Advances in Car Technology (Part 2)

Ok we have one - here's an opportunity to have one - if you got a point of view about something and want to share it - here's where you do it.
Chas
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Post by Chas » Mon May 21, 2012 2:43 pm

I think I may have an idea :idea:

The same volume of water should take longer (twice as long) to reach temperature than the oil. However, the water circuit has a thermostat which effectively means there is much less water than oil in contact with the engine. Only when the water reaches temperature does it flow into the radiator circuit. The oil has no thermostat and is being cooled from the outset.

How does that theory work..? :lol:

E24man
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Post by E24man » Mon May 21, 2012 2:54 pm

Chas wrote:I've made the point before that people shouldn't assume they can give their car the beans just because the water is up to temperature because the oil may only just getting warm :shock:
I learn't this through a Marine Engineering Apprenticeship
ade and liz flint wrote: I've got some thermocouples and a Fluke temperature meter....I'm getting tempted to fit them to the car, now! :lol:
You have too much time on your hands - I know, I can't talk :oops:

I suspect the chief reason is that the oil is being used primarily as a lubricant with some little cooling effect and that the coolant is being used as a, well, it says it all really. The highest temperatures will be at the point of ignition and around the combustion chamber; relative to the coolant the main volume of oil is a fair distance from the highest temperature source and isn't being used to draw heat away from that source.

Or something like that....
E24man

2001 Alpina B10 V8 Touring (1 of 12 rhd)
1997 Alpina B12 5.7 L (1 of 2 rhd)
1995 Alpina B10 4.6 Touring (1 of 1 rhd)
1985 BMW M635CSi (1 of 524 rhd made, but less than half left now)
1982 BMW 635CSiA (1 of only hundreds left from the thousands made and still valiantly fighting a rusty grave)

ade and liz flint
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Post by ade and liz flint » Mon May 21, 2012 3:15 pm

Chas wrote:I think I may have an idea :idea:

The same volume of water should take longer (twice as long) to reach temperature than the oil. However, the water circuit has a thermostat which effectively means there is much less water than oil in contact with the engine. Only when the water reaches temperature does it flow into the radiator circuit. The oil has no thermostat and is being cooled from the outset.

How does that theory work..? :lol:
The cooling water is also a pressurised circuit :think Add that to the equations :o
E24man wrote:You have too much time on your hands - I know, I can't talk :oops:

I suspect the chief reason is that the oil is being used primarily as a lubricant with some little cooling effect and that the coolant is being used as a, well, it says it all really. The highest temperatures will be at the point of ignition and around the combustion chamber; relative to the coolant the main volume of oil is a fair distance from the highest temperature source and isn't being used to draw heat away from that source.

Or something like that....
Not too much...enough 8) Nice to think about a puzzle on occasion.

I think the oil travelling around the pistons will warm pretty quickly, but has a small volume wrt the sump, as has the main bearing lubricant (with similar caveat).

Want to play, now :D
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joylove
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Post by joylove » Mon May 21, 2012 9:14 pm

Also, 9L of oil, how much water? Also, the water is pumped about, is the oil? If not, where is the Oil temp sensor? Finally, what is the surface area and length of the oil and water vanes when in a hot area?
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Post by B10BRW » Mon May 21, 2012 9:40 pm

I live 12 miles from the M25 via a dual carriageway, the Oil in my B3s BT takes that long to reach the proper temperature.
Don't give it the beans until I am on the largest car park in the world :D
Have no idea what the water temperature is , as BMW in their wisdom have not fitted a gauge :?

ade and liz flint
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Post by ade and liz flint » Mon May 21, 2012 11:00 pm

B10BRW wrote:Have no idea what the water temperature is , as BMW in their wisdom have not fitted a gauge :?
Yes, an odd omission on the E9x. So glad I have the performance steering wheel; my coolant temperature is on the display 99% of the time. Essential in my opinion :!:
Current:
E91 B3SBiturbo #127
981 Porsche Cayman GTS
Focus STline dog wagon

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Charles
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Post by Charles » Wed May 23, 2012 1:30 am

My daily morning commute is about 40 miles. The first 3 miles are B roads and then I'm on the A34/M4.

Whilst the water temperature reaches "normal" by the time I'm getting onto the A34, it isn't until about 10 miles later that I can feel the engine is hitting its sweet spot. This isn't that easy to describe but, before then, more vigorous acceleration results in the engine response feeling/sounding somewhat "thin".

I'm sure this is a reflection of the fact that the engine oil needs about 15 miles of good running before it reaches optimal temperature.

As for why the water and oil reach operating temperatures at different rates, factors such as volume of fluid, specific heat capacity and flowrate through the heat source are all relevant.

And when considering the difference between petrol and diesel engines in terms of reaching operating temperature, I can't help wondering whether the different flashpoints are a factor, along with combustion chamber pressures & temperatures and engine block design. Added to this, we can then factor in the thermal effciciency of the two fuels and it starts to get really complicated!!!

What really impresses me is the way that petrol engines are now achieving levels of economy that diesel engines used to - such that the differential between the two is beginning to close. For example, the 3.0 litre twin turbo in the B3 BT is achieving low 30s in mpg compared with the 3.0 V6 Turbo diesel in my Espace which struggles to get above 32mpg. Not quite a "like for like" comparison but one that begins to make the point, nonetheless.
Charles
Teacher of Chemistry and driver of ALPINAs - not necessarily in that order ;)
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