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Overheating Coincidence?


stswrx

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I just picked up a 99 STS, 126K. Some great advice on these forums, so I'm hoping the experts can help me out.

The previous owner said he'd taken it in (local shop, not dealer) because it was overheating and they told him it was a head gasket. He opted to sell the car rather than fix. I'm trying to confirm the head gasket diagnosis, so yesterday I topped off the coolant and let the car idle without the cap on the coolant tank for about ten minutes, occasionally revving the engine and adding coolant as needed.

Observations:

-The top radiator hose got hot.

-Serpentine belt seems a little loose, but is about as tight as the new belt on my 99 suburban

-I noticed a white foam form in the coolant surge tank after the car had been sitting for about 10 minutes.

-After ten minutes the temperature gauge on the dash crept up past center to about 2 o'clock

-Immediately after turning the car off, it sprung a coolant leak where one of the hoses meets the metal. Hose is on the drivers side, not the top hose coming out of the radiator. I'm assuming its coming from the bottom of the radiator?

Is the spontaneous leak related to the overheating? I'm assuming that if an obvious leak existed prior, the mechanics would have caught it. The car has been sitting for 5 months before i bought it.

Thanks!

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Repair any leaks you have found; if you are seeing a leak when the system is NOT pressurized, the source has to be obvious. Drain and refill the system with a measured 50/50 mix of Dex-Cool and (distilled) water. Add a tube or two of Bars Leaks Golden Seal powder to one of the hoses while you have the cooling system open.

The serpentine belt does not drive the water pump. There is a dedicated belt for the pump on the left side of the engine. Be sure the belt and tensioner are in good shape.

There is a 1/2" OD rubber hose connected at the top of the coolant reservoir. With a cold engine at idle, remove this hose and observe a small stream of coolant flowing. If no flow, your air purge line is blocked. And with the car sitting for 5 months, this would be high on the list of suspects.

The temperature going that high at idle is a concern. Could be a stretched pump drive belt, a failing tensioner, or something really bad. Did you hear or see the cooling fans operate?

Repair what you can find and do your idle test again, but put the cap on and let the system pressurize.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Maybe this diagram will help, Mike

post-2998-1182005113_thumb.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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The fastest way to confirm a head gasket failure is either a cylinder pressure test or test the coolant for exhaust gases. Other than that, JimD has just about covered everything.

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Fixing the lower radiator hose leak - there is a metal plate that screws into the block where the hose meets the metal.Is there supposed to be a gasket there? My car had only what appears to be silicone sealant.

I'm pretty sure the radiator fan was running while the car idled.

As far as eliminating the head gasket possibility goes - is the cylinder pressure test relatively easy to do? From my reading it sounds like you test with a gauge fitted into one of the spark plug ports. Do you have to test every port?

Thanks in advance!

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Fixing the lower radiator hose leak - there is a metal plate that screws into the block where the hose meets the metal.Is there supposed to be a gasket there? My car had only what appears to be silicone sealant....

If this picture is the part you are asking about, there are two possible gasket configurations depending on which style pump cover is installed on your engine. You can see the difference in the outboard shape of the cover; the latest design cover is on the right and the older pump cover is on the left.

If you are talking about the thermostat housing, yes there is a special gasket and the perimeter of the thermostat fits in the center groove of the gasket.

Water_pump_cover___gasket.preview.JPG

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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As far as eliminating the head gasket possibility goes - is the cylinder pressure test relatively easy to do? From my reading it sounds like you test with a gauge fitted into one of the spark plug ports. Do you have to test every port?

Thanks in advance!

Yes.

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The adapter is easily fabricated from an old spark plug. Grind off the crimp ridge so the porcelain can be removed. Then tap the ID for a 1/8" pipe fitting. Using 1/8" pipe, and an air fitting, fabricate the adapter as shown in the picture. Use Loctite on the threads so it won't come apart.

post-45-1182200972_thumb.jpg

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

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Anyone have a document or a link to one that spells out the cylinder pressure test procedure in small words? My shop manual doesn't arrive until next week and I suspect it may not spell it out in the gory detail I need.

Planning to put a new thermostat and gasket in this week to eliminate the leak. Which way does the thermostat go in? If the direction of flow is from the radiator via the lower hose to the water pump, does the thermostat point in the direction of flow, or against it? Please don't say it's installed the way the old one was because the old one was in the trunk.

Thanks!

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The springs end of the thermostat goes inside the cavity in the water pump cover. I do not think it is possible to install the thermostat backwards, but I had no reason to try.

Or another way to say it is the rubber valve end (the larger diameter end) of the thermostat will be toward the thermostat cover & hose.

Be sure to insert the perimeter of the thermostat into the groove in the center of the rubber gasket. When the gasket is properly installed, there will be a gasket seal at both surfaces of the big end of the thermostat.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Anyone have a document or a link to one that spells out the cylinder pressure test procedure in small words? My shop manual doesn't arrive until next week and I suspect it may not spell it out in the gory detail I need.

Remove the right front tire to access the balancer bolt. Remove all 8 spark plugs and the surge tank cap. The rest of the description is for one cylinder - repeat for the remaining 7. Use a wood dowel inserted down the spark plug hole and rotate the balancer pulley to bring the cylinder to top dead center. Install the adapter described in my previous post and block the balancer so the crankshaft does not turn. Connect shop air to the adapter and listen/watch for bubbles in the surge tank. If air rushes out the exhaust, rotate the balancer until the valves for that cylinder are closed and then watch the surge tank. If the head gasket in the vicinity of the cylinder is OK, there should be no bubbling or thumping noise in the surge tank. If you see bubbles or the tank erupts like a geyser, the head gasket is shot. Repeat for the other seven cylinders. It helps to have one person rotate/hold the crankshaft in position while the other person views the surge tank.

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

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Thanks for the quick reply. Clarifications:

Car needs to be in Neutral?

What PSI shop air?

Any useful tricks to get at the plugs in the back? The space looks tight.

No need to be in neutral - the car should be in park when it is up on jackstands. You're turning the balancer bolt, not the wheels. 100-120 psi for the shop air - My compressor kicks off at 120 psi so that's what I used.

You could also use one of those combustion byproduct detector kits but they seem to be around $50 and the adapter can be built for $5.

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

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I found a Lisle Combustion Leak Detector kit on Amazon for ~$40. Seems like a cheap test for head gasket. Anyone ever used it? Is it sensitive enough to find a small leak? If it doesn't work, no price is cheap enough...

On a related topic, brainstorming with a guy at the local parts store, he wondered if you could diagnose a bad headgasket by pressurizing the cooling system with shop air (to a pressure below the radiator cap setting of 16 psi). If it holds pressure, the gasket is good?

Any obvious flaws in this idea?

Thanks!!

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Check this for $47.50, this is the way I would go, remember that doing it yourself is always cheaper. Call your local radiator shop and get a price for them to do it, and you will run back to the $47.50 tester:

http://www.napaonline.com/MasterPages/NOLM...2f+Engine+Block

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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he wondered if you could diagnose a bad headgasket by pressurizing the cooling system with shop air (to a pressure below the radiator cap setting of 16 psi). If it holds pressure, the gasket is good?

Any obvious flaws in this idea?

Thanks!!

16 PSI may not be enough to force a very small leak. Consider that you're using 100 on shop air, and that the force of combustion would have to be much higher than that.

If you decide to pressurize the cylinders, remember that (as KHE alluded to) each piston is at TDC twice in a cycle. Once with valves closed (compression stroke) and once with valve open (exhaust stroke). If you're like me, you'll hit it on the wrong stroke the first time (but hopefully you won't wonder like me why the heck its doing that and then have to think, ok, how does this thing work? - but I digress...).

Once you get the first cylinder on the correct stroke (compression) to test, you can then follow it around the firing order to test the other cylinders.

Expect the shop air to push the piston down. I used a socket on the balancer bolt with a cheater bar braced against the floor to hold the crank from turning.

If you don't want to hassle with making the adapter for the air, you can get a hose made for this at a parts store. I've used them in the past to hold the valves while I swap valve springs.

Or if you want to get fancy, you can get one of these:

http://www.harborfreight.com/cpi/ctaf/disp...temnumber=94190

It is nice to have the air control valve at your fingertips for the test. And its a cool new tool to boot!

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If you pressurize your cooling system, if you have a leak, it won't hold or it will leak down. Personally, I am not comfortable with finding a head gasket leak this way, IF, you find one and force coolant into the cylinder, you could hydrolock your engine. This technique is great for finding leaks in your cooling system, but as I said, I would be reluctant to attempt to find a head gasket leak with this method.

As noted above, pressurizing the cylinders to 120 psi or so will find a leak in the head gasket. Look for leak down, bubbles in the tank or air in the exhaust

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 bought the test kit at Napa and ran it today. After replacing the thermostat I let the car idle for about 15 minutes. After it warmed up I put the test fluid on and over the course of a minute it turned green. It starts out blue and is supposed to turn yellow in the presence of combustion byproducts.

What does green mean? A small leak?

After 15 minutes of idling the temp gauge had almost reached the red Hot zone and I shut it down.

Another observation - It seemed like the top radiator hose didn't get hot until the temp gauge was well past the 12 o'clock point, closer to 2 o'clock.

Does this confirm a leaking head gasket?

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Did you ever replace the thermostat?

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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Sounds like a thermostat sticking closed to me.

GMTA ;)

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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Yes,the thermostat I ran the test with today was a brand new one.

The cooling fans came on. Would they turn on if the thermostat were stuck? What could cause the thermostat to stick other than a bad t-stat? Air in the line?

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Yes,the thermostat I ran the test with today was a brand new one.

The test you did does not sound conclusive at all. What did the directions say about the test turning green? Do you have any bubbles in the tank while it is running? For the temp to go red in 15 minutes is not a good sign. I would move to a compression test.

On the other hand, if you did not get all of the air out after doing the thermostat that would cause overheating also

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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Just re-ran the test. Results after 20 minutes

Topped off coolant level. Level had dropped about 2 inches overnight. Air in system?

T=0 - 5 min Idled without cap on coolant tank. After 5 min, temp gauge at 12 o'clock. Fans not running

T=6 - Closed cap on coolant tank. Started seeing very white exhaust. Temp gauge still at 12 o'clock

T=8 - Temp gauge unchanged. Fans not running

T=9 - started combustion byproducts leak test. Temp gauge at 12 o'clock

T=10 - Fluid had turned green from blue. Instructions only cite blue and yellow as possibilities.

T=13 - Fans on. Temp at 1 o'clock. Still getting white exhaust

T=16 - Fans still running. Pulled the purge hose (coming into the side of the coolant tank?) It's flowing air.

T=18 - Put green test fluid back on, after another minute it turned yellow. :( . Temperature had backed off a little from 1 o'clock position

T=20. Temp gauge still slightly below 1 o'clock. White exhaust. End test.

Conclusions?

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