Hello all. First time poster to the forum and I have a few questions...

2000 F150 5.4L Auto 2x

I was driving home from work last Friday and decided to use the AC for the first time this year. Within 15 minutes the temp ran up to H and my oil light came on. I didn't notice it until I saw the oil light pop on and pulled over immediately until it was cooled down enough to limp it home with the heater on. While driving home, the temp stayed 3/4 and I had no hot air blowing. Right away I thought t-stat. Picked one up this weekend and popped it in. Truck ran "ok" without AC but was still running too warm for my liking *slightly above normal operating temp*. I inspected all the hoses and the area around the water pump for weeping or leaks. I wasn't losing coolant that I could tell but I checked it anyhow just to be sure.

I decided to take the day off yesterday to do a complete flush of the cooling system. Installed a T on the input heater hose, drained the radiator and motor, then flushed it till the water ran clear. The flush took about 10 minutes to run clear and pumped out a bunch of scaly looking stuff and muddy colored coolant. I Drained the entire system again and put in 50/50 coolant/distilled water (Peak).

Took it out for a spin and the temp ran at normal for 20 minutes. Feeling pretty excited I'd fixed the problem, I turned on the AC. Ran at highway speed for another 10 minutes and the heat gauge began to slowly creep past normal. Turning off the AC and turning on heater helped the temp stop increasing and then began to fall several minutes later. I also noticed there was still no heat blowing with the heater on.

After getting it back home it appeared to begin creeping up again. Revving the engine to 1700 RPM would cool the system down. Idling it would creep back up. I was able to repeat this behavior several times.

I'm now thinking my problem may be due to poor circulation from the water pump.

Also, does anyone know how to keep the rear ABS sensor from going out? I have to change that thing about once a year.

Sorry for the long winded post.

 

From your discription so far, I would begin to think about replaceing the radiator due to partical blockage that has reduced the total cooling area.
As soon as extra load is added by A/C you might be at the marginal limit of cooling area with no reserve.
The motor has to work harder producing more heat driving the compressor.
The condensor in front of the radiator adds more heat to the cooling load and the transmission fluid adds a bit more heat to the coolant flow.
The sum of all these may be at the limit of cooling capacity.
Be sure the jug cap is good.
What usually happens is the old addage; in never gets any better!
As the issue gets worse, the coolant will begin to boil and overflow the jug 'after' a hard pull when the heat is highest just after shutdown but may hold off while in motion with enough airfow holding it off.
I had a Bronco II that had this issue with the radiator and was some time before a I discovered the blockage issue by the way it acted as above.
.
On the ABS sensor, unless it is in contact with the ring gear or getting excess heat from the exhaust system, it's hard to tell what is causing the short life unless the plug has a problem.
.
My heat experience is with a transmission fluid cooling monitor at the inlet of the radiator line; under high ambient outside temperatiures, the fluid goes up much higher just under normal driving and depending on the terain and how much time the trans is in other gears such as in stop and go traffic and in non-lockup operation and with A/C in use.
It gets up higher than one might think so the cooling system must have the reserve area to stay ahead of the cooling load.
I also run a thermostat controlled fan on the extenal fluid cooler that helps in extreme high temps of 90+ ° times to cool under low road speeds and to reduce the time the under hood temps are very high after shut down. The fan will usually run about 5 min after the motor is shut down to circulate outside air into the engine bay or until it senses the set temp under about 185. The pick-up reacts to both the transmission line and the engine bay temps, the way it's mounted.
Goodluck.

 

Thank you for the reply.

I have considered the idea of blockage/particle buildup in the radiator but dismissed it after reading info about someone having a bad impeller on their pump and describing behavior almost identical to mine.

I neglected to mention I ran a radiator flush additive in between flushing of the system and the drain was running clear during the last flush. Now that I am thinking of it, the radiator drain did more of a fast trickle rather than a nice even flow, and took what I thought was longer than expected to empty. I had to squeeze the top hose several times to get a nice flow. I'm guessing that's a good indication of bad radiator flow?

Also, when revving the engine to cool it down, the heater would blow hot like it should, then blow more tepid to cool as I let off the accelerator.

Another thing I completely forgot about...

Over this last winter the heater didn't perform very well and the engine temp would hover barely above the cold mark on the gauge.

I guess pulling the radiator is up next. *groan*

 

The drain trickle is the magic word.
The radiator is plugged in it's lower area.
Better to remove the radiator than it (and)the water pump.
Radiator is not very hard to remove.
Remove the trans cooler lines first, some hold-down clamps and rwo hoses and lift out.
You can't flush at home for this condition.
A reverse flush with chemicals, off the truck is the only way to open the small core channels, then test for flow volume to be sure it clear.
Good luck

 

i have a flush TEE in the heater hose line. YOu can connect a garden hose and open the radiator drain, or the cap and flush real easy. ALso can see the volumn and any crud in the flow. I pinch off the heater hose to make the water flush forward, then backward, and drain out the radiator bottom.