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Old 06-13-2014, 01:21 AM   #1
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Default Temp Gauge fluctuating

I have a 93 Hardbody 2wd with the 4 cylinder engine. I got the truck recently from a friend. I have noticed that the temperature gauge tends to fluctuate a lot. It has never overheated yet but I am concerned that there is an issue which may cause it to eventually overheat. I drove for over an hour at appproximately 60mph and the temp stayed at what I belive to be a norman temp according to the gauge. Here is a pic of what it was reading.


Once I get into city driving the temp gauge goes up. To about here or slightly higher.


I am acustomed to a vehicles temp reading to stay the same if nothing is wrong. I flushed the radiator and replaced the thermostat last month but this does not seem to have helped any. Does anyone have any suggestions as to what could be wrong. Or am I overeacting.
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Old 06-13-2014, 01:46 AM   #2
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Mine does the same thing. I wouldn't worry about it until it got past half way. If it gets above that, there is probably something wrong.
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Old 06-13-2014, 09:16 AM   #3
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mine never goes beyond the 1/3 mark. i mean it has, when i blew a hose, but normally its parked in the same spot every day.
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Old 06-13-2014, 05:58 PM   #4
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You probably have a mechanical fan clutch that is getting worn and not completely locking up, or is not locking up enough, at city driving speeds. Once on the freeway the moving air across the radiator is more than enough to cool the truck without the fan clutch engaged. Once you slow down and start the city driving, the clutch needs to lock good and solid when its really warm outside and the engine temp is also hot.
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Old 06-14-2014, 01:11 PM   #5
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Several people have suggested the fan clutch could be the issue. They have all said to let the engine run and attempt to stop the fan with a stick of some type. I have not been able to stop the fan and therefore do not believe that to be the problem. Can anyone offer more insight on this?

Also the temp has going slightly past where I showed it, that was just where it was when I was able to take a picture. The needle has gone as far as to cover up the horizontal lines for the thermometer symbol.
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Old 06-14-2014, 03:13 PM   #6
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mine was running warm when i got the truck. since then everything has been changed. ALL hoses, the rad, therm and water pump.

my fan clutch was shot to the point that you could stick your finger in the fan while the engine was at a high idle and it would stop.

does yours roar? mine sounds like a hurricane during in town driving.

get a meat thermometer. with the engine cold, remove the rad cap. insert the thermometer. start the engine. observe the trucks temp gauge and the actual reading the thermometer is showing. it should be no higher than 190 degrees at an idle under no load. 180 would probably be a closer number, but the rating of the thermostat usually causes the engine temp to run 5 to 10 degrees above that number.
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Old 06-14-2014, 06:54 PM   #7
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Sounds like the cooling system is doing what it's supposed to do. Like Tally said, you have plenty of airflow over the radiator at high way speeds, so you can transfer more heat from the radiator into that air flowing over it. In town, you have less flow do to slower speeds, which is why you need the radiator fan. If you can park it and idle it with no issues, then you're fine. If you're ever driving and it gets to the red on the gauge, you can turn the temperature up in the cab to help dissipate the heat. I'd say you're fine though.
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Old 06-14-2014, 08:21 PM   #8
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i'll try changing the clutch this week and will report my findings.
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Old 06-15-2014, 07:36 AM   #9
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I also recently have been having the issues with the temp gauge. I hit a coyote going about 100km/hr and the animal just clipped the passanger front corner and cracked the rad. I replaced the rad today and since then the gauge has been fluctuating pretty bad. anyone have any advice on how to purge the system? My overflow rez is full to the top. I'm thinking this good be part of the problem.
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Old 06-15-2014, 11:00 AM   #10
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the engine should have a bleed screw to release the air from the system. im not sure where it is located on the 4 cyl trucks. on the early V6 trucks, it was a bypass line that came from one of the heater hoses to the top rad hose.

i deleted that off mine. i couldnt bear to chop up 30 bucks in hoses for something so trivial. just make sure your truck is on level ground or slightly inclined in the front. air rises to the highest point so in theory, raising the front end should give assistance in getting the air out.

mine took about 10 minutes of idling with the rad cap off to purge all the air.
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