Oil in my coolant tank!!!!


Asked by Aug 28, 2013 at 09:29 PM about the 1998 Buick Century Limited Sedan FWD

Question type: Maintenance & Repair

There is oil in my cooling tank. I think it's engine oil because we are always having to
refill the engine oil. I knew we had a leak somewhere but today when I went to refill the
coolant it had a lot of oil in the tank. It pretty much looked like the cooling tank was full
of oil. My oil change was 3 months ago and it wasn't like that. Been driving just fine,
just always needs motor oil. I just buy it and fill it up again until I had the $ to go get it
looked at. It does NOT overheat or drive rough. I don't smell anything when I turn on the
AC. Anyone have any idea what it could be?! I fixed an intake and outtake manifold
leak and a crankshaft sensor about 4 months ago. Could the leak be back? Could it be
something less expensive??? Should I not drive it at all until I get it to the mechanic. I
can't get it fixed for at least 3 more weeks. Anyone know what it could be?!

16 Answers


Oil in the coolant means a gasket has failed. Usually the head gasket or could be a lower intake gasket not installed properly. I would not drive the car anymore till you fix the issue. You don't want the 2 fluids mixing. Besides fixing the gasket, your looking at draining and flushing the coolant and oil probably multiple times. Hopefully water isn't mixing in the engine. Get some mechanics to look at it to give you some estimates, the costs can probably exceed the cost of your 17 year old car.

4 people found this helpful.

Unless it's an overhead cam, a head gasket won't be the issue. Oil in the head on a standard engine isn't pressurised to overcome the coolant pressure so oil wouldn't enter the cooling system until there wasn't enough coolant to overcome the oil.if that was the case the crankcase would be full of coolant. Radiator has an oil cooler In it that runs 40-60 psi oil pressure. That's the only place where the oil would be entering the cooling system without coolant in the oil on an ohv engine. Ohc engine is very possible for a head gasket to cause this.

6 people found this helpful.
Best Answer Mark helpful

Thank you I'll take it in as soon as I can...hopefully my little car can be saved.


Did you end up fixing it? I have the same problem right now and Im trying to decide if i should fix it or not. My car was running fine, no problems at all. I only have about 25,000 miles on it and suddenly the temp light came on and I noticed brown in the coolant container. I took it to a mechanic who said the oil and anitfreeze mixed and I need to rebuild the heads on the engine. I am totally surpised! I went from no problems to having to possibly give up my car because it costs a lot to fix and might not be worth it. I was wondering what the outcome was, if you fixed it and if so, did the problem return anyway? Thank you so much! Any help is needed!

1 people found this helpful.

Rd what type of vehicle is it?


2002 Buick century limited

1 people found this helpful.

Have you ever done a coolant flush? Seems more like the coolant has turned from being old and has clogged the radiator, dexcool turns to a brown clumpy mess after the five year life. It eats up intake gaskets and clogs the cooling system causing the engine to gradually run hotter. Head gaskets on a push rod engine will never cause oil in the coolant without getting coolant in the oil first, unless the coolant is super low to begin with.

7 people found this helpful.

I could never get it fixed! It was too much. They pretty much said I needed a new engine. Hope yours doesn't get as bad as mine. Good luck!

3 people found this helpful.

How many places did you take your vehicle?

2 people found this helpful.

Hi John, I just had an oil change in the fall. Would they have done a coolant flush then? If the coolant was super low, wouldnt i just get a warning light and add more? What would cause coolant to get in the oil first? Ive been reading a lot about the dexcool problem. Is this just because I should have added more anti freeze sooner? Hi X, so from what I understand, you had put money into it and it kept breaking anyway. That is what I am afraid of. Was this all started because of Dex Cool? Im so sorry you had to experience this, I know im really upset about suddenly having to give up my car. I did not expect this at all. Just wondering if I should fix it or put the money into a new car? Thank you both so very much for your replies. They are very helpful as I try to make this decision! Best Regards, RD16

1 people found this helpful.

I took it to 2 places


If you didn't pay extra for a coolant flush then no the coolant wasn't flushed. not all vehicles have a low coolant light but yes if it's low you just add more. If a head gasket blows, intake gasket blows, head cracks, or block cracks that would cause the coolant to enter the crankcase, it won't do it every time though, it would have to happen in certain spots to create a leak into the crankcase, you could have any of those things happen and not get a coolant leak. Once the engine gets up to temp the coolant becomes pressurized, the only way oil would get in the coolant and not get coolant into the oil, at the same time, is if the area that is leaking is an area where the oil pressure can overcome the coolant pressure. With a push rod engine the oil in the head is not pressurized, so before the coolant gets under pressure there is a possibility that crankcase pressure could push a small amount of oil into the coolant but in about 3 minutes the coolant would flow into the crankcase. No coolant in your oil means it's not a head gasket. Oil cooler lines run to the radiator some are engine oil, some are trans fluid (trans fluid is a high deterrent oil), some even have both your engine runs 40-60 psi on the oil and the trans is the same and these pressures are achieved at startup immediately. A leak between the tanks in the radiator will allow the oil to pass into the cooling system while the engine is running, once the engine is shut off you may get minimal coolant that will pass back into the oil cooler but the temp of the engine will generally evaporate that fairly quickly.

5 people found this helpful.

You didn't mention the first shops diagnosis to the second shop did you?

3 people found this helpful.

I'm having the same problem, "unreal" coolant tank has oil, dont see any in radiator or oil. Dont make since. Car runs great! Any thoughts

I think the problem is, "It's a Buick Century 2000". I had the identical problem, put in a new engine. Now, four years later my coolant light came on. Same thing, oil in the coolant reservoir. I just retired and don't want to buy another car to drive 60 miles per week at most. We'll see what the diagnosis might be but suspect it will be a boat load of new parts or "You need a new engine". This seems to be a common problem with the 1998 to 2003 Buick Century, along with electrical problems.


I have had this issue on a 96 5.7L. a 97 5.0L, a 99 3.3L, a 03 3.4L and now a 01 3.1L. I am assuming at this point that the latest 3.1 issue is the lower intake manifold gasket same as the others.The coolant reservoir has oil in it but crankcase is clean, no coolant. Oh and since I have owned these vehicles since 96 and replaced the other 4 before 08 you would think that someone would have notified me about the GM intake lawsuit but no. Pretty sure some lawyers are busy spending the money they owe me.

2 people found this helpful.

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