Small amount of oil in coolant?

Very likely, fix it before it gets worse. It's very difficult to get all of that sludge out of the heater cores and radiator once it starts getting thick.

 

Once you repair the problem, you may want to drain the system, fill with water and dishwashing detergent. It should clean out the system if you run it for a while. Then drain thoroughly and refill with antifreeze and water.

 

Automatic dishwasher detergent, not the handwashing stuff, you don't want it "suddsing up" and piling oily soap bubbles all over the shop or driveway. Probably need to run the system with soap and water a few times to get all the oil, then rinse with straight water 2-3 times.

 

I should have mentioned automatic dishwashing detergent, such as Cascade.

 

It could be the cooler, but depending on maintenance of cooling system, it could be liners that are pitted bad enough from electrolysis or bad ground on block, that oil is being forced into cooling system through pitted liners.

 

Year/make/model of engine?? And what kind of truck would be helpful

 

I have a coolant filter with a water hose bib welded to it. fill the radiator with cascade dish soap and water leave the radiator cap off run the engine up to temp and turn the garden hose on just a bit to overflow the radiator, the oil will float so it help to push it out

 

I have oil in my coolant. its dark black and like grease. will the cascade trick do the job? I was told i had leaking oil cooler by several people.
the truck will run and idle fine. drive it loaded or empty it heats up quickly and i have to run engine fan. Any opinions guys?

 

Might be a head gasket starting to get weak