Erratic temperature gauge on 1990 Spirit w/ 2.5

When I start out, the gauge will be consistent in the "normal range."
When stopping for a red light, it will swing almost to the far-right of
the normal range. After getting up to a normal speed, it will move back
into the middle of the normal range.

I have changed the thermostat, but it did not help.

Is it possible that the fan is not coming on when idling?

Could the temp sensor be bad?

Do I maybe have an air bubble in the system?

Headgasket was replaced 3.5 years ago. Coolant in recovery tank, is
staying in the normal range. I am going to try opening the bleeder plug
to see if there is any trapped air.

Thanks in advance for any help.

Kirk Matheson

 

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

 

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