What engine temperatures are actually measured (not calculated or derived)

[Zathras]

On my '18 GT (not a performance pack) the digital gauges have a display for Cylinder Head Temperature (actually gives a number, usually around 200 F) and a display for Oil Temperature, which just shows a "virtual gauge" without numbers (just green and red zones). And the dash has a physical needle gauge that just shows C -- H. There is also an intake air temp and transmission temp reading in the digital display.

But my question is... what temperature(s) are actually measured by sensors on the engine? Are there actually thermocouple(s) directly measuring CHT temperature, coolant temperature, and oil temperature? Is the needle gauge on the dash based on engine coolant temperature, or CHT? The needle gauge is clearly programmed to read "normal" over a wide range of temperatures because it basically never changes position as you drive.

Basically, wondering which of these gauges is showing me a measured reading, instead of a reading that is just a calculation based on some other parameter. Thanks for anyone who can enlighten me.

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[EFI]

Head temp (CHT) is the only one that's actually measured through a sensor bolted into the head. Coolant and oil temp are derived off that and several other factors/parameters.

The oil gauge does have some ranges to it, but again that number is not exact but derived.

38-60° C (100-140° F) (low)
61-137° C (142-279° F) (normal)
138-146° C (279-295° F) (warm)
147-160° C (297-320° F) (hot)

 

[SCP440]

Most cars temp readings are averaged by the engine management so as not to worry the driver and in most cases the temp will sit in the middle unless the temp goes above a set amount of what the manufacturer considers is enough to warn the driver, there are some cars manufactured these days that dont even have a gauge and the driver just gets a warning if there is a problem.

 

[Keeffa]

So is there a sensor that measures the transmission fluid temperature.

 

[EFI]

So is there a sensor that measures the transmission fluid temperature.

On automatics yes, not sure if there is on in the manual. If continuing outside the engine, some cars are also equipped with a differential oil temp sensor but not all.

 

[Keeffa]

I have noticed something on the diff that could be a sensor but I've not found a gauge for it.

 

[luc]

I have noticed something on the diff that could be a sensor but I've not found a gauge for it.

It’s to issue a dash message/warning

 

[Keeffa]

I've seen some guys have put gauges up on the dash which look ok but not sure about that. But if it's for racing or just doing track days.

 

[ice445]

I have noticed something on the diff that could be a sensor but I've not found a gauge for it.

With cars that have the diff cooler it should have a temp reading in the same list as the other stuff

 

[Skye]

While automatics have a trans temp sensor, manuals do not, cooler installed or not.

My car is equipped with a factory diff cooler. I do have a temp sensor for the diff.

Attached is a reference: 2020 - 2023 OBD System Operation. This document details the voltage inputs and ranges for various engine readings and alarms.

CHT Temperature

Printed Page 120. There's both a "cold" end and a "hot" end reading for the thermistor, the device that changes is resistance with temperature and is part of the circuit giving a voltage output to the PCM.

I've noticed in a few references of a general engine/gauge coolant operating range: 170F-230F, 76-110C.

The PCM also has a "fail safe cooling" mechanism, implemented when temperatures meet or exceed a given limit. Reference: Ford 303-03B "Engine Cooling System Operation, 2020-2023 Mustang".

Stage 1: Alarms illuminate.

If the driver does not take action to bring temperatures under control, the PCM engages Stage 2.

Stage 2: Four cylinders have their ignition deactivated, RPMs are limited to 3,000.

If conditions continue, Stage 3.

Stage 3: PCM engine shutdown. The attached notes that, with a CHT reading of 270F / 132C or higher, fuel is cut to the engine.

Oil Temperature

PP 148: -40 - 302F, -40 - 150C

 

[Keeffa]

With cars that have the diff cooler it should have a temp reading in the same list as the other stuff

I don't have a diff cooler, it's just looks like it would be a sensor in the diff.

 

[Garfy]

Most cars temp readings are averaged by the engine management so as not to worry the driver and in most cases the temp will sit in the middle unless the temp goes above a set amount of what the manufacturer considers is enough to warn the driver, there are some cars manufactured these days that dont even have a gauge and the driver just gets a warning if there is a problem.

True. Entry level cars from Honda and Toyota for example (Yaris, Fit, etc.) merely have a blue and red indicator light. When you cold start the car, the blue light is on. The light turns off (on my Fit) after coolant reaches about 128 F; I don't know when the red one goes on as I've never ran my car hot though my daughter once had hers "flicker" on the freeway and she turned the A/C off and it went away. Found out that the condenser fan motor wasn't working; after replacing it, no more problems and the engine was fine so clearly it turns red well before any damage can occur to the engine (unlike many older domestic cars that by the time a red temperature light comes on, the engine is already steaming and damaged).

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