Temp gauge woes

[BMW_325i]

Hi all,

Hope you can help with a question about the temp gauge, and bear with me while i fill you in on the problem.

The temp gauge has displayed low for the 4-odd months ive had the car, usually below or sometimes just on 1/4. On a really hot (40 deg C = 104 F) day recently it just made it to halfway when sitting in traffic but then backed off.

I tested the temp gauge sender and had some odd readings so down to the local dealership i go and get a brand spangly new one. Job done i thought :(

The new sender defintely reads differently - takes longer to get to a stable temp... but... that is still below the 1/4 mark.

I follow the Bentley manual as far as testing the temp gauge itself - ground the sensor wire to simulate a high temp situation and make sure that the needle "moves upward".


My question is - how far upward should it go? all the way to red or not?

I'm seeing it get to about 3/4 mark, approx. 109C / 229F. Is that normal or indicative of a mildly retarded gauge ? :)

This is on a 10/87 325i.

Cheers
Brad

[jlevie]

It sounds to me like you might have a bad thermostat that is stuck open which is causing the engine to run cold. The low reading could be a gauge problem, but since the needle goes to the middle in stop and go traffic it sounds more like the thermostat.

As to what should happen when you ground the gauge wire, the needle should go all the way to the end of the red. A high resistance in the wiring or cluster, a bad cluster ground, or a bad SI board can cause the needle to not move all the way to the red.

[BMW_325i]

It sounds to me like you might have a bad thermostat that is stuck open which is causing the engine to run cold. The low reading could be a gauge problem, but since the needle goes to the middle in stop and go traffic it sounds more like the thermostat.

As to what should happen when you ground the gauge wire, the needle should go all the way to the end of the red. A high resistance in the wiring or cluster, a bad cluster ground, or a bad SI board can cause the needle to not move all the way to the red.

Thanks for the reply.

Should have mentioned that i initially thought it was the thermostat but the heater works fine so i believe not.

Also, the half-way reading has only ever happened once, on a very hot day.

Today was 35C outside and the gauge barely hit the 1/4 at a long stop before sitting around the 1/8 mark for the rest of the drive. I cant believe that the coolant is only 57C / 135F.


Next step is to check the cluster ground and wiring connections.

Will also get a thermometer into the coolant after a drive and see what that says.

Cheers

[jlevie]

A contact or IR thermometer applied to the thermostat housing is the best check of actual engine temperature.

[BMW_325i]

So i pulled out the cluster last night, cleaned the temp gauge connectors the cluster curcuit board and re-tightened the securing nut. Also located and cleaned up the cluster's main ground connection.

And got the same result :(. Crap.


Intermittently the temp gauge needs 'percussive maintenance' (a slap to the dash) at startup for it to register. I was hoping this meant a ground issue.

Everything else on the cluster works as expected so tonight i'll re-check the high temp situation and see what happens.


Question - is the heater working a definitive test that the thermostat is working properly (short of removing it to test in boiling water)?

Thanks

[bmwm42]

the heat in your car is no idicator imo mine worked just fine but the temp guage would barely make it above the blue but never above the quarter mark and on the odd chance that i would be stuck in traffic it would creep up to the middle but as soon as i would start driving back down it went. So i replaced the the thermostat and now temp gauge is in the middle right where it should be note i also replaced the si board temp guage but that didnt change anything until i changed the thermostat. its an inexpensive thing to change anyway worth a short imo

[BMW_325i]

So after my usual drive to work this morning, with the gauge on 1/4 I had the chance to check the coolant reservior with a thermometre, which read 76C / 169F. That should be almost the 1/2 way mark.

Either the gauge is wonky or the needle is not in the right position (I do know that the PO had some work done on the cluster at some point).

its an inexpensive thing to change anyway worth a short imo

I think you are right, i'm going to do a coolant flush soonish so that will be a good time to change the thermostat anyway.

Thanks

[BMW_325i]

To close the chapter on this issue, i recently had some parts arrive.

First thing was a fan clutch replacement a week ago - the car was sounding a bit like a bus so i figured the clutch was siezed. After the swap i noted that the temp guage read a little higher when warm, just on 1/4 mark.


Last weekend i had the time to replace the thermostat, and waddya know - a 71 deg C jobbie! In went the new stock 80 deg. Since then the guage reads around 3/8.

I'm happy with that.

[Kershaw]

what did jlevie tell you over a month ago?

why are you going to even ask for advice if you arent going to listen to it? changing a thermostat takes a lot less time than pulling a cluster.

[BMW_325i]

what did jlevie tell you over a month ago?

why are you going to even ask for advice if you arent going to listen to it? changing a thermostat takes a lot less time than pulling a cluster.

Eh? Who yanked your chain?

It was a process of elimination, following the Bentley manual. Heater worked so not supposed to be a bad thermostat as suggested.

And i dont just happen to have sparts parts laying around waiting...

And i was already changing the steering wheel so pulling the cluster wasnt that much of an issue.

So when the parts arrived recently, it got done.

And i did listen - that's why the parts got ordered.

But thanks for the kind words

[dandrewg]

Wait, earlier you said that you measured the coolant temp with a thermometer and the gauge was not where it was supposed to be. How would changing the thermostat fix that?

I'm only asking because I have the same problem. I've used an IR thermometer on the thermostat housing and have read temps above 160 deg. F while my needle was below the quarter mark. The cluster has a new main circuit board and new SI board. How do you know what temp corresponds to the half way mark on the gauge?

[BMW_325i]

Yes, but in thinking about it the coolant temp in the expansion tank wouldn't be teh same as the coolant that the temp sender reads.

Whether it would be higher or lower i dont know but...

Someone has mapped the gauge to actual temps, will find the link and post it.

*edit*

Here, about halfway down:

http://forum.e46fanatics.com/showthread.php?t=768078

[dandrewg]

Thanks for the link. Is it safe to assume that temp gauges among the whole BMW vehicle line are the same? At least on older vehicles?