Hello everyone, looking into buying a ‘85 C4. It has the L98 with an automatic. Seller claims there’s oil in coolant but no coolant in oil. After doing some reading it seems it’s fairly common for these engines that have the automatic for the transmission cooler to go bad. I’ve read the transmission cooler is apart of the radiator, making it an easy spot for the fluids to mix if there’s a failure. I’ll attach the picture included on the post. Please let me know what y’all think and if I’m digging my own grave. I believe it may be transmission fluid in coolant.



 

Welcome to the forums. You have a few options, you can run an external trans cooler and plug the radiator cooler. or replace the radiator. Then flush the whole cooling system.

 

Thank you. I’m willing to do the work but I want to make sure it looks like it’s more likely to be trans fluid in coolant than oil in coolant. Do you have an opinion on the picture? I would probably replace the radiator if it was the problem.

 

I don't see a picture but if there is oil in the coolant it comes from the transmission cooler. It is possible to get engine oil in the coolant if you have an engine oil cooler in the radiator that I don't think you have. Lots of replacement radiators out there, Summit racing ebay, Amazon, Just need to make sure it fits that car. 2in thick radiator would cool it just fine.

 

Welcome to the forum. If it's transmission fluid in the coolant then there's a possibility that there's coolant in the transmission fluid. To be entirely sure of which is the case, you could take a sample of both and send it off to a lab for analysis. Depending on what the results are, then you could flush one or both.

Let us know how it works out.

 

This is the image

 

Well that's about nasty. I would flush the cooling system before I replaced the radiator so you don't contaminate the new radiator. Fix a bypass hose on the transmission oil lines to the radiator, just take a hose and attach the trans lines together and keep it from the radiator until the new radiator is replaced. There is a radiator Flush you can use which is basically TSP that works well, Years back I mixed regular (green anti-freeze) with old Dex-cool and it had that rust color (nasty) and then I flushed it out later, it looked bad. one good long flush should do it. Off subject all the fluids in your vehicle should be replaced after 10 years, brake fluid power steering fluid, coolant, transmission and differential if needed.