94' saturn sl1. Replaced water pump and thermostate that was less than a year old. Still didn't fix it. gauge dances around. Guessing it may be the temp sensor... any advice or input? Doesn't show any signs of over heating. Just gauge not acting right and just suddenly started.

 

94's have two temp sensors -- 2 wire device mounted in head (ECTS) used by PCM , 1 wire device to drive temp gauge. Does cooling fan come on at 3/4 tick when gauge reads high?

 

No the fan don't come on.

 

Run a direct wire from the battery to the cooling fan and see if it runs. If not, then there's your problem. If so, it's either a bad relay or a short in the wiring somewhere.

 

The fan will turn on if I switch the a/c on for a sec and run for several minutes

 

Go back to Derf's comment. The Saturn has had a long history of problems with those sensors causing false indications of overheating problems and run-ability problems. As Derf said the 94 has two of them as described. Not only were the OEM sensors calibrated wrong in the first place, it went undiscovered for a long period of time so the aftermarket was also saturated with the wrong sensor. Fast forward to today and the dealers no longer exist although a local GM dealer may be able to order those sensors for you. If you go that route also check the wiring and the connector, any sign of damage, replace those too. GM had a replacement kit for them. If nothing else try a NAPA or CARQUEST Store for replacement parts but there is a real possiblity that they will still be wrong due to still being in stock and not sold. But what ever, if the water ain't boiling out and peeing on to the ground then the gauge is lying to you and the sensor is wrong. Replace the sensor. Even a new wrong one is going to be better than the old damaged and dysfunctional wrong one you are probably now using.

 

See what i can do.

 

from A/C comment, fan works. This means relay to fan also operational.
My earlier question was meant to discern whether the fan was following the dash gauge -- which case it would have meant that the temp fluctuations were real. But it does not. That's good.

This leaves us with 2 temp sensors -- one for the gauge and one for the PCM

In this case I think the dash one (1 wire device) is faulty -- either that or there is an issue on the instrument cluster you're not likely to find

I'd replace the 1 wire device AND

I'd also take the opportunity to replace the ECTS ( two wire device) and its connector -- this will ensure that the fan kicks on at the right temperature. The original design was a poor one and they all fail eventually leading to everything from hard starting, strange idling, to poor gas mileage.

ECTS + connector = $40
1 wire temp sensor = ?

GET BOTH FROM A GM DEALER if you want the right parts