Hi all!

I'm having some cooling system trouble, and I'm getting desperate.

I have an 03 f150 screw with a 5.4, and it recently began overheating. It only occurs after the truck has been parked for a period of time and the engine's cool. I've tried the obvious things: Replaced the thermostat, no luck. Replaced the water pump, also no luck.

Thing is... the coolant seems to circulate for a short period of time after startup, but then for some reason stops circulating. In other words, the heater begins to warm up, then cools off.

I'm using my phone with the OBDII bluetooth adapter and the torque app to monitor the temp. It will come up to around 150-170 degrees, then the heater will go cold. The engine continues to warm up, but the thermostat never opens. If I pop the hood, the thermostat housing is cool while the engine temp. is reaching 220-230 or more. When I shut down the engine for a few minutes and retry, or even push it by letting it idle while monitoring the temp. the thermostat housing will suddenly get hot and the coolant will start circulating normally, after which the system will function fine.

I'm scratching my head, and it's starting to get real thin up there. Any suggestions?

 

Does the upper radiator hose get hot when the thermostat opens?

 

After the thermostat opens, yes, it get very hot.

 

Sounds like you have another bad thermostat.

 

It sounds like you may have put the wrong thermostat in. Or it's a faulty thermostat

 

When I have the issue, the coolant crossover becomes cool to the touch while the engine's overheating. So there's no heat to cause the thermostat to open.

After a lot more research and talking to a few mechanics, it sounds like I'm leaking exhaust gasses into the water jacket, creating pressure in the top side of the engine and pushing the coolant back to the reservoir. I've found that I can bleed the air out through the heater core supply hose to get the cooling system "jump started". Once I can get hot coolant to the thermostat, the system begins to function normally with the exception that I can hear a gurgle in the heater core. So far, there's no water in the oil, but I'm sure its only a matter of time.

So it's beginning to look like either a $2000 top end re-gasket or a week off work doing it myself.

Thanks for the input and advice.

 

Before you do that, go to AutoZone or O'Riley's and borrow a pressure tester for your radiator. Put the cap on and pressure test it. Report back, its cheaper than spending $2k...