Quick Q needs Quick A: trace oil in coolant

Don’t let the title fool you. Unlike every other Q&A I’ve found in my research, this is not a case of an unknown source of oil leaking into the coolant. It’s actually much stupider — I mean, simpler …

Q: If a coolant-related repair had to be redone, and maybe 1/2 of the 1-week-old coolant was caught, but ran over some other parts on the way down so it was slightly darker and obtained a rainbow sheen, and that liquid was strained for solids but otherwise carelessly re-applied, how much trouble is that trace amount of oil likely to cause? In short, is it worth the time and expense (and, risk, in my neighborhood) to empty, flush, and fill again, or is that little bit just not worth the trouble here?

I think this basic Q could apply to all makes/models, but I’m no expert, so in case there are nuances here: 1997 Honda Accord LX with >315K miles and a 4-yr-old rebuilt engine. If the type of repair involved matters, it was replacing a heater hose from the engine block to … wherever that goes. Also, I’m only trying to keep this thing going a few more years, at least until the other car payment is done.

I wouldn’t worry about it.

If the coolant was strained before it was reintroduce and with just a tinge of oil to it won’t cause a problem. Afterall, when transmission coolers fail inside radiators they dump a lot of oil into the cooling system. And you never really get all the transmission fluid out of the cooling system.

Also, the cooling system doesn’t have any kind of filter. So whatever caused the coolant to turn darker will just circulate with the coolant.

Drive on!


@Tester: That was indeed a quick and appropriate answer which saved me time & effort and allowed me to drive the next day (vs. keeping it stationary until I could flush it). Thanks!

I agree with tester, but I would add that you should keep an eye on the oil and the transmission fluid. Note if either starts to take on a milky appearance and if they do, then action needs to be taken immediately, especially if its the transmission fluid.

Also keep an eye on the coolant overflow tank. If it starts to build up a layer of oil on top, look into this right away too.