Activation temp for cooling fan

[BlackBMWs]

I am trying to troubleshoot at least two new issues after my radiator gave out on me last weekend. I'm in denial over the possibility I may have damaged the head or gasket, but there's plenty to check out before I get to that conclusion.

I have a rough idle now P0100 and P0111 and a Cooling fan inconsistency issue. This thread deals with the cooling fan, I'm document the possible MAF or ICV issue in a separate more focused thread.

So, after reading the various threads on the H/S L/S fan relays and seeing them as clues, I tried to collect some data from my 97 Sport on how consistent the activation of the fans are.

Coolant level was fine with fresh 50/50 BMW coolant. Rad and water pump just changed. I believe the system is bled fine using Jess's instruction for bleeding in one of the threads.

I plugged in my BT OBDII dongle, so I could see the measured temp as it raised or lowered on my iPad. I ran the car up to the 12:00 position on the temp gauge (which on my car ranges between 98c and 115c).

The fan turned on at 100c the first time at what appeared to be low speed. It didn't turn on again up to 124 or 3/4 on the temp gauge. I didn't want to pass 3/4 on the temp gauge. I accelerrated to 2000 rpm and turned the heater on full. Temp dropped to 95c.

I turned heater off and let it idle again. The temp creeped back up to 120C, just short of 3/4 on the temp gauge with the fan never turning back on.

I turned on the A/C. The fan turned on with the A/C and turned off when the A/C is off.

Shut the car down. Pulled the H/S relay out of my 95 Sport. Tried the exersize again after letting the motor cool down for 20 minutes.

The fan activated at 96C and ran for about a minute. Once. then did not activate again. Hmmmm.

New H/S relay is $12. I have one ready for pickup tomorrow morning. I figure I will have an immediate spare to test with along with one Ed is sending me. I don't think that is the whole issue, but still trying to figure it out.

While the rad was out, I did bench test the fan for both low speed and high speed operation. Both seemed to work fine.

Still making observations, but I thought I'd document where I am just now and run it past you all. Thoughts?

Thanks!

[cooljess76]

hmm that's a head scratcher for sure. you said it did turn on in low speed mode, but it didn't come on until the needle hit 3/4? That's strange. I doubt you have a BHG, you'd know if you did. I'm wondering if the temp switch might be telling the ecu that the engine is cooler than it actually is.

[BlackBMWs]

Originally Posted by cooljess76

hmm that's a head scratcher for sure. you said it did turn on in low speed mode, but it didn't come on until the needle hit 3/4? That's strange. I doubt you have a BHG, you'd know if you did. I'm wondering if the temp switch might be telling the ecu that the engine is cooler than it actually is.

Maybe Jess. I'm reading the temps of the OBDII port. From a cold start, the fan first turned on at 100C. (After about 5 min at 12:00) it then turned off, then I watched the temp climb to 125C or so, and did not turn on again. At that point, I turned on the heater and reved to 2000rpm. Temp dropped to about 95c. (Man, my heater is hot... ) What was disturbing was there was no pattern as to when the fan would engage.

What I didn't try was to swap around the LS relay. As these relays are cheap, I can remove a few varibles by replacing both the H/S and L/S relays. I figure the key pieces are the coolant temp sensor off the rad, the two relays and the fan switch at the fan itself.

Is there another temp sensor on the block? I'll observe what speed the fan turns on to vs. the speed when the A/C is switched on. I believe I read somewhere that the A/C triggers the H/S relay.

Thanks for chiming in!

Best, Rich