say that the exhaust "air" that prevents the stat from accurately getting the temp of the hottest point of coolant in the block over time will lead to wild some wild stretching that no gasket can over time survive.

Seems the worst case for the N* is the unclamping of the heads - which can be called "stage 2" of a little air in the coolant when it's unknown and/or not addressed - where of course the engine will need to be broken down.

sprinter, your mission if you choose to accept is to help us verify this wild thinking. :)

BTW, I would think the hole should be up since air travels up in water.

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Is it located before or after the thermostat. I'm not sure how the N* cools. - or even how a purge line works.

I am saying the air needs to get past the thermostat and flow to the highest point (radiator cap), where after approx 16 psi, the cap will release the excess pressure (and release the air). the water pump will suck the water in from the bottom hose & cool the engine, so the excess air on top will not affect cooling.

If someeone with a minor leaking HG, will the purge line expell the air on it's own, or would the bolt need to be opened manually?

Air would get past the stat when it opens no? Air will rise to the highest point of the cooling system, that being the bolt with a hole in it, and then it will be pushed out into the tank.

Keep in mind that air rises and it will get to the high point in the system, which is the bolt with a hole in it.

The head gasket leak is leaking super heated gases into the cooling system, that is the biggest problem, the heat, not necessarily the gases. Getting the gases out is insignificant once the head gasket is breeched

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Looking at the picture of the thermostat I see the hole and reamember the one I got from advance having it too it has a stopper maby check valve? When egine is running it looks like it won't blead the air out because the preashure of the water will be up agaist the stopper from the water pump but if you shut the engine off the air could possibly then bleed out through the hole. I wonder wheather that should be up down left right etc when placed in the car. I thought this when I was putting my thermostat in but didn't do anything about it. As for changing the thermostat it is not to bad. Air box, airfilter, upper and lower plastic splash gaurds on car. then just remove 2 screws and the hose.

Here is a bad picture of where the thermostat is located. It is on the inlet side of the cooling system on the engine.

As for what causes the engine to overheat when a bad HG is present There are prob. different ways for different conditions. As for me sofar mine is deff due to the thermostat sticking closed no if and or buts. When it opens I can do a wot run when I am shure the heads are pushing a ton of gas out the HG but it won't over heat until temp fully drops and thermostat closes again. After it is closed then the cycle of an air pocket building up there and not letting it open can happen again. If that makes any sense. Its hard to fully explain my experiences over the computer.

You think your overheating due to a bad HG is due to the thermostat sticking closed? Absolutely NOT

If you have a bad head gasket, you are overheating due to the bad head gasket NOT because of a thermostat, superheated gases enter the cooling system causing boiling and heating the coolant

IF you have a sticking thermostat, and we have seen them stick, REPLACE the STAT, but they just dont stick UNLESS they are bad, they dont stick because of bad head gaskets.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Is it located before or after the thermostat. I'm not sure how the N* cools. - or even how a purge line works.

I am saying the air needs to get past the thermostat and flow to the highest point (radiator cap), where after approx 16 psi, the cap will release the excess pressure (and release the air). the water pump will suck the water in from the bottom hose & cool the engine, so the excess air on top will not affect cooling.

If someeone with a minor leaking HG, will the purge line expell the air on it's own, or would the bolt need to be opened manually?

Air would get past the stat when it opens no? Air will rise to the highest point of the cooling system, that being the bolt with a hole in it, and then it will be pushed out into the tank.

Keep in mind that air rises and it will get to the high point in the system, which is the bolt with a hole in it.

The head gasket leak is leaking super heated gases into the cooling system, that is the biggest problem, the heat, not necessarily the gases. Getting the gases out is insignificant once the head gasket is breeched

Yes, that's what we are saying. air passes thru the tstat when it opens - but once it closes, air will no longer gets past it. I believe the bolt hole is after the tstat - or in a position where it is not directly above the tstat. On early stages, it is really not "super heated gas, but just a few bubbles of hot gas that immediately gets cooled by the coolant. The problem is that it never allows the tstat to open, thus becoming hot gas along with super heated coolant. If the tstat had a way to keep that little bit of air flowing up top, it should be OK.

I have read people saying "when I make sharp right turns the car cools down" - it's not a mystery at all, it is just the hot coolant splashing up opening the tstat enough to get the air up & out.

Also, once the system is allowed to get hot & stay hot & pressurized, the gases have a tougher time getting into the coolant passages.

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Looking at the picture of the thermostat I see the hole and reamember the one I got from advance having it too it has a stopper maby check valve? When egine is running it looks like it won't blead the air out because the preashure of the water will be up agaist the stopper from the water pump but if you shut the engine off the air could possibly then bleed out through the hole. I wonder wheather that should be up down left right etc when placed in the car. I thought this when I was putting my thermostat in but didn't do anything about it. As for changing the thermostat it is not to bad. Air box, airfilter, upper and lower plastic splash gaurds on car. then just remove 2 screws and the hose.

Here is a bad picture of where the thermostat is located. It is on the inlet side of the cooling system on the engine.

As for what causes the engine to overheat when a bad HG is present There are prob. different ways for different conditions. As for me sofar mine is deff due to the thermostat sticking closed no if and or buts. When it opens I can do a wot run when I am shure the heads are pushing a ton of gas out the HG but it won't over heat until temp fully drops and thermostat closes again. After it is closed then the cycle of an air pocket building up there and not letting it open can happen again. If that makes any sense. Its hard to fully explain my experiences over the computer.

You think your overheating due to a bad HG is due to the thermostat sticking closed? Absolutely NOT

If you have a bad head gasket, you are overheating due to the bad head gasket NOT because of a thermostat, superheated gases enter the cooling system causing boiling and heating the coolant

IF you have a sticking thermostat, and we have seen them stick, REPLACE the STAT, but they just dont stick UNLESS they are bad, they dont stick because of bad head gaskets.

I do not believe that is what Sprinter is seeing. his thermostat is opening normally. it's until it closes where it will never open again. as he says if he keeps riding the car hard - thus keeping it open, it will not overheat. If you have an engine that is in the earliest stage where it is bubbling a little air into the coolant, once a condition exists where one hose is hot & the other is cold, you will soon be expelling super heated air & super heated coolant into the overflow tank.

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Looking at the picture of the thermostat I see the hole and reamember the one I got from advance having it too it has a stopper maby check valve? When egine is running it looks like it won't blead the air out because the preashure of the water will be up agaist the stopper from the water pump but if you shut the engine off the air could possibly then bleed out through the hole. I wonder wheather that should be up down left right etc when placed in the car. I thought this when I was putting my thermostat in but didn't do anything about it. As for changing the thermostat it is not to bad. Air box, airfilter, upper and lower plastic splash gaurds on car. then just remove 2 screws and the hose.

Here is a bad picture of where the thermostat is located. It is on the inlet side of the cooling system on the engine.

As for what causes the engine to overheat when a bad HG is present There are prob. different ways for different conditions. As for me sofar mine is deff due to the thermostat sticking closed no if and or buts. When it opens I can do a wot run when I am shure the heads are pushing a ton of gas out the HG but it won't over heat until temp fully drops and thermostat closes again. After it is closed then the cycle of an air pocket building up there and not letting it open can happen again. If that makes any sense. Its hard to fully explain my experiences over the computer.

You think your overheating due to a bad HG is due to the thermostat sticking closed? Absolutely NOT

If you have a bad head gasket, you are overheating due to the bad head gasket NOT because of a thermostat, superheated gases enter the cooling system causing boiling and heating the coolant

IF you have a sticking thermostat, and we have seen them stick, REPLACE the STAT, but they just dont stick UNLESS they are bad, they dont stick because of bad head gaskets.

I do not believe that is what Sprinter is seeing. his thermostat is opening normally. it's until it closes where it will never open again. as he says if he keeps riding the car hard - thus keeping it open, it will not overheat. If you have an engine that is in the earliest stage where it is bubbling a little air into the coolant, once a condition exists where one hose is hot & the other is cold, you will soon be expelling super heated air & super heated coolant into the overflow tank.

He said it was STICKING!, and drew the WRONG conclusion

Since the thermostat opens as a result of HEAT, why is is closing where it will NEVER open again? And if it is sticking it should have been replaced, its a no brainer job to replace.

The thermostat does NOT open due to coolant PRESSURE, it opens due to HEAT, so how its CLOSING is beyond me. His theory of driving it hard is wrong. If he thought he was UNSTICKING it by flooring it, that is wrong, plus it should have been replaced, if he badly overheated the engine in the past to eliminate a bad stat, for $23 and 30 minutes work its childs play to replace

If he is driving it hard and the temp is lowering its simply because he is turning the water pump faster

Try this experiment, drive 60, and watch your temp gage, it will be about say 205 or half way for those who do not have a digital gage.

Now drop your engine into 3 or 2 so that the engine turns higher RPMS, you will see the temp DROP, that is due to the water pump turning faster, it has NOTHING to do with the thermostat opening or staying open, you have increased the RPM thereby increasing the RPM of the water pump, thereby increasing water flow!

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Is it located before or after the thermostat. I'm not sure how the N* cools. - or even how a purge line works.

I am saying the air needs to get past the thermostat and flow to the highest point (radiator cap), where after approx 16 psi, the cap will release the excess pressure (and release the air). the water pump will suck the water in from the bottom hose & cool the engine, so the excess air on top will not affect cooling.

If someeone with a minor leaking HG, will the purge line expell the air on it's own, or would the bolt need to be opened manually?

Air would get past the stat when it opens no? Air will rise to the highest point of the cooling system, that being the bolt with a hole in it, and then it will be pushed out into the tank.

Keep in mind that air rises and it will get to the high point in the system, which is the bolt with a hole in it.

The head gasket leak is leaking super heated gases into the cooling system, that is the biggest problem, the heat, not necessarily the gases. Getting the gases out is insignificant once the head gasket is breeched

Yes, that's what we are saying. air passes thru the tstat when it opens - but once it closes, air will no longer gets past it. I believe the bolt hole is after the tstat - or in a position where it is not directly above the tstat. On early stages, it is really not "super heated gas, but just a few bubbles of hot gas that immediately gets cooled by the coolant. The problem is that it never allows the tstat to open, thus becoming hot gas along with super heated coolant. If the tstat had a way to keep that little bit of air flowing up top, it should be OK.

I have read people saying "when I make sharp right turns the car cools down" - it's not a mystery at all, it is just the hot coolant splashing up opening the tstat enough to get the air up & out.

Also, once the system is allowed to get hot & stay hot & pressurized, the gases have a tougher time getting into the coolant passages.

When the engine is at operating temp, the stat is always OPEN, it never closes 100%, it might range from 50% open to 100% open during your drive to maintain its rated temp but its NEVER 0% at operating temp open when you are driving your car. It is 0% when you start out. At its rated temp it is 100% open.

Try an experiment, Take a stat, get a thermometer, suspend it in a pot of hot water, and watch the stat as the temp increases and decreases, it will never close at 195 or 190 (whatever the spec is) degrees, heat keeps it open, if you turn down the heat, it will close, to open it raise the temp back up to 195 or 190. It will be 100% open at its rated temp. It will begin slowly opening at a fairly low temp like 170 or so, but it will NEVER close fully until its temp drops substantially.

So if the engine is HOT above the stats rated temp of 190 or 195 where the stat is 100% open, how is the stat closing unless it is defective and if it is defective, why is it in the car?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Here is a description of a Mr. Gasket stat

MR GASKET HIGH PERFORMANCE THERMOSTAT -- 195 degrees; Manufactured from brass and copper; Designed to resist large variations in coolant pressures that occur at high rpms; Opens at the right temperature regardless of engine rpm; Legal for sale or use on race vehicles which may never be used on highways; With Mr Gasket's limited 90-day warranty.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I believe that the purge line bolt with a hole in it is located at the TOP of the cooling system

Is it located before or after the thermostat. I'm not sure how the N* cools. - or even how a purge line works.

I am saying the air needs to get past the thermostat and flow to the highest point (radiator cap), where after approx 16 psi, the cap will release the excess pressure (and release the air). the water pump will suck the water in from the bottom hose & cool the engine, so the excess air on top will not affect cooling.

If someeone with a minor leaking HG, will the purge line expell the air on it's own, or would the bolt need to be opened manually?

Air would get past the stat when it opens no? Air will rise to the highest point of the cooling system, that being the bolt with a hole in it, and then it will be pushed out into the tank.

Keep in mind that air rises and it will get to the high point in the system, which is the bolt with a hole in it.

The head gasket leak is leaking super heated gases into the cooling system, that is the biggest problem, the heat, not necessarily the gases. Getting the gases out is insignificant once the head gasket is breeched

Yes, that's what we are saying. air passes thru the tstat when it opens - but once it closes, air will no longer gets past it. I believe the bolt hole is after the tstat - or in a position where it is not directly above the tstat. On early stages, it is really not "super heated gas, but just a few bubbles of hot gas that immediately gets cooled by the coolant. The problem is that it never allows the tstat to open, thus becoming hot gas along with super heated coolant. If the tstat had a way to keep that little bit of air flowing up top, it should be OK.

I have read people saying "when I make sharp right turns the car cools down" - it's not a mystery at all, it is just the hot coolant splashing up opening the tstat enough to get the air up & out.

Also, once the system is allowed to get hot & stay hot & pressurized, the gases have a tougher time getting into the coolant passages.

When the engine is at operating temp, the stat is always OPEN, it never closes 100%, it might range from 50% open to 100% open during your drive to maintain its rated temp but its NEVER 0% at operating temp open when you are driving your car. It is 0% when you start out. At its rated temp it is 100% open.

Try an experiment, Take a stat, get a thermometer, suspend it in a pot of hot water, and watch the stat as the temp increases and decreases, it will never close at 195 or 190 (whatever the spec is) degrees, heat keeps it open, if you turn down the heat, it will close, to open it raise the temp back up to 195 or 190. It will be 100% open at its rated temp. It will begin slowly opening at a fairly low temp like 170 or so, but it will NEVER close fully until its temp drops substantially.

So if the engine is HOT above the stats rated temp of 190 or 195 where the stat is 100% open, how is the stat closing unless it is defective and if it is defective, why is it in the car?

I agree with you - however I believe it's possible that air is acting as an insulator and for a moment, super cooled air (relative to being in a hot engine) closes the tstat enough to close it 100% - and prevents it from ever getting hot enough to open at all.

I'll have an opportunity also to test this over the weekend (Thankfully it's not my caddy!!)

Thanks all for providing constructive feedback & I'll update soon.

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I doubt that 100% air (or more likely steam) ever reaches the stat coming from the radiator, and even so, its not likely that it would be below 195 degrees.

Here is a video that shows a stat opening from heat no water involved, when a head gasket has failed, it it not likely that either air (or more likely steam) or coolant is below the stats rating of 195 degrees.

http://www.youtube.c...feature=related

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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By the way here is a diagram of the cooling system. You will note that the 'spring' end of the thermostat that senses the temp faces the HOT side of the engine. not where the cooler coolant is coming from the radiator, where you say the AIR/STEAM would be. Plus it is drawing from the BOTTOM of the radiator, if there is THAT much air/steam in the cooling system, you will have bigger problems than an AIR pocket because the radiator would need to be empty

NSCoolingSystemCircuit.jpg

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Here is a video that shows a stat opening from heat no water involved . . .

Mike,

That was just ever so slightly more exciting than watching a video of paint drying. :D :D :D

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