Accuracy of boost and egt gauges

[Hodge]

My local diesel places completely bypasses the in-car gauges and use their own calibrated ones.
I've been questioning my autron gauges or it's install/setup. It seems very "moody". For example sometimes on a hot day, hard driving the EGT's seem rather lower than usual. Then for instance this rather coolish morning, I was just crusing down to bunnings and EGT's jumped to 400, the car wasn't even warm enough. So whos to say whats accurate.
This sort of concerns me, as when it comes to my dawes/valve setup I haven't got a solid confirmed reading to calibrate up against.

[threedogs]

@ hodge higher revs will give you lower temps. travel at 60 kph
check your temps them hit the OD button EGTs wiil get lower as revs increase

[BillsGU]

My local diesel places completely bypasses the in-car gauges and use their own calibrated ones.
I've been questioning my autron gauges or it's install/setup. It seems very "moody". For example sometimes on a hot day, hard driving the EGT's seem rather lower than usual. Then for instance this rather coolish morning, I was just crusing down to bunnings and EGT's jumped to 400, the car wasn't even warm enough. So whos to say whats accurate.
This sort of concerns me, as when it comes to my dawes/valve setup I haven't got a solid confirmed reading to calibrate up against.

Any tuning place worth their salt will use consistant readings from their own instruments and not rely on the unknown. Next time you have a tune ask them to put a "T" piece in the vacuum line and compare your gauge. The EGT is a bit more difficult as he will have to replicate load and revs twice - with his gauge and then with yours.

I have Autron gauges and they always seem stable and consistant - but I have not had them calibrated or compared so I don't know how accurate they are. Also - I don't know how accurate they have to be. Within 1 degree C, 10, 50, 100? What would be considered to be too inaccurate?

[threedogs]

yeah good point billsgu why do they have to be accurate ,cant they be ballpark for example.
No two 4x4 are the same so who cares, PSI values aren't set in concrete again ball park or a guide

[Wizard52]

Any tuning place worth their salt will use consistant readings from their own instruments and not rely on the unknown. Next time you have a tune ask them to put a "T" piece in the vacuum line and compare your gauge. The EGT is a bit more difficult as he will have to replicate load and revs twice - with his gauge and then with yours.

I have Autron gauges and they always seem stable and consistant - but I have not had them calibrated or compared so I don't know how accurate they are. Also - I don't know how accurate they have to be. Within 1 degree C, 10, 50, 100? What would be considered to be too inaccurate?

Hopefully they could be within say 50 degrees because if it shows 500 or 550, and is really 600+, we could be approaching disaster.

[the evil twin]

EGT gauges are easy to check.
Pyrometers are a milli-voltmeter and quality ones like Autron, VDO etc are usually very accurate around +/- 10 degrees C.
The easiest way to check your calibration is with a millivoltmeter across the thermocouple at the back of the gauge.
Because of the laws of physics thermocouples put out quite specific voltages across their temperature range.
In our trucks it is 99% a K type thermocouple in use so if you google a K type chart you can see what temp should be indicated for a particular voltage reading.
To calibrate the gauge on it's own on the bench I use a millivolt source
Pyrometers usually either work OK or go off scale when faulty BUT they do need to be installed with the correct thermocouple wire.
Intermittent jumps etc is usually indicative of a wiring issue or loose connection.

Boost gauges are a tad more finicky to check
Easiest way on a mech gauge is to pop the line off and tee in another gauge
Elec gauges were the sensor goes under the factory sensor on the intercooler are a tad more problematic as it is usually harder to tee in.

[BillsGU]

EGT gauges are easy to check.
Pyrometers are a milli-voltmeter and quality ones like Autron, VDO etc are usually very accurate around +/- 10 degrees C.
The easiest way to check your calibration is with a millivoltmeter across the thermocouple at the back of the gauge.
Because of the laws of physics thermocouples put out quite specific voltages across their temperature range.
In our trucks it is 99% a K type thermocouple in use so if you google a K type chart you can see what temp should be indicated for a particular voltage reading.
To calibrate the gauge on it's own on the bench I use a millivolt source
Pyrometers usually either work OK or go off scale when faulty BUT they do need to be installed with the correct thermocouple wire.
Intermittent jumps etc is usually indicative of a wiring issue or loose connection.

Boost gauges are a tad more finicky to check
Easiest way on a mech gauge is to pop the line off and tee in another gauge
Elec gauges were the sensor goes under the factory sensor on the intercooler are a tad more problematic as it is usually harder to tee in.

Then I guess you would need an accurate / calibrated thermometer so you can work out the mV output at a certain temperature. How accurate it a normal thermometer?

[the evil twin]

Then I guess you would need an accurate / calibrated thermometer so you can work out the mV output at a certain temperature. How accurate it a normal thermometer?

Hiya Bill,

You don't need another thermometer, the thermocouple is your thermometer, you just can't read it.

A thermocouple generates a specific voltage at a specific temperature. The "accuracy" of the temperature indication is governed by the display.

You can therefore either...
a) monitor the voltage from the thermocouple with a millivoltmeter and use the K type tables for the temperature.
As an example if your millivoltmeter reads 12.5 millivolts (mV) the gauge should display 305 deg C, 12.6mV is 310 deg, 10.0mV is 245 deg etc etc
OR
b) disconnect your thermoucouple leads at the gauge and connect a millivolt source. Most of the field process test gear will do this next bit and any instrument/elec workshop will. Apply the voltage as per the table and check the displayed temp

EDit... you can even make a test setup at home out of a dry cell battery and a couple of resistors if you have a good multimeter

[BillsGU]

Hiya Bill,

You don't need another thermometer, the thermocouple is your thermometer, you just can't read it.

A thermocouple generates a specific voltage at a specific temperature. The "accuracy" of the temperature indication is governed by the display.

You can therefore either...
a) monitor the voltage from the thermocouple with a millivoltmeter and use the K type tables for the temperature.
As an example if your millivoltmeter reads 12.5 millivolts (mV) the gauge should display 305 deg C, 12.6mV is 310 deg, 10.0mV is 245 deg etc etc
OR
b) disconnect your thermoucouple leads at the gauge and connect a millivolt source. Most of the field process test gear will do this next bit and any instrument/elec workshop will. Apply the voltage as per the table and check the displayed temp

EDit... you can even make a test setup at home out of a dry cell battery and a couple of resistors if you have a good multimeter

Thanks ET. I see what you mean now.