I just put a rigid lower radiator hose in my 89 RS, 305 TBI to avoid the dreaded hose collapse that causes these cars to overheat. The car immediately ran much cooler than ever before, it actually ran too cold. So I decided to replace the 160 thermostat I put in with a 180 thermostat to help it run hotter. Right away I noticed oil in the coolant all around the radiator cap and thermostat, plus it was floating in what I drained from the radiator.

There is no coolant in the oil or trans. The car does not have an oil cooler.

This car has always run great and has never had any problem like this before. My question is what could changing the old lower radiator hose with a much higher flowing hose break to cause oil in the coolant, but not coolant in the oil or trans?

BTW, I checked other oil in coolant posts and they were no help.

 

Auto trans? Could be trans fluid

 

I had the radiator tested today, it's good. I'm looking for a 350 crate motor now.

 

How was it tested? In car with the trans lines off? The internal trans cooler could have gone bad. Just one of a few ways a oil can get in the coolant.

 

It was tested out of the car by a reputable mechanic. I told him I suspected the trans cooler and he verified the trans cooler is fine. The car has 203,000 miles on it. The engine has done it's job, it's time for a heart transplant. I'll be posting pictures but she's going to be sitting for awhile.

 

Gotcha. Good luck with the swap