850 Fan not operating completely stumped. Help!!!

minorl850 · Post by **minorl850** » 30 Oct 2022, 20:19

Hi everyone. I haven't posted in quite a while.
My 1995 850 T5R has a problem that I really need your help with.
Three days ago, I drove the car about 10 miles. no problem. Parked for three hours and when I got back decided to go get some gas.
At the gas station, steam was coming out of the engine bay on the right (passenger's side). The temperature gauge was in the middle.
I got out of line, parked, shut of the engine and opened the hood to find water coming out of the reservoir under the cap.
interesting. I'm thinking, low coolant, so I add some, start it up and drive about a mile and same thing happens.
Ok, I get it towed home.
i'm pretty good with cars, so I'm thinking, thermostat or water pump. so I order a new water pump and thermostat from FCP.
While I'm waiting for it to arrive, I remove temperature sensor by the thermostat, and test it in hot boiling water. I appears to be working, as temp rises, the resistance is lowering.
I then test the thermostat. in boiling water it opens at 90 degrees C (194 F). Hmmmm
I test the fan by grounding the fan relay and nothing. no fan. Also, no fan when I turned on the AC.

So, I replaced the water pump and thermostat. Took the fan apart and repaired it. Tested the fan relay and they now work.
I also went to a local pick a part and got another fan that works and tried that also.

Start the car and no fan and water boiling after a little while.

I then check the wiring of the temperature sensor all the way to the ECU. Continuity.
I then check the wiring of the two fan control wires all the way to the ECC. Continuity.

I make sure the connectors are tight.

Shoot! it's got to be the ECU right? I swap a used ECU and same problem. no fan.

When I ground the fan relay and the fan runs, It does not boil over.

I stared the car once and the fan came on instantly. I'm thinking, great!!! it works now, then It hit me. Why is the fan running with the car cold?

Shoot, I forgot to connect the temperature sensor connector. Car runs rough. Check engine light is on. NO signal from temp sensor.
Reconnect it, clear the code, start the car and no fan after warm, turn AC on, still no fan.

What the heck is wrong?

Maybe the temperature sensor?

I'm stumped.

Help!!!

thanks,

1995 Volvo 850 T5R 297,000 miles, (completely restored with engine rebuild, trans, suspension, etc.)
1983 Volvo 244T 321,000 miles (completely restored)
1970 Plymouth Barracuda, in-violet purple ground up restoration.

Post by **Chuck W** » 30 Oct 2022, 21:22

The fan relay might be bad. Does the fan turn on when you manual ground the two control wires? ( I can't quite tell from your post if you did this and what you "grounded" when you tested the fan/relay)

Could also be a radiator cap that is bad and not holding pressure.

The ECT sensor could be faulty/old and not reading properly. Do you have an IR temp sensor to point and shoot at it to check temps. The sensor could be reporting a "low" temp value.

minorl850 · Post by **minorl850** » 30 Oct 2022, 22:05

Thanks for the suggestions.

I thought I did mention that I did ground the relay and the fan did turn on after I repaired the fan. I also, got a used fan from the pick a part (just in case) and two used fan/relays. They all tested good.

So, Hmmm. Interesting that the fan was bad initially until I repaired it.

So, this could have started the problems. maybe?

I ordered a new temperature sensor today.

I will used my IR temp sensor tomorrow to check temperatures.

By-the-way, when you say ETC sensor, you are referring to the temperature sensor next to the thermostat, correct?

Also, I will try a new radiator/reservoir cap tomorrow. Does this affect the temperature and affect the fan?

Thanks,

Post by **scot850** » 30 Oct 2022, 22:39

Be careful of using any ECT other than Volvo OE part. This is one of the parts that is very sensitive in these cars.

Neil.

Post by **manovlov** » 31 Oct 2022, 01:42

minorl850 wrote: ↑30 Oct 2022, 22:05
...
Also, I will try a new radiator/reservoir cap tomorrow. Does this affect the temperature and affect the fan?

Thanks,

To me, if the cap reservoir fails, the coolant gets out and at a moment, there's not enough coolant in the circuit", the engine warms, not enough liquid and boiling coolant... Chuck is right with the coolant reservoir cap, a track to follow. When you fill the coolant reservoir, to the moment it begins to boil, what about the level of the coolant in the tank ? There must be plenty of liquid on the alternator and the accessories belt ?

Post by **Eddystone** » 31 Oct 2022, 11:39

Sounds an awful lot like the problem I was just posting about the temperature sensor below the thermostat housing.

The Facet temp sensor is sold by FCP with many good reviews and is working so far in my car. They sell for about $18 on Amazon U.S.

Neil, I'd question those Volvo OEM sensors. The one in my car only lasted 184,000 miles and looked like hell when I took it out.

But seriously, it was all green with corrosion and purely nasty. Sometime when things LOOK that bad, they are bad.

Post by **scot850** » 31 Oct 2022, 16:45

Sounds like it was leaking! Call Volvo and ask for a warranty claim.

The usual issues are the other end of the sensor cable at the connector to the main harness. Either the wire connections or wires start to corrode or the actual connector corrodes at the contacts.

Neil.

minorl850 · Post by **minorl850** » 31 Oct 2022, 23:44

Thanks all for the suggestions.

I'm still waiting for the new temp sensor to arrive from FCP.

As I mentioned, I checked the wiring from the temp sensor to the ECU physically and for continuity. Perfect.
I also checked the wiring from the ECU to the cooling fan relay (yellow and yellow/white wires) physically and for continuity. Perfect again.

I also replaced the ECU with another ECU to test and same problem.

What I noticed is that the yellow and yellow/white wires never get to ground potential to turn the cooling fan relay on. This tells me that the ECU either is faulty or the temp sensor isn't working properly to send the ECU a signal to turn the fan on. But I tried two different ECUs and they both didn't solve the problem.

In the meantime, I am wiring a simple relay to supply ground potential to the cooling fan relay terminals to turn the fan on when the car is either on or in the number 2 position.

But this is really bugging me.

Thanks,

Lawren

Post by **hausmeister** » 01 Nov 2022, 02:32

Did you measure the ECU is commanding the relay on? You checked continuity, but I would also try and check if the fan is being commanded on with the car running and hot. Check at the pins to to the relay? If it does I would exclude the ECU from troubleshooting. If both don't trigger the relay on, it should be likely the temp sensor or maybe still some wiring/other problem? If it has OBD2 you could check the coolant temp the ECU is seeing.
Anyway I don't have much input here, but I think you never mentioned measuring if the ECU triggers the relay.

Post by **Eddystone** » 01 Nov 2022, 04:01

As hausmeister posted, I used the Torque Android app with a bluetooth OBD2 reader. Torque will let you see what the temperature sensor THINKS the temperature is. In my case, it was reading lower than the actual temperature, and the fan was never commanded to turn on by the ECU. My car was overheating with an INDICATED sensor temp of only 185 F. The fan did not come on. With the new sensor in, my dash temp gauge reads in the middle, and the coolant temperature via OBD2 at normal operation is an indicated 195-203 F when everything is fine. This temp stays very stable. As I have written recently, the first sign that the temp sensor had gone bad was when my dash gauge was always reading lower than normal, and that was because the sensor was sending it incorrect data.