Looking for advise.

1994 Ford f150 5.0liter, automatic. The truck has had this issue for a long time and I am determined to figure it out. Maybe one of you fine folks could help.

The truck stays nice and cool or right at the thermostat opening point all day long regardless of outside temp when idleing or driving under 60 mph. BUT, after about a half hour of highway speeds the temps start to climb to the red zone. Changing RPM will affect the temp gauge, letting off the gas pedal will cause fluctuations. Flooring it will sometimes drop the temp down back to normal. The gauge is going up and down like air pockets or steam is trapped in the cylinders.

So of course I have replaced many parts trying to fix this:
Radiator (cheapy, aluminum and plastic).
A new genuine Ford thermostat, and cap. Also tried a 180F thermostat.
New Hi flow water pump from Summit.
New upper hose with a spring installed.
Lower hose looks good and still has spring in it.
NEW HEAD GASKETS, oh yeah that was a hell of a job. The tabs are in the front they are installed right.
Flushed coolant. Burped system a million times.

Guys, what should the flow look like when the stat is open??? Looking in the filler neck I see almost no movement but the level will change when I rev the motor. If I dissconect the top radiator hose (thermostat removed) coolant does move, although slowly.

Should the coolant blast out of the disconnected upper hose, or just a steady stream?????

 

Ford F150 Forum - Community of Ford Truck Fans - Powered by vBulletin

PM me and we can talk Chevy's.. Even if it's where's the best place to hook the tow chain to the front of a Ford when pulling with a Chevy..

 

LOl. I really don't need more salt rubbed in this wound dude!

 

I had a car once that would be fine for hours and all of a sudden overheat. Rodded out the radiator, new thermostat flush ect. Kept on doing it. Turned out to be the water pump. Changed it and all was good. I still don't understand how I could drive hours with no trouble and all of a sudden, in seconds, be overheating. I see you changed the water pump already. Pressure test the system?

Les

 

Didn't have a pressure tester but did get a brake bleeder vacuum on the radiator inlet. It held vacuum (engine luke warm). I was trying to suck any air bubbles out.

 

Stupid question #1 : are you sure the temperature gauge is reading correctly ?
( when it says HOT, check the inlet hose to the water pump with a point and shoot temp meter,
unless you are a brave soul and want to open the radiator cap and use a thermometer ...)

 

Yes sir she gets hot! radiator gets hot, top hose hot and bottom hose hot. Before I added a spring to the upper hose it would suck it flat for a few seconds. Rev the engine a few times and the pressure would return. Expansion tank has been cleaned and hose going to it is new. When the system is up to temp whether there is pressure in the upper hose or not, I can not feel any coolant flowing. I disconnected the upper hose waited for the stat to open and saw some movement. It came out into a bucket slowly. That's where I'm stuck. I don't know what the correct flow should look or feel like.

 

I can only say that the 350 Chevy in my 1990 Suburban BLASTS the water out of the engine.
( I forgot to tighten the upper hose once, cranked it up and was working under the hood when it got up to temperature. )
Blew the hose off the thermostat housing and hot water/coolant sprayed everywhere.

 

Ok thank you!

That's what I thought. It should be flying out of there! Ford dealer has a Genuine Ford water pump for $60.00. Think I'll try that. There is some confusion about forward and reverse rotation pumps, I wish I looked at the impeller before installing the Hi-flow from Summit. YUCK, I WANT TO WRENCH ON MY CROSSFIRE not a truck!

 

I installed the new FoMoCo pump and removed the radiator and backflushed it with a garden hose. Lots of rust particles came out. Seems like it did the trick.