93 civic 178k, D16z6

No evidence of coolant in oil, and vice versa. Car operates normal.
Overflow tank level was high one day, so I looked in the radiator and noticed the fluid level was beneath where it can be seen. Topped off the radiator, and same thing a few days later.

Replaced radiator cap. Same problem.

There is no clogging in the line between radiator and overflow tank. There is also no leak (tested line with vacuum gauge) in this particular line. I put the line onto the radiator, and still no leak with vacuum gauge.

What the frick is wrong here?

 

That is what my car did with a small leak in the head gasket. Get the radiator completely full and take the cap off (cold), start the engine (cold) with the cap off and rev it, look for bubbles in the radiator.

 

radiator leak?

 

I had a 91 civic 1.5 that did this but much much worse. car would push most of the coolant out of system in about 10 minutes and start overheating. i would bleed the coolant and steam would come out for several minutes while bleeding. I have a 94 probe gt that started doing the same thing last year and its currently parked. that car has a fill cap on the engine. after a 4 mile drive to work i would have to add about a 1/2 cup of water to top it off after work.

sorry to say but i agree with MK... head gasket leak. its weird how they seem to leak through the coolant jacket but not leak oil or mix them. and i wouldn't really drive it until its fixed either cuz u can do damage from overheating and also if coolant is getting back into the combustion chambers it will start to corrode and could end up causing ring failure.

 

Yeah there seems to be a constant flow of tiny air bubbles when the thermostat opens. Dang.