1995 Saturn SC2 Overheating Issue

1995 Saturn SC2 Overheating Issue
Problem:Car overheats will at idle or driving around town. Does not overheat on Highway or Interstate.
Temperature Gauge shows a little below 1/4 while driving on Highway or Interstate.
There are no leaks anywhere.
The coolant is not discolored.
Check Engine light has not come on.
The fan does not turn on until A/C is turned on.
Tried turning on A/C when it gets hot to turn on fan - does not cool down.
Only turning on heater will cool down.
I have not let it get over 1/2 on Temperature Gauge before turning on heater to cool down.
Does not idle or run rough - no hesitation or stalling.
Does not smoke.
Can smell antifreeze when turned off after it gets hot - not from exhaust - can smell on reservoir side - probably boiling

Items to Check:
1)Thermostat - working properly (Sticking) Upper radiator hose does heat up when engine heats up - is not cool to the touch
2)Radiator Coils / Front Grille - Blocked Radiator is clear - I have no grille
3)Hoses - collapsed Hoses are not collapsed
4)Oil Level - low Just had oil changed - level is OK
5)Belt - Bad / Need Adjustment Belt may need replaced, has plenty of tension
6)Fan - Broken or Cracked Blades / Faulty Motor / Blown Fuses Fuses are OK, Blades are not broken or cracked, fan will come on when A/C is turned on
7)Coolant - Bad, need flush Just checked - Coolant is OK
8)Coolant - wrong mix
9)Check radiator cap - have pressure tested, missing or bad seal gasket
10)Radiator Core - blocked / trapped air
11)Catalytic Converter - Blockage
12)Thermal Sensors - 2 wire sensor (PART# 21025106), 1 wire sensor (Part #21020124) need replaced
13)Power Train Module (PCM) - replace
14)Water Pump - Working properly
15)Head gasket - leak Coolant in reservoir does not have a "chocolate milk" film in it
16)Head - warped/ cracked
Please let me know if I need to check anything else or if anyone has any suggestions on what the problem is.

Fantastic post!!!! Easy to read...right to the point...all the details about what you though to check and what you checked..Vitals right at the top.....AWESOME!!! This is how everyone should post problems!!! Kudos!!!

Now to your issue....you forgot one thing. The Engine Coolant Temperature Sensor. This one little sensor needs to be checked and replaced. Your stock one is made of resin and cracks, sending bad data to the PCM. New ones are brass. The ECTS is used for many subsystems of the car including but not limited to: Air/fuel mixtures, idle rpms, transmission functions (auto), Fan control, emission systems and more. Your car has two sensors, you need to replace the one with the 2 wire connector located under the EGR. Also check the connector to be sure there is no corrosion.
ahhh here this will will help :) :http://youtube.com/watch?v=JC0U53w_Htk

Also, you might want to replace your thermostat. Your normal operating temperatures should be at 1/2 as per the guage. Fan should not come on untill almost redline. The guage increments are different for '95 and earlier years, meaning your fan turns on at the same temperature my '02 turns on even tho the gauge on the dash says differntly.

Again...well done post :smile:

I thought the engine coolant temperature sensor was the 2 wire sensor (PART# 21025106) on item 12.

Is there another sensor?

I was going to replace the 2 wire sensor (PART# 21025106) and the 1 wire sensor (Part #21020124).

Thermal sensor. I guess you meant Engine COolant Temperature Sensor :) We are talking about the same part then. Replace the one with the 2-wire connector.

I have a 1998...My cooling fan does not engage with A/C turned on. However, the car only overheats if I idle w/ A/C on (I assume since the fan never comes on anymore). I have checked voltage @ the fan motor connector and it does not change from zero volts with the A/C on or off.

Will a bad ECTS keep the relay from energizing, even with A/C turned on?

No the A/C should turn on the Fan overiding the ECTS. However replace your ECTS anyway as it is probally a stock resin one which cracks.

After that check the fan relay in the under hood fuse box. It is the same relay as the a/c so switching relays will tell you if its the relar or not. If the fan doesnt turn on, it could be your fan that is bad. They usually last about ten years anyway. Let us know what you find

Good News/Bad New:

First, a quick way to check the entire radiator cooling fan circuit: unplug the radiator fan, shove a test light into the electrical connectors, start the car, turn on a/c. If the test light lights, it is the fan motor.

Good news--my curcuit is good all the way around.
Bad news--at 10 years old & 110k miles in san juaquin valley, the fan motor is shot!
Good news--you can replace just the motor for less than $40, and not the enitre assembly (@ $120)--one left thread nut (fan blades) and three more screws (motor to shroud) saves over $80 and only takes two more minutes. :cool:

Another person who sees the beauty of the saturn s-series...such a wonderful thing:grinyes::grinyes::grinyes:

I have a 98 SL2 that is also overheating (boils out of the new cap) and I am suspecting the temp sensor (2 wire). per the scan tool (reading the computer) it over heats at 155F does the temp sensor still make sense, the dash gauge shows about 1/4 and the too hot light blinks???

Change your ECTS ASAP

Also be sure the fan turns on at 3/4 as per the guage. Check your coolant levels, making sure they are full.

Normal operating temperature for your car is 1-2mm past 1/4 as per the guage.

I assume this should be around 190F? Also any trick to filling the system. With the tubing running from the throttle valve to the reservoir there should be any issue with vapor lock, correct?

I assume this should be around 190F? Also any trick to filling the system. With the tubing running from the throttle valve to the reservoir there should be any issue with vapor lock, correct?

Stock thermostat opens at 195F.

Correct. That hose creates a slight vacum in resiviour IIRC.

However do not rule out the possibility of a bad radiator. With a '98 its over ten years old. Usually in most cases that about when the stock radiator goes.

Stock thermostat opens at 195F.

Correct. That hose creates a slight vacum in resiviour IIRC.

However do not rule out the possibility of a bad radiator. With a '98 its over ten years old. Usually in most cases that about when the stock radiator goes.


A bad radiator as in leaking or are they known to plug?

Both really. Some like to get hair line cracks in the plastic housing. The one on my '94 pluged up

Looks like the temp sensor (ECTS) was the problem. all seems fine now. wow the fan does not kick on until 221F eish. Excellent thanks for the help.

s series don't really have a problem with vapour locks, just fill the reservoir until full and wait for the thermostat to open then fill to just over the line and take it for a good ride then check again and top off