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99 STS Overheating and no heat


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My friend just bought this car and wants me to help him fix it. My initial thought was head gasket causing the overheating so I can a compression test on it. With a cold engine all cylinders registered between 158-165 psi so it seems to me headgaskets are good. I let it run for a while with the radiator cap and it reached normal operating temp and stayed there. I put the cap back on and within probably 3 minutes you could hear the coolant boiling in the resivoir and coming out of the cap a little bit. This whole time there was no heat coming out of the vents. The entire time the vents were set up at 90° and they were blowing cold air. There are no DTC codes. Any help here please????

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1) Check the purge line to make sure that coolant is flowing from it first. The purge line allows air to get out of the system, if air is in the system, the waterpump will not be able to circulate coolant.

2) Immediately replace your thermostat, if it is binding, it may not be opening

3) check the coolant concentration, it must be at least 50% coolant to 50% distilled water

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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Smell of the coolant tank... see if it smells like exhaust...

I checked that first. No exhaust smell.

1) Check the purge line to make sure that coolant is flowing from it first. The purge line allows air to get out of the system, if air is in the system, the waterpump will not be able to circulate coolant.

2) Immediately replace your thermostat, if it is binding, it may not be opening

3) check the coolant concentration, it must be at least 50% coolant to 50% distilled water

Is the purge line the small line from the side of the resivoir tank to right around the throttle body?

I'll get on the other stuff asap and post results. Thanks guys

Edited by mcampau
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....Is the purge line the small line from the side of the resivoir tank to right around the throttle body?

Yes. The 1/2" OD rubber hose connected to near the top (1.5 " below the top surface) of the reservoir. Actual coolant flow is from the coolant crossover assembly via a hollow bolt near the upper hose connection (and the engine lift bracket) to the throttle body and out of the throttle body to the reservoir. This line sees water pump pressure at all times.

With a cold engine at idle, you should see a steady stream of coolant when you disconnect the reservoir end of the rubber line.

No purge line coolant flow can mean the reservoir (cold) level is too low OR the purge line is blocked somewhere. And the most common "somewhere" is the hollow bolt.

Sputtering purge line coolant flow can mean there is air remaining in the system OR the puge line is "partially" blocked. See hollow bolt above.

The easy way to eliminate air is to bump the throttle to 3,000+ RPM several times when the thermostat is open. The time consuming way is to operate the vehicle at thermostat open temperature and allow to cool back to ambient. Several times, as many as four times.

When the system is at ambient temperature, the proper coolant level in the reservoir is approximatley 2.5" to 3" below the top surface of the pressure cap threads.

It's hard to overstate the importance of the proper coolant level with engine cold or ambient.

We can only hope the cooling system has been properly serviced with 50% Dexcool and 50% (distilled) water.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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The line had a perfect stream of coolant. Coolant level was good.

Replaced the thermostat and no change. I also boiled the old thermo to double check it and that opened right when it should.

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Hmmm, check the water pump belt

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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Hmmm, check the water pump belt

Brand new water pump and belt a couple weeks ago. No change. I think Im down to pulling the heads and checking the gaskets.

oh my God, PLEASE don't act stupidly, THAT is NOT necesary, there are definitive ways of checking the head gaskets without pulling the head, you pull the heads and you will have a BIG BIG problem

You say you have no heat, explain that, low heat typically means low coolant

Have you pressure tested the system? Do the cooling fans come on? Is the radiator clear?

You can purchase a coolant tester from NAPA to check the coolant for combustion by products...

Detail the overheating problem again for us and tell us EVERYTHING you have done, this is the FIRST I have heard about the water pump, why was it changed?

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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Hmmm, check the water pump belt

Brand new water pump and belt a couple weeks ago. No change. I think Im down to pulling the heads and checking the gaskets.

oh my God, PLEASE don't act stupidly, THAT is NOT necesary, there are definitive ways of checking the head gaskets without pulling the head, you pull the heads and you will have a BIG BIG problem

You say you have no heat, explain that, low heat typically means low coolant

Have you pressure tested the system? Do the cooling fans come on? Is the radiator clear?

You can purchase a coolant tester from NAPA to check the coolant for combustion by products...

Detail the overheating problem again for us and tell us EVERYTHING you have done, this is the FIRST I have heard about the water pump, why was it changed?

By no heat I mean when the vehicle is running there is never any amount of heat coming out of the vents. The engine can be up to operating temp but all that comes out is ambient temperature air. The blower works fine.

I have not pressure tested the system. My friend is on his way to pick one up right now to do that.

My friend just bought this car knowing it had overheating problems. The car was a fantastic deal, if we get this fixed.

Bought the car 3 days ago. Was told the vehicle started overheating for the previous owner who took it to some general mechanic shop. The mechanic couldn't figure out the problem so he sent it to a local dealership. They told him it was the water pump so they replace it along with the thermostat and the belt. He drove it away from the dealership and got 4 or 5 miles when it started overheating. He had it towed to his house and put it for sale. A couple weeks later my friend bought and towed it to my house. It looked a little low on coolant so I topped it off with a little water and started it in my driveway with the rad. cap off to watch it. After a few minutes it reached normal operating temp on the gauge and had a little steam rising out of the reservoir tank. There was also a fair amount of steam coming from the exhaust but no sweet smell. After about 15 minutes the temp never rose above the middle of the gauge. I put the reservoir cap back on, 2 minutes later there was steam rising out of the closed cap and I could hear boiling in the reservoir(temp gauge still said normal). Still no heat out of the vents. I shut it down and let it cool off. One by one I pulled off every small coolant line and inspected it for blockage, with compressed air I blew out ever line and every orifice in the block. I saw nor felt any blockages. Next pulled every plug and did a cranking compression test with all cylinders coming out between 158 psi-165 psi. Tonight I just drained all the coolant into a clean bucket so I could inspect it. It is dexcool but the color seems off. It's sort of a murky orange/brown color with a lot of, best way to describe it, sediment. Probably 3/4 to 1 cup of it in there. Thats as far as I have gotten.

Seriously, thank you for taking the time to be so thorough helping me.

Edited by mcampau
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Do me a favor and check the tank for cracks, as you may know, the tank is part of the cooling system and it holds system pressure. If you are losing system pressure it will boil at a low temp.

Your pressure test should turn up something, see what you find, it must hold 16 to 18 PSI without dropping

Have you checked to make sure that the CAP is good and that it is the correct cap? Anything that permits the system NOT to hold pressure is suspect

How about the fans? are they coming on?

Consider that the radiator is clogged also. You do not seem to have head gasket symptoms, I dont see 1) any misfires, 2) no smell at the exhaust or at the tank. If it were bad enough to overheat idling, you would have obvious symptoms

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'll go check the tank very closely right now. Ill repost the results as soon as my friend shows up with the tester. I dont have a tester for the cap so I guess Ill pick up a new one. The fans did not come on. The temp gauge never got hotter than middle of the gauge so I don't believe they should have.

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I sort of ghetto rigged a pressure test for the cap. I removed the reservoir, plugged the small nipple, and inserted my blow gun into the larger nipple at the bottom. I wrapped the blow gun nozzle with some towels to help it seal. With my compressors regulator set to 10psi output the air comes hissing out rapidly from around the rad. cap. Does it sound like that could cause my problems??

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I sort of ghetto rigged a pressure test for the cap. I removed the reservoir, plugged the small nipple, and inserted my blow gun into the larger nipple at the bottom. I wrapped the blow gun nozzle with some towels to help it seal. With my compressors regulator set to 10psi output the air comes hissing out rapidly from around the rad. cap. Does it sound like that could cause my problems??

:lol:

That was an interesting way to test the cap, but effective, blink.gif

Yes that certainly does sound like your problem, check the flange on the tank for cracks and replace the cap...

Keep your fingers crossed

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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Hmm, you say the fans dont come on, so she is not getting excessively hot or you have a cooling fan problem, but I dont think so. Do me a favor, idle the engine and turn on the AC... the fans should come on when the AC is on.

You said something interesting above, you said, it boiled and the temp was half way or normal. Now this could be false boiling, because superheated gases from a breeched head gasket are boiling the coolant, OR, it could be no system pressure.

If your AC is off, the cooling fans dont come on till about 228 degrees, with the AC on, the fans run continuously. With no system pressure, you could be boiling before the fans come on at 228 especially if you are less than a 50/50 concentration. If you had false boiling from escaping combustion gases, you WOULD smell exhaust fumes in the tank.

Keep your fingers, that your cap or tank is leaking pressure

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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Have you checked for codes yet? If not check for codes

Go to the top of this page, go to caddyinfo.com, click HOW TO, then DTC codes and follow the directions for your year

Post any codes here. maybe you have an actuator problem that is messing up your heater

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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Have you checked for codes yet? If not check for codes

Go to the top of this page, go to caddyinfo.com, click HOW TO, then DTC codes and follow the directions for your year

Post any codes here. maybe you have an actuator problem that is messing up your heater

First thing we did was check the codes. There were no codes anywhere related to the engine, cooling system or heater-A/C. I picked up a new rad cap and am going to throw that on and put it back togeother. Amateurzone (autozone) didnt have a pressure tester with the proper adaptor for the threaded on reservoir caps, so I'll have to try and find one tomorrow. In the reservoir I found a number of large chunks of what I have to guess as some sort of stop leak crap. Im attempting to flush that out right now. Ill put it back togeother and run it right now and post the results.

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I got all of the chunks of crap out of the reservoir and re-assembled everything. I filled it back up with just straight water to test it out. After running for probably 45 minutes with the new cap on it did not overheat!!! There was some noticeable heat out of the vents with it idling but not as hot as I expect it to be. If I rev it up a little bit the vent temperature gets much hotter. Is that common with northstars? Ill take it out for a test drive tomorrow before I drain out all the water and fill it with the proper mix. I seriously can't thank you enough for all the help. If that really did take care of the problem he just picked up a loaded, immaculate 99 sts with 154,000 miles with new tires, new wheel bearings, and new water pump for $1350, plus $5 for a new radiator cap! HAHA!! :yupi3ti: The previous owner couldn't figure out what was going on with it.

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Good for you!

I have news for you, it was not the prior owner that could not figure it out, it was as you said >>> a General Mechanic Shop and a Local Dealership that could not figure it out!!!

Was told the vehicle started overheating for the previous owner who took it to some general mechanic shop. The mechanic couldn't figure out the problem so he sent it to a local dealership

It amazes me how poor mechanics are these days when we can sit here behind a KEYBOARD and diagnose, guide and fix these cars.

Now that you see the value of Caddyinfo, consider joining as a supporting member, there are benefits and you will help support this great resource...

Let us know how it runs, Mike

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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Not sure what is going on with your heat, it sounds like you might have a vacuum issue, reving the engine should not affect the heat delivery, maybe someone will chime in. However, give the system a few warm up, cool down cycles for the cooling system to stabilize...

Does your parking brake release when you put the selector in Drive? Does it idle smoothly? Do you hear any vacuum noises in the car or under the hood?

You say you have NO codes correct?

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 havent set the parking brake. It idles very smoothly. There are no vacuum noises what so ever. Correct, no codes.

The HVAC doors and park brake release are all electric.

If the cabin temperature problem persists, the system will eventually set a "B" code wnen a door actuator gets out of synch.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Thanks Jim, I didnt know that the electric parking brake release was in 99, it is my understanding that the programmer has a vacuum connection is that not true in 99?

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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Finally took it for a test drive. While driving it nicely it didnt overheat. At idle it still have very little vent heat though. When the motor gets above about 2000 rpms the vents heat up to where they are supposed to be. I took it on the highway and really got on it. Right after that the temperature spiked to about 3/4 of the way up the gauge and the vent heat went ice cold. After pulling off the highway there was some water boiling out of the radiator/reservoir cap. I let it cool down for a while then drove it home nicely and it did fine. Any ideas??

Does using dexcool/water instead of straight water raise the boiling point?

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