GM 3800 V6 - coolant in oil

My son has a 2005 Impala with the 3800 engine. I know there are two kinds of 3800 engines - those that have the intake manifold gaskets replaced and those that will have the intake manifold gaskets replaced. This car has 170K on it and I assume the intake manifold gaskets have been replaced - never seen one last that long.

A month ago the car was low on coolant and the tempature was varying a lot. A shop checked it out and found the water pump leaking and the heater core mostly plugged. Pulled it apart, flushed the system and replaced the water pump. About a week later after that work I changed the oil (5000 miles) and sent it in for a check at Black Stone labs. It came back with a small amount of coolant in the oil (.85% - less than 1%) I'm not familiar with the water pumps on these. Can a leaky water pump leak into the timing chain cover on the 3800 series 2? Or am I looking at digging into the engine? When it was low on coolant it never got hot - at first we thought the vanes on the pump were mostly gone - at idle the temp would creep up (Stop light) but as soon as the car started moving the temp would drop back to normal.


Black Stone recommended shortening the oil change interval and of course to keep sending the oil in for monitoring. Beside the intake manifold where else is it common for these to leak coolant into the oil?

Thanks for the help.

At that small amount, If no other symptoms, I would give it a dose of stop leak pellets and see what happens.

At that many miles I would be hesitant to invest a lot of time or money unless it's just an especially well kept car.

If yours has the oil cooler, yes. It can get in there that way.

don't have any specific advise

HOWEVER. my mother in laws buick with 3800 seized completely due to the gasket failure. and the dealer had fixed it twice already.

That's kind of what I was thinking. I wished I had drilled the shop on the semi clogged heater core - I am wondering if its already had some stop leak dumped in it.

The car is nothing special - a $2000 beater to drive getting 25 MPG instead of my F250 that's getting 9 MPG.

The most common issue on those was the upper (plastic) intake manifold had a port that used coolant to heat the throttle body. But when this was leaking the cylinders usually filled up with antifreeze. With that many miles it just might be the lower intake gaskets now too ? I think the lower part is alum.

Lower intake gaskets. Use the GM set. GM fixed the problem and used an aluminum carrier instead of plastic. If the upgraded gaskets are used, they will never fail again. A lot of people like to use the cheap Felpro set that will fail again.

If that's the one I'm thinking about, the heater is known for air locking.

The engine and radiator need to be full or the heater won't work.

In the shop I worked in we saw that on more than one occasion. The transcooler/radiator were a unit and a failure in that component can cause oil in the cooling system or coolant in the oil.

Stop leak is about the worst thing you can put in a car's cooling system. Just about guaranteed to plug up a heater core with the radiator following close behind.

Maybe on an old tractor that has the old brass radiator and no heater core, but never on a car.

With such a tiny amount of coolant in the oil, I would not even worry about it. After all, didn't you say it was a $2000 beater car?

Also, since you already had a plugged heater core, putting stop leak in will insure that it will soon plug again.

One other thing. There is no direct path for coolant to get from the water pump to the crankcase oil. A failed or failing timing cover to engine block gasket is the only possibility that I know of. I suppose that could happen, but it is unlikely.

The upper intake will be the revised plastic intake (metal insert for egr passage) Even if it was leaking it would burn through the cylinders (and run like crud-misfire), or hydro-lock the cylinders. Coolant can still migrate into the oil here, but the above symptoms would come first. There is no oil cooler on this engine so no leaks there.

The lower intake gaskets are a known problem area and they can leak internally into the lifter valley. Timing covers are known to leak too but usually external. I really can't say stop leak products are good or bad, and most will not clog anything if used as directed. Some OEM's actually have their own stop leaks, mainly the pellet type, see below.

Most 3800 engines have already had a dose
of the AC Delco pellets during a fubar
recall 15 years ago for a supposed
throttle body coolant leak. We replaced
the throttle body nuts and put stop leak
in them, but I think the real reason was
to stave off intake gasket leaks due to
the shear volume of 3800s that exist.

"There is no oil cooler on this engine so no leaks there."

Some of them did indeed have an oil cooler.
Click here

Wouldn't it be coolant in the transmission - like a lot of Nissans end up with?