Erratic temperature gauge on 1990 Spirit w/ 2.5

More then likely your heater core is stopped up and not allowing the coolant to flow thru the cylinder head as designed. I would guess you don't have much heat coming from the heater?

Glenn Beasley Chrysler Tech

The heat *seems* to be okay. I guess that I could try moving the slider back to *cool* when it happens, and see if it cools down. Would this by-pass the heater core?

-KM

It has nothing to do with the slider if the heater core is stopped up. Get the vehicle good and hot and feel the heater hose going into the heater core and then the other hose coming back out of the heater core, if one is really hot and the other kinda warm it is probably due to a stopped up heater core.

Glenn

Thanks. That sounds easy enough. If the core does have some blockage, can it be flushed out, or will I most likely have to replace the core?

-KM

If you think that could be the problem just disconnect both hoses from the heater core and connect them together and drive it. if the fluctuation is gone, replace the heater core. I have never had any luck trying to flush them out due to the crystallization inside

Hi...

Respectfully wonder if the heater core was blocked sufficiently to affect water flow at idle, wouldn't it still be blocked at high speed? Granted the water pump may push a little harder, but...

I'd like to suggest that after a good long run he pull into his own driveway, leave it running while he pops the hood and looks at the fan(s). If they're not running wait a few minutes and see if they start, before the temp gauge gets too high?

Just a thought, not anywhere near a mechanic.

Take care.

Ken

It is very possible that the fan isn't turning on. I guess I would have thought that if the OP could have replaced the Thermostat he would have made sure the fan would turn on at idle. And reading the OP post again I am seeing at the bottom where it says could it be the fan.

Glenn

Maybe this can be caused by one of the fans that is not working when the vehicle is idle. I have the same problem with my car. As soon as I stop for a red light, temp. gauge goes up and then goes down as I am driving. It goes even lower when driving at high speeds down the expressway. Check the fuses of the fans .

I can check the fan. At what tempurature should the fan come on at idle? I also noticed that if I turn on the A/C, the fan will come on immediately.

If I turn on the A/C, which causes the fan to come on, should I expect it to cool down soon?

-KM

Hi...

Don't know the temperature, but again suggest that you just come back from a drive, leave it idling, pop the hood and watch for the fan to come on. At the same time keep an eye on the gauge to make sure it doesn't seriously overheat.

The fact that the fan comes on with the A/C doesn't eliminate the possibility that the coolant temp sensor hasn't failed, or come disconnected, or corroded. Don't know where it is on your car, but should be in the block very near to the thermostat housing.

A hint that the sensor may have failed might be that your idle speed be higher than normal, and that your fuel economy be noticeably reduced (the engine always thinking that it's cold, so running a little richer and faster)

Take care.

Ken

With a scan tool the fan is supposed to turn on at 212 degrees. If the coolant switch that controls this fan becomes disconnected or loses connection the default for the engine controller is to raise the idle and turn the fan on all the time. Just let the vehicle idle, a/c off and see if the radiator fan turns on before the temperature gauge red lines. my guess would be it does turn on.

Glenn

Thanks Glenn. I will give that a try. I have noticed that there appears to be two sender switches on this engine. One is located near the thermostat housing, and the other is located in the head, more to the left. Is one for the fan, and the other for the gauge?

-KM

The one for the gauge is to the left by the a/c compressor and the coolant temp sensor that controls the fan is on the thermostat housing area.

Glenn

Is the sensor that controls the fan a switch? If I were to short the two pins together, would that close the relay and make the fan come on?

-KM

No. It's a thermistor.

Simply unplugging it should cause the fan to come on.

This will set a trouble code which can be erased by disconnecting the battery.

I agree about the partial restriction in the heater core, and would suggest that some variety of stop leak or a severe overusage of RTV during the headgasket repair is to blame.

Based on my experiences with this odd temp gauge fluctuation phenomenon on 2.2/2.5 Chrysler models, I would disagree about the temp gauge position not having any effect on the symptom. I assume that this vehicle has the H-style bypass heater valve, which allows full flow when the heater cable is in the cold position, thereby eliminating any gauge fluctuation caused by the core restriction. If the heater valve in question is not of this design I apologize for my misinformation.

Toyota MDT in MO

This is exactly what my 1992 Shadow 2.5 has done since day one. The fans are coming on, the radiator/heater has been flushed regularly, has had many thermostats, and I never have to add water. The only weirdness is that the heater (guage says normal) never puts out hot air after a cold overnight shutdown, untill you stop the car, turn the car off for 5 minutes, then start it up and take off. THEN the heater will run you out like a blast furnace. Been that way since its been brand new, and nobody knows why. Yes, its been burped several times, and always after an antifeeze change. D

Hi Deke...

Can't help but wonder if perhaps your lower radiator hose is collapsing? (vacuum sucking it closed while it sits and cools down overnight)

Might be an interesting experiment if you'd consider replacing it with one that has a coil spring in it when the time comes.

Take care.

Ken

sufficiently

Its a sensor. As aarcuda said by disconnecting the sensor the fan will turn on, the idle may flare up and the check engine lite will turn on. Did you allow the engine to run until the gauge went to almost overheat? Did the fan turn on?

Glenn