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Q: Cooling system issue - 1999 Chevrolet C3500

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Several months ago, I did some repairs on the truck by myself. I had the radiator replaced. I installed a new lower intake manifold as well as new gaskets. It was all fine. The only issue I had at the time was loss of coolant. Now when I drive it, the truck is running fine and has no trouble starting. However, I had the oil checked and it turned into sludge and I found there is coolant in it. The radiator is full of this now. I thought that it's defective. It is spitting oil and is full of bubbles. I filled the cooling system with air but to no avail. Did I do the repairs badly and caused this or is it something else causing this? Do you have any advice what I should do now?

The lower intake manifold gasket you replaced seals both coolant, and oil passages. It is possible that coolant (under higher pressure) is leaking into an oil passage. It is also possible you have a bad head gasket - leaking coolant into an oil passage when you shut the truck off hot. A professional mechanic, like YourMechanic can help isolate this issue and address the possible coolant leakage you may be having.

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