I have a 1997 F150 4.6L with 183k miles and the engine is overcooling

Little background:
- Coolant has been flushed
- New Theromostat(s)
- New fan clutch
- Heater core relaced 50k miles ago

I've read similar topics on the net concerning this problem, but none of the topics cover my exact problem.

The engine temp never reaches normal range. Heater used to make your eyes water. Engine operating temp on the temp gage is 1/3 cooler than the motor ran previously. Now temp only climbs about 1/4 of the way into the normal range.

Temp can be verified by grasping top radiator hose which is only warm after 20 minutes of driving.

Coolant reservoir holding pressure after 24 hrs of idle time

Now here's the perplexing part; I removed the plastic cowling to get to the radiator and slid a piece of cardboard between the radiator and the evaporator as a shadetree test.... The cardboard is tight against the radiator. The cardboard covers 7/8ths of the radiator surface area. 30 miles of driving...ZERO change in engine temp. Zero

After the cardboard test, I can still place my hand on the top radiator hose and hold it there. Engine doesn't make any tinking sounds associated with the cooling of a hot engine. The engine is only warm to the touch.

Here's another tidbit....when I FIRST run the engine for say 3-4 miles and heater begins to blow slightly warm air then come to a stop, the heater will blow cold air. The temp gage falls back to cold and will sometimes slowly rise back to lukewarm and actually blow lukewarm air. Other times the temp gage drops, heater blows cold then the temp gage spikes to super hot. Shut engine off for a few seconds and lukewarm temp returns thru the heater and temp gage reads warm....This is an indication of trapped air in the system.

So how in the heck can I have trapped air (which woud make an engine run hotter) and still have an engine I can touch with a bare hand after running it for miles....?

If any of you brainiacs can figure this out I'd really appreciate it...

 

you should be fine. it sounds like your motor was running warmer than it was suppose to and you got use to it. not hot just warmer than it was suppose to. if its about 1/4 of the way into the normal area then it sounds like its fine. but others may disagree.

 

Your new thermostat may be defective.

 

check your coolant level

 

I would swap out the Thermostat, I just had the exact same thing happen in my Mustang GT after I installed a new thermostat. went and got another one, and all was back to normal again.

Good Luck!

 

coolant level is good

three new thermostats tried (all 195's)

And NO the temp isn't normal. It will barely defrost light fog on the windshield

Key point is the cardboard which blocked 7/8ths of the radiator did not cause the engine to overheat or the coolant to boil over after driving 30 miles.....(this eliminates the thermostat theory)

 

can you spin the fan by hand when the engine is cool? are you putting the thermostat in the right way?(spring down)

 

Paralyzer may have pinpointed the problem. Your symptoms sound like a "stuck open" thermostat to me too.

The engine generates heat when running - that is a constant you can't change. It cannot suddenly stop that property.

The cooling system gets rid of that heat, but its ability is moderated by the thermostat. If the thermostat is open, the radiator will be "overly" effective in removing that engine heat (even if it's covered). You don't say where you live, but I'm betting it's not Arizona. If you're in a cold climate, the engine needs very little cooling effect from the radiator.

You MAY have a fan that's always on, but I'd rank that possibility as fairly remote.

You DO want to correct this. It's not good for an engine and fuel economy (or the environment) to run below the design temperature.

- Jack

 

Not a Brainiac, but I'll throw this out there. You sure you are installing the thermostat right side up ?

It could happen :o

 

I'm not one either, jbrew, but doesn't putting it upside down cause it to stay open like Paralyzer said? (And, it HAS to be a thermostat problem, doesn't it)?

- Jack

 

That sounds right to me.

I know it fits either way

Iduno, sometimes you can get it in your head that it goes certain way, when actually it's the opposit.

Then u kick yourself.

 

Boy, is my backside sore!

I can't begin to tell you the number of times I've discovered, "I'm really stupid"!

- Jack

 

Yea, I'm still recoperating - Doc says next week I may be able to sleep laying down again.

 

Thanks for all the responses.

Yep the thermostat is installed correctly. There is actually a small air bleed hole that you have to align to the 3:00 position also. There have been 3 new (back to back) thermostats installed. Last one I installed was tested in hot water to verify operation

I live in Illinois, but had the same issue in the summer (gets pretty warm here)

Fan blade can be spun by hand when cold and wont move when engine is "hot"

I'll try another thermostat from another supplier just to be sure, but the odds are that isn't the issue. If I've had 3 bad stats in a row I should've played the lottery instead....

Thanks for all the inputs

 

if the thermostat opens at the correct temp then its not running too cool. the thermostat will close if the coolants too cool.