Can't help with IC expertise, but ATM I can recount my experience with EGTs with various air flow testing I've been mucking about with.
My issue has been trying to maintain coolant temp with A/C on in my auto tdi.
On any day without A/C I get low 80's coolant temps .. so I don't get any overheating per se.
With A/C on, I used to get well over 100°C just on an easy cruise .. eg. at between 80-100 k/h.
Any hill, and subsequent little bit of load on the engine .. and by that I mean even a slight rise, as in a freeway overpass!! .. would see coolant temps rise dramatically.
Not too far from me is my preferred test hill called the Pentland Hills, a steepish long climb about maybe 2, maybe 5klms, rises about 300m(maybe more, can't remember exactly) ..but it's been great for testing coolant and EGT levels under various conditions.
ATM I've tweaked the IP to run at the borderline of dangerous EGT levels to maintain some power.
Climbing the Pentland Hills in my tdi, has always seen it drop to 80-ish k/h where it then unlocks the torque converter, then speeds up a little and locks up again.. and so on .. very annoying.
And all I want is for it to have just enough power to get up at (say) 85 in 4th lockup. So I've played around with the IP to try to get that.
But of course EGT then always gets to the danger zone(700°C). tweak IP fuelling down a little, and it helps.
Note too tho I'm not the type that pushes hard, I'd be lucky to use more than 3/4 throttle once a year, and if so it'll be for testing only.
Anyhow!.. tweaked and twiddled and mucked about with .. I'm relatively happy with where I've set the IP pump for now, and I can manage EGTs by backing off .. but up till recently I've never managed to get more than half way up Pentland without peaking EGT, and therefore having to drive to 'manage' it. Easy to do, but always the same issue.
A few weeks ago, I thought to remove the grille to test it's impact on coolant temp with A/C on. Makes a massive difference (min 10°C, average 15°C, in some cases 20°C ... differences with it removed) so the conclusion is that the grille design is far from ideal.
But I think it's more than the grille, and looking at the A/C condenser fans they are the real culprits .. not so much the grille.
I have plans to remove them and test with both removed and then each one to see how cool it runs that way too.
But while I've been dong this on and off, as time allows between work and hot ambient temps .. the other day I drive up the Pentland Hills again with grille still removed 38°C day .. and EGT peaked only a few meters from the top of the rise.
That is, this has been the first time I've been able to maintain 95k/h up the Pentland in the Tdi (with the exhaust system I currently have).
So just getting better flow from outside, through the grille(easy to do whilst it's not there!) and past the condenser rad to the IC has helped me massively.
I'm curious myself too now to know my charge temps too.
Curious as to what thermometer/probe setup you used to test.
Were they both the same type? That is, if different, could they be measuring temperature with differences in accuracy .. etc. etc.
Arthur.
'99 D1 300Tdi Auto
'03 D2 Td5 Auto
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