Alright everyone. I'll try to make this quick. First of its one of those rare 95 SE preludes. H23a1. We had one of those small radiator hoses in the back start slow leaking while under pressure. The car started to overheat. We caught it relatively quickly, then found the issue and replaced the hose. Coolant was off color milky. We replaced and moved on. Coolant seemed to disappear, and the person who did the work did not bleed the system. It overheated for a short time again. When I say short time i mean less than 30 seconds at idle.
We Drain coolant, It's milky. I'm thinking head gasket because of the overheat. I put those head gasket tester kits on it. Two different ones, neither showed positive for exhaust gases. We changed the oil and transmission fluid after all this and no signs of water in it.The coolant in the radiator stays clean until it goes through the engine. I pressurized the coolant system to 20psi and used a bore scope to see if there was any coolant bleeding off into the cylinders. None. Held pressure for 30 minutes. The thermostat was definitely sticky/sticking so we replaced that after all the fluid changes. After running the car again, coolant still looks like someone put milk in it. On the last coolant change we drained the block and the radiator.

I'm thinking maybe the oil cooler is contaminating it somehow? Completely at a loss.

Any other ideas on what is causing the milky coolant? Could it be residual?

 

2 things I would check is the head gasket might be leaking it's coolant into the oil and not into the cylinders. Though time consuming is to remove the oil pan and pressurize the coolant system again and watch for leaking coolant inside the block.
That or remove the oil cooler, cap one line connection on it, attach a line to the other, submerge the cooler in water and pressurize the line watching for bubbles if the cooler is leaking..

 

Thanks Max,
Those are both good ideas. The oil looked fine when we just changed it though, No liquid or off color. If anything the transmission fluid was what looked bad, but it just looked brown, which didn't surprise me because most of the fluid in the transmission is 25 years old. (previous owner didn't change it, so although it was very low mileage when we got it, it still had the original trans fluid.) I have done two changes so far for the tranny. The radiator and therefore trans fluid cooler has less than 500 miles on it, so I'm hard pressed to believe that is where the issue is, but it could be. Plus the fluid doesn't seem to turn color until it goes through the block, or maybe it just needs to circulate? Maybe I will bypass both coolers and see how it plays out in the radiator. Its cold out right now so It would be the time to do it if I was going to.

Think i can get away with bypass without a proper cooler in line?

 

I think I kind of misread your info.. Your talking about the oil from the tranny and not the engine oil? Does your car have a auto tranny with the oil cooler running through the bottom of the rad? If so, then it could just simply be the radiator needs to be replaced as the cooler line inside may have developed a leak.