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BMW 635CSI – Best Gas Mileage Speed

Question:

At what speed does an automatic BMW 635CSI get the best gas mileage? Mega Man JobCrunchersUnite.com

Response:

At what speed does an automatic BMW 635CSI get the best gas mileage?

Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear. But who has the will-power to do that?  Not me… -Fred W

Response:

At what speed does an automatic BMW 635CSI get the best gas mileage? Seriously? Slowest speed you can maintain in top gear.

…without labouring the engine (fuel system will compensate for increased load and consumption will increase)…

Response:

At what speed does an automatic BMW 635CSI get the best gas mileage? Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear.

In my 85 635CSi, it will tool along at 1000 rpm in 5th gear no problem.   No matter what I do, I can’t seem to do better than 17 or 18 mpg, and that is combined city and highway driving.

Response:

– Hide quoted text — Show quoted text – At what speed does an automatic BMW 635CSI get the best gas mileage? Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear. In my 85 635CSi, it will tool along at 1000 rpm in 5th gear no problem. No matter what I do, I can’t seem to do better than 17 or 18 mpg, and that is combined city and highway driving.

Combined driving is not a very good test.  Try calculating when you do some straight highway cruising.  As a point of comparison, I routinely get around 23-24 mpg (US gallons) in my E34 540iA.  But I tend to drive, umm… a bit over the speed limit (70-80 mph) on the highway. -Fred W

Response:

– Hide quoted text — Show quoted text – At what speed does an automatic BMW 635CSI get the best gas mileage? Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear. In my 85 635CSi, it will tool along at 1000 rpm in 5th gear no problem. No matter what I do, I can’t seem to do better than 17 or 18 mpg, and that is combined city and highway driving. Combined driving is not a very good test.  Try calculating when you do some straight highway cruising.

I have…it tops out around 22mpg for 65mph cruising. Not like I would expect better from a 20 year old 3.5 L6   I also have a manual gearbox, that would give me a slight edge over the old three speed auto.

Response:

– Hide quoted text — Show quoted text – At what speed does an automatic BMW 635CSI get the best gas mileage? Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear. In my 85 635CSi, it will tool along at 1000 rpm in 5th gear no problem. No matter what I do, I can’t seem to do better than 17 or 18 mpg, and that is combined city and highway driving. Combined driving is not a very good test.  Try calculating when you do some straight highway cruising. I have…it tops out around 22mpg for 65mph cruising. Not like I would expect better from a 20 year old 3.5 L6   I also have a manual gearbox, that would give me a slight edge over the old three speed auto.

I can get over 25 mpg under the same conditions with my ‘97 540i stick with 193000 miles on it. Mark Folsom

Response:

– Hide quoted text — Show quoted text – At what speed does an automatic BMW 635CSI get the best gas mileage? Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear. In my 85 635CSi, it will tool along at 1000 rpm in 5th gear no problem. No matter what I do, I can’t seem to do better than 17 or 18 mpg, and that is combined city and highway driving. Combined driving is not a very good test.  Try calculating when you do some straight highway cruising. I have…it tops out around 22mpg for 65mph cruising. Not like I would expect better from a 20 year old 3.5 L6   I also have a manual gearbox, that would give me a slight edge over the old three speed auto. I can get over 25 mpg under the same conditions with my ‘97 540i stick with 193000 miles on it. Mark Folsom

I know it’s a different car, but my old 1978 Jag XJ6 4.2 Coupe (I6 engine) with a manual overdrive gearbox was most economical when cruising at around 65-75mph, as that was just around peak torque rpm in overdrive. (3200-3400rpm) This rpm will not be true for all cars however, there are a lot of other factors to consider such as headwinds, aerodynamics, individual engine tune etc. Badger.

Response:

My 1984 635CSI gets in the low 30’s on the highway.  I’ve been commuting from San Diego to Las Vegas and it’s been getting excellent mileage.  I cruise it 5th gear between 2K and 2.5K.  Great for an ‘OLD" car.

– Hide quoted text — Show quoted text – At what speed does an automatic BMW 635CSI get the best gas mileage? Technically?  Idle speed, like 5mph. Seriously? Slowest speed you can maintain in top gear. In my 85 635CSi, it will tool along at 1000 rpm in 5th gear no problem. No matter what I do, I can’t seem to do better than 17 or 18 mpg, and that is combined city and highway driving. Combined driving is not a very good test.  Try calculating when you do some straight highway cruising. I have…it tops out around 22mpg for 65mph cruising. Not like I would expect better from a 20 year old 3.5 L6   I also have a manual gearbox, that would give me a slight edge over the old three speed auto.

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