Sludge/Oil residue under Radiator cap


New Member
Oct 1, 2007
I've been trying to track down a coolant leak from the front and back of the engine. I finally made it out to get a pressure tester for the cooling system, but when I pulled the radiator cap off it was covered in a layer of black sludge, kinda felt like chapstick. Coolank had a light layer of it floating on top as well. I gotta assume it's oil contaminating the system, but does this give any clues as to where my leak may be? The coolant leak is pooling on top of the timing cover and dripping down the backside of fengine. Maybe a lower intake manifold rather than a head gasket/bolt?

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Recently finished repairing my rear
15 Year Member
Aug 26, 2004
West Los Angeles, CA
Possibly bad lower intake gaskets (between the heads and the intake) It's also possible you have a blown head gasket. I had that happen TWICE with my V6 - I was getting exhaust into the coolant causing the same residue you describe. Do you see any white smoke coming from the exhaust? A sweet-smelling exhaust? You could also be burning coolant.