Oil Pan heater

[Goran]

Thanks for those links. The Webasto aux heater is a lot more powerful, wow 5kw I didn't know. I was hoping it would pass some heat onto the oil since D2s already have that oil cooler which is like a heat exchanger, but I guess the oil isn't flowing so it would take a long time for heat to transfer to it from the coolant.
I'm guessing some sort of valved set up with the electric oil pump in parallel would be needed so it is bypassed when the engine is running?

[awolfinsheepsclothes]

Very interesting Goran you could send the water from your webasto through a heat exchanger bonded to the sump, it would take a while to transfer the heat to the oil. Where are you going Siberia? Pumping oil would be a big strain on a battery around 10amps. Are you after a quicker warm up for economy or engine wear? Have you seen the accusump? This stores pressurised oil so you can have full oil pressure before the starter motor even turns.
Cheers dave

[jza8]

Originally Posted by Goran

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.

It was under the tank, as back then, there was no winter diesel, so it would get too thick in cold weather. Another trick was also to mix some petrol in the tank and also in the the oil.

[ainarssems]

There is no oil flow while engine is off so heat is not being transferred to oil through OEM heatexchanger when auxiliary heater is working. Fitting electric pump to push oil through engine and OEM heatexchanger would be tricky and would require powerful pump drawing a lot of current. I was thinking of lower powered electrical pump just sucking up oil from sump, pump it through external heatexchanger and dump back in in the sump.

[Goran]

Originally Posted by awolfinsheepsclothes

Very interesting Goran you could send the water from your webasto through a heat exchanger bonded to the sump, it would take a while to transfer the heat to the oil. Where are you going Siberia? Pumping oil would be a big strain on a battery around 10amps. Are you after a quicker warm up for economy or engine wear? Have you seen the accusump? This stores pressurised oil so you can have full oil pressure before the starter motor even turns.
Cheers dave

I got a bit interested reading about oil, and found out that viscosity at 40C is 72 (for Edge 5w30) but at 10C its around 400! and at operating temp. its supposed to be around 12 to 14.
I was a bit deceived by the Webasto heater, after 20mins the coolant is already up to 50C, and after just 5 mins of driving its at 90. But then I started logging the oil temp and it takes a good 15 minutes for it to get up to operating temp. Unfortunately once a week I go to the local supermarket which is only 2 miles away. Now I know the oil never gets up to temperature on that short journey. Call me crazy (because I am ) I have started doing a warm up drive of a few miles down the A2 before I park at the supermarket so at least the oil got up to temperature for a short while.
So I got the wolverine heater in the hope to bring oil up to temperature quicker when I have to do short journeys.
I like the coolant pipe idea, something like a pipe in a kettle or warm water boiler?

Originally Posted by ainarssems

There is no oil flow while engine is off so heat is not being transferred to oil through OEM heatexchanger when auxiliary heater is working. Fitting electric pump to push oil through engine and OEM heatexchanger would be tricky and would require powerful pump drawing a lot of current. I was thinking of lower powered electrical pump just sucking up oil from sump, pump it through external heatexchanger and dump back in in the sump.

Good point about pressure needed to pump through the whole system.
I have some rc airplane lipo batteries which will easily hold 12V if the current is only 10A, so I will give the wolverine pad one more chance to see if it can do anything when it produces its stater 125W rather than the 36V I managed at the last attempt. The additional oil cooler and pump sounds like a lot of extra work and I dont know if I trust myself to not introduce leaks in the oil system.

[ainarssems]

Some numbers for comparison, these are not exact numbers precisely calculated or measured but should give general picture.

4.2l D2 engine consumes 1.4-2l of petrol in idle, average energy density for petrol is around 8.7-8.8kWh/l so if we take average fuel consumption in idle at 1.7l/h it produces almost 15kW of energy every hour at idle. Most of this energy is heat, some goes to drive gearbox and some is used as mechanical energy to turn the engine but converts back to heat from the friction. Part of the heat comes out through the exhaust but most goes in coolant and oil, i am going to guess at least 10kW. How long would it take for engine at idle to get coolant and oil to working temperature? - I have not tested but I guess quite a while. When you compare 125W heater it's only 1.25% of the heat that engine transfers to coolant at idle.

The Webasto aux heater is a lot more powerful, wow 5kw I didn't know

Auxiliary heaters are normally in range 2-5kW for passenger cars depending on vehicle and engine size. In case of Audi of this vintage (A6/A8) it's 4kW for diesel and 5kW for petrol.

Remember an A8 engine is typically 200 to 300kW and this is just a couple of light bulbs

It's 250 or 265kW for S8 engine in D2, but that is only at full power. Cruising at steady 60-70mph it will only produce around 20kW. Nevertheless internal combustion engines are only 30% efficient at best of times, typically you are looking at more like 20% in which case for every 20kW of mechanical power there is another 80kW of wasted heat produced. Part of this goes in the exhaust and part in cooling system(typically 1/3 of total power so around 33kW in this example) while small part is conducted to surrounding air. How much goes in cooling system and how much in the exhaust depends on operating conditions- at low rpm and low load like idle more will go in cooling system, at high rpm and high load(full throttle) more in exhaust.

At full power efficiency is a lot lower, maybe like 10% so engine producing 265kW of mechanical power will produce 2400kW of heat but at these conditions most of it will go out of exhaust and less in cooling system, still possibly 300-500kW or more.

[Goran]

I have some new data.
Using a 110Ah Bosch S5 battery which is in a very poor condition, I got the following results.
At start:
VCDS oil temperature before connecting battery to pan heater: 8C
Battery voltage under load: 11.7V
Current: 9.0A
Watts: 105.3W

after 30 minutes
VCDS oil temperature: 12C
Battery voltage: 11.0V
Current: 8.5A
Watts: 93.5W

Conclusion, it seems that it takes 7.5 minutes to heat the oil by 1C with input average wattage of around 100W

[HPsauce]

Originally Posted by Goran

Conclusion, it seems that it takes 7.5 minutes to heat the oil by 1C with input average wattage of around 100W

So maybe up to 8C in an hour; the "ball-park" estimate was in the same ball-park!

Originally Posted by HPsauce

given how much oil is in an A8 engine, maybe a "handful" of degrees in an hour.

[Goran]

Yes, just under 10 degrees per hour, I guess it meets expectations for such a small heater.
I left it on for another half a hour, the temperature increase seems to be linear,

after 60 minutes
VCDS oil temperature: 16C

I was in a rush to go, I forgot to check battery voltage and current at the 60 minute mark.

Perhaps with a battery that can hold voltage over 12V and deliver 10A so you get the rated 125W it may be able to heat the oil by 10C per hour.
If I decide to throw more money away I could get another one of these to half the time.

[Goran]

I realised I have a small 200W 240V to 12V dc mains power supply at home. So I experimented a bit more yesterday. It saved me throwing away £34 for a 40Ah starter battery for this purpose.
With stable output of 13.74V and 9.5A (roughly 130W) this is what happened

start:
VCDS oil temp = 8C

60 minutes:
Oil temp = 18C

120 minutes
Oil temp = 23C

It was promising at the 1 hour mark, 10C per hour, but something went non-linear in the second hour, only raised by another 5C.

I drove after that, and it took only 10 minutes to get oil up to 80C, but took another 5 minutes to get to 85C. I gave up measuring after that. All slow 30mph roads and traffic lights. Coolant was heated to 35C before leaving so this helped too.

I am quickly realising, this was a fun experiment, but in practice its going to be a real pain heating oil for 2+ hours before every first trip of the day. I think I will only be bothered to use this heater for only the coldest days 0C or below.