Cylinder Head Temperature Always Reads 140F on Cold Start

[PBBLASTER]

Does anyone else's car read 140F on cold start no matter what the ambient temperature is? Mine would read 140F even when car sat for 8 hours in 20F weather. The cylinder head temp won't budge until the actual temp goes above 140F. The dash temp gage operates as expected.

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[Wraith6668]

Does anyone else's car read 140F on cold start no matter what the ambient temperature is? Mine would read 140F even when car sat for 8 hours in 20F weather. The cylinder head temp won't budge until the actual temp goes above 140F. The dash temp gage operates as expected.

Thats how mine is too, I think its just the lowest it can read so it says that until it reaches 140 and goes above. Obviously it's starting way lower in this 20° weather we've been having but probably can't read any lower.

 

[Alan Applegate]

I'd bet this is due to a limitation of thermistor.

 

[robvas]

MegaZilla 2.0 would be great in a Fairlane

 

[PBBLASTER]

I'd bet this is due to a limitation of thermistor.

The gage has linearity. I don't know why they wouldn't at least try to fake it.

 

[Alan Applegate]

Thermistors are nothing more than resistors which change their resistance with temperature. Their linear region is rather narrow, so when large variations in temperature need to be measured, IR detectors are often used due to their wide bandwidth.

In this specific case, a run-of-the-mill thermistor is both inexpensive and prudent.

 

[glenng6]

Mine does the same and I would think that is standard behavior for all GTs. Glenn

 

[Zig]

Does it produce cabin heat accordingly?

 

[PBBLASTER]

Does it produce cabin heat accordingly?

It produces cabin heat according to the needle gage. This meanit blows cold air while numerical reading indicates 140F on cold start. This false floor of 140F has to be a bug. No way the PCM doesn't know the actual temperature. It runs too good at 10F to have the PCM thinking it's 140F.

 

[Skye]

As a reference, the Gen 3 engine and S550 have a CHT floor of 110 F/43 C.

 

[Zig]

As a reference, the Gen 3 engine and S550 have a CHT floor of 110 F/43 C.

Imo unacceptable that the driver needs to perform the calculations considering they are providing a computer to display the information. Does the ‘ambient’ temp gauge/reading have the same ‘floor’? Similar software in the truck but doesn’t seem to exhibit the same ‘bug’.

 

[Skye]

Does the ‘ambient’ temp gauge/reading have the same ‘floor’?

The S550 engine cold air inlet has a floor of 0 F.

The outside air temperature, I checked for a floor and couldn't confirm. I know it will read into -F.

 

[robvas]

Each sensor has a range that it works in. Ambient air will never need to go to say 250f, and coolant won't ever need to read -25f, so they probably just use a sensor that works in the useful range for that application. Each of those is probably a different sensor that works differently.

 

[Zig]

Each sensor has a range that it works in. Ambient air will never need to go to say 250f, and coolant won't ever need to read -25f, so they probably just use a sensor that works in the useful range for that application. Each of those is probably a different sensor that works differently.

 

[robvas]

What am I supposed to be looking at?

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