2015 Chevy 1500, 5.3 Oil overflowing coolant tank. No water in oil.

Checked oil cooler in radiator both with 20 psi of air and 22.5 inches of vacuum. No evidence of leak.

Old school, so I pulled the left head, then realized this motor has no high oil pressure anywhere near a water jacket at the heads.

Any other ideas??? Or should I pull the trigger and blame the block?

  • So, there is oil in the coolant? If yes, that sounds like a blown head gasket... Either on your left or right bank...
    – Alimba
    Mar 14, 2020 at 12:24
  • 1
    I'm with @Alimba here. The most common cause of this is a bad head gasket where the oil, which is at a higher pressure than the coolant, is flowing into the cooling system. It could be a cracked block but a head gasket is much more likely.
    – jwh20
    Mar 14, 2020 at 12:29
  • You two don't pay much attention (Alimba & jwh20)? There are no high pressure oil passages which the head gasket contains, so it cannot be the head gasket at fault. Oil moving to the top end of this engine flows through the push rods. The only oil flowing past the head gaskets is return oil which is low pressure (er, no pressure?) and is gravity fed back to the sump. Mar 14, 2020 at 13:47
  • 1
    To the OP: Are you sure someone didn't add oil to the coolant on accident? Mar 14, 2020 at 13:48


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