Bit of a thread revival...
Yes, It is possible to adjust the temperature gauge scale.
I have been test driving some revised values in my car recently, and am now confident to be able to say that it is all working as I intend
The standard gauge is not much use, as pointed out previously, the dash has the following standard values
Start moving (bottom of Blue) = 15
End of Blue (Cold) = 52
1/4 Mark = 64
Arrive at halfway (start of buffer) = 75
leave halfway (End of buffer) = 115
3/4 Mark = 120
Red (overheat) = 125
When looking in to the fan behaviour on the different engine variants I have found the following information: (edit - Updated with the information SD1Too Supplied in post 6)
1.8
Low speed: on 104, off 98
High speed: on 112, off 106
KV6
Low speed: on 100, off 96
Medium speed: on 106, off 102 (not used on 2 speed systems)
High speed: on 112, off 108
Diesel
Low speed: on 100, off 98
Medium speed: on 106, off 102 (not used on 2 speed systems)
High speed: on 112, off 110
This means that on all engine variants the cooling fan is running at high speed before the temperature gauge has even moved above the half way point (ie things are getting really out of hand already).
so I have changed the following values on my car :
start of buffer = 80,
end of the buffer = 95
3/4 = 110
This means that the gauge starts to move above 'normal' before the fans come on, and is at nearly 3/4 before the high speed fan comes on.
With a petrol I would be tempted to apply lower values to the end of buffer & 3/4 point to better reflect the actual fan behaviour (possibly starting with end of buffer = 90, and 3/4 = 105).
I could do with some details regarding 'normal' temperatures seen when driving on a 1.8 & V6 to see if these values make sense - edging slightly above 'normal' in stop start traffic is fine, but there is no point going above 'normal' for normal driving (the risk is the driver ignores the gauge as 'it always goes above half now')
I have now driven for a month with my settings, and have seen the gauge rise above the halfway point when in stop start traffic towing a caravan, but usually it stays in the 'normal' position.
(Testing has also involved writing lower values across the range to force the gauge to declare an overheat condition, as I don't think I can achieve those temperatures on a diesel without doing silly things that might actually damage the engine).
If anybody local wants their gauge modifying, contact me - As pointed out previously this is not something the standard T4 can do (and I don't believe this is something that TOAF can do either),
Chris