Oil in radiator
 

Hi, I have a 1998 silverado with a 5.7 vortec engine, 124,000 miles. I recently started to experience a miss while pulling hills at highway speed, I started to look into it today and found I have what appears to be engine oil in my radiator, it's actually a blackish thick fluid when I open the radiator cap, not the milky white that you usually see when water and oil is mixed, would this maybe be a head gasket or intake manifold gasket? Any help please? What checks might I do to find this problem. I have also lost some anti freeze from the holding tank, but do not see any water in the engine oil.
Thanks,
Karl

Gotta do a compression check on your cylinders. The one place that is common to have a leak is right above #8. Do that check first.

You could also have a leaking oil cooler in the radiator. I would say that is the cause more likely than a cylinder leak is, but do a compression check anyway.

Yeah if ur cylinders check ok then check for oil coolant leaks.

Hi again, thanks for the ideas, I will try to get the time to look into it this weekend. I will let you know what I find.
Karl

Hi, I havent been back in some time due to a heart attack and open heart surgery, the oil cooler in the radiator was bad, and the miss was from a problem with the vortec heads. I had the heads redone and the problem was solved. Thanks to everyone who answered.

wow good thing you're okay!

Glad you both got all fixed up (you and the truck that is).