Coolant Temp fluctuation?

[bimmerR75]

Hey there,

Not sure if im going crazy but my auxiliary fan seems to be working fine, changed out the radiator temp switch with the bavauto 81/89c switch. Yet it seems my coolant temperature is constantly moving in between the 3/4 (from the middle) mark and the middle and back to 3/4 or in between. Is it normal for there to be slight variation or should it consistently sit at 3/4?

Until recently it basically sat at 3/4 but lately its been moving and a bit more temperamental.

Coolant level seems to be at the right mark when engine is cold, but perhaps theres not enough and thats causing the fluctuation?

[ak-]

During what driving habits is this happening? Sounds like a weak clutch fan to me.
Is the needle moving or jolting to the 3/4ths mark?

[estoguy]

Also, check the grounding nuts on the back of the cluster. Loose ones can cause temp gauge fluctuations as well.

[bimmerR75]

During what driving habits is this happening? Sounds like a weak clutch fan to me.
Is the needle moving or jolting to the 3/4ths mark?

I use it as a daily driver, it typically will move throughout the day between the 3/4 and half during city driving. Highway it stays at a solid 3/4. Its slowly moving.

[bimmerR75]

Also, check the grounding nuts on the back of the cluster. Loose ones can cause temp gauge fluctuations as well.

I have been meaning to do that. Going to work on that tomorrow and see if that fixes the issue. The gauge at start up is getting stuck at the bottom, if I tap on the cluster a couple times lightly it pops up to the blue where it should be at start up.

The grounding nuts may be the issue, will tinker and report back.

Thanks everyone!

[MR E30 325is]

This screams a small bubble of air in the coolant to me.

If nothing else pans out I'd bleed the coolant system.

[dnguyen1963]

If the needle stuck at 3/4 during normal operating condition and assuming that your coolant system is in good condition then I would check the SI/Main board for corrosion and breakage in solder lines. Use an IR gun to verify the actual temp of your engine.

[Gregs///M]

Unless you have had your SI board refurbished by us, don't trust your temp gauge. Even SI boards from E30_dad and Programa only change the batteries and capacitors but the transistors that help power and control the temp gauge are not replaced by anyone except us. We replace all transistors, voltage regulators, capacitors and batteries.

Additionally, you will need to inspect your temp gauge for copper oxidation as well as the condition of the landing pads on the main board.

When the SI boardand/or temp gauge is failing, it will error on the high side. You can try tightening the 7mm nut behind the gauge but if your SI board is not refurbished, it will still be inaccurate.

In the end, be sure there are no air bubbles. Bleed, bleed, and bleed to make sure there are none. Your temp gauge sending unit should read around 1000 ohms at room temp. Good luck!

[e30davie]

I wonder if a stuck thermostat could cause this? If its stuck say half closed, it would cause the coolant to heat up at lower revs but cool down at higher revs?

Id start with bleeding the air as suggested, as the air would be around the thermostat which may give similar symptoms to a stuck thermostat.

A properly working cooling system, once up to temperature the temperature should be pretty much solid. That is the thermostat's job after all.

[bimmerR75]

This screams a small bubble of air in the coolant to me. If nothing else pans out I'd bleed the coolant system.

Id start with bleeding the air as suggested, as the air would be around the thermostat which may give similar symptoms to a stuck thermostat. A properly working cooling system, once up to temperature the temperature should be pretty much solid. That is the thermostat's job after all.

When I changed the radiator temperature switch I lost some coolant, refilled it. Once refilled I unscrewed the "bleeder screw" on the top of the thermostat housing and turned on the engine and waited for there not to be air coming out, but coolant, soon as coolant came out, closed the screw back up, is this the proper way to bleed the air out? Sorry for the questions haha, every month I am learning something new on this car by doing the work myself. Appreciate all the advice.

Going to try out cleaning the backside of the gauge points via the instructions in this video and tightening the nut. Hopefully that will work, but if someone could confirm whether or not my bleeding process was correct, that would be a huge help. As if its not, I am sure it may just be air as you suggested as it seemed to be working fine until my old switch went dead and I replaced it.

[bimmerR75]

When I changed the radiator temperature switch I lost some coolant, refilled it. Once refilled I unscrewed the "bleeder screw" on the top of the thermostat housing and turned on the engine and waited for there not to be air coming out, but coolant, soon as coolant came out, closed the screw back up, is this the proper way to bleed the air out? Sorry for the questions haha, every month I am learning something new on this car by doing the work myself. Appreciate all the advice.

Finally getting a chance to address the cluster today. Would anyone be able to verify the bleed procedure. I see things all over the net about bleeding with the car jacked up. Coolant is flowing from the bleed screw when the car is sitting level, and engine is on. So not sure if that means there are no air bubbles, or that you have to have the car on ramps/jacked to really see if theres air stuck.

[Das Delfin]

it shouldn't be at 3/4. Your temp needle should be between 1/4 and 1/2. The original fan switch is designed to switch on the low speed at 3/4 and the high speed at full hot.

If it stays at 3/4 while driving on the highway it would suggest a coolant mix with too much antifreze (never go more than 50/50) or an air bubble in the system.

[bimmerR75]

it shouldn't be at 3/4. Your temp needle should be between 1/4 and 1/2. The original fan switch is designed to switch on the low speed at 3/4 and the high speed at full hot.

If it stays at 3/4 while driving on the highway it would suggest a coolant mix with too much antifreze (never go more than 50/50) or an air bubble in the system.

This isn't a photo of my car, but this is exactly where the needle lies when I'm on the highway. It previously used to stay at this level, but not it slightly moves between that mark and almost the middle, then back.

[MrBurgundy]

I agree with the IR temp reading to make sure that the car is not actually getting hot. This way you'll know if its an electrical or mechanical problem.

[jeffnhiscars]

That's close enough to where your needle should be to not be concerned. Mine is rock steady a little above that and will rise closer the the halfway mark when sitting at idle for any length of time. If you only lost a little coolant you may not have a major bleed issue but being in LA chances are your temp dial is set to max cool. Turn it to full heat to make sure no air is trapped in your heater core, def check actual temps with an IR gun and do a newspaper test on your fan clutch.