Weird over heating then not (Long story)

[akbossman]

In April I put a new thermostat and water pump on my 91 Navajo 5 speed with 260K miles. Thursday I got on the throttle hard and it stuck so I pushed in the clutch and then quickly turned off and on the ignition. I stop at the store for 4 or 5 minutes and come out to loud hissing sound. I drive to the back of the parking lot and it is pouring anti freeze out under the truck pretty bad. I am only 6 miles from work so I try to baby it back and it over heats bad. (my bad) I let it cool add water and no leak. (OK bad water pump?) I let it run and every thing seems OK until I turn it off and the overflow tank that I had completely filled was boiling. I pulled the hose leading into the overflow tank off and super hot air came out from quite a while. When I drove it home it once again overheated and boiled the overflow tank. So I again figured bad water pump.On Monday I had to take a short trip that turned long and no problem except I have no heat????? Tonight i just pulled the fan and belt and turned the pump and it seems to move water from the noise I hear.
Do you think the pump is bad? I hate to change it if it is something else. The large amount of water still is weird. I guess I pull it of in the AM. Thanks.

 

[Anime]

The thermostat is stuck closed.

When it gets stuck closed, the water boils because it's under extreme pressure and has nowhere to go. So it backs up, and boils over into the overflow tank, which of course overflows and the water/coolant leaks out.

Replace the thermostat with a 195 degree Stant superstat. Add new coolant and do the burp procedure to purge all the air.

You may also need to check for oil leaks from a blown head gasket if it overheated really badly.

 

[akbossman]

Thanks Anime! It was replaced at the same time as the pump Doh! here we go.......

 

[Turdle]

Get a new radiator cap also--it might be venting pressure and allowing boil over.

 

[Anime]

The thing about thermostats is if they overheat even a little, the wax in them gets ruined and it will never work correctly again.

Getting a new radiator cap is a good idea too, though I would only get the Motorcraft one and not an aftermarket. They are just a few dollars and well worth it.

 

[akbossman]

well it still is overheating. Going to pull the thermostat out to see if that works? (There isn't and anti freeze in the top radiator hose ) or just replace the water pump too. Errrr. I think I boiled my poor oil too........

 

[Anime]

It's just the thermostat. No need to replace the water pump. There's no coolant in the top hose because the coolant level is low from it all boiling out under pressure.

You can just drain the radiator, pull the thermostat housing, replace the thermostat, refill using the burp procedure, and it should be fine.