While I like the thinking, I don't reckon it can be dT due to compression, as the PD injectors do their compression in the cylinder head, and there's a. only one sensor and b. it's not near the top of the block AFAIK...

fuel temp guage is coming out of the front of engine above oil filter[on pd]....i found so far that spoofing it up the temp the engine runs smoother than spoofing it down....so far i'm just driving around town an fuel economy is up 3mpg or so....no change in power noticed.........

i want to get vag com out soon test it on motorway see what happens using the car a bit harder

and see what readings i get