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1998 STS overheating!


UKcat

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I think we are experiencing the same problem with our '98 STS; 139,000 miles; never much overheating problem. Suddenly, periodically, it ran a little warm; this weekend, temp. guage shows 3/4 mark; goes back down with rest, but elevates again pretty quickly. I changed the thermostat Sunday night; no help. Monday, I changed the water pump and belt; no help.

About a month ago, I did have to replace the starter; PITA!!! Why is the dang thing under the intake????? With the aide of a service repair manual, it was not a big job; went pretty well, I thought. Now, I am wondering if I did something to cause this overheating problem.

I have read all of these posts on here about headgasket problems; it sounds like we are headed that direction also. My question is, WHY??? Are these engines prone to do this after a period of time??

Also, this is not the first time that I have replaced the water pump; that was about two years ago, I think. This time, I did it, hoping that it would fix this problem, but it did not. We did a reverse flush of the whole system last night with a Prestone flush product; filled it back up with plain water; I guess we will try the "bubble test" tonight :( .

Anybody got any more ideas???

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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UKcat means you have a RH drive vehicle, right? If so, there may be some differences under the hood to accomodate moving the controls for RH drive.

As many times as you have had the cooling system open, have you checked for coolant fluid flow through the air purge line? With the engine at idle and preferably after a cold start, remove the rubber hose that connects to the top of the coolant reservoir. There should be a small steady stream of coolant from the hose.

The plumbing connected to that rubber hose passes through the throttle body and connects to a hollow bolt adjacent to where the top radiator hose connects to the coolant crossover assembly. I will provide pictures if you need them.

This purge line is a parallel path for coolant circulation that allows any air in the system to be burped into the reservoir. If this purge line is not flowing properly, there is the possibility of a pocket of air circulating in the cooling jackets. And air does not transfer heat anywhere near as well as a liquid.

You may have other or different problems but that purge line must be flowing properly.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Sorry, no, UKcat means KENTUCKY WILDCAT FANATIC!!!! Our car is front-wheel drive.

We had been told that maybe there was an air pocket in it; however, the surge line seems to be flowing o.k.; wish that was it, but I don't think it is.

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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No, we don't. Is it possible that I did something while the intake was off to cause this problem now, or is it something that has been on-going and is just now obvious???

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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You are not losing coolant and that is a good thing; you can forget about head gaskets for now.

You have a relatively new pump and belt. What about the belt tensioner? Can you feel spring tension when you press down on the top surface of the belt? My belt deflects less than 1/2".

You said plain water is in the system. Not a good idea; if you have not already done it, replace the water with a 50/50 mixture of Dex-Cool and distilled water.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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The plain water was left in the system last night after the flush. Got tired of fooling with it and quit. Figured we could do the bubble test before we put the dex-cool back.

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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O.K.; we did the test for bubbles in the resevoir bottle, but I am not sure when or what type of bubbles I am supposed to see. From a cold start, removed the cap, started the car. It ran at idle 13 minutes; at that time, the normal operating temp. for the car was reached on the guage; sorry, I don't know the number, but it is at the "straight-up", half-way point of the guage. I saw no bubbles of any type during this whole time. At the 13 minute point; the fluid in the bottle began to raise; as it reached the top of the bottle, it bubbled and burped over. It did this three times before we shut it off.

Is this the bubbles I was supposed to see, or not???

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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If you saw no bubbles during the 13 minute warm up period, that is good. If the head gasket was bad, you would have likely seen bubbles from the start or very shortly there after.

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As you saw when you used the manual, changing the starter is not a bad job. If you have been under the car, you know there is no room for it. Under the intake is a perfect location, its in a cool location and they RARELY go bad. No coolant runs through the intake so its doubtful that you did anything when you changed the starter.

You have done quite a bit of work and analysis already. Is your AC on or off? With the AC OFF, the cooling fans only run when the temp reaches about 226 to 228 degrees then the temp drops down to about 216 and then cycle starts over again.

With the AC ON, the cooling fans run constantly, keeping the temp down. You will see less peaks with the AC ON as compared to with the AC OFF because the temps with it OFF cycle HIGH...

Just a thought, 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/

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Did you see the fans running at all? You might not be able to hear them; I have to bend over and take a look at them. When all the pieces of the cooling system are operating properly, the engine would sit there at idle all day long and cycle the fans ON and OFF to maintain the temperature. But the pressure cap would have to be in place.

And you can expect the water you have in there to boil before the fans are turned on because 1) the pressure cap was off, and 2) there is no Dex-Cool in the system. The water temperature is going to reach 212 degrees before the fans come ON.

Here is a link to a link with numbers on the temperature gauge http://caddyinfo.ipbhost.com/index.php?showtopic=12726

You did not mention checking the water pump drive belt tensioner.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Yes, both of the fans are running.

When I replaced the water pump, I also replaced the pump belt, but not the tensioner. It seems o.k. to me, but I am not sure, exactly what it should show. How loose, or tight should it be; should it have "give" in it or be tight? This could be the problem, I guess, but I don't know.

Unless we come up with something pretty quick; we are going to have it towed to the dealer tomorrow or Friday; I don't know what else to do.

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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.... but not the tensioner. It seems o.k. to me, but I am not sure, exactly what it should show. How loose, or tight should it be; should it have "give" in it or be tight?

See post #6.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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I don't see it stated, did you check for codes? Could you be getting a false reading on your temp gage, either from the gage itself or from the coolant sensor? Could you have dislodged the coolant sensor connection? Have you checked for codes?

Last night filling it with water did nothing to determine if it was fixed. Now that you have reverse flushed it why don't you fill it with coolant (50/50 with distilled water) and let it go through a couple of warm up cool down cycles.

Did you buy an AC DELCO thermostat or aftermarket?

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 just went out and felt of the water pump belt. It really does not give at all; it is pretty tight. Is this good or bad??

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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"As you saw when you used the manual, changing the starter is not a bad job. If you have been under the car, you know there is no room for it. Under the intake is a perfect location, its in a cool location and they RARELY go bad. No coolant runs through the intake so its doubtful that you did anything when you changed the starter."

************************************************************************************************

In reference to your quote about the starters rarely going bad; I wanted to add this bit of info. for the next person who thinks their starter may be bad.

All winter long, on extremely cold mornings, my car would not start. It was actually "dead in the water"; would not even grunt; it would make a clicking noise, but nothing more. You could jump it and it would start right away; we replaced the battery, even though we were pretty sure it was not bad; it was not; nothing changed. We finally gave up and decided it must be the starter; did not want to replace it because I figured it would be a PITA!!!!!!.

Anyway, when I got to the point of taking the intake off, the entire cavity was filled with a MOUSE NEST!!!!!!! After I cleaned this out; I proceeded to unbolt the starter. The battery cable was a little loose. I really believe that the nest and the battery cable were the problem and not the starter, but I was already to the point of replacing it, so I did. But I still don't think it was bad.

Just wanted to throw that bit of info. out there. Has anybody else encountered anything like that before???

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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I don't see it stated, did you check for codes? Could you be getting a false reading on your temp gage, either from the gage itself or from the coolant sensor? Could you have dislodged the coolant sensor connection? Have you checked for codes?

Last night filling it with water did nothing to determine if it was fixed. Now that you have reverse flushed it why don't you fill it with coolant (50/50 with distilled water) and let it go through a couple of warm up cool down cycles.

Did you buy an AC DELCO thermostat or aftermarket?

I don't think the temp. guage reading is wrong; the car is deffinitely overheating; Tuesday it reached the point of getting a message about the engine being hot and automatically shutting the A/C off. This happened after driving about 5 miles. It is the first time that it has gotten that hot.

I have not checked for codes; don't actually know how. I guess we will just take it to the dealer and hope for the best!

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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Has anybody else encountered anything like that before???

Haven't encountered it, but heard of it in the blower motor area. The little rascals can get in anywhere. I set traps by the corners of every door in my garage to discourage them from taking up house keeping in my garage, house or car. You'd surprised at how may I stop at the perimeter every fall.

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I did have to replace the starter; PITA!!! Why is the dang thing under the intake????? With the aide of a service repair manual, it was not a big job; went pretty well, I thought. Now, I am wondering if I did something to cause this overheating problem.

I have read all of these posts on here about headgasket problems; it sounds like we are headed that direction also. My question is, WHY??? Are these engines prone to do this after a period of time??

Also, this is not the first time that I have replaced the water pump; that was about two years ago, I think. This time, I did it, hoping that it would fix this problem, but it did not. We did a reverse flush of the whole system last night with a Prestone flush product; filled it back up with plain water; I guess we will try the "bubble test" tonight :( .

Anybody got any more ideas???

Have you removed the purge line to the surge tank and verified that coolant streams out of the hose?

The starter is under the intake because there is not room to package it in the conventional location next to the hot exhaust manifold/pipe. The added benefit is the starter stays cool, dry, and dirt/grease free. Most last the life of the car. The problem with the intermittent start on your car was undoubtedly caused by the loose battery cable. Personally, I'd rather change a Northstar starter where I can stand up over one mounted in the conventional location with grease, rust, dirt, etc. falling in my face... When I Timeserted my '97 STS, It took me 20 minutes to remove the intake manifold and I had never done the job before.

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

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Yes, we have checked the purge line; while it still had the 50-50 mix in it, and since we reverse-flushed it and was letting it run with water in it. The line seems to working fine; when I took it loose, with the engine running, I got a steady stream of fluid out of it.

We have run out of ideas; we have tried everything the service manual suggested; basically the same things that all of you have suggested on here also; no luck. I just don't think it is a blown headgasket; if it is, it is minor; but I don't know what else to do. I sure as heck can't drive it like it is.

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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My 98 STS sounds like it had the same problem you are having. It would drive fine but then the temperature gauge would shoot up, I would get the messages A/C off etc., and I had just replaced the thermostat as well. After a while, the temperature would come down, sometimes as quickly as it went up. I thought maybe it was defective and took it to the dealer. They said that they would have to tear into the engine to figure out what was wrong but that I would probably have to replace the engine. That engine is apparently no longer available so they were getting me prices on a used one. I decided not to spend the money on the car since it had 159,000 on it so I traded it in for my 06.

Wish I had better news for you. Maybe your dealer can find the problem and fix it.

Max

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I am hoping for better results than you had, but am not optimistic at this point. We really thought it was going to be something simple; maybe not.

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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humor us. list in painful detail each and every item you hace

done as well as the conditions that it was done under and

the details of how the overheating presents itself.

the fix can be only $10 or as much as $3,000 but w/o

the details we are trowing darts at the wall

Yes, we have checked the purge line; while it still had the 50-50 mix in it, and since we reverse-flushed it and was letting it run with water in it. The line seems to working fine; when I took it loose, with the engine running, I got a steady stream of fluid out of it.

We have run out of ideas; we have tried everything the service manual suggested; basically the same things that all of you have suggested on here also; no luck. I just don't think it is a blown headgasket; if it is, it is minor; but I don't know what else to do. I sure as heck can't drive it like it is.

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I have pretty much stated every thing we have already done. I am not sure exactly when this first started; I think it may have been last fall. One day, while traveling in the eastern Kentucky mountains, the temp. guage went up to about the 3/4 point, which is very unusual. Most time, it never goes past half-way. We stopped for a while; after checking the coolant bottle, it was a little low, so we added some coolant to it.

I will admit that we have not done the recommended coolant changes like this forum states that we should have done; WE DIDN'T KNOW!!!! I don't remember when I first changed the water pump; possibly two years ago; I did flush the system and put in new coolant then, but I did not add the pellets; again, I didn't know!!!

The sudden overheating started last weekend. Twice, after driving about 15 miles, the guage went in the 3/4 level. It was not a false reading; the car was pretty hot; coolant was overflowing from the reservoir bottle on both occasions.

Sunday night, I decided that the thermostat may have been defective, so I got a new one (not Delco) and put it in. I refilled the system and started the car and let it idle about 10 minutes. It reached normal operating temperature and seemed to be o.k., so I drove down our street about two miles and turned around to come back to the house. The temp. guage got in the 3/4 level before I got back home.

Monday, I got a new water pump. I really did not think that it would be the problem, but I figured that I might as well try, so I put it in. Again, I refilled the system, started the car, let it idle about 10 minutes, and drove down the road. Same results; it got hot again before I got home.

Tuesday, somebody suggested that I had trapped air in the system. It does not seem that the radiator hoses get hot; I wondered if maybe the coolant was not circulating properly. I took the uppper hose loose at the fitting and poured some new coolant in the hose so that it would flow directly in to the radiator. I started the car and took the purge line loose at the reservoir bottle. It flows out of the line as it should.

Wednesday, I drained the whole system and reverse-flushed it. I filled it with water and added a Prestone flush product. It states that you are supposed to start the car and let it idle until it reaches normal operating temp. and then drain it out and refill, again, with plain water and repeat the idle process.

When I refilled the system with clean water I took the cap off of the reservoir bottle and watched for bubbles. The car idled for 13 minutes without a sign of any bubbles. Finally, the level of the water in the bottle rose up in the neck and ran over. As it reached the top of the bottle, it made one bubble as it ran over. I did not know if that is what I was supposed to be seeing or not.

We had the car towed to the dealer Friday; they are supposed to look at it Monday. I didn't know what else to do.

My "other car"

100_05472.jpg

1968 Pontiac GTO, 400, 4 speed, 366 h.p., matching numbers car

*Get well soon, John Force!!!*

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