Changed out thermostat a couple of weeks ago. Yup, got a Ford unit. Anyway the last few days have seen a loss in coolant. I checked all hoses, heater, clamps etc. Then found signs of antifeeze below the overflow tank. So I opened the hood this a.m. and fired 'er up to watch any action.
So here's the picture:
coolant at about 4" high in the tank at start up.
Immediately the coolant level begins to rise in the tank, and keeps rising until tank is full.
Keep watching engine temp (sorry, no real gauge)
As engine reaches near Normal, checked upper rad hose, it was under great pressure. About this time the new 16lb rad cap vented, and in short order the thermostat cycled.
Fluid subsided in the tank to original height minus vented product.
From then on, everything cycled as normal.
Is this normal? I thought the coolant would be in equilibrium until the thermostat opened, as the pump pulls from the bottom of the rad and pushes into engine. Could it be a bypass issue?
Guys...any help here is greatly appreciated.

 

No it's not normal. Almost sounds like the water pump is turning in the wrong direction or the plumbing is messed up.

 

I guess the thermostat wasn,t your problem

https://www.ford-trucks.com/forums/7...m-96-f350.html

 

It sounds like a head gasket to me. The overflow is rising because air is displacing water.

I don't see how it could be the bypass. The bypass is only one thickness of metal long... it goes right from the bottom of the thermostat to the pump suction.

 

X2 with Joe_13894

There are chemical tests that can detect Carbon Monoxide in the cooling system. If that tests negative then you look some place else.

Were you having this same problem PRIOR to changing the thermostat??

Both answers will be a clue.

Rog

 

WALJON: Yeah, guess not. although the original was not the right one.
Kawa: Yes, I have been having this problem for some time.
Joe:I had thought it might be a head gasket, but if the coolant remains the same level after the first thermostat cycle, I'm not so sure?
Where do I find this chemical test for CO? At Napa or something like that? I'm in the interior of British Columbia.

 

Napa would probably have the kit but so would many GOOD repair shops and they don't have to be a diesel repair. I don't know what the kit costs, you can check that out (I just yesterday gave my kit to my neighbor) but I wouldn't expect the test to cost a whole lot as it only takes a couple and it's a fail/pass test.

Rog

 

Skemcis, here is a thread with a very similar problem as yours, except it was a 95. Upper hose hard as a rock. Anyway he finally found the radiator was 85% plugged.

https://www.ford-trucks.com/forums/6...g-problem.html

Hope it's not a head gasket ...

 

Kawa: Thanks for that.
Hussler: Thanks for the link. I am beginning to suspect a head gasket. I think I will take it in for a pressure check. The only thing that really stumps me is that after the initial blow out, everything works normally. I would have thought that exhaust gases in the coolant would make it continually over pressure, and keep popping the rad cap. Could it be a weak head gasket that seals up as the engine gets to operating temp? Seems to me I heard about that somewhere in the distant past.