'98 SL2 Cooling Fan Won't Turn On

At idle, engine temp just gets hotter and hotter. Coolant boils over from
reservoir when this happens. Fan never kicks on unless I turn on A/C. I
have replaced the coolant temperature sensor (to PCM, not temp. guage) but
no joy. Ideas?

 

I think the CTS for the computer feeds the temp gauge on the dash for
98's.

Questions:

1. What is the temp gauge when you 'suspect boiling'

Ideas:
I believe you are hearing things from the reservior, but it might be
normal. My SL's would make lots of bubbling noise too.

Remember, if you really believe you have a over heating problem, then
you need to get the car professionally looked at. Having had a car
over heat once, the engine later failed. Becareful.

later,

tom @ www.WorkAtHomePlans.com

 

Another thing: Consider replacing the reservoir cap. I replaced mine
and saw coolant consumption drop to zero. A bad cap could cause
boiling over at the reservoir.

The fan is controlled by software. As long as the CTS is working
correctly, the dash gauge, fan, and fuel mixture are all handled by
the PCM using that common data source (in late models like my '97). If
you connect a scan tool (not just a code reader), you can read the
actual temperature the PCM is seeing. As long as that number is less
than the spec, some 200 degrees F as I vaguely recall without looking
it up, the fan won't come on.

If you're getting actual overheating, not just an instrumentation
problem, another possibility is a bad thermostat. I've been stranded
more than once with a bad 'stat (not in a Saturn) so I replace them
prophylactically whenever the cooling system is drained. The coolant
boils over and overheating can warp the block. The other failure mode
is the engine running too cool, wasting gas. Either way, I don't trust
thermostats.

If it's not overheating on the highway, my first guess would be the
reservoir cap.

RK Henry

 

What RKH said. Or, possibly, a clogged radiator, or a bad temperature
sender (there are two) or the fan relay or a blown head gasket ....

Bob

 

Do the easy and cheap stuff first.

I am assuming that the coolant is clean and at the correct level and that
there are no leaks or collapsed hoses.
Check coolant rad and air conditioner rad for blockage from dust or dry
grass. Wash well with a hose from the back (with engine off). If it is
very dirty you may need to remove the rad to clean properly.

Use a temperature gauge to measure the coolant temperature. How you
accomplish this will depend on what tools you have available. I would
suggest taping a thermometer (under some insulation) touching the upper rad
hose near the engine. Start the engine and watch the thermometer and the
temp gauge in the dash. As the engine warms up you should see a rapid rise
in the rad hose temp when the thermostat opens. I cannot recall at what
temp the fan should start but it is quite high (>200F IIRC someone here may
give us a more accurate figure or you can do a search on Google groups as
this is a frequent thread)

Does the thermometer indicate that the thermostat is functioning properly?
Does the engine overheat?
When you turn on the AC this should start the fan. Does the engine still
overheat or does the running fan cause the dash gauge and thermometer to
cool?
Does the coolant boil?

Good luck and keep you hands away from the fan.

 

It overheats only at idle? If so I suspect a blockage in the rad. When you
drive down the road and it doesn't overheat its because the flow of
coolant is faster and getting by the blockage enough to keep you cool. If
it is a stat it would overheat all the time. If your rad cap is bad the
coolant would boil over past the resevoir and you would be able to see
that. If your system has be open or added to you might have air in the
system which could cause incorrect readings from the temp sensor. and
overheating...but that would be all the time. The key to your prob is that
it only overheats at idle. I say your rad is blocked up.