Question : '96 3100 - Oil Accumulation in Coolant Reservoir

[Century7667]

The subject line about sums it up. I've got a '96 Buick Century that I've owned since new. Meticulously maintained with oil changes every 2-3k, hoses and coolant replaced every 5 years (dexcool). I keep an eye on it.

Last year, I noticed a slow accumulation of a black substance in the coolant reservoir. I'm not sure what it is, but I can only assume it's oil or transmission fluid.

In 2002 the LIM gasket was serviced (extended warranty - I usually don't buy those, but this time I'm glad I did ).

The oil is CLEAN, and I mean there's no sign at all of any coolant in the oil. It is using coolant, but I'm not sure it's related as my wife has commented on odor in the cabin. I might have a heater core issue, but I'm not sure.

The engine has about 148k on it, and otherwise runs fine aside from the cold engine piston slap that it's always had.

Where would I start to troubleshoot this? As it is, the cooling system needs to be opened because the thermostat is stuck open (been that way for a few years). I plan on replacing that, but I'm not sure this is the time, as a fully heated engine will probably stress whatever problem it's having.

What could this be? Head gasket? Leaky trans cooler?

Any thoughts?

Thanks!
Ken T.

[TGP37]

When the engine is cold, remove the radiator cap. Fill up to the top and then start the car. Observe the coolant for bubbles. You should also get a cheap hydrocarbon test kit for the radiator fill. It will tell you if combustion gasses are entering the coolant system.

That indicates a bad head gasket.

A mayo like light chocolate film under the oil fill cap indicates a leaky LIM gasket.

Moisture inside the cab on the windshield indicates a leaky heater core. Also has a sweet syrup smell.

Does the vehicle have excessive exhaust "smoking" when fully warmed up? Or is it dripping water out the tail pipe? Another indication of a leaking head gasket.

[60dgrzbelow0]

This is an older thread with some wise advice from some of the best who labour to give is all good information. Pay particular attention to what "betterthanyou" had to say on this matter:

http://60degreev6.com/forum/showthread.php/38895-3400-leaking-oil-into-coolant

This advice comes from another site...but worth noting for the great referral to Ben and Jon's business for some necessary components to do this repair right:

http://ls1tech.com/forums/racers-lounge/1244388-had-pleasure-repairing-infamous-gm-3-1-3-4-lower-intake-come.html

And it never hurts to get your hands on a set of these:

http://www.ebay.com/itm/1996-Buick-CENTURY-OLDSMOBILE-CIERA-SL-Service-Shop-Repair-Manual-SET-OEM-96-/170761745340?pt=Motors_Manuals_Literature&vxp=mtr&hash=item27c23173bc

[Century7667]

Thanks for the replies and the links! I overhauled the engine's cooling system last weekend (radiator, water pump, hoses, and t-stat). I washed out the coolant reservoir real well, we'll see if it dirties up again.

I have to say though, the oil is PERFECT, and there's absolutely no sign of moisture anywhere in the crankcase, cap, etc.

Still, I am haunted by betterhanyou's words: "LIM gasket. It always is."

We'll keep an eye on it. If the oil re-appears, then then I'll rip the top off the engine. Needs plugs anyway, (149,000 miles! Runs perfect! Yeah, I'm putting in new AC Delco Platinums (original eqiupment in 1996)).

Thanks!
Ken T.

[pocket-rocket]

You should also get a cheap hydrocarbon test kit for the radiator fill. It will tell you if combustion gasses are entering the coolant system.

I just bought one of these from Autozone (I hate that store...) last weekend. $25 for the tester and $8 for the fluid, I believe.

[TGP37]

Still, I am haunted by betterhanyou's words: "LIM gasket. It always is."

Ken T.

The thing is, when the LIM gasket fails at the coolant port, coolant is dumped into the oil. Typically oil will not pollute the coolant in a LIM failure.

A head gasket failure, however, can push oil/fuel/gases into the coolant system and not pollute the oil that bad.

If the oil is bad, LIM. If the coolant is bad, head gasket. Now, it isn't a promise as strange things can happen. Gasket can fail in strange ways like weeping coolant only down the side of the block.

The vehicles history can tell a lot. Neglected auto trans fluid can increase the chance the ATF cooler line in the radiator is busted. If the engine was over heated just once, suspect a failed head gasket.

[pocket-rocket]

A van I worked on recently (99 Montana) never had a coolant change (at least it didn't look like it, and it has around 120k on the clock). The coolant ate a hole in the oil cooler between the oil and coolant cavities and was mixing the two there. Getting that crap out of the engine is one thing, but cleaning it out of the engine, radiator, front heater core and rear heater core just plain sucks.

I did find out putting some dish washing machine detergent in some hot water and adding that to the coolant system works wonders for cleaning that junk out. Otherwise the chocolate pudding like junk likes to stick to everything until the engine gets to operating temp, and then it still doesn't like to come out because it floats on top of water...

[TGP37]

I found connecting a flush kit to the hot water heater really helped. Especially if the heater is turned up prior for extra hot water.

Dishsoap would work because it is a surfactant. Isopropyl Alcohol will greatly enhance the surfactant's job removing the oil. If you can get a hold of some Corexit, that would really clean the oil out very well.

But I warn, Corexit can be dangerous and might not be appropriate. But it WILL remove the oil mess with a flush, lol. Might be overkill.

Even some laxatives would work well cleaning the oil out. As many are just consumable surfactants. Imagine dumping a laxative in the coolant, lol.

Anything that can precipitate metals and other minerals in the water will also help increase a cleaners ability to remove organic soils on metal walls.

[Century7667]

The thing is, when the LIM gasket fails at the coolant port, coolant is dumped into the oil. Typically oil will not pollute the coolant in a LIM failure.

A head gasket failure, however, can push oil/fuel/gases into the coolant system and not pollute the oil that bad.

If the oil is bad, LIM. If the coolant is bad, head gasket. Now, it isn't a promise as strange things can happen. Gasket can fail in strange ways like weeping coolant only down the side of the block.

The vehicles history can tell a lot. Neglected auto trans fluid can increase the chance the ATF cooler line in the radiator is busted. If the engine was over heated just once, suspect a failed head gasket.

Both are possibilities. The ATF has never been changed on this vehicle, to my great shame. I never get excited about ATF filter changes, and now I'm told it's better to leave it alone. The 4T60E runs great, but the fluid looks really bad. So there's a possibility.

Since this is my wife's car, I don't drive it much, and I don't keep as close an eye as I should. It did get hot a few years ago (low coolant snuck up on me, water pump), but it wasn't "cooked." Still, it does use a little oil, which would indicate to me that it must have gotten pretty hot.

It's looking less and less like a LIM though, as the oil is pristine. Won't make a difference though if I have to peel off the heads.

I'm guessing an exhaust gas kit would be in order. I'll have it again this weekend as the fuel pressure regulator is leaking, so that will have to be addressed.

Ken T.

[pocket-rocket]

Dishsoap would work because it is a surfactant.

I didn't use dish soap because of the bubbles and I read it is hard to get out. Dish washing machine soap doesn't bubble up and came out easy-peasy.

Lol@ the laxative idea. I'm sure it works, but it does sound funny

[TGP37]

You could inspect the spark plugs and see it any are cleaner then the rest. Holding paper 1" from the tail will show a head leak if the paper gets wet. The radiator fill neck will bubble on decel from reving in park (while bone cold obviously).

But, it is entirely possible the ATF fluid is contaminating the coolant, not motor oil. Many radiators have an ATF cooling line and they can burst/crack.

[Century7667]

I wanted to write back to wrap up this thread. It's nice when people give you advice, and well, you all deserve to know how it came out.

In March, I smelled coolant around the car, and it was low. I wasn't sure where, but it was in the area of the water pump (unlikely, only 50k in the pump).

So, I decided enough was enough, and tore into it. The water pump was failing after all.. So, I replaced the water pump, the thermostat (stuck open for a number of years now), and .... the radiator. In short, a cooling system refit. The only thing I didn't replace was the heater hoses (only 3 years old). If not for my wife, I would not have been able to get the lower bolt of the thermostat housing off and on again. I don't see how any man can get his hand in there.

After almost 2 months, the coolant is still Dex-Cool red-orange, no contamination. The transmission fluid looked like hell, but the old 4T60E is still running fine. I've been told not to touch it since it has never been changed. I dunno.

Anyways, looks like it was the trans-cooler coil in the radiator that was the culprit.

Thanks all!
Ken T.