I have the subject engines 1989 vintage. They are closed cooling systems (heat exchangers). I'm getting a small amount of engine oil in the heat exchangers. There is no water in the engine pan. Does anyone have any ideas how the oil might be getting into the closed cooling system. Engines are running fine and they have 800 hours. Thanks

Oil cooler? Head gasket?

Which SIDE of the heat exchangers are seeing the engine oil?
You have an oil cooler also plumbed into the loop, and you may be losing oil from the oil cooler, and then it could be getting into the raw side of the heat exchanger.

If, however, you are getting oil in the closed side of the heat exchanger, then it's from an internal source.

I'm thinking oil cooler as well. on my crusaders the oil cooler is before the heat exchanger...

Thanks for the responses. I'm seeing the oil in the closed side cooling system. When changing the anifreeze, I noticed some oil in the plastic catch tank for overflow of the coolent. So I'm guessing there may be a problem with the heads and/or head gasket.