Temp Gauge Fluctuation
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Temp Gauge Fluctuation
My 1996 F150 has been having an unusual problem with it's temperature gauge.
It only occurs some days.. probably about half the time. - But when I am driving it and it does act up, the temperature gauge will fluctuate from the O (In NORMAL) all the way to the end of the L. This happens after the regular warm up cycle - It is fine all the way up to the N when it warms up.. I've noticed when I set cruise on 60MPH, it likes to start climbing. It can go from the O to the L in about 3-4 seconds, then it will go back down a little bit, climb back up, then go back down.. Just random fluctuations. (slow-delayed movements, not very erratic). The other day it actually climbed up in to the red, near the "H". I parked the truck, got out, popped the hood and put my hands near the engine and it wasn't radiating immense heat, it was just normal. I also felt the radiator hoses and they were all warm but definitely not HOT. The truck is also not sucking a bunch of coolant or anything, I've been checking. I live in northern Michigan, so the temps here are pretty cool at the moment. Could this be a sensor problem? Any help would be appreciated. Thanks.
It only occurs some days.. probably about half the time. - But when I am driving it and it does act up, the temperature gauge will fluctuate from the O (In NORMAL) all the way to the end of the L. This happens after the regular warm up cycle - It is fine all the way up to the N when it warms up.. I've noticed when I set cruise on 60MPH, it likes to start climbing. It can go from the O to the L in about 3-4 seconds, then it will go back down a little bit, climb back up, then go back down.. Just random fluctuations. (slow-delayed movements, not very erratic). The other day it actually climbed up in to the red, near the "H". I parked the truck, got out, popped the hood and put my hands near the engine and it wasn't radiating immense heat, it was just normal. I also felt the radiator hoses and they were all warm but definitely not HOT. The truck is also not sucking a bunch of coolant or anything, I've been checking. I live in northern Michigan, so the temps here are pretty cool at the moment. Could this be a sensor problem? Any help would be appreciated. Thanks.
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
I assume you mean the heater blows out heat, not just that the fan works? I should have clarified when I asked the first time.
When you say the radiator was 3/4 full, do you mean somewhere like 2 inches below the fill cap?
Was the engine completely cold when you checked the fluid levels? I'm thinking if the radiator was not full the reservoir should have been empty.
When you say the radiator was 3/4 full, do you mean somewhere like 2 inches below the fill cap?
Was the engine completely cold when you checked the fluid levels? I'm thinking if the radiator was not full the reservoir should have been empty.
Cargo Master
Joined: Jan 2004
Posts: 3,118
Likes: 149
From: South Dakota
3-4 inches below the cap was probably enough for the coolant to circulate. You might try filling the radiator full and see what happens, don't forget anti-freeze if you need it(I don't know where you live).
I would check the tube going to the reservoir and make sure it is not plugged or has a hole in it.
I would still guess you have a bad thermostat.
I would check the tube going to the reservoir and make sure it is not plugged or has a hole in it.
I would still guess you have a bad thermostat.
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Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
I would check the temp sender. I just went through that on my '95, 302, Eddie Bauer.
After replacing the busted radiator, the leaking water pump, the loose fan clutch, top and bottom radiator hoses, and the NON Motorcraft t-stat, mine was drifting between N-L.
Finally, I used my DVOM and Ohmed out the sender. It was bad. I even Ohmed out the sender wire to the cluster while I had it out. That it left the sender.
After replacing the busted radiator, the leaking water pump, the loose fan clutch, top and bottom radiator hoses, and the NON Motorcraft t-stat, mine was drifting between N-L.
Finally, I used my DVOM and Ohmed out the sender. It was bad. I even Ohmed out the sender wire to the cluster while I had it out. That it left the sender.
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Joined: Feb 2021
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I know this is an old thread, but I'm curious if 96fonefitty ever figured out what this issue was? My 96 5.8L is doing exactly the same thing. I bought the truck last summer, and it has done this since I've owned it. I replaced the timing cover gasket, water pump, thermostat, and radiator in October due to the radiator and timing cover leaking coolant. While I've stopped both of those leaks, the temperature gauge is still fluctuating as it did beforehand. The only issue that I do still have is my coolant level hasn't remained full. I've had to refill the radiator and overflow reservoir multiple times since October. No apparent leaks that I can tell. I plan on trying to burp the system again this weekend, which I've already done after finishing replacing all of the items that I did, to hopefully eliminate that possibility. What do you guys think? Could air pockets be causing the gauge to fluctuate? Maybe something with the temperature gauge sending unit?
Mountain Pass
Joined: Jan 2014
Posts: 214
Likes: 37
From: Madison Ohio
Sounds like you have a coolant leak some place. Possible heater core, or cracked hose some place. Might not leak until system builds up some pressure. Your system should have worked all to most of the air out by now. Low coolant level will make your gauge bounce up and down. warm air pockets will drive the gauge up, and colder water pockets hitting the sending unit will drive the gauge down. Track down your leaks or leak. Ive had hoses not seal on the plastic radiator fittings. IF that's your issue Ive had good luck with using Indian head sealer on the fittings before slipping the hose on.
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Sounds like you have a coolant leak some place. Possible heater core, or cracked hose some place. Might not leak until system builds up some pressure. Your system should have worked all to most of the air out by now. Low coolant level will make your gauge bounce up and down. warm air pockets will drive the gauge up, and colder water pockets hitting the sending unit will drive the gauge down. Track down your leaks or leak. Ive had hoses not seal on the plastic radiator fittings. IF that's your issue Ive had good luck with using Indian head sealer on the fittings before slipping the hose on.
Fleet Mechanic
Joined: Mar 2009
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From: Sacramento Delta, CA
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Any update @96EddieBauerEdition ?
Not sure if this has been mentioned, but I can say that once the truck is warmed up and has been on the road for 10 minutes or so, the fluctuating gradually calms down and the temperature gauge needle mostly settles to the middle of “NORMAL” as it’s supposed to.
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