TLDR - looks like her fan isn’t coming on so need to systematically evaluate signals and wiring ? Can you guys in early P80 land help here?
Post follows
My '95 850 GLT, Greta, has been a wonder car, a reliable workhorse passed on to both my kids while in college, seemingly bulletproof. Troubles would happen with our other cars- an old VW that's hell to find parts for, two OG Saab 9-3's that'll make you wanna rip out your hair sometimes, but with nothing but regular oil changes and am occasional time-up, Greta would always be there.
Well, it seems I reached the limits of taking her for granted and she has finally demanded my attention. Mea culpa, mea culpa...
She overheated. Thankfully, it happened as I was pulling into my driveway. I got the "coolant low, turn off engine immediately" warning and shut her down immediately.
Relying on perpetual optimism and blind faith, I set about trying to soothe whatever was ailing her and love her back to life.
I started with:
Oil and filter change
Engine coolant and radiator flush
New heater core + o-rings
Fresh coolant
New platinum plugs
New NGK plug + coil wires
New OEM thermostat
New OEM ECT sensor
Replaced wires from middle port of fan relay to "y" of the harness to ECM (they were a bit dark and stiff)
Along the way, I addressed several other things I came across that needed attention:
Tightened loose hose fittings on coolant reservoir tank
Thoroughly cleaned TB
New TB gasket
Replaced rock-hard vacuum lines
Cleaned out flame trap (100% plugged solid) and pcv hoses above intake manifold (but not oil trap)
New air filter (oiled k&m type)
Degreased and pressure-washed undercarriage to clean off spilled coolant and oily residue and give me a clean slate for detecting any future leaking.
There is a small oily leak coming from the area between the oil pan and transfer case (transmission?) to the immediate left (drivers side) of it. Not sure if it's engine oil or ? gear oil perhaps? It's honey-colored and clearly not ATF.
Noticed the two small wires from center plug of fan relay (yellow and yellow-gray) were dark and somewhat brittle, so spliced in new wires, just to "y" of harness to ECM. Salvaged and reused silicon boots on new bullet connectors.
Confirmed
12v to fan relay (single red wire at plug 3, passenger side),
fan comes on with AC switched on.
I started her up, drove her gently about 10 miles and
she began to overheat again
. Engine was visibly very hot, coolant was steaming and reservoir nearly empty,temp gauge in dash gave NO indication of overheating (normal 3 o'clock) and
fan was NOT on.
I figured something must be off in the cooling fan system, so I started over.
Pulled tstat and ECT sensor.
Bench-tested tstat in boiling water - confirmed opening in hot water (but slowly) - good
Bench-tested ECT sensor (checked resistance changing inversely with temp changes) - good
Re-installed both, plus a missing crush washer at the sensor (saw leak here during overheated test drive)
Topped off coolant.
Connected battery and confirmed power to fan (12v at single red wire on relay, plug 3/passenger side)
Started car, turned on AC, and NO FAN.
I ordered a new relay, but have no idea if that will help.
Now I'm just STUCK- afraid to test drive her even with a new fan relay, and confused as to what/where to check for the underlying problem.
Maybe this is an AC sensor problem? I refilled the refrigerant two summers ago when it was blowing warm air and I very rarely use the AC at all. Maybe twice in the two years since the recharge. Could lack of use be causing an issue with the sensor?
Where is the AC sensor that informed the ECU to activate the engine fan? How can I test it without dumping out all the refrigerant?
As you can probably tell by my lengthy message, I tend to overthink or analyze things excessively. I genuinely want to understand what's happening and what is causing the trouble, but each new possibility is days and days of tracking down something that may be a complete waste of time and effort.
How can I determine if the problem lies with the fan relay, the fan motor, the ECT sensor, the ECM, the high speed/low speed wiring, or even the sensor/signal from the AC?