2001 SC2 OVERHEATING-Cooling fan wont turn on, WORKS WHEN a/c IS ON
 

2001 SATURN SC2

Driving on freeway is does fine, but when Im stop and go or idle it starts to overheat. Boiled out of the Recovery cap.
The fan come on when I turn on the A/C and blows Ice cold, but turns off ass soon as I turn off the A/C.
The Fan will not turn on when the temp goes up.
DID THE FOLLOWING
Replaced Cooling fan relay
Replaced Coolant Temp sensor
Changed Recovery cap, due to the fact that it boiled over from there
No leaks from anywhere else

is it the fan Still, even though it works with the A/C on ??
Should I change the thermostat as well before I change out the fan?
Or am I missing something else on this ?

Thanks for the help.
DINO

Please go post an intro post, we would like to know more about you and maybe gain a new member, too many people like to post and dissapear hahaha.

First question is where do you live / what is your daily weather like / what is your commute like? Is it an automatic or manual? Mileage?

How high on the temp gauge did you let it get before you turned on the A/C to cool it down. And how high on the temp gauge was it when it began to boil over?

Since you replaced the cap, has it boiled over since? Have you attempted to let it heat up and once it is close to red start driving or turn on the A/C?

If the fan comes on with the A/C, the relay is good, and the fan is most obviously good.

When you replaced the coolant temp sender, did you go to a dealer and use an OEM Part (ac delco brand is gm oem I believe, not sure of part number, derf will probably know that) and also replace the sensors wire connector? These cars do not like aftermarket sensors for some reason.

How long have you owned the car? If you have owned it since new/for a long time, has the coolant ever been changed. Over the years coolant will break down and lose its cooling abilities/ boiling point will lower. When it boiled over did it smell like coolant? If there is more water than coolant in there it will boil faster, plus an old cap not keeping it under the correct pressure can make it boil sooner.

Is the car eating/losing coolant, you say no leaks so I will assume no. But if it is, you could have a head gasket going out, over-pressurizing the system (however this is more unlikely, you would notice a white smoke or haze out of the exhaust) You would also have chocolate milk for oil and milkshake for coolant, this would be very obvious. If it is an automatic trans, and the trans cooler (inside the radiator) could have cracked and mixing coolant with atf, but this would also be very obvious. (i.e. funky looking coolant/ trans not shifting correctly, also unlikely)

Could also be clogged radiator fins. Easiest thing to try would be to jack up the car (while cool) and take a hose and clean the rad by flushing water through the fins. This will take awhile, and do not use too hard of a stream too close to avoid damaging the fins. I suggest a hose with no nozzle and just use your finger to create a slightly stronger stream. It would be easier with rad out of car, but you can probably do it from inside the engine bay out(if you remove the air box and resonator, and maybe the fan)

If the thermostat hasnt been changed in a long time, or you dont know when it was done, it may not hurt to check/replace it. Could be stuck closed or not opening fully. Also a good excuse to flush whole system and refill with fresh antifreeze.

Excuse the book, but that is everything I can think of off the top of my head. Im sure others will chime in but I think there is plenty of information to get you started

Aftermarket ECTSs are not calibrated specifically for the S car's application, meaning their resistance vs temp change behavior is not the same as the OEM part. Search ECTS on any saturn forum and you will find close to 45,788,456 posts about using the GM sourced part. Not bashing you---don't even know where your part came from -- just letting you know it is a very very very very very common S car issue. Also obtain and replace ECTS connector w GM part. I've heard these have come out aftermarket -- no idea regarding form fit or function so I cannot blast these. It's 2 contacts and wires --only Dorman could screw that up.

1) Please measure the resistance of the ects stone cold (please note approx outside temp)
2) Please measure the resistance of the ects with the temp gauge reading 3/4 --then turn on the air co to avoid an overheat

3) with the engine running cool, put a paperclip across the two contacts of the ECTS connector--they should be clean and free of green gunk and corrosion. Clean them if not. If the fan does not turn on (paperclip simulates crazy high coolant temp) you likely have a wiring issue in the ECTS circuit

I think there is more than one cooling fan relay.

Not to my knowledge.

Any progress on this one?
Did you ever make the resistance measurements above and try bridging the connector as described?

Changing the thermostat would have been the first thing I'd have done. Then pressure test the frigging radiator cap.

But we'll never know since he turned out to be a one n done. And appropriately banned.

Which to me signals that one or more of us were correct in our diag, and, like many, he has no manners and neither tells us it's resolved nor thanks us.

Ungrateful bastard!

you guys gave a lot of good information and suggestions. I sure wish he had told us what he found.

I'm always impressed at the depth of knowledge from members on this forum.

Coolant sensor on 1.9 DOHC engines
 

A paperclip across the contacts will not work. The temp sensor is two separate single-lead sensors. One lead goes to the gauge, and the other controls the fan. I had this same problem with my '98 SC2 years ago. You have to measure resistance from each lead on the sensor to the block, or to the brass body of the sensor itself. There is no connection between the two terminals.
I know this is an old thread, but the subject came up recently. As the owner of three Saturn's (09 Aura 3.6, 04 L300 2.2, 98 SC2 DOHC), and former owner of a fourth (97 SC2 DOHC) for 16 years, I want to keep them ALL on the road. Saturn was the last great American car company....