Last year i bought a 92 Bronco XLT with the 5.0 and an E4OD. For as long as ive had it the temp gauge has fluxuated...usually going higher than normal and then coming back down. The pattern was pretty regular...im assuming with the thermostat. Last week the temp suddenly went off the gauge HOT and didnt come down until i pulled over and turned off the truck. Sat for 5 or 10 minutes and restarted...temp gauge was back to normal and drove home fine.

This week i replaced the thermostate with a 195...while doing this i noticed that whoever replaced it the last time installed it backwards. So naturally i figured that was the source of all my issues. after replacing the thermostat and burping the system the gauge seems to be reading a little more steady, but still on the HIGH side...needle is more toward the "L" where it says "Normal". There still seems to be some fluxuation while driving so im wondering what else could be the problem and whether not my gauge is even reliable enough to use.

Thanks!

 

The factory temperature sender/gauge is known to be very inaccurate. Most likely the sender is bad. Easiest way to tell is verify the real water temperature. I use a cheapo infrared temperature gun pointed at the thermostat housing.

If the temperature is steady, but the gauge is varying or reading high it's most likely the sender.

 

Thanks for the tip...ive been wondering about that myself. On a similar note - ive been battling a cabin heater problem for a while as well. When its cold out the heat output is warm at best. I had an 82 Bronco in the past that would run you out of the cab so i was surprised this one is so weak. I changed the heater core and went through the entire HVAC system but never got it corrected. All of my heater hoses heat up nicely...definitely dont want to keep a hand on them for too long.

Is it possible this is a related problem? Maybe an issue with coolant flow? Trying to figure out why the engine would be hot and the heater would be cold...despite receiving hot coolant.

 

I'd say if your heater hoses heat up a lot but your cabin air ins't hot, then it's probably not the coolant that's the issue. That could be a stuck blend door or something like that.

I second getting a cheap infared gun to check the temps just to be safe. Harbor Freight sells them and they are pretty accurate for something like this.

However, If the gauge isn't really off, being at the "L" in the "Normal" range is much hotter than it should be running. Not enough were you would be doing any immediate damage, but I wouldn't want it to be staying that high long term (if the gauge is in fact reading correctly). When I had my 302, the gauge was about at the "R" to "M" range driving around with Arizona summers. When I put my flex-a-lite fans in, it pretty much stayed in the "O" range.

Some things you should check are to make sure there is no debris in front ot eh AC condenser, or in-between the condenser and radiator. Also, doing a coolant flush wouldn't be a bad idea if you haven't done so before, ESPECIALLY if you have ever had anything other than distilled water and antifreeze in there. Tap water or anything else will take a big toll on the coolant system and that can and will clog the radiator, eventually making them leak.

 

My 90" needle is around the "N." "M" is overheat.
IR thermometer as advised above.
"

 

I know you said you burped it, but I came across this in the Ford manuals I have. Never done it like this, interesting.

 

Sorry for the delay - I ended up checking the temp at the thermostat with an infrared temp gun and found that was generally between 195 and 205 after driving around in stop and go traffic. The needle still waivers a little from time to time but generally sits around the "A" on the normal scale. No other symptoms to related to over heating as far as i can tell...so im assuming ive got a bad sending unit?

Any thoughts?

 

That's interesting. When I first got my 1986 F250 the temp gauge would barely move. Replaced the sensor and now it usually rides around the"A" as you stated. My 1992 Bronco rides over in the "N" area. Couldn't hurt to see what a new sensor would do.

 

Most likely a bad sending unit as noted previously.