By mistake, I put 4 qts of 10W30 engine oil in my radiator. How can I clean it out? I've seen suggestions for using dish washing detergent. Is that safe? I am thinking of using DAWN because it emulsifies oil. What do you think? I have a 2000 Toyota 4 Runner 3.4 L 5 speed.

  • Interesting. I wonder how well the oil cools. Run it as an experiment, use radiator flush kits to flush it out. There is a release valve below the radiator. Add ample water and flush agent in the radiator as the car is running and also, add the same to the reservoir. Use distilled water the whole way. Aug 9, 2017 at 20:29
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    Welcome to the site. I'd highly recommend you not use DAWN dishwashing liquid to clean out your engine. While it would ultimately break down the oil, it will also foam to no end. This will cause you huge issues in the end. Foaming (to any degree) will critically degrade the cooling system which relies on contact of the liquid to the metal to transfer heat. Also, once the Dawn is in the system, what are you going to use to get it out? Also, running the engine while pouring water into is a very bad thing to do ... great way to warp a head, especially aluminum heads. Aug 9, 2017 at 22:33

3 Answers 3


Check out how to flush your system on this SE question : How do you clean out blue devil (sodium silicate/liquid glass) out of your cooling system?

DO NOT add DAWN washing up liquid - this used to be added to the fountain in the square in Coventry by students and would put foam down the street for a hundred yards... :)

Flush the system and you can use tap water for the flushing, but once you are done use the correct fluid / water mix and run it and keep an eye on it.

I don't think you want to use your vehicle as an experiment, unless you have a spare...

Do note that some racers do add oil to the cooling system, at least in the past, to reduce friction form the pump but only 10 or 20ml...

A quote from the link (to prevent link rot...)

If it is not sticky, then you can use a garden water hose, as long as you have a better than good flow rate, fit the hose to the bottom rad hose and feed the output from the top hose into a large bucket.

Use the full flow rate but it may be easier to remove the thermostat - otherwise you have to have the engine running hot to open the 'stat... Even if you remove the 'stat then it can help to have the engine running but it won't get hot.

Also, do the same for the rad...

If it is sticky then you may consider a tank and external pump to do the same thing, oh and be VERY careful if you add a chemical to help remove the "sludge". Make sure it won't kill the seals.


The reason for dishwasher soap is because it will not foam up. If you already ran your engine you will need to flush it a few times most likely. If you didn't run you engine. You could remove your lower radiator hose and flush out the radiator. But will most likely have oil residue in the coolant no matter what. You'll just need to get as much of the 4qts out. Good luck.


I know these engines (Toyota 3.4L), so I would suggest you to remove radiator (4 bolts, 2 from each side, 2 hoses to engine, no transmission oil cooler, as it is manual as I understood), and just run tons of water through it. Also remove thermostat (3 bolts, easy to remove) and run tons of water through upper coolant hose. This way you will make sure, that no harm will be done by chemicals. After that I would just use distilled water and change it couple of times in 10, 50, and 100 km intervals, until you see, that it does not contain any oil.

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