Temperature fluctuating

[zole2112]

1997 540i...when I'm driving around town the temperature gauge will stay centered as normal for a while but then it will start rising. When I drive at highway speeds, tach basically over 1800 rpm, the temperature will stay at normal or slightly above. If the temp starts rising if I either rev the engine or hold the idle speed at around 2000 rpm the temp will then go back down. It's winter and prior to this the heater air temp will get cold.

I did loosen the bleeder screw last evening but didn't get any air out, could there still be air trapped? What else could be the issue?

I change the water pump last summer along with the thermostat. My coolant level sensor always tells me to check coolant level but it is at the maximum.

Thank you'97 540i auto

[JimLev]

Does the clutch fan work OK?

[Mike S]

Try turning on your A/C, your aux fan should kick in. If it doesn't your aux fan is the problem.

[JB007]

My main fan behind the rad with rthe fan clutch works but I could never get the electric "pusher Fan" to work. When should this come on? How do I check it? I understand that there are 2 types 3 pin and 4 pin.
I am having overheating probs. Is it true that the original thermostat housing is plastic and prone to damage so its replaced my aluminium housing.
Can I just buy the thermostat and gasket and keep the original old plastic housing?

thanks

[JimLev]

I've posted a few times how to troubleshoot the Aux (Pusher) fan in front of the radiator. You should have a 3 speed fan.
You either have bad resistors, a bad fan motor, or bad relays.
Use search to find it, it was a long post.

[edjack]

bleeding operation. It would appear that there is still air in the system. The failure of the aux fan will not cause the heater to turn cold.

Here is the procedure for the V8:

Bleed cooling system via Jim Cash

First - coolant should never be to the "top" of the expansion tank.

I think there are 2 versions of the expansion tank but I suspect they both have the float and indicator stick. Assuming you have the stick indicator it the top of it should never be above the lip of the filler opening rim.

That "expansion" tank is supposed to be mostly air - leaving room for the coolant to expand and compress the air as the coolant heats up.

If you overfill it then it will come out the escape valve and suck air back in - air in the system can cause levels to vary and bring on the alarm.

Bleed the system with the following proceedure - and it is necessary to raise the front end of the 6 cyl cars to do this


------
Cooling system bleed procedure – M62 engine (E39 – 97 version)


- with cold car
- top up coolant to proper level.
- leave rad cap loose

This stage bleeds air trapped in the heater system.
- turn on ignition switch to position 2 (no start)
- set temperature selectors on the climate control to max temp.
- manually set the fan speed to low (lower end of speed range)
- start engine (check that climate settings have not changed)
- after 5-10 seconds of running rev the engine 3-4 times to about 2500 RPM - hold
there for about 5 seconds each time.
- shut off engine (should not run for much longer than about 30 seconds - you just want
to shut if off before it starts to generate any heat and expand the coolant).
- inspect the coolant level and top up again if necessary.
- tighten the coolant fill cap.

This stage bleeds air from the engine, rad and fill tank.
- now warm up the engine (drive a bit if you wish)
- with engine running CAREFULLY / SLOWLY open the bleed screw. Hold a rag around the area to prevent any excess splashing. Keep the screwdriver in the slot of the bleed screw so you can close it quickly.
- you should have some air/steam escape - progressing to some bubbles of coolant.
- as soon as it progresses to the stage where you are seeing liquid coolant come out then close the bleed screw. Do not over tighten - it is all plastic threads and you can easily turn too far at which point the screw jumps back a thread and you have to re-tighten. Just make it snug with all coolant stopped.
- when the car is cold again re-check the coolant level and top up again if necessary.

You may have to repeat the bleed procedure 1 or 2 more times over the next week. Can "probably" skip the stage for the cold start bleeding of the heater system.

If the level continues to fall below the correct level then have the system fully pressure tested - explaining to your service manager what you have already done.

It is very important that all leaks be sealed so that the system can operate at full pressure. The engine computer is programmed to keep the coolant temp at about 108C at "most" times (there are exceptions) and the only way it can maintain that temp is if the pressure can be maintained - system fully sealed.

Ed in San Jose. BMW CCA member since 1987 (Nr. 62319). Golden Gate Chapter. '97 540i 6 speed. Build Date 3/97. Aspensilber over Aubergine leather.

[zole2112]

Thanks guys, I'll be able to work on it again tomorrow. I'll check out the aux fan and re-bleed.'97 540i auto

[PeterBivo]

& there was air in the system, it would've given you issues months ago, so I'd say thermostat.

[JB007]

Hi Jim. I am pretty sure that I have the metal t-stat housing. Can I just change the t-stat and gasket or do I have to change the whole thing. Does it come as one piece(t-stat and housing)?

thanks for your help

[Craig in Canada]

If the heater temp gets cold the problem isn't the main fan, aux fan or the thermostat, IMO

His problem is that the gauge reads too hot while the heater goes cold. My first guesses at this combination of symptoms is a bleeding problem, headgasket problem (leading to continuous bleeding problems) or a water pump problem.

Without the "heater going cold" symptom, then all of the usual fan checks should be done starting with the main fan.

[JimLev]

It isn't displayed properly here, the t-stat really isn't removable from it's housing on the left side in the link below.
see #6

[JB007]

Is there a way to test if it is the thermostat thats causing the overheating Jim?

[JimLev]

Put it on the stove and watch what temp it opens up at. Do it a few times to make sure it doesn't stick.

[JB007]

[JimLev]

unless you wreck the t-stat.

[JB007]

[JimLev]

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[JB007]

[zole2112]

Problem solved! I re-bled the system, purged some air and now the gauge is dead center and rock solid. Thank you for your help, saved me spending $80 on a thermostat that I didn't need.'97 540i auto