Bavaria temp gauge question

[73bav]

Hey everyone, this is Fabian and I am relatively new to the forum here. I had a long weekend working on the coolant system overhaul on the 72 automatic Bavaria. I have a question about the temp gauge readings. The white lines represent what temperature range in degrees Fahrenheit? I know the temp sensor is based off resistance that the cluster then displays. The reason why I am asking is I believe the temp gauge is reading incorrect. I replaced the radiator with a new mobile tradition unit, converted the thermostat housing to the late style "A" casting with a new OE thermostat (m30b35 e34). I also installed three 10 inch electric fans ( two pullers and one pusher for the aux condenser) set to come on at 90 degree C. The temp switch (new BMW OEM e30) and original sensor sit side by side in the thermostat housing. I cleaned the old temp sensor and Ohm'ed it out and the readings were 620 ohms @ room temp. Then I heated the sensor up with a heat gun while taking readings and it read 34 ohms. (I don't know the max temp the heat gun can produce) Any who, I filled the coolant with 50/50 with a littler water wetter and did a cold bleed first to prime the system. Then ran the engine till operating temp and bled again. I will bleed again tomorrow but I feel the system is mostly air free. All radiator hoses are in good shape with overflow hose flowing.

For those who want to skip the above read here. The engine will idle for a good period of time with the temp increasing slowly. Temp will rise past the first and second white line and go in between second white line and red zone until the fans kick on at 90 degree C then the temp will fall back to the second white line. It will continue this for many cycles but never reaches the red zone. Is 90 degree C really that far up the temp gauge or is the gauge off? The duration of this trial was 30-45 min on a cold 40 degree day. Last thing I checked was the ground from car body to plus on battery and its is a constant 13-13.9 volts while engine is running. Could the cluster have a bad ground that could be misleading me?

Thanks,
Fabian

 

[HB Chris]

Since most use 75 or 80 degree T-stats I would think 90 is too high to wait for fans to come on. You didn't say what T-stat temp rating you are using though. And the late housings use a different T-stat, use the wrong one and it never opens.

 

[73bav]

I am using a new m30b35 thermostat from a 1992 e34 535 which should be 82 degree C. I checked the gap for the thermostat to the back of the hole in the housing which was about 5mm or so. I know there are differences in the thermostats from the old to new style. I used a late housing with a late thermostat. Unless there are differences in the late housing as well like 4.1 to 4.2 letter A castings. That or the new thermostat is faulty so I can test this with boiling water. I just wanted to rule out that the temp gauge is misleading by a poor ground. I can replace the temp switch to a 80 degree C one. I just used a 90 degree C because I had one laying around.

thanks,
Fabian

 

[HB Chris]

You're on the right track and have the proper housing/T-stat.

 

[Mike Goble]

90°C isn't too high to turn your fan(s) on. You want the fan to be able to drive the temperature down enough to turn itself off. If your fan off temperature is lower than the normal operating temperature it might never shut off.

I use a 2-speed pusher fan from a 90's BMW in my Bav and turn it on with a 90°C switch for low speed and a 99°C switch for high speed. It turns on occasionally, and has never been to high speed.

I wouldn't get too worked up about the temperature gauge reading mine is all over the place. I added a mechanical temperature gauge to my car and it's very consistently around 175°F during normal operation. When I'm sitting still for a long time, the fan comes on at 195°F and goes off at 185°F.

 

[73bav]

I have been busy lately with college and putting Isettas together so apologize on the late replies. Thank you for the responses HB Chris and Mike Goble. Over the weekend I will install a discrete temp gauge to have re-assurance and also sync the zeniths with the STE BK meters. What values should I expect in Kg/Hg of vacuum at idle? Summers get hot here so I am trying to get the car ready for the months to come. Wasn't there a OEM option for the coupes to have additional gauges that were mounted on the dash?

thanks,
Fabian

 

[HB Chris]

No additional gauge option, some have added them where speaker grille resides though.

 

[73bav]

Hello everyone, so over the weekend I installed that discrete temp gauge and found that the OEM vdo temp gauge was indeed off. 187 degree F is the 2nd white line on the vdo temp gauge and I assume it is supposed to be around the middle of the gauge. I am considering swapping the cluster temp gauge with another one that I have. My question is do the vdo temp gauge and temp sensor need to be matched up? Are there numbers to look for a matching pair or does this not matter? Also got time to sync the zeniths to the best of my ability following the old work shop manual I had. I did find that the distributor vacuum advance diaphragm is leaking or torn. I did the suck test on both the advanced side and retard side and there was no reaction to the motor. Makes sense because the idle is a steady 1050 and when the car is put into drive or kick the ac on the motor drops idle substantially. For now I will leave the carb adjustment alone until I swap the distributor out with another one with pointless ignition. I hear there is a hole I can plug with my finger on the carb to see if the car is running rich or lean. Where is this hole?

Thanks,
Fabian

 

[HB Chris]

Post #18 here, Jerry is the expert.

http://www.e9coupe.com/forum/showthread.php?t=17535