Why Is There Motor Oil In My Car’s Coolant?

engine oil in coolantI have a Buick Century,  I have noticed motor oil in the coolant. I had the radiator flushed a year ago but after a while the oil was back in the coolant.

Someone told me to have the coolant flushed again and add Blue Devil Head Gasket Sealant to the radiator, and  it would solve all my problems. Do you think that will fix the problem or is there something else you would recommend.


Hi Chris


Wellllllll, not real sure you have a “problem” not to uncommon to see a little oil residue in the coolant from time to time. I would first HIGHLY recommend you get a pressure test or the cooling system , which will show if there is a coolant leak somewhere internally inside the engine.

Sometimes you will see a LITTLE white looking foam/froth on the underside of the engine oil cap, this is usually due to a very small coolant leak at the head gasket which is inside the engine. A little oil can get into the coolant via a leaking head gasket, or just from a previous coolant repair, like a radiator replacement.

This is how you use the tester (which you can borrow from an auto parts store)

This is a quick and cheap test any mechanic can do for you. If you still suspect there is an internal issue then sure, it won’t hurt to try a “head gasket” type of coolant sealer.

I have never used the sealer you mentioned, but have had GREAT success with  K&W Engine Block Sealer, which is available at your local auto parts supplier.

Here is the link to MY instruction on how I use K&W Engine Block Sealer to repair blown head gasket issues and internal coolant leaks.

Click To  – How To Use K&W Engine Block Sealer

Also this is a video I made talking about how to use it…my way, which is easier than the can instructions.

In any case, unless your engine is overheating, or you are constantly adding coolant and or engine oil I don’t really think you have much of a problem here, not enough to get excited about anyway.

Please share this with your friends
Austin Davis

Posted in: Head Gaskets

11 Comments on "Why Is There Motor Oil In My Car’s Coolant?"

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  1. Virgil Singleton says:

    I have a 2001 monte carlo 3400 series and i have water in my oil. So I guess all of my coolent is going directly in to my engine.Do you think K&W engine block sealer would work for me?Is their something else that would work faster? I live in Tn.and it does get below freezing here. Hope you can help.

    • Austin Davis says:

      Yes it would be worth a try. Its a cheap and easy guess that will not hurt anything. If that does not work you will have to remove the cylinder heads and. 1. resurface the heads 2. check for cracks 3. do a valve job and replace the head gaskets….not a cheap and easy guess 🙁

      I would get a cooling system pressure test FIRST, you might have coolant leak in the intake manifold gasket, which the sealer will NOT repair, and its not as expensive and involved as a head gasket leak.

  2. Keith says:

    Hey Austin, great site here. I found it from your youtube video. Any way, my question has to do with a buddy’s 2000 accord 2.3 4 cyl. Recently he had his radiator spring a leak (Common with these plastic tanks) and it’s been sitting in his garage since. He did hit the hot mark for a brief period of time before shutting the car down. He says he just pulled over as soon as the gush of steam came out.

    I’ve owned Hondas in the pasts and the radiators are a real piece of cake so I offered to help him replace it. Upon closer inspection, I noticed grey goop coming from the radiator and under the radiator cap. His oil dipstick was dry, so I can’t confirm that there’s water in the engine oil, but I’m going to pull the filter and do a oil change when I change the radiator.

    My first thought was this is early stages of a head gasket failure being the grey goop in the cooling system. A head gasket failure started making more sense because he had complained about hesitation / misfire a few weeks prior to the radiator blowing up and I was thinking perhaps his distributor was on it’s way out. Also, when I checked his over flow tank there was absolutely no coolant in there, bone dry.

    Any way, it’s got 180k on the engine and he’s looking for a short term solution and I was thinking perhaps the K&W sealant would work. Only problem is that I’m concerned if this will work since there’s oil in the coolant and assuming there’s no coolant in the oil. What are your thoughts?

    Also, i’m wondering if i should bypass the heater core while running the sealant since it’s easy to do. I’m a bit worried about clogging something up as I’ve always been against using sealants for a long term fix. I understand this is super heat activated, but i guess it’s just an obsessive nature of my personality.

    I figured we’d give it a shot since this is short term fix, but I wanted your blessing. Thoughts?

    • Austin Davis says:

      Thanks for your comment! I have had great success with K&W on overheated Honda engines, so it would be a good candidate. You MIGHT have a small seep from the headgasket, I would pressure test it to see if it can hold pressure for an hour. Its not too uncommon to see a small seep on these older Honda’s and it really does not hamper driveability.

      Do a pressure test, replace the radiator and take for a test drive. If you just want to use the sealer anyway, more as insurance, no problem, you can block off the heater core…but we never do, and follow the instructions on my video. Might also do a tune up for the miss complaint.

      The repair should be PERMANENT if there is a leak, and if the sealer can get to it.

      • Keith says:

        Awesome! Thanks for the advise. Just to confirm, in the event there is in in fact oil in the cooling system due to a head gasket failure, would the sealant work? I ask because I started to get the idea that if there’s coolant is in oil, the sealant will work but not oil in coolant scenario. Sorry, for the repetitive question, I just want to make sure you caught that.

        I plan to do this this week and was thinking of immediately putting 70 +/- miles the first trip and then racking up the miles from everyday driving to the 500’th mile before i dump the cooling system and replace with coolant. Thanks again!!!

        • Austin Davis says:

          Keith, it would be worth trying the sealer, but you are correct usually its the other way around that the sealer works best…coolant in oil. It’s a cheap and easy GUESS, so I would try it but I would also make sure there is not a problem with the radiator if you have an oil cooler internally installed in the radiator. That is usually the culprit, or an intake manifold gasket leak.

          • Keith says:

            Hey Austin, so I wanted to report back with positive results. To recap, the car experienced an overheat condition due to a radiator crack on my buddy’s car. I offered to help him change out his radiator and upon closer inspection I found there was some milky grey goop scattered around his cracked radiator. I feared it was the worst case scenario being it’s a ‘00 Honda Accord and head gaskets are likely to go bad on high mileage and neglected engines. I told him the repair was in the neighborhood of 1k and my mechanic confirmed that. He’s in a bind right now and can’t replace the car nor did he want to dump that kind of money into this car even if he could. We were going to just replace the radiator and call it a day until I ran into your video. I decided why not? It couldn’t get worse than it was.
            I had to say it was a long journey as I was really over thinking a lot of stuff. My experience had it’s ups and downs. I started off with installing the new radiator and filling it up to get it back to my place. While doing this, I watched how the vehicle behaved and it gave me a good idea of how bad the head gasket was. If I were to rev the engine, coolant would gush out (I did this to get the car quickly warmed up and get the air out of the system). It was so bad I had to run out and buy one of those big funnels that locks onto your radiator so I would just let water sit in it while the air bleed and not make a mess. I also noticed when it idled, it would have slight foam and air bubbles would constantly come out. These obviously were exhaust gasses that was getting pumped into the cooling system. Also the vehicle idled poorly.
            I proceeded to drive the vehicle for a day. I noticed the cooling system would gurgle when I shut the car off after a drive cycle. I know this was the exhaust gasses in an over pressurized system; even the upper radiator hose was bloated and too firm. Well I got the car back to my place and proceed to flush the system completely with RO water I had on tap (I know it’s supposed to be distilled and in my opinion, RO water was close enough) I did this four times until the water came out really clear. I know using pure water was probably excessive given the car’s condition, but it’s my OCD nature.
            Once flushing was done, I first went with the original K&W orange can as I thought it was less likely to clog anything up being it’s just flaky and seals when dry. I mixed it up with very warm RO water and threw it in. I let the car idle for an hour because I wanted it to be all over the system before I shut down the car for the night. No lie, the car started to idle normally! I was pretty encouraged at this point because it was a good sign! So the next day I capped the radiator and filled the reserve tank and drove off. I had a gallon of water in the trunk just in case as you advised. After the first day I noticed the car did consume a little water from the reserve tank and the system would still gurgle after I shut the car off. However, that problem completely went away after the first day of driving. Another good sign right? I had topped off the reserve tank that once time and drove the car for the 500 miles as expected over the week. It performed just fine, temp gauge didn’t budge past the normal mark, and the car stopped consuming water, no bad signs.
            So come the day I needed to flush out the K&W and put in a 50/50 mix of coolant. Well, this is where the difficulty came in. I was on my third flush of RO water and noticed the vehicle behaved oddly. The bubbles started coming back and slight gushing when I revved the engine was apparent. I was so discouraged! I couldn’t believe it and was really upset because I couldn’t understand how everything that was going so well was going so wrong. I realized that I completely spaced and didn’t turn the heater to hot, and didn’t open the bleeder valve during the multiple flushes. I figured I must have run the engine hot and messed up the K&W seal.

            I was left with one thought, I need to do this whole ordeal again! This time I thought I’d go with the K&W Green bottle with “Nanotechnology”. It mixed up well and when I threw it in the system with pure water again. Unfortunately I started to have trouble. First my heater went out, I feared the worse and cracked open the radiator cap and noticed brown fiber chunks floating around. This had to be the fiber stuff from the green bottle, as it wasn’t there when I flushed the original K&W out. I thought to myself, well I’m just going to go with it since it’s already in. Next thing I know my radiator started to have visible moisture around the seams of the top tank and the system seemed to be more pressurized. I ordered a replacement radiator and waited for it to come in the mail and kept driving the vehicle in the meantime. The radiator stopped weeping and the system returned to normal pressure. Although the temp gauge did move a tick past its normal mark one time while driving the vehicle, but that went away shortly after I managed to put a little over three hundred miles on the vehicle and I wanted to get the K&W out. My nerves were peaking!
            I got the new radiator and I proceeded to actually back flush the cooling system and heater core separately with a garden hose. Chunks of the Nano K&W came out and after a good long flushes and back flushes, but I was confident all the stuff eventually was flushed out.
            I installed the new radiator and flushed out the system once again with RO water and proceeded to put in coolant. Being that I already had an engine full of RO water, I threw in a bottle of concentrated coolant as this would have been the proper 50/50 of coolant and water. To my surprise, after bleeding the air out the three were no bubbles coming out! I was shocked! I also decided to push my luck and rev the car to 3k rpm until the cooling fans came on. NO GUSHING COOLANT! I did this for another fan cycle and the coolant in the funnel was perfectly still! NO BUBLES OR GUSHING COOLANT! I let the car idle for an hour and the coolant in the funnel was still. The signs of the head gasket failure I had previously were gone! The car seems to be performing fine and clogged heater was working again.
            I checked the compression after everything was wrapped up and I got decent readings all across: 186, 183, 185 185. Unfortunately I didn’t do this Prior to adding K&W because I already knew there was a head gasket leak. How long this will last for? I have no idea, but I am fairly confident I just bought my buddy a year of a trouble free cooling system as hoped.
            Thanks again for that video and your advice. It was your video that turned me onto this idea and look into K&W as opposed to the other brands that I was worried would clog my system. I was always a sceptic of quick fixes and I’m a fix it right kind of guy, but in this situation, the mechanic in a can fit the scenario and I love experiments! HAHA!
            Sorry for the long reply, but I wanted to put this out there for anyone who might have a similar situation. Good luck!

          • Austin Davis says:

            Awesome Keith, thank you so much for your detailed reply. Hopefully it will benefit others with similar situations.

  3. mike b says:

    Im having the same issue with my mustang. Should i use a sealer in the coolant system or one that goes in the motor oil

  4. Anonymous says:

    There is certainly a great deal to find out about this subject.

    I like all of the points you’ve made.

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