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Advances in Car Technology (Part 2)
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Chas
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PostPosted: Mon May 21, 2012 2:43 pm    Post subject: Reply with quote

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..? Laughing
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E24man
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PostPosted: Mon May 21, 2012 2:54 pm    Post subject: Reply with quote

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 Shocked


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! Laughing


You have too much time on your hands - I know, I can't talk Embarassed

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....
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2001 Alpina B10 V8 Touring (1 of 12 rhd)
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ade and liz flint
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Joined: 02 Jul 2010
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PostPosted: Mon May 21, 2012 3:15 pm    Post subject: Reply with quote

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..? Laughing


The cooling water is also a pressurised circuit Think Add that to the equations Surprised

E24man wrote:
You have too much time on your hands - I know, I can't talk Embarassed

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 Cool 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 Very Happy
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joylove
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PostPosted: Mon May 21, 2012 9:14 pm    Post subject: Reply with quote

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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B10BRW
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PostPosted: Mon May 21, 2012 9:40 pm    Post subject: Reply with quote

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 Very Happy
Have no idea what the water temperature is , as BMW in their wisdom have not fitted a gauge Confused
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ade and liz flint
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PostPosted: Mon May 21, 2012 11:00 pm    Post subject: Reply with quote

B10BRW wrote:
Have no idea what the water temperature is , as BMW in their wisdom have not fitted a gauge Confused


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 Exclamation
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Charles
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PostPosted: Wed May 23, 2012 1:30 am    Post subject: Reply with quote

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.
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