caurilio

03 s2000 with 80k miles. Car drives strong with no overheating or smoking issues. About six months ago I was doing some maintenance and decided to change the coolant. Found brown oil sludge in the radiator overflow tank and the underside of the radiator cap. Cleaned out the tank and changed the coolant. Rechecked it a few days ago and again, found traces of oil. I read about possible issues with the oil cooler, so I bypassed it and tested it, no leaks. Pressure tested the cooling system, no issues. I have not done a compression test or leak down test since im not dealing with the combustion chamber. Yesterday I decided to flush the system so I can get an idea of how much of what I've seen is fresh and what's accumulated.

After several cycles of flushing water through the system, I finally started to get everything clear. Oddly it eventually got to where there was no traces of oil getting in the system. Will be checking it in a week or so of normal driving.

If the problem persists I will be pulling everything out and having the block and head checked for cracks. Any other advice or suggestions would be appreciated

spets

Are you sure it was actually oil in the coolant, and not just old/contaminated coolant or rust particles? Especially if the coolant in the car was anything other than the OEM Honda coolant?

zeroptzero

bad head gaskets are so rare on these cars. I would have your used engine oil analyzed as it will detect coolant in the oil, among other items.

Have you or any previous owner in the past used Redline Water Wetter in the cooling system ?. That product will fall out suspension and it forms a brownish sludge when used with Honda coolant, it looks exactly like an oil product. It happened to me on past Hondas and I've never used it again. It is a good product for it's intended purpose, but it doesn't work so well with Honda coolant. Just a guess in case you have used it. The overflow tank is where it often accumulates as it falls out of suspension during the cool down process.

caurilio

When I changed the coolant the first time, it was NOT oem coolant. No fluids have been tested, just going by appearance. I'm at least the 3rd owner of the car so I don't know what other fluids or chemicals have been used.

zeroptzero

I'm willing to bet it is a combination of different coolants and chemicals causing some sludge in the system over time. For peace of mind send out a used oil sample to a company like Blackstone Labs, if you have oil in the coolant you will have coolant in the oil and it will be detected.

downloader

oil would leave a ring at the top or your coolant reservoir

caurilio

Update: Confirmed that it was oil mixing into the coolant. Check engine light came on about 3 weeks ago for thermostat malfunction. Found out the oil deteriorated the seals on the thermostat. I decided to pull the motor and tear it down and have it inspected and tested by a machine shop. Should know something this week. Will keep this updated with what is found

Slows2k

I'd flush it again and disconnect the oil warmer/cooler 1st.