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Posted a message 4 or 5 weeks ago asking if anyone was having the issue I was suffering with. Truck is a 1997 f150 4.6 with 200,500 miles. After driving on the highway for 10 or so minutes usually in very hot weather, the temp gauge would spike to hot. You could pull over, shut the key off, restart, and "most" of the time the gauge would return to normal and you could continue on your way for 10 or so minutes more, then it would do it again. Sometimes it would go into limp mode, most of the time not. Replaced both temp sensors on the intake late last year which didn't fix the problem. Took it to the local Ford dealer and the mechanic there said it was a leaking head gasket. I told him BS! Never added coolant, never boiled over, never misfired. Just to be sure I wasn't full of BS myself, purchased a combustion leak test kit that you stick in the radiator and the fluid changes color if there is indeed combustion gas getting into the cooling system. Also had the plugs changed so I could look at them and see if one or more was washed clean by coolant. The plugs had normal wear and tear, and after 5 combustion leak tests all were negative. Didn't want to take the truck to the junk yard, but didn't want to blow a bunch of good money on something that couldn't be found. Decided to throw a few parts at it along with some labor and see if that would repair the issue. Had a mechanic change out the t stat, water-pump and both sensors again. So far, the issue is solved. Not sure which part, or parts, were defective, but ran it out on the highway and no more temp gauge spiking.
When I had similar problem at my Acura past year it was just radiator cap sticking. First replaced temperature sensor wrongly. Car parts say he know guys that replaced everything just like you only to figure it was cap. If it stick in closed position coolant can not fluctuate to reservoir and back.
there have been a few posts over the years talking about the fan blades on the water pump failing or wearing down a lot on the 4.6 motors....... ?? maybe loss of water flow.
In regard to bbsitum, radiator cap was first thing I changed. So yes, you're correct,many times a 10 dollar part that's easy and obvious to change creates what you think may be something a lot worse.
To Steve: If you mean the impeller on the water-pump shaft, that's what I was thinking as well. My brother said it may be possible that the impeller is slipping on the shaft, so the cooling system is not getting proper water flow. And when I purchased the truck and changed all the fluids, the coolant looked like Dairy Queen hot fudge they put on Sundaes. So I thought maybe the impeller was half gone ate up by acid. It was neither. But, the pump was just beginning to seep and the bearing was about to go so the change was at the right time. I mean, the pump lasted for over 200,000 miles. Ford did a good job making a reliable part.
Will probably never know which part, or combination of parts, created this headache. But thinking it was the just t stat that was defective. I purchased an inexpensive infrared thermometer from O'Reilly's so I could check the temps all over engine and radiator. The t stat housing showed 205 degrees which is 15 hotter than thermostat is supposed to be. Possible that 15 degrees was enough to tell pcm to turn on the money light and peak the temp gauge
The t stat housing showed 205 degrees which is 15 hotter than thermostat is supposed to be. Possible that 15 degrees was enough to tell pcm to turn on the money light and peak the temp gauge
Negative. That's a perfect normal observation/reading. Besides, that era of engine had separate sensors for the gauge and the cluster.
You'd probably do best to use a scan tool or equivalent to monitor the ECT pid to see if there is a correlation between the aberrant gauge operation and PCM-reported coolant temps.
It very often happens with a new thermostat going beyond 200 degrees the first time the motor is started and goes high temperature beyond before opening then settles back to normal operation.
Over the course of time, I have had two of these aftermarket stats go cool to the 185 range after a few years. This tends to increase engine torque a noticeable amount and takes a small hit on fuel mileage.
You would never know this unless a Scanner was used to take a look at the full operating temperature. The Dash gauge usually will not show this unless you really pay attention or never notice it.
For the PCM to go into limp mode it takes CHT well above 225 to cause it.
Good luck.
always ask for old parts to inspect...
i had a crack on exhuast port it would only leak when there is no back pressure
but you didn't say u was losing water
my old pump ....i put 200miles on it the day before i pulled it
temp gauge would peg and then would drop to normal crazy never use plain water
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