Hi all. 1987 F250 with 460 - carbureted. I finally sorted out wiring and vacuum hoses and rebuilt the Holley 4180. Put it al back together and fired right up. A little timing adjustment and it runs beautifully. No smoke from the exhaust at all.

After test driving it about 15 minutes, I noticed the temperature gauge had not moved from the Cold position. Popped the hood and the overflow tank was overflowing out the top. I figured stuck thermostat. Let it sit til the next day and put in a new t-stat. There was no coolant below the thermostat housing.

Installed my new stat, started it ip and let it run long enough to see the temperature gauge finally move a little bit. Coolant was still bubbling out of the overflow. I did not feel any water moving through the upper radiator hose. When I reved it, a couple of times, the upper hose sucked in.

I let it cool down a bit to remove the cap so I could check for movement of the coolant. I added water and when I started it, the water started belching out of the radiator neck. Big belches. Then I noticed bubbles in the overflow. I know - blown head gasket. BUT, is it possible that there is just a huge air pocket in the motor that needs to be bled out? I didn't want to run it that long in that condition. Pulled all the plugs and they are dry. No white smoke from exhaust. No coolant in oil. No oil in coolant.

Looking for someone's advice on the best place to begin troubleshooting. Pressure test radiator? Compression test?

Thanks!

 

From my experience, it shouldn't take that long to get the air bled out. It could be thats all it is though.

 

In 23 years I've never had a problem filling the block.
The heater loop bypasses the thermostat so I don't see how the Tstat could become airbound.
The radiator is holding if you don't see any coolant externally and the cap vents to the catch tank. Pressurize the loop and see how long it takes to bleed down.
I would say the pump impeller is rotted or sheared off if it weren't sucking the hose flat.

 

Your symptoms do lean towards a blown head gasket except for one big one, the hose being sucked closed. That pretty much proves it's not a head gasket as a head gasket leak would pressurize the coolant system. And proves that the thermostat isn't letting anything by.

Does the system build pressure when hot? Can you squeeze the hose when it's hot, if you can you need a radiator cap.

I always drill a 1/8" hole in all my thermostats to make sure I don't trap air under the thermostat, I suggest if your cap is good that you pull the thermostat one more time and drill a hole in it to make sure the air under the cap can escape.