Perplexing overcooling on 97 4.6
I have a 1997 F150 4.6L with 183k miles and the engine is overcooling
- 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...