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Old 09-16-2009, 09:22 AM   #61 (permalink)
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About pulse and glide I would like to point out that if I turn of the engine in my car in Finland by turning the key to the stop position there is the side effect of engaging the steering wheel lock.

You don't ever want to be traveling 50mph with the steering wheel locked in position.

With this in mind I would recommend that you check how your car behaves when turning off the engine before you try it at high speed.

Also on a diesel you don't win that much from turning off the engine as it uses very little fuel on idle.

A friend of mine said that when he once had to park his diesel overnight at below zero F temperature, and he had no block heater, he just left the engine running over night and it consumed less than a gallon of fuel.

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Old 09-16-2009, 10:38 AM   #62 (permalink)
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Quote:
Originally Posted by milesgallon.com View Post
if I turn of the engine in my car in Finland by turning the key to the stop position there is the side effect of engaging the steering wheel lock.
The solution to that is you don't turn the key all the way to the stop position. Maybe cars are different in Finland, but I haven't heard of a car without an accessory position. In the accessory position the electronics are engaged, but the engine is off. The lock does not engage in this position.
After shutting the engine, you then immediately turn the key back to the run position (without going to start first) so that you can reengage the engine instantly using the clutch.

Quote:
Originally Posted by milesgallon.com View Post
Also on a diesel you don't win that much from turning off the engine as it uses very little fuel on idle.

A friend of mine said that when he once had to park his diesel overnight at below zero F temperature, and he had no block heater, he just left the engine running over night and it consumed less than a gallon of fuel.
If you are using the P&G technique, the engine isn't at idle, it has to work to regain the lost speed during the coast phase. My question is about the amount of fuel required for acceleration in comparison to the fuel lost to engine inefficiency during steady state driving.

Besides, a gallon is not a small amount of fuel!
Depending on how much gas costs where your friend lives, a block heater would pay for itself in about a week or two.
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A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 09-16-2009, 10:52 AM   #63 (permalink)
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Actually he did have a block heater but was at a place with no electrical outlet near the car, maybe at the cabin I don't remember. A gallon is not much if the alternative it that the car won't start at all in the morning which is quite possible with a diesel at sub zero temperature.

I was suggesting that with a diesel you might leave the engine running while coasting as the fuel used in idle is minimal. I would worry about the long term wear on the engine from re-starting it every mile.
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Old 09-16-2009, 10:56 AM   #64 (permalink)
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Ah, well, that makes a lot more sense then.

I doubt that restarting wears the engine much. It stays warm over such a small time off, oil pressure builds in like a second. It probably wears the clutch and transmission faster though. And of course the starter - but I have a lifetime warranty on that!
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Quote:
Originally Posted by Piwoslaw View Post
A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 09-16-2009, 11:25 AM   #65 (permalink)
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A 6.9 or 7.3 IDI (not sure which one is in the truck) isn't exactly a "modern" Diesel They are great engines, just not very modern compared to what we have now.

Jacob You said you added a vac pump to operate the brakes with the engine off? Where did your brakes get vacuum before you added the pump? certainly not from the engine....

As for reduced pumping losses due to not having a throttle plate keep in mind the diesel's high compression ratio and heavy duty rotating assembly compared to gassers.
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Old 09-16-2009, 11:46 AM   #66 (permalink)
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A direct injection diesel engine will start cold just fine at -40 F, at least mine does.

My idle fuel usage is 0.15 gallon per hours. Minimality is always relative, when you're trying to squeeze over 70 mpg, diesel idle fuel usage is very significant.

I'd say additional wear is slim to none.
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Old 09-16-2009, 12:18 PM   #67 (permalink)
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I have no idea if mine is a direct injection or not (Opel Astra 1998 with something about ECO printed in bold letters on the engine) but it has noticeable difficulties starting at -10C which would be +14F.

Before the Opel we had a diesel Mercedes (an charming old heap of rust from 1985), it was a pain starting already at -5C/23F

On the other hand I have seen the newer diesel BMWs start at any temperature without a heater, that's must be the ones you're talking about.
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Old 09-16-2009, 12:30 PM   #68 (permalink)
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Simon,

I'm pretty sure your engine have a rotary injection pump. You should get your timing checked and adjusted to max advance spec. It'll start much easier in the cold.
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Old 09-16-2009, 12:55 PM   #69 (permalink)
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Will advance timing affect the fuel economy?

I normally use a block heater both for fuel economy and to reduce engine wear so cold starting is only a problem when there is no electrical outlet available.
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Old 09-16-2009, 01:18 PM   #70 (permalink)
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Quote:
Originally Posted by CoastRider View Post
A 6.9 or 7.3 IDI (not sure which one is in the truck) isn't exactly a "modern" Diesel They are great engines, just not very modern compared to what we have now.

Jacob You said you added a vac pump to operate the brakes with the engine off? Where did your brakes get vacuum before you added the pump? certainly not from the engine....

As for reduced pumping losses due to not having a throttle plate keep in mind the diesel's high compression ratio and heavy duty rotating assembly compared to gassers.
Its a 6.9L, last year they used them.

Before I put in the electric pump, it used a belt driven mechanical vacuum pump. I'm pretty sure that is the standard on most diesel engines, no?
Since the belt runs off the crankshaft, it stops with the engine. As a side benefit, I got to take off one more belt driven accessory load from the engine.

I have thought about the higher compression ratio, but given how much more efficient a diesel is (for a given power output) I'm thinking the inefficiencies of the gas design must outweigh losses due to higher compression ratio.

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Originally Posted by Piwoslaw View Post
A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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