to those with aux water temp gauge - cluster vs aux readings??

[Sh3rpak!ng]

My VDO aux water temp gauge (which goes to the port in the head of my M42) consistently reads about 205* in highway cruising and around 210 when on-course (rallycross). IIRC our Chumpcar (M20B27) also runs about 205 during long enduro races pretty consistently. Neither has ever had any overheating issues (both cars run high-CFM Spal fans). Both have the sender in different locations, FWIW.

BTW, both cars use 12 or 14ga wiring.

Chumpcar runs distilled. Rallycross car runs a standard antifreeze/distilled 50-50 mix (since it runs in very sub-freezing temps in the winter).

What t-stats, aux fan switches, water pumps and radiators do you run?

That sounds quite similar to mine. I just changed to an 80c t-stat from 88c and flushed the system. I'll fill with distilled and water wetter. so we'll see what happens. Also changed the water temp sender since I had a new one on hand fwiw.

Next I'll rewire the gauges and verify good ground on the engine block.

[TobyB]

As to grounding, it's crazy, but sometimes the bolted connection to the head isn't a good
enough ground! So running a wire directly to the housing IS a very good idea.
I drove myself nuts on this one once- the housing was a bit corroded under the bolts,
and that was enough to let it 'float' electrically enough to throw off the gauge.

No help, but I like a mechanical gauge for water temp and oil pressure.

They tend to fail less, and when they do fail, you usually know they're dead.

The mechanical water temps are not always all that accurate, even the good ones- it's always wise to
do the boiling water test first thing, before you destroy the packaging...
On the other hand, they tend to be REPEATABLE, so they always tell you the same thing for the same temp.

t

[Sh3rpak!ng]

As to grounding, it's crazy, but sometimes the bolted connection to the head isn't a good
enough ground! So running a wire directly to the housing IS a very good idea.
I drove myself nuts on this one once- the housing was a bit corroded under the bolts,
and that was enough to let it 'float' electrically enough to throw off the gauge.

No help, but I like a mechanical gauge for water temp and oil pressure.

They tend to fail less, and when they do fail, you usually know they're dead.

The mechanical water temps are not always all that accurate, even the good ones- it's always wise to
do the boiling water test first thing, before you destroy the packaging...
On the other hand, they tend to be REPEATABLE, so they always tell you the same thing for the same temp.

t

Yea, I'm running an s52 with all the senders in the head, but I've heard stories about slightly poor grounding causing strange things with low voltage sensors etc like a temp sender.

Bottom line, I know the car isn't overheating. It's just frustrating to be uncertain of the EXACT correct temps.

As mentioned before I had zero issues running the EXACT same gauges, senders, wiring etc. on my e36.....

[CorvallisBMW]

As to grounding, it's crazy, but sometimes the bolted connection to the head isn't a good
enough ground! So running a wire directly to the housing IS a very good idea.
I drove myself nuts on this one once- the housing was a bit corroded under the bolts,
and that was enough to let it 'float' electrically enough to throw off the gauge.

This is good to know, especially for those (like me) who have a new gauge threaded in to a 25-year-old aluminum t-stat housing that's gasketed and RTV'd to the head.

I noticed that my new VDO temp gauge will read 100C while the factory gauge is still dead-center (running an 80C thermostat in the m30b35 currently). The fans (which are on an 80/88C switch) didn't come on until I saw closer to 105C on the VDO gauge. I wonder if I might need to ground the sender. Time to do some testing!

[Sh3rpak!ng]

This is good to know, especially for those (like me) who have a new gauge threaded in to a 25-year-old aluminum t-stat housing that's gasketed and RTV'd to the head.

I noticed that my new VDO temp gauge will read 100C (212F) while the factory gauge is still dead-center (running an 80C thermostat in the m30b35 currently). The fans (which are on an 80/88C switch) didn't come on until I saw closer to 105C (221F) on the VDO gauge. I wonder if I might need to ground the sender. Time to do some testing!

Those are more or less the same temp readings and behavior I get between my vdo gauge, the factory gauge and the aux fan. Only difference being I have an s52. Weird.

It's never easy or simple is it?

[UNHCLL]

VDO gauges read high, regardless of how you ground them.
We've used IR, probe, and comparative gauge readings between a stock BMW gauge and VDO, VDO is always higher.

[Sh3rpak!ng]

VDO gauges read high, regardless of how you ground them.
We've used IR, probe, and comparative gauge readings between a stock BMW gauge and VDO, VDO is always higher.

Hmm, interesting. Was there any trend as to how much higher?

any suggestions for a more accurate gauge?

[CorvallisBMW]

Hmmm, I have an IR gun at home. i'll have to check it vs the gauge.

[Sh3rpak!ng]

Hmmm, I have an IR gun at home. i'll have to check it vs the gauge.

I tried to do the same, but it seems there aren't many good accessible places to take accurate measurements...

[CorvallisBMW]

I tried to do the same, but it seems there aren't many good accessible places to take accurate measurements...

You also have to account for the emissivity (heat transfer efficiency) of certain materials when using non-contact methods. As an example, copper conducts heat more efficiently than rubber, therefor pointing a gun at the outside of a copper container full of boiling water will show aroung 99C, but a rubber container might show just 80C. Therefor the aluminum thermostat housing will likely show a different reading than the rubber radiator hose.

/enginerd

[Sh3rpak!ng]

You also have to account for the emissivity (heat transfer efficiency) of certain materials when using non-contact methods. As an example, copper conducts heat more efficiently than rubber, therefor pointing a gun at the outside of a copper container full of boiling water will show aroung 99C, but a rubber container might show just 80C. Therefor the aluminum thermostat housing will likely show a different reading than the rubber radiator hose.

/enginerd

Yup exactly. I knew that but then decided not to post the full explanation. I had a feeling you guys are enginerds just like me.

So basically I have no good places to point the IR gun. Aluminum thermostat housing is unreliable, and the polished aluminum radiator is worse. I think I might make some small spots on the radiator and thermo housing with black matte spray paint so I can get good IR readings.


More OT, I changed temp senders and the thermostat from 88c to 80c last night. The thermo change is easily noticeable on the cluster gauge which now holds about a needle width to the right of the 1/3 mark. The vdo aux gauge shows "cooler" than it did before, but still not accurate (no surprise). It shows more like 195-200F now. I think I might just look for a better gauge and sender combo. This is really annoying. Guess I got lucky with the gauges I bought for the e36 since they seem to be spot on.

[CorvallisBMW]

AFAIK, VDO is regarded as some the the best gauges you can get. I would trust them over the factory temp gauge, as it is "damped" in the middle and designed to show mostly whether you're very cold or very hot, not to show small fluctuations around your normal operating temp.

[Sh3rpak!ng]

AFAIK, VDO is regarded as some the the best gauges you can get. I would trust them over the factory temp gauge, as it is "damped" in the middle and designed to show mostly whether you're very cold or very hot, not to show small fluctuations around your normal operating temp.

On the e36 and newer cars the cluster gauge is "damped" in the middle. On the e30 and older cars, the cluster gauge is not "damped".

Sorry if I am making things confusing. I have both an e36 and e30. I know the e36 cluster gauge is useless, but the e30 cluster gauge is not.

[CorvallisBMW]

Really? I always thought it was damped. I guess I learned my new e30 fact for the day :)

[Sh3rpak!ng]

Really? I always thought it was damped. I guess I learned my new e30 fact for the day :)

Yup! afaik there is no damping on the e30 and older water temp gauges. They added the damping to the newer cars (~2000 and newer) because "people got upset/didn't like" seeing the temp gauge moving around. So basically on newer cars it's just a fancy idiot light that tells you:
A) needle to the left - engine is cold
B) needle straight up - engine is between slightly warm and almost too hot
C) needle to the right/red light - WAY TOO HOT SHUT IT DOWN NAOWWW

Now, as to how accurate that e30 temp gauge is, I have no idea. Though, thus far it seems to respond accordingly to any changes I have made to the cooling system.