Operating Temperture

First post, I have a 91 318i.
When driving the needle for the temperature gets about half way and then maybe a hair toowards the hotter side, sometimes the needle will kinda "bounce" to the 3/4 mark and back down and then sometimes stay a hair before the 3/4 line, turning on the heater lowers it down some.
When I turn on the car at normal temp, hit the a/c button the aux fan does not turn on, the guy I bought it from said he thinks the k5 relay is bad, would that cause it?
I was thinking of flushing the system, getting some water wetter (helped a lot in previous cars) and changing the Temp switch and/or the cooling fan switch. Checked all fuses, all of them are fine. What else besides a bad fan would cause this? I spun the fan and it seems to spin without much resistance.

Thanks!

Try a new thermostat and while you're at it, a new water pump.

Well im trying to figure out the aux fan, the belt that drives the engine fan seems maybe a tad on the loose side, I will be doing that tomorrow.
I'm wondering if the k5 relay would have something to do with the aux fan, I'm not huge on electrical and how to test relays and jumper wires and all that.
But I will try a new thermostat. Whats the stock temp on them? Autozone and Napa seem to be both different yet both say OEM temp.

There are 3 or 4 different temp. thermostats for E30s... I'm not exactly sure what they are. But I'll say they're all roughly around 185 Fahrenheit

on relays, the easiest way to test them is to get a new/working one and put that in and test. but there could also be a broken wire as well. its an old car, electrical does get brittle.

thermostat, youll want a 86 or 88 degree C. since you do live in an area with more consistent temperatures, you can run a lower temp t.stat.

I'd go with checking your clutch fan. My mazda b2200 had a bad clutch fan, sometimes when it would get a hair over normal I would kick the heater on and it would cool back to normal. Could just be ready to quit

Originally Posted by r916

First post, I have a 91 318i.
When driving the needle for the temperature gets about half way and then maybe a hair toowards the hotter side, sometimes the needle will kinda "bounce" to the 3/4 mark and back down and then sometimes stay a hair before the 3/4 line, turning on the heater lowers it down some.
When I turn on the car at normal temp, hit the a/c button the aux fan does not turn on, the guy I bought it from said he thinks the k5 relay is bad, would that cause it?
I was thinking of flushing the system, getting some water wetter (helped a lot in previous cars) and changing the Temp switch and/or the cooling fan switch. Checked all fuses, all of them are fine. What else besides a bad fan would cause this? I spun the fan and it seems to spin without much resistance.

Thanks!

The aux fan should turn on when you push on the air con button.
Check fuses 19 and 20.

There is a dual temperature switch that is screwed in the top of the radiator...I think it is top right on the 318is. The Green/Black wire should have +12 volts on it when ignition is ON. When the temp goes up to 90 Deg centigrade the +12 volts gets switched to the Black wire and the aux fan should switch on at low speed...irrespective of whether the AC is turned on or not.
When the water temp gets to 99 degrees Centigrade the +12 volts gets switched over to the Black/Brown wire and the fan should go into high speed.

So you need to put a voltmeter on the Green/Black wire at the dual temperature switch and should find +12 volts with ignition ON. Then take a paper clip and short the Green/Black wire to the Black wire and the aux fan should run at low speed. Now move the paper clip between the Green/Black wire and the Black/Brown wire and the fan should go into high speed.
If this does not happen then you have bad relays K5 or K7 or a fuse blown or your fan is burnt out or seized.

The correct thermostat for your vehicle should be rated at 88 degrees centigrade...the six cylinder models are supposed to run cooler at 80 degrees centigrade...you can test your thermostat in a pot of hot water to test that it opens.

The mechanical fan should be able to be stopped with a rolled up newspaper when the engine is cold but should shred a rolled up newspaper when the engine is VERY hot.

You may have a bad water pump or merely air pockets in the cooling system or you may need a new radiator cap to keep the system pressurised.

a loose ground nut on the back of your temp gauge could be part of your problem

To test the fan and relays just pull off the radiator switch wires and short them together with the ign on, engine does not have to be started. Fan must run and you can check the two speeds.
If nothing happens then you can start poking around with a volt meter.