I've changed my DIS over from F to CPetrolDave wrote:+1ArthurPE wrote:I've (and others) have noticed an increase in oil temp
Since I had SW0090 fitted the oil temp is about 3-5 Celsius hotter under the same conditions.
The louder and more aggressive exhaust note, and the better mpg I'm seeing both fit with the combustion process changes.
was running ~ 90-95 C (195-205 F) or so, now 95 to 100 (200 to 210)
this would indicate change in the process with more heat being generated
one deposit casue scenario (imo) is unspent fuel getting on the valves
the engine runs homogenous mode, ie, fuel injected as air is drawn in, intake stroke:
if the fuel is injected at high enough pressure, and expands rapidly, as it would...high pressure (100 bar) to low pressure (atm ~14.7 psi) (one advantage of DI, as it does so it absorbs heat to to expansion and cools the charge) it may escape the cylinder before the intake valve closes...this would allow fuel to coat this cylinders, and adjacents in the firing order, intake valves causing deposits...
the good news is this is easily manipulated via SW changes
inject when the valve is almost (or fully closed)
or on compression, as in true DI lean burn
run leaner
some minor mechanical changes may help
suppose the injector nozzles aim at the valve backside or towards the top of the cylinder
revise them to shoot straight down (or some other direction) less likely to allow some leakage
I think Audi is working the problem, and will not say anything until they have a proven solution
BMW did this with the e46 engine failures, they blamed it on the owners, etc., until they determined the problem (rod bearing clearance) and a solution (replace bearings), then they issued a service action...it's SOP