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.

You know what causes that :slap: 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.:sunglasse

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.

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.

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.