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Erratic Temperature Gauge

o' dannyboy

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big apple
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'93 xlt
Please help! This problem is driving me NUTZ!

The temperature gauge on my '93 XLT is possessed. The temperature gauge used to stick to N/O once up to temperature. Now, it can go up past L and back down to below N. After a period of time, the fluctuation will stabilize a bit but continue to drop and rise, usually resting below N (colder than ever before). Along with the temperature gauge fluctuating, the anti-freeze will bubble out of the reservoir when the temperature moves up past M or A. The needle will drop back down after this coolant loss.

Prior to this crazy gauge fluctuation, I noticed occasional over heating with coolant loss through the reservoir. I replaced the thermostat (stock) and the radiator cap. I attempted to "burp" the system.

Other observations:

Fan moves easily when cold (by hand). Fan clutch okay???

No sign of coolant in the oil or vise-versa.

Water pump seems to be pumping coolant through the system.

Possibly related:

On cold start-up, the truck starts a little rough, idles rough and sometimes will want to die as it takes off from parked position. For a couple of minutes after cold start there seems to be a bit of smoke from exhaust which clears-up at temperature. After it comes up to temperature, the truck seem to run fine with no smoke - 3 to 5 minutes.
 
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o' dannyboy

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Another thing:

When the temperature gauge goes up the heater blows cooler and visa-versa.
 
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StryctNy9e

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1993 XLT Exploder
I would start bt changing the thermostat but it may not cure the problem. My story, On my old engine my thermostat went out, so I replaced it. I replaced my motor a few months later and on the new engine the t-stat would go all the wat to the L on NORMAL, and then it would open and drop down to the O. This worried me, so I swapped the t-stat with the new one out of my old engine. Still had the same symtoms except it would now go onlt to the A, then drop back down. It bugged me but now the T-stat settled and the problem went away.

These firs gen thermostats are made with a wax ring so when they get old, and maybe when breaking in, they tend to be a little sticky and dont want to open. I would start by repacing the thermostat( three bolts & 5$) give it time to settle, while keeping a eye on the gauge and go from there. Dont forget to have the breather at the top.

Good Luck.
 
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beauboy

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I have the same issue as Odannyboy, but without the coolant bubbling out. I've read many posts on here about using a thermostat with a "weep hole"(?). That plus burping is supposed to cure the erratic thermostat problem (or so many on here say).

You may want to check out the "weep hole" thermostat.
 
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FL.Cracker

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I had a similar issue that turned out to be a bad connection at the temp sensor for the gauge (not the temp sensor for the computer). I had to cut the wire back a bit and solder a new piece to the connector. Easy fix, worth checking out.
 
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det107

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I was taught that when spinning a fan, the fan clutch should have a drag to it. Anytime it spins freely, it's a sign of impending failure-
 
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o' dannyboy

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New Thermostat & Radiator Cap

Thermostat and radiator cap are new. Has the "weep" hole.
 
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Roadrunner777

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I'm pretty sure you have air in your system, and it's going to be tough to come up with a root cause. Can you get it filled and burped? I can turn my fan easily but it stops right away. Does yours, or does it keep spinning a little bit?
 
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o' dannyboy

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Fan

I'm pretty sure you have air in your system, and it's going to be tough to come up with a root cause. Can you get it filled and burped? I can turn my fan easily but it stops right away. Does yours, or does it keep spinning a little bit?

The fan turns but, does not spin easily. Also, when the motor is shut off the fan only turns an additional 1/4-1/2 turn - no spinning. Stops pretty quick.

Thanks for the help!!!
 
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StryctNy9e

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Weep hole is the hole I was talking about on the thermostat. It is a air bleed hole. It should be positioned at 12:00. To burp the system you have to lift the radiator as high as you can, this forces all the air to the top of the radiator. Also It took me a couple drives to get all the air out.

The air bleed hole lets the air out of the block and into the radiator without letting the anti freeze out. The thermostat opens at 198 degrees, if you have a 198 degree thermostat wich is what first gens call for.
 
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o' dannyboy

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Update

I burped and filled and burped and filled a few times. Currently, both the temperature gauge and the heater continue to fluctuate. The difference now, is that the fluctuation seems to be less severe, from below N to R/M. It seems that as the gauge goes up, the temperature of the heat coming out of the cabin vents seems to decrease although, this doesn't always seem to be consistent. Sometimes the heater puts out almost cool air and other times very hot air. Coolant still occasionally bubbles out of the reservoir tank.

After the motor comes up to temperature, the fluctuation seems to level off and the gauge settles around N for most of the time but, is still not consistent.

Observations:

- Thermostat - New.
- Radiator cap - New
- Fan clutch engages and can not be stopped with a doubled-up piece of cardboard.
- Water pump works and seems to circulate coolant.
- No apparent leaks, anywhere. Only out of the reservoir when too hot.
- No oil in the coolant and vise a versa.
- No white smoke out of exhaust.
- At idle, when the heater is set to Defrost the motor RPMs drop about 300 rpms and almost feels like it may stall but does not.

Maybe I need a good flush or a new heater core or... other????

PLEASE HELP!!!

Like I mentioned, IT'S MAKING ME CRAZY!!!

Any cooling system experts out there???

Thanks!
 
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Iron Weasel

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Cool air out of the heater core and fluctuating temperature gauge sounds to me like you may still have air trapped in the system somewhere.
 
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huntman58

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What shape are your hoses in?
A clasping hose can also do this by restricting the flow from the say pump to the motor and heater core. How old are the hoses and or when were they changed last?

Are you sure the water pump is working at full flow such as with out the cap on the radiator you can see the coolant flowing very freely in it? I ask as I had a water pump that the impeller was bad but the pump did not leak weep or give any clue at all but that I could not keep it cool at low speeds no matter what I did in then end once I change the pump problem ended .

I would start with checking your hoses and also doing a very good flush but pull the thermostat first before you flush as that way you will fully flush every thing.
 
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Jason94sport

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Bypass the heater core to test. Take each hose going to it & connect them together using a barb coupler.
Could be a plugged heater core for your airflow issues. Sounds like a bad water pump to me for the cooling issues.
It likely a piece of the water pump broke off & went into the heater core resulting in a blockage.

Also these gauges suck. Are you sure it's even giving correct info? Also pressure test the system. Rent a tester.
 
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Tony H

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When the temperature gauge goes up the heater blows cooler and visa-versa.

Sounds like you are low on Coolant in the radiator. OR Water pump impellar might be slipping on it's shaft.

Engine HOT and no Heater means coolant is not circulating into the heater core. Not enough coolant to circulate OR impellar is not pushing
 
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Turdle

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Cool air out of the heater core and fluctuating temperature gauge sounds to me like you may still have air trapped in the system somewhere.

bingo. You need to raise the front of the truck real high, get the radiator cap higher than the heater core. ( high place will hold the bubble)


Also, you mention a slow leak. This slow leak become a large one at engine speed under load. Any loss of pressure in the system will allow in internal boil. A leak is a loss of pressure.
 
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Jason94sport

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bingo. You need to raise the front of the truck real high, get the radiator cap higher than the heater core. ( high place will hold the bubble)
That shouldn't be necessary. It's a pressurized system. Any air that's in the system will force it's way to the radiator once proper PSI is reached. Unless there's a blockage in the system somewhere.
 
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Turdle

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That shouldn't be necessary. It's a pressurized system. Any air that's in the system will force it's way to the radiator once proper PSI is reached. Unless there's a blockage in the system somewhere.

It'll go a lot faster. Try it.

:D
 
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kkjb4x4.0

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First gen? 4.0? Coolant loss? Upper intake gaskets or head gaskets on their way out. look for coolant leaking on drivers side engine bank.
 
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