Detroit coolant issues

This is what I would do (1) replace thermostats AND SEALS (many don't replace seal) (2) since coolant will be drained, blow shop air through your heater core by disconnecting both rubber lines at inlet/outlet of core as close to firewall as possible. When you refill coolant do not fill to tip top of neck. You must give room for expansion.

 

Mines doing the same thing, Don’t think it’s pushing any water, though. Just replaced Waterpump, as it was leaking, new hoses. Got straight water in it now, Was hoping I had air pockets in system, but I think the thermostats got out of whack, while I ran it low on coolant. It’s happened before, usually after overheating. Did you get yours fixed? I was going to suggest shutting off water valve, if you have an air over electric heater control valve on either the bunk or Cab. A bad one will put air into the system, Usually not until the Cab or Bunk hits the temp setting on heater control knob, then valve closes, and air leaks into the coolant. Puts a lot of pressure, 130 lbs or so, all of a sudden. Hard to diagnose, since it depends on heater temp setting, and is intermittently either full on or full off.

 

You can tell by looking at heat control valves, if there’s a small air line running to it. It’s air/ electric type.

 

I bet you the entire Ranch your radiator cap is weak, tired, insufficient pressure at that cap. Toss it on a cap tester and pull pressure, its going to pop at way less than required factory design pressure.

I had that happen several times and all the kings men and shops could not trace it until I remembered my old 302 ford doing the same #### thing with a weak 3.00 cap long ago. The engine was badly designed as it was but we knew nothing in them days. (Manifold cooling plumbing was not optimal)

 

Good point, I’m going for new thermostats and cap, That covers everything. My trouble started when waterpump started leaking. Just hoping I didn’t cook the head gasket, running it that way.