Diesel engines: Free-wheel downhill or leave in high gear?

[Watty]

Calling all the diesel-fundi's...........
Does a diesel engine still use fuel when you on a long downhill in 5th gear?
or should I just free-wheel in neutral?

bin told that the engine in neutral will use more fuel than running against compression in high gear.......... Huh?

true, or false?

 

[Billwill]

I dont know about fuel consumption but I worry about freewheeling downhill as you could overheat the brakes in keeping within the correct speed as regards other traffic...I prefer to use engine braking to control the speed...my 2002 CRD has rear drums so I am quit concerned about brakes overheating.

 

[CRD Joe]

Tony is right! On good steep hills take her out of cruise (you should always be in cruise otherwise) and let her coast. The computer will cut fuel injection to an almost non registerable amount. Youll get maximum mileage.

 

[tulsa]

Tony is right! On good steep hills take her out of cruise (you should always be in cruise otherwise) and let her coast. The computer will cut fuel injection to an almost non registerable amount. Youll get maximum mileage.

There is nothing more irritating to me than the transmission down shifting to limit speed when in cruise control.

 

[Midgear]

If you leave cruise control on (I noticed this the other day)--

I had my cruise control set at 65, came up over a hill, and down the other side, not even paying attention, I felt the Jeep downshift.. DOWNSHIFT.

I thought "oh hell not the transmission" and looked at my speedo and I was doing about 72-73 MPH, it slowed to 65 and it upshifted.

I thought holy shit.. this clumsy ass Jeep is smarter than I thought.

what that has to do with this thread.. I have no idea. cruise control I guess.

also- on a random note, if I turn overdrive OFF while climbing a hill at 30-35, the RPM's drop from 2200 or so down to about 1500 and it pulls harder, yet at lower rpm..

confusing little bastard.

edit:

There is nothing more irritating to me than the transmission down shifting to limit speed when in cruise control.

Just seen this post.. you beat me to it.

edit #2.. this was my 666th post.. wtf

 

[CRD Joe]

Youre both right. On steep hills I take her out of cruise and let her coast so she wont down shift. As you reach the bottom of the hill and start to slow down to your previous cruise speed just punch her back in.

 

[tulsa]

Midgear,
The cruise control settings in the US CRD's are over-controlled. The throttle is used very aggressively to maintain speed to within +/- 1MPH even up very steep hills which is easier to do because of the CRD's torque, however down shifting occurs within 3MPH over the set speed to control over speed going down hill. Not what I want.
Lewis

 

[Michel_KJ]

There is nothing more irritating to me than the transmission down shifting to limit speed when in cruise control.

Question, does the ****** with a 3.7L the same ? Downshifting if the speed is over cruising speed ?

Michel.

 

[ThunderbirdJunkie]

Yes. ALL modern automatics do it.

 

[JLRockies]

diesels don't have a gas pedal

 

[bmrrwolfe]

 

[azmotoman]

Hauled a trailer downhill from a rally and used the 'speed control'. Don't know about the gas models, but the speed control on a CRD is more than just a 'cruise' option. It downshifted and maintained speed as I descended. SWEET!