Overheating, Cooling fans not coming on

['98 Roura]

Hello all!

I have a 1998 Aurora that seems to want to overheat slightly. After driving a bit, the temp gauge hits 200 and stays there, then after a few minutes it climes to 220, 225, 230, ect... I checked the coolant level and cap and they were both fine. I replaced the thermostat with a brand new AC-Delco one and it didn't help much. Then I noticed the fans weren't running. I checked and tested all three relays and the fuses and they all worked fine. I fiddled with the relay on the firewall and strangely, the fans kicked on once it hit 200. I put everything back together, closed the hood, and ran it again but the fans wouldn't come on again when it hit 200  . I blasted the AC and the fans still refused to come on. Then for kicks, I hot wired the fans to the battery and they both worked. I'm not sure what else to test and check. The car runs well and is in very nice shape and I don't want it to overheat and damage the engine (I know those northstars are temperamental ) Any ideas? Thought I'd ask all you pro's before I go to a shop lol. 

Thank you!



(UPDATE!) I jumpered pin 30 and pin 87 on the firewall relay and both fans kicked on, and I got 12 volts from pin 85. Pin 86 is the ground that goes to the ecm and I'm not sure how to test that. With the ignition key on, I get about 3.8 volts across pins 85 and 86.

[aphex]

The fans will also kick on with the AC on. The fans aren't programmed to come on until like 229! I'm driving a 98 as well that wants to surge out the cap when I idle too much. Some people will run the AC to keep the car cool which seems to make my situation worse. I'm about to do a dye test on the cooling system as well as send my pcm to get tuned to turn the fans on at a lower temp. Of course, after I do a combustion leak test just to be safe.

I don't know if anyone does the tuning on the forum here. I was surfing www.northstarperformance.com/tuning.php and for $119 they remove the speed limiter, remove 1st gear lockout, and change the fan operation. The site says fan speeds but I believe they mean operating temps which I was going to verify.

['98 Roura]

Apr 5, 2018 21:50:24 GMT -6 aphex said:

The fans will also kick on with the AC on. The fans aren't programmed to come on until like 229! I'm driving a 98 as well that wants to surge out the cap when I idle too much. Some people will run the AC to keep the car cool which seems to make my situation worse. I'm about to do a dye test on the cooling system as well as send my pcm to get tuned to turn the fans on at a lower temp. Of course, after I do a combustion leak test just to be safe.

I don't know if anyone does the tuning on the forum here. I was surfing www.northstarperformance.com/tuning.php and for $119 they remove the speed limiter, remove 1st gear lockout, and change the fan operation. The site says fan speeds but I believe they mean operating temps which I was going to verify.

We turned the AC on full blast on the fans didn't come on, we even tried unplugging the coolant level sensor and they still wouldn't come on. My troubleshooting seems to have narrowed it down to the wire going from pin 86 on relay #1 to the pcm. I wonder if the driver in the pcm is acting wonky.

[aphex]

That certainly is strange, my fans turn on but I still have an issue with the slight overheating during idle. The fans not coming on with the AC would point to the relay.. Do the fans kick on when it goes upwards of 230?

[RCA1186]

What were the outside temps when you kicked on the AC? If I remember correctly the compressor won't kick on even if you call for the AC unless it's above 43 degrees. I have if a feeling that if the compressor doesn't kick on then the fans wont either. You can try pulling the coolant level sensor from the bottom of the surge tank, that will keep the fans on but you will get an error message.

You also have this option.



Here is the operating range of the fans (image borrowed from one of Sall's posts)






When it overheats are you driving or idling? If driving, I'd check for blockage in front of the radiator. Also check for slippage of the water pump belt/pully. Could even be possible the waterpump belt tensioner isn't putting enough tension on the belt to spin the waterpump correctly. I think the pumps themselves are pretty bulletproof minus leaking.

[tigger]

Apr 5, 2018 21:27:43 GMT -6 '98 Roura said:

I jumpered pin 30 and pin 87 on the firewall relay and both fans kicked on, and I got 12 volts from pin 85. Pin 86 is the ground that goes to the ecm and I'm not sure how to test that. With the ignition key on, I get about 3.8 volts across pins 85 and 86.

I don't have a schematic for the '98, but if it's like the '01...

Start the engine and work quickly, haha! Ohm across 86 socket and ground, should be infinite. Unplug the coolant level sensor (or turn on A/C) and repeat, should be zero to very low resistance.

If both check out, bad relay.
If both read open (infinite resistance), bad connection to PCM.

HTH

[emarkay]

Pressure check radiator. Small leak will not allow coolant to go above 212 locally. Amazing what difference new radiator accomplished. Of course look at all other overheating possibilities.