Immediate coolant pressure

[DylOrr]

I bought a lbz engine out of a salvage yard for a truck. I rarely see any of them come in with troubles because normally a truck has to be running to wreck it. Only one I've ever had a problem with I come to find out the salvage yard runs them on starting fluid.

Anyways, the engine I bought for this truck is being weird. It's building immediate pressure in the coolant system upon start up. I haven't let it sit overnight or anything. It doesn't overheat. Heat works good. Doesn't puke coolant driving. But here's the thing. If the coolant cap is off the coolant will push up until it about hits the overflow tube then it will bubble back down. And continue to do that as long as I let it run. Pushes up bubbles down.

Anybody have any ideas?

 

[DylOrr]

Update. Went to drain coolant. Undid the clip at the radiator and very little coolant cane out. Didn't even drain the overflow. Undid big hose from overflow and drained all the coolant out into a bucket from that hose. Refilled the system and I cannot get coolant into the lower hose. It's all air.

Wondering if I didn't get an obstruction in the lower hose or water pump while everything was apart.

 

[Ron Nielson]

Just a WAG, clean or replace your cap on the tank. The cap lets air in and out at the appropriate time. If it's dirty, it might not work correctly. Many people just wash them with dish washing detergent, very hot water and a brush and blow them dry with compressed air.