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I had the head on my '92 Bronco 4.9L ported and polished with bigger valves and a cam. Ever since I got it back it has run very cool, according to the temp gauge. I know that these gauges aren't the most accurate, but the heater doesn't work as well as it used to, so I think it actually is running cool. I changed out the thermostat twice, the last one a little hotter. I also put in a new heater core. All to no avail.
Any ideas as to what is causing this thing to run cool? Is it related to the rebuild? Thanks.
Running cool could be due to the fan clutch is seized up. This happened on my truck and the added load on the water pump bearings blew out the pump, in the the back woods while I was trout fishing. Not nice. So check that your fan moves relatively easily when the truck is stopped with the engine off. If it doesn't move or moves with great difficulty, replace the fan clutch.
I have significant drift in my instruments as well. The fuel gage is about 20 % off at this time, it reads low. I suspect the same for the volts, temp and oil pressure gages.
autocar
What year is your truck? Post-'86? If so, the only way all the gauges could drift together is a dirty connection at pin 13 or 1 of the L instrument cluster connector, or at pin 3, 7, or 10 of the R connector. 13 is the power to all the gauges; the rest are the grounds. The voltmeter goes across pins 13 & 1.
What temp thermostat did you put in? The stock thermostat on the EFI engines was 195 iirc. That should put you in the middle of the 'normal.' So if you put a lower temp on, that very well could be it....
My truck is an '89. I don't know/think that the gages are drifting together but I think they individually might be drifting due to each of their old age. Is this possible? I'm getting rid of the truck in a couple months so I don't have the time/energy to look into it.