Fluctuating temperature gauge
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Senior User
Joined: Aug 2003
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From: Rocky Mountains
Fluctuating temperature gauge
Suddenly my temperature gauge has started to fluctuate up and down like a bouncing rubber ball. The gauge needle varies from about half way between the cold and normal range up to about half way between the normal and hot range. It does this quite rapidly at times. My radiator is only about one year old and it never seems to over heat, but I'm concerned about this new development. Any ideas?
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Joined: May 2004
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From: Phoenix, Az
Mine has done the same thing for the last 4 or 5 years. Replaced WP, thermostat, made no difference. Temp swings from the "N" to the "L" (as in NORMAL)on the gauge, then eventually swings less as you drive longer. I just had the radiator out for condensor R&R, and filled cooling system up. Temp ran almost to the "L", until some coolant leaked out down to it's "normal" evel. Then temps stay down between the "M" and the "A". After swinging back and forth for a while, of course.
Oh yeah- 90 Ranger, 4.0 V6
Oh yeah- 90 Ranger, 4.0 V6
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Joined: Jun 2004
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some of my theories include air (steam) pockets in the engine. I've had two mechanics tell me that these engines are really difficult to get all the air out of. I once had the heater core replaced by a mechanic and drove around all winter with no heat until I took off a heater hose and used a garden hose to circulate water through the system. Somehow the core stayed empty of coolant, so I'm sure it could happen elsewhere.
Post Fiend
Joined: Jan 2003
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From: Connecticut
4.0L Coolant By-Pass Kit
Originally Posted by nightshifter
some of my theories include air (steam) pockets in the engine. I've had two mechanics tell me that these engines are really difficult to get all the air out of. I once had the heater core replaced by a mechanic and drove around all winter with no heat until I took off a heater hose and used a garden hose to circulate water through the system. Somehow the core stayed empty of coolant, so I'm sure it could happen elsewhere.
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From: Rocky Mountains
Wonderful info. I have eliminated the gauge by doing the resistor substitution test. With a 100 ohm resistor the gauge read exactly on the cold level and with a 10 ohm resistor the gauge read exactly on the hot level. I then ohmed the sender unit itself and with a cold engine it read 2600 ohms and it's supposed to read 73 ohms. So I am going to start by replacing the sender unit. Another interesting note....I priced a sender unit at Advance Auto Parts and they want $18.99. I called Autozone and they want $3.99. I imagine someone has the parts mixed up, but I will update when I get the correct part installed. I appreciate the help guys.
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Post Fiend
Joined: Feb 2003
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From: Eastern WA
I've been down the road of the fluctuating temp gauge about three or four times in the 10 years since I've had my Ranger (4.0L). First go around, the temp sending unit and the thermostat were replaced under warranty (24,000 miles). After the warranty expired, I started replacing both when the problem surfaced. The last time it happened, I replaced the temp sending unit only to fix it (easier to try than replacing the thermostat). I'd say try the temp sending unit first.
BTW, I've noticed that these trucks can be stubborn when it comes to purging the air out of the system. When servicing the cooling system, I like to park it with the front end higher than the rear. I fill the radiator as best as I can before starting it, run it until the thermostat opens, fill it, and repeat this a few times. I then take it for a drive and let it cool overnight, topping the burp tank in the morning. I monitor the burp tank over the next 2-3 days, topping it off when the engine is cold, until finally the coolant level is on cold when the rig has sat overnight.
BTW, I've noticed that these trucks can be stubborn when it comes to purging the air out of the system. When servicing the cooling system, I like to park it with the front end higher than the rear. I fill the radiator as best as I can before starting it, run it until the thermostat opens, fill it, and repeat this a few times. I then take it for a drive and let it cool overnight, topping the burp tank in the morning. I monitor the burp tank over the next 2-3 days, topping it off when the engine is cold, until finally the coolant level is on cold when the rig has sat overnight.
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Joined: Apr 2004
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From: temple, pa
the temp gage sensor is indeed $3.99 at azone. the temp sending unit for the computer, a separate sensor, is the $18 one. i just replaced my temp gage sensor with the $4 one from azone to fix a sporadically working temp gage, and it works fine now. regardless, it is a very cheap easy fix.
chad
chad
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From: Rocky Mountains
I replaced the temperature sending unit (or switch as some people call it) and it seems to have cured my fluctuating temperature gauge. In the process I found another problem. My air filter had been crammed in crooked and was allowing air to bypass the filter. So I decided to clean the MAF because of all the dust allowed to bypass the filter. I went to the sticky on MAF cleaning and found my '95, 3 liter has a different arrangement than the one shown. I removed the MAF from the air cleaner assembly and I can see the two filaments for the sensor. There is a plate behind the two filaments held in with torx security screws. Since I can see the filaments, is it necessary to remove that backup plate before spraying them with cleaner? Note...when replacing a temperature sending unit, it is wiser to drain the coolant rather than trying to plug it with your finger while fiddling with the temperature sensor as the Haynes manual suggests. I spent another hour cleaning up antifreeze. Live and learn I guess.
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From: Rocky Mountains
I found the security torx heads at Autozone and was able to remove the back plate. Everything is back together and running well. Still puzzled how the air filter got wedged in so crooked. Thanks Rock.
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