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2000 Honda civic oil in antifreeze resevoir

I have oil in the little plastic resevoir of my 2000 Honda Civic. It does not overheat and I noticed that their is no foam in the oil dipstick (no water in motor). Somebody told me that it is my radiator. Any suggestion…Thanks in Advance…X

Automatic or stick?

I suspect that Remco is wondering if it’s tranny fluid in the coolant. The 2000 Civic automatic uses the same unit to cool both the tranny fluid and the engine coolant.

I’d suggest that you check your tranny fluid per the owner’s manual before driving any further.

If you have an automatic transmission, there is a heat exchanger inside the bottom tank of the radiator that the ATF is pumped through to keep it cool. If this leaks, then you would get oil in your overflow tank. Check your transmission fluid for any discoloration, it should be bright red.

If there is any discoloration of your ATF, you must fix this immediately or you will damage the transmission. Honda does not recommend that you flush their transmissions so you will need to get the radiator replaced first, then either do three to four transmission drain and refills in a row or find someone that has a fluid exchange machine, not a flush machine. You want one that uses the transmissions pumps to exchange the fluid, not one that has its own pump.

Personally, I’d just do the four in a row drain and refills in accordance with a procedure published by Honda. The Honda dealer should know how to do this. BTW, use only Honda DW-1 ATF, nothing else.

Does the contaminated coolant only appear in the plastic reservoir and not in the coolant in the radiator?

I’ve noticed that on my Hondas, the coolant in the reservoir can often get dirty and look nasty while the coolant in the radiator and the rest of the cooling system looks fresh and clean. It is due to dirt in the plastic reservoir, not oil.

This begs the question: Are you sure it’s oil in your coolant, and not just dirt?

@the same mountainbike - yup. That’s exactly what I’m thinking. ATF will feel and look like oil if it is mixed with coolant.

Yup, that it will. I hope we hear back from the OP. He/should could be on the cusp of a serious problem here.

Found what I thought was old dirty oil in my granddaughters 1993 Buick Skylark’s coolant tank. Checked trans fluid, no sign of antifreeze, none of the spark plugs was green. Car was running finr except for a noisy timing chain.

Took it to my mechanic who has a busy, high volume shop. He said " I don’t think it is oil and I don’t think it will hurt anything. They all do that"- presumably old GM cars.

The only thing I can think of is that it ts a breakdown product of Dexcool left in too long.

The car ran fine for the next two years and then she sold it.