Temp guage not reading right

tjs4x4 · Oct 7, 2010

So for awhile now, my temp gauge hasn't been working right. It will read normal when its warmed up, and other times it won't read beyond the C even though I KNOW its warmed up. Would this be a coolant temp sending unit or sensor? Or would it be a faulty gauge or what???

adsm08 · Oct 7, 2010

It could be any of those things, or wires. Any particular time that it does it (rain, cold, hot, car upside down, etc) or is it completely random.

4.0B2 · Oct 7, 2010

is aftermarket an option? that'd be easiest fix...

but the sending units aint expensive. and you can check them somehow... with an ohms meter i think?

tjs4x4 · Oct 7, 2010

It happens randomly...its getting worse, more and more often its not reading at all. Any diagrams where the unit/sensors are?

adsm08 · Oct 7, 2010

I'd guess its the gauge in the cluster.

tjs4x4 · Oct 7, 2010

Hm ok. I guess I can find one in a junkyard and try that.

tjs4x4 · Oct 8, 2010

Ok, so now its not even showing that its reading at all. My fan is working constantly, the hoses are so freakin hot I nearly burned myself just barely touching them. Ideas??

kimcrwbr1 · Oct 8, 2010

Sounds to me like the connector not being tite crimp it a little with a pair of pliers sand the sender connection and scrape the female connector with the end of a small file to rough it up and make sure it pushes on tite.

tjs4x4 · Oct 8, 2010

What connector?

tjs4x4 · Oct 8, 2010

I'm going to start with the sensor/temperature switch. See if that works. I sure hope that this isn't damaging my engine.

doorgunner · Oct 8, 2010

there's an ohm test for the sensor.....with the engine cold, the sensor should read a certain amount. After the engine is started the ohm rreading should change noticeably as the engine warms up .... maybe I saw the test in the Tech Library...grounding the dassh gauge should cause the gauge to max out hot if it's working correctly.(that will eliminate having to take the dash apart)

but it's definately a concern if the hoses are getting that hot.....Got a good basting thermometer that you could hold against the upper radiator hose just to be sure of the temp when the engine is warmed up good????????

Earl43P · Oct 8, 2010

Have you checked the coolant level?

Even a good sensor can't read any temp if the coolant level is low and yes that'll cook your motor and likely blow a head gasket.

2nd guess would be a stuck thermostat, but it should at least register "some", as in up higher than when it's not running, key in Run.

You should paste from the PMs, you've gotten a lot of good advice, including the fan clutch.

Coolant level, replace the thermostat, it may be a bad sender - check its connection, and also take off the radiator cap, then start it. Goose the gas while you watch the coolant level in the radiator (keep your face away). It should FLOW when the thermostat opens and you goose the gas. It'll take a while to warm up to that point. No flow could be a bad water pump.

Don't open a hot radiator cap.

^^Like he said, the coolant sensor has ONE WIRE, not two. Should be in the front, near and behind the top radiator hose. The two wire one is for the computer. Use a paper clip to ground out that one wire, while someone watches the gage. It should go to full HOT pretty quick. Un ground it or turn the key off so you don't blow a fuse.

tjs4x4 · Oct 8, 2010

I tried to spin the fan while engine off, it spins, but not freely, it stops within a second or so. Acts like its sticking. I gotta replace that fan too, just noticed two cracks.

Coolant level is normal, up to where it should be in the radiator. No coolant in reservoir though. Will have to check and see if the coolant level goes down when the engine cools.

I have a thermometer that I can put up against that top hose, and see what the temp is.

Thanks for all the info guys, will keep posted.

kimcrwbr1 · Oct 8, 2010

It takes quite a bit to hurt the 2.8 mine should be dead. Do your other guages act erratic if you take the wire to the sender and touch it to ground the guage should read hot and you should have around 8 volts pulsing going to the sender. See if you are getting the same signal to the oil pressure and fuel level. The senders provide a ground to the guage. Erratic almost always is electrical check the connector to the guage cluster/circuit board for corrosion and the board itself. If you have A 180 degree t-stat it is going to be hot up to temp 130 degrees will make your skin bubble after a couple minutes. run it with the radiator cap off and put the thermometer in the coolant. grab the lower hose going into the water pump it should be alot cooler.

tjs4x4 · Oct 8, 2010

Gonna try some things tomorrow when I get home from work, see if I can check coolant levels when cap is off. Will check temperature of coolant as well, along with the bottom radiator hose.
So the sensor that has only ONE tiny wire that directly sits on it is the sensor? The one that has a plug in that is alot bigger is what?

I've replaced the entire cluster once already. Wiring harness should be in correctly, I can check that, but that would have to be on a day off. Do not feel like peeling apart the dash after a day of h*** called work.

Temp guage not reading right

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