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

[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?

[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]

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.....

[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]

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.

[irish44j]

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).

[Sh3rpak!ng]

I'm not sure what brand your gauge is, but on my VDO gauges the instructions called out very specifically for at least a 14ga grounding wire. They said that anything smaller could affect gauge accuracy. How thick is your ground wire on the gauge itself?

Hmm, good call. I forget what I used though it might have been a smaller gauge. Also I wired them all together for power and ground. I think I'll give that a shot first.

[CorvallisBMW]

I'm not sure what brand your gauge is, but on my VDO gauges the instructions called out very specifically for at least a 14ga grounding wire. They said that anything smaller could affect gauge accuracy. How thick is your ground wire on the gauge itself?

[Sh3rpak!ng]

On the new sender for auxiliary gauge you can do a mod to it.

Get a 1-2foot section of thin wire 16-20 gauge would do it.
On one end crimp an eyelet large enough for a 10mm
Bolt
On the other end strip the insulation about and inch from the tip
Twist the strands
Tin the tip of the strands of wire with a soldering iron.
On the sending unit get some sand paper and scratch the coating off a spot and solder the wire you just prepped to the sending unit.

Then find a suitable grounding spot.
This might help the sending unit ground properly and get a more accurate reading.

Thanks, sounds like a solid solution. However, if bad ground is the issue, I'd rather check the engine grounding, as I'm sure it would affect more than just the aux temp sender. All other gauges seem to be functioning appropriately

I didn't have issues like this in my e36 with the same gauges, senders setup the same way :hitler:

[iwantspeed]

ordered an 80C wahler. Installing this weekend. Though, I'm not sure that's the full issue. It still seems like my aux water gauge is being weird. I have an extra sender I'll swap and see if anything changes

On the new sender for auxiliary gauge you can do a mod to it.

Get a 1-2foot section of thin wire 16-20 gauge would do it.
On one end crimp an eyelet large enough for a 10mm
Bolt
On the other end strip the insulation about and inch from the tip
Twist the strands
Tin the tip of the strands of wire with a soldering iron.
On the sending unit get some sand paper and scratch the coating off a spot and solder the wire you just prepped to the sending unit.

Then find a suitable grounding spot.
This might help the sending unit ground properly and get a more accurate reading.

[Sh3rpak!ng]

Me too.

OP, try another thermostat.

t

ordered an 80C wahler. Installing this weekend. Though, I'm not sure that's the full issue. It still seems like my aux water gauge is being weird. I have an extra sender I'll swap and see if anything changes

[TobyB]

standard operating temp on the track is 180-190 and at those temps the cluster needle is showing at roughly 1/4.

Me too.

OP, try another thermostat.

t

[Sh3rpak!ng]

Food for thought:

I couldn't remember what aux fan switch I installed, just looked up the invoice. It's an 82C switch 6131136427282 with one speed (only 2 prongs, so its either on or off)

It cycles on and off if I let the car sit idling. Probably 10 seconds on, 30 seconds off

So that means the switch is seeing a normal fluctuation of coolant temp around the 82C mark on the "cold" side of the radiator. Couple that with what I see on the cluster temp gauge (needle width to the left of center, give or take a little more or less) and I am becoming skeptical of the accuracy of my aux water temp readout.

I just ordered an 80c thermostat which I'll install this weekend along with AC parts. We'll see what happens at the gauges.

[Sh3rpak!ng]

i believe your temps are a little high.
I really dislike the stock gauges I don't really trust them.

i run mostly distilled water and 2 bottles of water wetter from redline.
stockish m20 so it doesn't totally apply
e36 m3 mishimoto radiator
stock clutch fan
stock fan shroud
e36ti temp sending unit
16inch Spal pusher auxiliary fan
MASSIVE LEE fan brackets
adhesive backed foam between the radiator and core support
stock temp rating thermostat
auxiliary VDO gauge runs 180-185 all day long in traffic or track conditions

I also run distilled + water wetter. I don't have shrouding between the radiator and core, but I will add that this weekend plus AC install. Though I don't see that as being the issue.

Keeping a closer eye on the aux gauge, I see a solid 200F while highway cruising. This is driving me crazy. Idk wtf is going on. Basically every part involved in the cooling system of the car is new, and or a major upgrade to stock.

[iwantspeed]

i believe your temps are a little high.
I really dislike the stock gauges I don't really trust them.

i run mostly distilled water and 2 bottles of water wetter from redline.
stockish m20 so it doesn't totally apply
e36 m3 mishimoto radiator
stock clutch fan
stock fan shroud
e36ti temp sending unit
16inch Spal pusher auxiliary fan
MASSIVE LEE fan brackets
adhesive backed foam between the radiator and core support
stock temp rating thermostat
auxiliary VDO gauge runs 180-185 all day long in traffic or track conditions