TheSamba.com :: View topic - Any accurate NON digital readout cylinder head temp gauges?

Fri Oct 30, 2020 4:48 am

I have been playing around with GM dashboard dial stepper motors, 0.5 degree resolution.
They seem to work quite well attached directly to GPIO pins of a microcontroller, running off 3.3 volts.
I am slowly working through making a replacement fuel gauge for a Late Bay with the hot wire fuel gauge that rots away.
Which has illumination based on a WS2812 LED module so the backlight colour can be changed , or change colour based on fuel level.

So you can have an analog input, or listen to e.g. PLX MFD traffic.

So rather than using moving coil meters, use stepper based meters.

Sun Aug 21, 2022 7:52 am

Does anyone have any knowledge or schematics of how this type CHT gauge is supposed to be wired ?
It uses the ring type sender under the spark plug.

Mon Aug 22, 2022 3:27 pm

Just to throw some gas on the fire...
I have been using Westach gauges for over 20 years in various ACVW's.
For CHT, none of the Westach gauges are cold junction compensated, even the TSO stuff. They are calibrated for a 75ºF cold junction.
All Westach CHT gauges use a Type J thermocouple with 48" leads, which is long enough to reach from #3 to under the rear seat bench. Having the cold junction inside the car's interior will limit the cold junction error to ~25ºF, because by the time the engine warms up enough for CHT to be of interest, it's usually between 50º and 100º inside the cabin. Then, you do the arithmetic in your head to get the CHT.

Uma makes some nice instruments as well.
It seems to me that I have read someplace that Uma CHT gauges are cold junction temperature compensated. However, after looking through the Uma catalog, I have seen no mention of cold junction compensation. So who knows?

In any event, once you become accustomed to what is "normal" for your car under various conditions the CHT gauge will alert you when something abnormal is happening.

Mon Aug 22, 2022 5:09 pm

What kind of connector is on the thermocouple on the meter end? A Digital milivolt meter gauge sounds interesting.

Tue Aug 23, 2022 4:50 am

My Fluke 87 meter does not have a thermocouple socket.
I measure thermocouple MV output with standard leads clipped onto the thermocouple wires.

Plotted on a graph, the thermocouple output looks pretty linear.

Tue Aug 23, 2022 7:23 am

mondshine wrote: Just to throw some gas on the fire...
I have been using Westach gauges for over 20 years in various ACVW's.
For CHT, none of the Westach gauges are cold junction compensated, even the TSO stuff. They are calibrated for a 75ºF cold junction.
All Westach CHT gauges use a Type J thermocouple with 48" leads, which is long enough to reach from #3 to under the rear seat bench. Having the cold junction inside the car's interior will limit the cold junction error to ~25ºF, because by the time the engine warms up enough for CHT to be of interest, it's usually between 50º and 100º inside the cabin. Then, you do the arithmetic in your head to get the CHT.

Uma makes some nice instruments as well.
It seems to me that I have read someplace that Uma CHT gauges are cold junction temperature compensated. However, after looking through the Uma catalog, I have seen no mention of cold junction compensation. So who knows?

In any event, once you become accustomed to what is "normal" for your car under various conditions the CHT gauge will alert you when something abnormal is happening.

Thats interesting!

As noted earlier in this thread, at least two people I know with aircraft and using the Westach gauges "Swear" theirs were compensated.

It makes me wonder whether they are just plain wrong or whether the gauges were set up compensated for them by a service, the seller etc.....or with a widget like at the link below.

I will have to see if I can get ahold of them at some point....but its nice to know.

I have always figured that if I cannot find what I need....I still like the Westach units and could simply live with short mental arithmetic like you mention :lol:

Here is that link. I may have posted this before. It shows circuit schematics for three different methods of building a cold junction compensator. The parts are cheap at digi-key.

https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/4026.html

Ray

Tue Aug 23, 2022 7:33 am

I used the Harley Davidson Stewart Warner greenline guage and with the motor running I shot the head where the sending unit is installed and after 5 minutes running, it was only 7 degrees off. I think, that is pretty good. Only use it for comparisson. I got the Harley sender that goes into the head.....welded up a boss, then screwed it in. I really dont like the looks of the new style digitals. I wanted something old school. REMEMBER comparisson only.

Sun Sep 28, 2025 5:56 am

raygreenwood wrote: mondshine wrote: Just to throw some gas on the fire...
I have been using Westach gauges for over 20 years in various ACVW's.
For CHT, none of the Westach gauges are cold junction compensated, even the TSO stuff. They are calibrated for a 75ºF cold junction.
All Westach CHT gauges use a Type J thermocouple with 48" leads, which is long enough to reach from #3 to under the rear seat bench. Having the cold junction inside the car's interior will limit the cold junction error to ~25ºF, because by the time the engine warms up enough for CHT to be of interest, it's usually between 50º and 100º inside the cabin. Then, you do the arithmetic in your head to get the CHT.

Uma makes some nice instruments as well.
It seems to me that I have read someplace that Uma CHT gauges are cold junction temperature compensated. However, after looking through the Uma catalog, I have seen no mention of cold junction compensation. So who knows?

In any event, once you become accustomed to what is "normal" for your car under various conditions the CHT gauge will alert you when something abnormal is happening.

Thats interesting!

As noted earlier in this thread, at least two people I know with aircraft and using the Westach gauges "Swear" theirs were compensated.

It makes me wonder whether they are just plain wrong or whether the gauges were set up compensated for them by a service, the seller etc.....or with a widget like at the link below.

I will have to see if I can get ahold of them at some point....but its nice to know.

I have always figured that if I cannot find what I need....I still like the Westach units and could simply live with short mental arithmetic like you mention :lol:

Here is that link. I may have posted this before. It shows circuit schematics for three different methods of building a cold junction compensator. The parts are cheap at digi-key.

https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/4026.html

Ray

I'm in the UK, so I'm struggling to find any of the recommended gauges brand new. Do you know if any of the ones on the following website are suitable? They do seem to have a few Westach gauges:

https://skycraft.ltd/collections/cht-egt

Sun Sep 28, 2025 6:09 am

Westach is still in business; https://www.westach.com/

The gauges in my 181 look like this:

Sun Sep 28, 2025 6:33 am

Thanks for the pic! Sorry if I wasn't clear but because I am in the UK, the availability of most of these US-made gauges is limited. There are some second-hand Westach products for sale in the UK at the following link but I wanted to know if any of these were the correct ones for this application:

Skycraft:

https://skycraft.ltd/collections/cht-egt

Sun Sep 28, 2025 3:28 pm

I find it hard to believe that Westach would not ship to the UK.
It certainly would not hurt to ask.

I have used Westach products in several VWs, and always purchased then directly from Westach.

Good luck.