Recently I was given a 1989 Buick Park Avenue V6, it has 100k, one owner, garage kept, and is overall in mint condition, all original, it seems to run beautifully. However, upon checking the fluids, the trans and oil are clean, but there appears to be oil in the coolant reservoir(appears brown, and thick). Research hints it may just be the oil cooler, and to replace the radiator/hoses. There is no smoke, it runs smooth and quiet, if I hadn't check the fluids I wouldn't have known anything was off. If it's a leak, must be slow, as it isn't yet noticeable. I honestly don't know how old the coolant is either, this legitimately sat in a garage for over a year, and possibly longer before that. Curious about some other recommendations, with no other symptoms, i'm hesitant to jump right to a head gasket or cracked head. That would also make me sad, as there are maintenance records from the elderly man who owned it until he passed, and it was obviously well loved. As mentioned, she starts right up, quiet as a mouse, and runs smooth, no smoke.

If it seems plausible its a crack in the cooling system, looks like I can get what I need for under a $100 and easy fix, thoughts?

 

 

Sometimes people add "stuff" to a cooling system with the hope of doing something good, we don't know if that was the case here.

It might be a good idea to flush the cooling system and add only the correct mixture of anti-freeze and water and see if the oily condition returns. If so, you go from there , if not the coolant change will certainly do no harm. What do you think?

They don't make em like that anymore and you found one of the good ones ! Nice car and in great shape.