Oil in engine coolant?

[JSWrightOC]

Subject: Oil in engine coolant?

Hello everyone, long time lurker, first time poster. I come here seeking advice on a problem I've come across...

A friend of mine owns a 2000 Chevrolet Malibu with the GM 3100 engine in it. The vehicle has about 105k miles on it, and the owner has owned the vehicle since it had about 23k. Recently she has complained of a coolant leak, which I traced to the coolant reservoir overflow hose. The cooling system in this vehicle uses a pressurized type coolant reservoir, with a 15PSI pressure cap venting to the atmosphere. I suspect that the relief valve in the cap is bad (though I have no means of checking it) but that is not the primary reason why I am posting here.

These are my observations -

I noticed a brownish-grey residue inside the coolant reservoir clinging to the sides, and a few globs or drops of it were floating on the surface of the coolant. I scraped some off, and it feels greasy/oily when rubbed between the fingers.

The engine oil looks used, though clean (doesn't have a chocolate milkshake look), but it is well above the full mark on the dipstick (on a level parking lot). The oil was changed a couple thousand miles ago. As far as I know, the user doesn't top off her oil, and I don't think the lube place would overfill it that bad (I estimate 1/3-1/2qt high, after 2000 miles of driving). My observations on the oil may have nothing to do with the situation.

None of the auto parts shops in my area carry a glycol test kit for engine oil, and I am not aware of any kits that test for oil in the coolant (which would be more useful in this case). My initial conclusion is that there is oil in the coolant, and possibly coolant in the oil, which would mean a bad head gasket or preforated block.

-Can I find a single glycol test kit anywhere?
-Does a test for oil in coolant exist?
-Thoughts for the cause of the symptoms?

I had a couple people suggest that perhaps a leak sealer was added to the cooling system, but the owner has had the vehicle since 23k miles, and has never added anything but antifreeze and water. I can't imagine anyone putting leak-stop in a cooling system that new, unless there was a known problem with coolant leakage from the factory and a sealant was added as a precautionary measure.

Any advice is much appreciated!

 

[Gary Allan]

Although there may be something sinister going on here...the "scum" in the expansion tank is not uncommon (for many of my vehicles -anyway). You will, no doubt, get many responses here that say "it's the intake gaskets" ..simply because you said "coolant leak" and it's one of the alleged intake gasket leakers (or so I believe) ..but they probably stopped reading there and didn't catch the residue you report in the expansion tank. This is the first time, for me anyway, that this has been reported for this situation as a side effect. That's not to say that this isn't that situation ...

Do a used oil analysis on the oil ...that will tell you of any migration of coolant into the oil. It won't tell you if oil is in the coolant. I haven't seen it work both ways yet.

Bulk delivery system frequently overshoot on the dialed in amount (or the clown dialed in the wrong amount).

 

[Vilan]

Are they using a Dexcool type coolant? If they're using standard green coolant, that stuff might be silicates depositing out. I use green, and when I cleaned out my overflow tank a couple months ago, the bottom had a pretty thick layer of goo the same color you mentioned.

 

[JSWrightOC]

Gary,

I'm pretty sure the leak is from the overflow tube. After the owner drove the car to meet me at the auto parts store, there was fresh coolant spilled in the engine compartment directly below the overflow tube, and there was no pressure buildup whatsoever in the coolant lines. I have a 2000 Grand Prix GT with the 3800 II engine, so I am familiar with the intake manifold gasket leak - mine has already been covered under warranty a few years ago. This 3100 engine has a metal intake manifold, so I am not sure it suffers from the same problem that the 3800 does (which has a composite upper manifold).

Vilan,

Yes, they are using Dex-Cool. The coolant in the system is a nice orange color, probably starting to get a little old (2000 model car, it's 2006 now, the stuff is good for 5 years?) but there is no standard coolant in it that I am aware of.

When I removed and inspected the pressure relief cap, I noticed there was a thin oily film on the inside, and I could see where the surface tension of the coolant droplets gave it that "water on oily surface" appearance. The cap felt oily, too. After seeing that, I gave the gunk in the reservoir a closer examination.

I'll reccomend an oil analysis, and I've already told her that she needs a new pressure cap and a cooling system flush. A long road trip is coming up soon, and I'm concerned that, if it is a head gasket, it will leave her stranded. This is the only vehicle she has to drive.

Thanks guys for the quick responses.

 

[lewk]

I would also check the coolant recovery tank to be sure its not cracked or broken. air introduced into these OAT type coolants can cause the very situation your describing.my astro had a similar look and feel when I changed from green to dex-cool. It was flushed by a shop. no problems now, keep the coolant level full and under no circumstances would I leave the coolant in for 5/150. try prestone instead of the texaco dex-cool. much bettr product imho. good luck