Oil in Coolant but no Coolant in Oil

I have a 98 Transport Montana with 137K miles. I have had the classic head gasket failure as I have ready in many posts here back in April 04, 2004. It turns out both heads had small cracks and had to be replaced with remanufactured ones. The shop I went to and who I have trusted for other repairs said they think DEX cool is a disaster of a coolant and recommended to put the classic green coolant in. They flushed the entire system and filled with green antifreeze. $2500 later I was back on the road. Since then I have put on about 20K miles, with no coolant loss, and just recently I had a leak in a coolant hose and lost enough coolant to cause the engine to overheat but I caught it right away and shut it down. Since then I have fixed the leaky hose and replaced the water pump and refilled the radiator and reservoir with fresh "green" ethylene glycol antifreeze again. What I am finding now is that my coolant reservoir has the coagulated light brownish sludge floating on top. Thinking that there is oil in the coolant I drained the oil pan, catching the first bit of oil to emerge, in a glass jar to see if there is coolant in the oil. I could find no evidence of water being in the oil pan. So I am confused. Can oil get into the coolant but the coolant not get into the oil?? How can this be? Isn't it all one oil system? Does this problem point to a intake manifold problem? I did read in one of the posts on this issue that maybe it's not oil at all that is floating on top of the reservoir but DEX COOL residue re-surfacing? I did check the oil fill cap and the pcv to look for the "creamy" substance but found none. I am not sure of the next steps to take. I plan on trying to keep the car for one more year or about 15K miles. Any suggestions are appreciated.

Andy

You ask a good question. Have you looked at the transmission fluid? Don't know what transmission fluid mixed with the green anti-freeze would look like, but it is a possibility that the transmission cooler located inside the radiator could be leaking.

Let us know what you find out.

What you are seeing is leftover Dex-cool that has reacted with air. Think of it as like corrosion. It appears in systems that aren't maintained properly. While it looks nasty, it really doesn't cause problems unless there is a significant amount of it...enough to plug up passages. If your system isn't cooling as well as it should, you might look into it. Otherwise you are probably fine.

If you are paranoid, you can send a sample to an analytical lab like Blackstone Labs (http://www.blackstone-labs.com/). The can tell you for sure for about $20.

But to answer your question, yes oil can get into the coolant but not vice versa. Not real common though.

And I'd also recommend finding a mechanic that knows what the hell he is talking about. Dex-cool isn't a problem. People not maintaining their system is the mail problem. Dex-cool is just the scapegoat. Mechanical failure, like in your case, also happens. Again, Dex-cool gets the blame when it had nothing to do with it.

So what is the peanut butter like substance in DexCool filled radiators?