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Overheating 1999 Deville


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So this is my brief history with car. It is a 99 deville, with 150k on it now boght with 140. Overheating problems started when I drove to florida and back actually i drove there fine and on the way back it overhated first time baked the oil and all I did was change the oil and add coolant and it made it back to NY with no problems. Then I did a stupid thing and added the barsleak tablets into the coolant cantainer after that I noticed temps started to go up. Im about three weeks the hose that connects to the thermastat cracked and I fixed that and all was well again,

Then recently I noticed temps started to go up again into the 240 then go down so I filled it up with dexcool and drove it around tonight really rough like opening throttle all the way for some time and repearting, i wanted to see how it would hold up. and now the car overheated to the point that even if I add coolant the temps just keep going up.

Im not too technical with the caddy but have been reading through these forums for past year.

How can I check if head gaskets are on the way out? I see nothing coming out of the exhaust and the oil is clean.

How can I properly diagnose the radiator and the water pump?

My situation with money is really critical now and i really dont want to invest into fixing things if there is a chance that head gaskets might be failing.

Thanks in adnance AL

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To check for bad head gaskets...

get the test kit from NAPA or Auto Zone that tests for exhaust gas in the coolant.

Or you can take it to a radiator shop and have them test it.

BUT...do not test it if you have just added fresh coolant to the reservoir.

Once you know if there are exhaust gases in the coolant or not... then you can decide which way you want to proceed.

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Overheating that is caused by the beginnings of head gasket failure are usually quick temperature spikes. A creeping up of the temperature us usually something else, like the fans not coming on or a slipping water pump belt, a clogged radiator, coolant mix too far away from 50-50, etc.

Quick temperature spikes are most often caused by a blocked bypass hose. That's a 3/8" hose that goes between the water pump, near where the top radiator hose comes out of the engine, and the surge tank. If you can turn the heater on and stop this, it's the bypass hose. If that doesn't do it, then either that's not it or the heater core is blocked, too. You can check by taking off the radiator cap, pulling the bypass hose off the surge tank fitting and starting the engine; if it doesn't flow quite well even with the engine at idle, it's clogged.

Another cause of temperature spikes is a sticking thermostat, the wrong type thermostat, or the thermostat installed backward. Since you haven't touched your thermostat since before the problem was first noticed, that's not likely the problem.

Head gasket failure usually begins with using a lot of coolant for no apparent reason, no drips or puddles. Something like a couple of quarts of coolant going away every few thousand miles is a red flag under any circumstances and should be tracked down. It could be a cracked radiator tank or a leaking hose fitting or water pump, but whatever it is it should be fixed. A pressure test will reveal leaks, and may also show a leaking head gasket if it's bad enough; that's how I diagnosed mine.

The first temperature spikes from head gasket failure come right after a heavy engine load, like a WOT freeway on-ramp to highway speeds, pulling a significant grade at highway speeds, etc. and will occur about 30 seconds after you go back to normal throttle, and will be a quick movement of the temperature gauge and a fairly quick fall-back to normal temperature (around 12 O'Clock on the temperature gauge) without overheating. Most people will miss this.

If the car has overheated at least once since you last added coolant, you can have it tested for combustion products. A good radiator shop can do it, but I once had a dealer tech tell me that he couldn't check the coolant for combustion products. You may be able to smell coolant in the tailpipe; the best time to check are right after you start the car cold in the morning. You might try smelling the tailpipe by pulling over and killing the engine right after it overheats and walking around the car right then. But a test for combustion products by a good radiator shop is the definitive test.

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150,000 miles is pretty good before overheating began

Have a radiator shop test the coolant for combustion by-products or get the NAPA test kit. Also have the them pressure test your cooling system to check for leaks. You might also smell inside the coolant tank and see if you smell exhaust fumes.

If the testing does not turn up combustion by products, check the purge line for coolant flow.

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Checking the purge line for coolant flow is very easy - I'd do that first just to rule it out. With the engine cool, remove the 3/8" hose that connects to the surge tank near the top. Start the engine and there should be coolant flowing out of the hose. If not, trace the line back to the waterpump area and unclog the fitting where the hose connects to the waterpump cover area.

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

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Checking the purge line for coolant flow is very easy - I'd do that first just to rule it out. With the engine cool, remove the 3/8" hose that connects to the surge tank near the top. Start the engine and there should be coolant flowing out of the hose. If not, trace the line back to the waterpump area and unclog the fitting where the hose connects to the waterpump cover area.

Very true Kevin, that should be done first as its easy and should be eliminated.

I had edited the title of this thread to remove the negativity, and my judgement was affected by the original title

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Thanks for all the help. I will test for head gasket tomorrow. Meanwhile I noticed a couple of things. Radiator behind the condenser is a little warm on left side and not warm at all on the right side. Could this mean radiator is stuffed or hoses leading to radiator are stuck.

Also ran the car idle today it went up to 235 or so the went down to like to 220 when fans kicked in higher gear at idle then as soon as I started to drive it climbed back up again to 250.

Also I actually changed the thermostat and the coolant when I first got the car so Im thinking of changing the thermostat to the ac delco one cause I installed a $6 cheap one.

Any ideas Thanks

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Cheap Thermostat == Trouble, sooner or later, probably sooner.

Get the genuine article. Part numbers and prices from Rock Auto:

Gates 33808, $10.59

Stant 14228, $11.21

AC/Delco 131128 $22.89

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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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Thanks for all the help. I will test for head gasket tomorrow. Meanwhile I noticed a couple of things. Radiator behind the condenser is a little warm on left side and not warm at all on the right side. Could this mean radiator is stuffed or hoses leading to radiator are stuck.

Also ran the car idle today it went up to 235 or so the went down to like to 220 when fans kicked in higher gear at idle then as soon as I started to drive it climbed back up again to 250.

Also I actually changed the thermostat and the coolant when I first got the car so Im thinking of changing the thermostat to the ac delco one cause I installed a $6 cheap one.

Any ideas Thanks

Does the radiator get warm after some driving?

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will change thermostat tomorrow and radiator doesn't get hotter when driving but then again only drove for like 5 minutes.

Thanks for all the help. I will test for head gasket tomorrow. Meanwhile I noticed a couple of things. Radiator behind the condenser is a little warm on left side and not warm at all on the right side. Could this mean radiator is stuffed or hoses leading to radiator are stuck.

Also ran the car idle today it went up to 235 or so the went down to like to 220 when fans kicked in higher gear at idle then as soon as I started to drive it climbed back up again to 250.

Also I actually changed the thermostat and the coolant when I first got the car so Im thinking of changing the thermostat to the ac delco one cause I installed a $6 cheap one.

Any ideas Thanks

Does the radiator get warm after some driving?

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See what the new thermostat does, and if it does not help, check the radiator again after driving a little. Btw, what is the ambient temperature where you are driving?

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Im in NYC so temps have been in the 90's lately nut know like 85. will change thermostat tomorrow and check if radiator gets more hotter.

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Check the purge line to make sure it flows also, if you are not flowing your water pump may cavitate and that would cause you to have a radiator like that....

Do you know how to check the purge line?

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If the purge line is clear, do the block test before throwing any more money and parts at it.

no. how do you check it?

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On the top of the coolant tank there is a 3/8 inch hose, NOT the overflow hose that is attached near the cap, the other hose that connects to a pipe that runs across the engine toward the throttle body.

Start with a COOL engine, not a hot one, have the engine off

Gently pull the hose off of the tanks nipple, and let it hang, go into the car and start the engine, go back and look at the hose, coolant should be flowing steadily from that hose, let us know the results

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/

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HI

Very hectic day today... but had some time to mess with it.

I pulled the purge line off and coolant only was coming from the tank nipple not the hose. other things that happened i dropped car off with my buddy who has some more tools them me he did a pressure test there was no leaks so he added water so the proportion of dex cool to water is like 80 water 20 coolant now and the car drove fine today did not overheat at all. Drove for about 3 hours. Tomorrow I will follow the line to water pump and try to clear it. Is the end to the water pump easy to get to? and what can I use to clear it?

Is it ok to run on more water the coolant it is really not cold here for another couple of months?

im going to try to clear the purge line and put in a thermostat ac delco one this week and see what happens.

i know im not doing the block test maybe I should do that after doing the purge line but I just dont want to loose this baby so i keep on telling myself its something external lol.

On the top of the coolant tank there is a 3/8 inch hose, NOT the overflow hose that is attached near the cap, the other hose that connects to a pipe that runs across the engine toward the throttle body.

Start with a COOL engine, not a hot one, have the engine off

Gently pull the hose off of the tanks nipple, and let it hang, go into the car and start the engine, go back and look at the hose, coolant should be flowing steadily from that hose, let us know the results

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You have established that the bypass/purge line was clogged, which would explain the overheating, and you are making sure that you have the right AC/Delco thermostat installed and you are going to clear the clogged bypass hose.

You should definitely add anti-freeze to get to coolant to about 50-50 because poor coolant mixture is a know cause of overheating. I suggest that you use an antifreeze testing gauge when you do this to get it right and avoid guesswork.

You probably will have the problem solved when you are done. I would just drive the car for a few days and see if everything is all right before I did anything more.

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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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I am on Long Island, Al

OK, first, never put water into the tank, always mix coolant 50/50, you need to balance your system now, by letting the coolant out and adding balanced coolant. Your 80/20 balance allows the mix to boil at a lower temperature. Changing it to 50/50 will raise the boiling temp and add corrosion protection. When you are done balancing the coolant and removing the debris from the purge line you should use the cooling supplement tablets use 4

GOOD, it seems your purge line is clogged, that is great. The air purge line is part of the "throttle body heater circuit", it is NOT part of the water pump as you have suggested.

Here is a photo of where the purge line goes on my 96, you need to remove the hose from the nipple at the throttle body. You will notice that the bolt nipple has a hole down the middle of it, you must remove that bolt and clean out the hole, it gets clogged sometimes stopping AIR from getting out of your system.

DO NOT DO NOT try to BLOW it out from the coolant tank side of the hose, that will only temporarily solve the problem

In this photo, the purge line "bolt with a hole in it" is to the right of the upper hose

WaterPumpandRadiator022-1.jpg

Pre-1995 - DTC codes OBD1  >>

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

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Is it ok to run on more water the coolant it is really not cold here for another couple of months?

Won't hurt anything (for a short period).

I pulled the purge line off and coolant only was coming from the tank nipple not the hose.

OK, sounds like maybe the purge line is plugged, BUT there should not be any coolant coming out of the nipple unless it was overfilled. If it was at the proper level (1/2) then I have to ask, was it being run at operating temperature with the cap off? If not, then I'd be concerned that exhaust gases where pressurizing the tank and forcing coolant out of the open nipple. If clearing the purge line does not help, you need to do the block test.

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  • 1 month later...

how do i replace the radiator in a 98 deville

Please start a new thread on this topic, this question is off topic here

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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