1999 Olds Sil. Thermostat?

[Bill Wilky]

I have a 1999 Olds Sil. with the 3.4 engine. I am having overheating problems. The water pump was replaced about 2 years ago. I am thinking maybe the thermostat, but not sure where it is located. Is right under the bleed off on the driver side of the engine or back further. Its overheating and then goes back down and back up to the red again with 1/2 mile. Does this consistently now. The heater only blows cold air. Nothing in the oil. No drips under car. Only thing I can come up with is thermostat. Any ideals would be appreciated.

[merc81]

You know what causes that and its not likely the thermostat.

You need to plan for some engine work and soon I'm afraid.
Read the older posts here or on the chevy venture thread about the engine intake gaskets & or head gaskets. We all hope its something else, but in the end, you know what has to be done.

[roadrunner2]

Originally Posted by Bill Wilky

I have a 1999 Olds Sil. with the 3.4 engine. I am having overheating problems. The water pump was replaced about 2 years ago. I am thinking maybe the thermostat, but not sure where it is located. Is right under the bleed off on the driver side of the engine or back further. Its overheating and then goes back down and back up to the red again with 1/2 mile. Does this consistently now. The heater only blows cold air. Nothing in the oil. No drips under car. Only thing I can come up with is thermostat. Any ideals would be appreciated.

Your post has me thinking in two different directions. Mainly because it is slightly confusing.

IF the gasket is allowing coolant into the engine the following post will apply. IF not.....(go to end of post).

The LIMG (Lower Intake Manifold Gasket) is leaking coolant to the inside of the engine which then mixes with the engine oil and eats the bearings and journals.

If you continue to drive the van you will be replacing the engine.

Depending how long the coolant has been diluting the oil will signify how much can be saved.

Obviously you haven't done a search for this problem or you wouldn't bother posting.

All GM vehicles with a 3.4L V6 (and other sizes) from 1996 to 2003 have had this fault and the age and mileage has never been a timing factor of the gasket breach.

There already has been a class action suit with GM over this problem and has since been settled.

I just got a $400 refund as their idea of compensation for the aggravation the LIMG caused.

Now, because you say the heater only blows cold air, I'm tempted to agree with you on the faulty T-stat.
It may be stuck OPEN, NOT allowing the coolant to heat up and then be circulated through the system.

NOW, you say the engine overheats, as far as the T-stat goes, when the engine overheats and the top rad hose isn't hot, the T-stat is probably stuck CLOSED.

That said, the engine overheating with no external coolant leak part makes me agree with the previous poster, hence my LIMG post.

The T-stat is located at the end of the lower intake manifold on the drivers side of the engine compartment.

Ensure the old seal comes off and the new T-stat is inserted in the correct direction. When replacing the T-stat housing bolts (2) torque them to 18 ft lbs.

One thing is for certain, if the new T-stat doesn't correct the overheating problem you should have a coolant pressure test done and be prepared for the worst.

It's an expensive fix due to it being a labor intensive repair job.

[Bill Wilky]

I was messing with it some more last night. It now has the milky look in the engine. Head gasket. But now trying to figure out what made it blow. Has 94,000 miles on it. The head gasket was changed at about 42,000 miles, years ago. Could a thermostat sticking cause it to blow the gasket? It was driven for maybe 2 miles once it got hot. I parked it since.

[roadrunner2]

Originally Posted by Bill Wilky

I was messing with it some more last night. It now has the milky look in the engine. Head gasket. But now trying to figure out what made it blow. Has 94,000 miles on it. The head gasket was changed at about 42,000 miles, years ago. Could a thermostat sticking cause it to blow the gasket? It was driven for maybe 2 miles once it got hot. I parked it since.

The 'milky' oil gives you bad news.

This is a classic symptom of a blown lower intake manifold gasket. Not a blown HEAD gasket.

Are you certain it WAS a blown HEAD gasket before?

If it were a blown HEAD gasket your tail pipe would be blowing white smoke constantly.

As you read in my last post about just this problem, get a coolant pressure test done NOW before more damage is done.

When the intake manifold gasket breaches (allows coolant to seep through and mix with the engine oil) it is of no fault of your own doing.

GM screwed up big time (What else is new?) when they made a crappy design (1996) for this gasket in that the gasket bolt supports gave way and as a result the manifold mounting bolts became loose, allowing air to mix with the additives in the Dexcool coolant.

The coolant mixes with the engine oil and damage results. End of story.

GM devised a new 'redesigned' gasket and made it available in Feb/03. Felpro and others have a gasket similar you can use.

The GM gasket comes as a kit with new bolts and new torque values, locktite for the bolt threads and torque specs. Also it has the 'new' gaskets.

Because your engine has over-heated it would be wise to have the manifold checked for warping before re-assembly.

You've likely read and heard everyone yowling about GMs 'Deathcool' among other names. Not so.

Dexcool never was the leading culprit in this fiasco.

The gasket was always the fault.

If the gasket hadn't collapsed the bolts wouldn't have become loose and the air never would have been able to mix with the coolant.

Could a sticking t-stat cause a blown gasket? No.

[drkoraf]

I have a similar problem that just started suddenly. I have a 2000 Olds Silhouette Premier with 187,989 miles. Once the van warms up, the temp guage shows normal and my heater works fine with plenty of heat. After 25-30 miles or so of driving, suddenly the blower gives me cold air, the temp guage shoots up to the top and the idiot light showing "engine temp hot" comes on whereupon I quickly pull over and let it cool off. There is no discoloration in the oil and I'm not leaking any oil or coolant, and no smoke in my exhaust. There is no discernable leaking around the head, intake manifold gasket seals or t-stat housing and coolant level remains steady.

I've checked all of the posts here related to the gasket problems but I am convinced this is not the problem. Instead I think the T-stat is suddenly sticking closed and needs to be replaced. I will check the top rad hose next time this happens to see if it is hot or cold but does my diagnosis sound right to anyone else?

Oh yea, anyone know how to force open a power slider that won't unlock electrically or manually?

[roadrunner2]

Yes, you could be right.

You won't be able to force the slider without doing damage.

Remove the fuse for the door from the underhood fuse box (over the battery) and after a few seconds, replace it. This resets the door module.

I did this with the 2000 I had and it worked, but I'm not positive this will answer your problem.

[drkoraf]

Interesting development and followup to my previous post. Since I saw no discoloration in my oil, no visible leaking around the gaskets, no oil or coolant leaks and no loss of power, I assumed it was a bad T-stat and replaced it. Unfortunately, after replacing my thermostat I experienced the exact same problem with the engine blowing hot air initially then only cold and overheating. Since my water pump was replaced last year, I ruled that out and assumed it could only be one of two things...a clog somewhere in the radiator or hoses, or a bad manifold gasket that was leaking exhaust into the coolant.

Since it's easier and cheaper to check for exhaust gases in the coolant than it is to replace a radiator, I visited my local AutoZone and picked up some test strips ($10) made just for this purpose. They look just like the test strips you check your pool's water quality with but test for specific compounds in the exhaust. You pop your radiator cap off and dip them into the coolant and if they test positive, your manifold gasket is leaking and blowing exhaust gases into the coolant.

Unfortunately, my gasket is indeed leaking. So, unwilling to spend $1500-$2000 repairing the manifold gasket (mostly labor cost because the labor for this on a 2000 Olds Silhouette Premier is a bitch!), I opted instead for a quick solution that, while NOT fixing the manifold leak, would allow me to continue to drive the vehicle for months/tears more, though with minimal heat for the van's interior cabin. In essence, I cut the guts out of the T-stat so that it would allow unencumbered coolant flow while maintaining a seal in the t-stat housing. Now, I can drive the vehicle with almost no noticable loss of performance and the temp guage needle never moves more than a hair above the bottom line. Interestingly enough, I still seems to get enough warm air blowing into the cabin to reach an internal air temp of appx. 70 degrees which is more than adequate to defrost the windows and make for a comfortable interior. Yesterday it was close to 20 deg. here in the Boston area and I had no problems!

Additionally, I was afraid that the check engine light would come on but it hasn't (yet) and I don't believe I will have any problem getting an inspection sticker, but I won't know until my current sticker expires and I need to get tested.

So, in summary, use the test strips if you suspect you have a manifold gasket leak before doing anything else, and then consider gutting your T-stat as a quick way to keep driving before you undertake the much more expensive repair of your manifold gasket. I stress that this is NOT a long term fix but will allow you to keep driving without doing any real serious damage to the engine. I'll let you know how I'm doing a couple of thousand miles down the road!

[merc81]

In my experience (that's getting to be quite a bit now, all my friends bring their vans over here), when the engine starts out fine then suddenly overheats with concurrent loss of hot air from the heater, its always the head gasket.
Combustion gas gets forced into the coolant causing large air pockets to combine and allow the engine to overheat. You may or may not have coolant in your oil--that comes from the LIM gasket, but whats the difference? You need to replace all the gaskets for this fix anyway.
Its the air pockets that cause the heater to run cold, and the fact that the engine gets cooler when pulling a hill or otherwise running higher rpm is due to the water pump's increasing effect as it spins the available coolant into the engine. You should notice the overflow tank gets full and even overflows, but when the engine is allowed to cool, all that water gets sucked back into the system again.
Either gasket failure IMHO is cause for complete overhaul down the the head gaskets. Its just too much effort to get down there to stop at the LIM--better to do the whole job regardless. And running the van very long with this problem is just asking for engine failure--from cam bearings seizing or warped heads and scored cylinder walls. If you like your van, get it fixed sooner rather than later.

[drkoraf]

Hey Merc, how hard was it to do all your gaskets?

[drkoraf]

Hey Merc, how hard a job was it to replace all of your gaskets?

[drkoraf]

Hey Merc, how hard a job was it to replace all of your gaskets?

[Bill Wilky]

It's a very tough job to do it inside the van. If you can put it on a lift and take the engine out from the bottom makes it a lot easier. There are 6 main bolts that hold the engine and transmission to the body. Of course you still need to undo hoses, wires, and steering. But it leave the enginge on the ground and you can take it apart very quickly. It sounds like alot of work this way but its amazing how easy it made the job. I ended up replacing lower and upper gaskets. Make sure that you get the better gaskets from a place like KOI. If you go back to GM, they will give you the same faulty gasket that failed to begin with. Then you get to do this in about 50,000 miles again. After doing all this work and finally getting the air pocket out that was giving me some false reading on my temperature gauge it runs great. Only issue I have now is that the sliding door stopped working. Did all the resetting codes but nothing.

[drkoraf]

Thanks for that info! My 2000 Silhouette has 189k on it so I don't know if I'll fix it or trade it in. I love the van but there comes a point of diminishing returns so we'll see, but the fact that I just replaced the shocks, brakes, water pump and put new Pirelli P4 all-season tires on makes the decision harder. BTW, my slider did the same thing. I made the mistake of taking out the radio fuse from the panel under the dash and had no success so I then took out the radio fuse from the fuse block under the hood and left it out for 10 minutes before re-installing it and trying the door reset procedure and voila! My slider now works great!

[kidfam]

What is the name of the test strips at Autozone? I want to get some to check my 98 Sillhouette.