Temperature Gauge

[tyromechanic]

Can someone tell me how I can make sure the temperature gauge is reading the right engine temperature?

[shogun]

any problems? What you see on the cluster gauge, is not the real accurate temperature. For a rough check you can use a contact-less thermometer. This shows the temperatures http://www.nmia.com/~dgnrg/tempgage.htm
I have explained that before: There were in the past a lot of discussions what is right or wrong when the temperature gauge on the cluster temp indicator is right or left of the 12 o' clock mark.
The fact is:
Temperature indication on the BMW is not linear, they call it 'tableau', basically the indicator at 12 o'clock can mean everything between roughly 75-110 degree Celsius (depending on the temp support values programmed). Everything in between 75-110 is just 12 o'clock. Plus/ minus 1-2 mm to the right or left (deviation cased by the parts installed). The analog signal is processed in the instrument cluster and compared with data in the coding plug. A corresponding signal is sent to the instrument. Five temperature support values are stored in the coding plug. Exceeding the temperature limit stored in the coding plug will additionally send corresponding warning information to the check control and display it there.

That is written and shown here on page 4 of the instrument cluster check control training reference book http://www.e38.org/e32/BMW_pdfs/INST_info.pdf
What is NOT shown in the English version I found in the German version, that page showing the temperature diagram curve, and there one can see the so-called 'tableau' between 75-110 degree Celsius.That depends on the engine type and the five temperature support values in the cluster chip.

[ross1]

Can someone tell me how I can make sure the temperature gauge is reading the right engine temperature?

The temp gauge is dampened and intended to remain centered within a range of acceptable temps. If it strays much from center you have an issue.
There are no temperature indications to be right or wrong. It is a glorified "idiot" light that will give some warning of impending overheat, provided the gauge is monitored.
An aftermarket gauge can provide real temperature readings. Unless racing these are merely affectations, there is no need for it given a properly functioning cooling system.
If your engine is running well, not overheating or overcooling then who cares if the coolant temp is 190* or 210*?

[jclausen]

What is it reading now or what is the position of the needle

[fo3]

The temp gauge is dampened and intended to remain centered within a range of acceptable temps. If it strays much from center you have an issue.
There are no temperature indications to be right or wrong. It is a glorified "idiot" light that will give some warning of impending overheat, provided the gauge is monitored.
An aftermarket gauge can provide real temperature readings. Unless racing these are merely affectations, there is no need for it given a properly functioning cooling system.
If your engine is running well, not overheating or overcooling then who cares if the coolant temp is 190* or 210*?

^What he said.
Unless you're racing, driving up mountains, towing etc then you'll need to fit a proper gauge. Otherwise if it's around the middle, that's all you need to know.

[tyromechanic]

Hi everyone,

I apologize. I got really busy and didn't have time to check the forum. I busted the original motor. It heated up and didn't stop on time and the head broke. When I was driving the car with its original engine, the needle in the gauge would always be a little below the 12 o'clock mark. I FULLY understand that the gauge marks a range of temperatures.

However, with the rebuilt engine, the needle stays right in the middle. I AM GUN SHY! I don't want to bust the head again. I was hoping to find a way to read the temperature when the gauge marker in at 12 o'clock and compare it to the acceptable range of temperatures.

Thanks!!

[a777fan]

You might want to run the cluster functional test to ensure your temp gauge is capable of sweeping through its full range and doesn't get hung up anywhere. The needle should sweep smoothly through the entirety of the range from cold to hot. I have seen a couple that get 'stuck' or are a little clunky.

[tyromechanic]

It sounds like a great idea! I just do not know how to run a cluster functional test. I will look it up.

[theBMWbeast]

The self test is not a feature on the early clusters unfortunately

[a777fan]

The self test is not a feature on the early clusters unfortunately

Bah!

Good on you for reading his sig.

[ross1]

Hi everyone,

I apologize. I got really busy and didn't have time to check the forum. I busted the original motor. It heated up and didn't stop on time and the head broke. When I was driving the car with its original engine, the needle in the gauge would always be a little below the 12 o'clock mark. I FULLY understand that the gauge marks a range of temperatures.

However, with the rebuilt engine, the needle stays right in the middle. I AM GUN SHY! I don't want to bust the head again. I was hoping to find a way to read the temperature when the gauge marker in at 12 o'clock and compare it to the acceptable range of temperatures.

Thanks!!

Understood.
Did the gauge indicate the overheat?
Your previous low reading may have been an indication of low coolant, not in constant contact with the sending unit.
Coolant is now at proper fill?
As I said before if it strays much from center you have an issue. You already know these engines don't tolerate overheating well so if any suspicions watch the level and gauge like a hawk.
There is no unobtrusive spot for another gauge but if it gives you peace of mind perhaps a temporary set up without cobbling up the dash would tell you actual temps v. the BMW gauge.

[fo3]

Does the gauge smoothly rise from c to half as it's warming up? If you drive the car on a warm day then park it, then 5min later switch the ig on has it registered over half? (on hot days when I did this is would be well over half, so I knew the gauge was working and could read higher). There's a lot of heat soak into the engine shortly after the pump and fan has stopped working, hot engine, no flow, hot engine bay etc. That should be reflected even in a dampened electronic temp gauge.

It's not just watching the gauge, it's knowing the service history, and hood up and frequently inspecting for leaks, or hoses that could burst etc. In a previous life my car had a new head gasket because the coolant tank cap wasn't sealing.
E: Even in one of my 1970s cars a long time ago a hose burst and that gauge didn't read it due to lack of coolant to heat up the sensor! It was way before EFI and dampened sensors etc, they're just no good at quickly reading air temp.

The sender for the dash isn't required for anything else is it? On my m50 the EFI has it's own sensor, so add you own sender and mech or undampened gauge instead. What about putting a sensor where the air bleed screw is, or get rid of the fan switch on the side(or T in) , just a quick thought but you would need to know expected temps outside the c.h. to know what is normal.

Anyway, might make you happy but first I think it's more important to know how dampened or accurate your dash guage is. try the just switched off on a hot day heat soak test.

[tyromechanic]

The gauge indicated the overheat when I busted the engine.
Coolant is now a proper fill.
Insofar as watch the gauge like a hawk, it is exactly what I am doing.
The gauge raises smoothly until it reaches the exactly 12 o'clock. It stays there.

Thank you for your comments and help!
Most Respectfully,