Oil Pan heater
 

I just bought one of these. Its only 125W and its the 12V version.
I don't expect great results but I am hoping it will raise the oil temperature a bit on those cold days. Right now its set up to run from an external 12V battery, I don't want to kill the starter battery (its on its last legs).
There is a 250W 240V model, but I don't have easy access to a plug so I'm going to try this smaller model first.
Also, I ignored the instructions step where it says sand the paint off your oil pan. No thanks! I think it will be ok, and if the heater fails that's preferable to ruining the oil pan.

I'll post up results when I get a chance to try it.

http://forum.a8parts.co.uk/attachmen...1&d=1413834177

http://forum.a8parts.co.uk/attachmen...1&d=1413834177

I do not think 125W will make any difference, specially as it's not insulated in any way. Back in Latvia we had 2x 3kW heater coils from industrial boiler DIY mounted inside the sump of tractor, that was because the old USSR oils turned to gel at -30C and pump would not pick it up at all. It was taking a good hour to raise oil temperature near 0C at those conditions on the insulated sump.

It'll only make a difference if running all the time from an external power supply, maybe enough to raise the temperature a few degrees.
Remember an A8 engine is typically 200 to 300kW and this is just a couple of light bulbs.

Might consider something like this coolant heater for VW diesels but use it somewhere in the oil flow: http://www.ebay.co.uk/itm/GENUINE-VW...item4d14c417c4

It uses 3 glow plugs each 140-150W

Try grabbing a 125w light bulb, its quite hot so i would have thought that this pad would raise it a bit, no?

Indeed, a bit.
Do the maths; given how much oil is in an A8 engine, maybe a "handful" of degrees in an hour. And most of that would conduct away into the much bigger mass of the engine block.
So a little bit.

Eventually.....

I like these stories from the USSR. My dad told me in Russia, and even in Serbia truck drivers used to light a fire under the oil sump (or maybe under the diesel tank?) on those cold -20 or -30 days.

I don't expect much, it is only 125W. Back of cigarette packet calculation, specific heat of engine oil is around 2000J per kg to raise by 1C, lets assume density is 1kg per dm3 (although its less), so 7.5l x 2000 = 15000J to raise by 1C. 15000/125 = 120sec to raise by 1C. If I want to raise by 10C it should take 20minutes. But lets say only half the area of the pad heats the oil, the other half is wasted, so perhaps 40 minutes to raise temp by 10C. But this excludes the volume of oil pan, etc, so probably a lot longer.

I'll give it a go and let you know what happens.

I love it when it gets super geek.

First attempt - fail. So much for theory :)
VCDS oil temperature at start: 11C
VCDS oil temperature after 20minutes: 11C

It was the battery's fault anyway. 12V 7.2Ah Aino Micro could not even supply 8A without its voltage collapsing to around 6V after only 10 minutes. I left it connected for just over 20 minutes anyway. Current dropped to below 6A, so that's around 36W input. After load was removed it recovered back to 12.3V
Next time I will try a proper starter battery with more capacity.

Pretty much as I predicted. You already have auxiliary heater which provides 5kW of heat. You just need to get that heat from coolant to the oil. Possibly auxiliary electric oil pump and oil to water heatexchanger.

pumps: http://www.ebay.co.uk/sch/Car-Parts-...ctric+oil+pump

Heat exchabnger something like this :http://www.ebay.co.uk/itm/plate-HEAT...item3ce94b3c66

Another way would be to make the oil circulate the engine while it is off but heater working but that would be bit more complicated I guess.