Hey guys. A fellow Reatta owner is having a weird issue that we can't quite figure out...

He'* getting oil in his coolant resevoir, however, the engine oil seems to be free of any coolant. He has drained it out and checked it. We're not certain if its engine oil or transmission fluid yet. He'* not getting a lot of oil in it, but there'* a bit.

3800s virtually never have bad head gaskets, so we've ruled that one out for now, though it is possible this is an uncommon case. A while back he had the timing set replaced, so there may be a possible problem there. He said that the mechanic that did it isn't the best, so do note that. BTW, do the timing cover and water pump bolts need thread sealant or RTV on them?

Is it possible for the stock tranny cooler to leak into the radiator? They are built into each other after all, but I don't know how they're separated from each other inside.

Another thing we thought of is a possible breach in the intake manifold gaskets. Oil/coolant pass by each other there.

We're both surprised that we've got oil in the coolant, but no coolant in the oil, for as you guys know it typically goes the other way around.

Thanks guys.

Id suspect the radiator first because the car probably would be running like hell and overheating in this situation if it were the intake gaskets.

pull the oil cooler/trans cooler lines and do a pressure check on the cooling system and see if coolant comes out of the holes for the coolers on the radiator....

It'* just a loop of tubing inside the end of the radiator, and yes, it can leak transmission fluid into the radiator. It would be good to check the transmission fluid for traces of coolant.

If it'* engine oil, there'* only a couple of places where the high-pressure oil could be forced into the lower pressure coolant circuit without having the reverse happen when the engine is shut off.

I guess what I'm saying is if he'* not seeing coolant in the oil, but just engine oil in the coolant, then it would have to be a crack inside the block or at the rear cover where high pressure oil crosses from one lifter galley to the other and also lubes the balancer shaft. That'* the only place I can think of where high pressure oil is near a coolant passage on the same gasket.

Additional thought... Did GM ever offer a factory aux oil cooler on the 3800 ? If so, there'* another potential leak point, since GM did some of there oil coolers backwards (instead of routing engine oil up to a cooler near the radiator, the used a aluminum heat exchanger at the oil filter boss and routed coolant to it...kinda bass-ackwards, but it did work on the V8'*)

CLM: what are you referring to as the "rear cover"? The timing cover?

As far as I know, yes, Reattas have the tranny cooler that connects in with the radiator. If it really is just a tube inside of it, I can see how a cross between them is possible there.

My fellow Reatta owner, Nic, has read you guys' posts and is going to look into it tomorrow. He wanted me to add to this that he had to add a pint of ATF, so this may very well be the issue...the transmission lines in the radiator.

If I'm thinking right, the ATF is under higher pressure when the car is running, thus putting some ATF in the coolant. I suppose its possible that coolant may be getting into the ATF with the engine off, but it may just be a pinhole which won't let much through at all. I'm going to discuss with him the possibility of having the ATF lab tested by Blackstone Labs quick, which should be the show stopper cuz they can pick up any trace of coolant in it

Thanks again guys

My mistake, I was thinking of the Series II blocks with the rear cover. An LN3 wouldn't have that, as it just has freeze plugs & pipe plugs on the bellhousing end of the block.

BTW, there'* an instant test for a leak in the transmission cooler. Get under the car and disconnect the hose clamps that connect the transmission cooler to the transmission. Plug one hose, and blow compressed air into the other one. Now look down into the radiator...see bubbles and you got a leak in the cooler.

The leak is probably one-way (ATF to coolant) The transmission cooler lines operate at a higher pressure than the 10-15psi of the coolant circuit.

My fellow owner is going to have CLM'* test performed tomorrow morning. Thank you guys, from the both of us.

I've got an update...

Nic, the Reatta owner, did the transmission cooler test (air compressor air into one line) and didn't get any bubbles. This would mean that the tranny cooler is okay.

He then had the system flushed out 4 times and cleaned the inside of the coolant tank. He'* starting fresh to see what happens. He also told me that they've found another loose bolt in the water pump / timing cover area. He'* also certain that he didn't have this issue before the timing chain was replaced.

Nic again said that the mechanic that worked on his timing chain has a bad habit of not tightening hardware (not just torquing, but just tightening). Its looking like the issue is somewhere in the timing cover. You guys think this is plausible still?

And another thing...he'* also found a coolant leak with the intake manifold.

Thanks guys.

Correction: Nic pointed out to me that the intake manifold leak is oil, not coolant

At this point, I'd be talking to the mechanic'* boss. There'* a oil passage on the front cover left side, just below the water pump, that is very near the coolant inlet on the block face. If the fellow turning the wrenches screwed up, it is possible that the coolant and oil could be mixing there....though, I would expect to not only find coolant in the oil, but the thing would be bleeding fluid like crazy.