Gear selection

[dalkill]

Being relatively new to diesel driving I'm constantly second guessing my gear selection.

On flat road going thru gears I find changing at about 2500 rpm makes it easier on the following gear. Just seem to labour otherwise.

Then up hill I worry even more.
Sir lowry pass is normally my yard stick. Normally loaded 4/5 guys with fishing gear

2.2 sfa ... eish .. flat foot 60 3rd gear
2.7 ifs ... 80 but also 3rd at very top
300tdi suzie... 80 but at top on occasion 3rd if truck involved
3.0 D4D. .. just did it once but had to drop to 4th to keep 80

Buddy of mine use to say he climbs it out in 5th gear. Not sure if he doing 100 which would help maintain 5th.. but being the good law abiding ave speed fearing citizen I am I keep to 80.

So is it normal for me to have to drop to 4th at the top?

[ChrisF]

Diesel is a strange beast !!!!

YES, it is "possible" to climb some steep hills in high gears .. NOT advisable !!

A diesel makes more horses by pumping more diesel into the engine. You now have the power, AND a lot of excess heat in the top.


Try to get a drive in a diesel with an EGT gauge - this monitors the temperature of the exhaust gasses.

N1 Panorama koppie - 5th gear, put foot and she looses no speed - and the EGT goes up to 600 degrees. Granted this is short lived and the temperature drops as soon as you go over the koppie. But think of the prolonged high temp when climbing Sir Lowries ...

Same hill, gear down to 4th - still keep the speed, but the EGT now reads about 500 degrees.


If in doubt - rather gear down and keep the engine cool.

[dalkill]

thanks chris. Will rather geardown as you suggested to save the engine

[Mars]

I agree with Chris. in addition to what he is saying, it is never a good idea to let an engine labour. Petrol or Diesel. This is more true for a Diesel as the compression is high and the forces transferred onto the con-rods, big end and main bearings are tremendous. This is increased exponentially when you let the engine labour.

[Rianc]

Under normal driving conditions I change at 2500rpm, and try to keep it just above at 2700rpm where the torque band is in sandy, climbs etc. I rather change down to keep this momentum, should it be required but try to keep the needle below 3500rpm.
Rian

[Mud Dog]

I agree with Chris. in addition to what he is saying, it is never a good idea to let an engine labour. Petrol or Diesel. This is more true for a Diesel as the compression is high and the forces transferred onto the con-rods, big end and main bearings are tremendous. This is increased exponentially when you let the engine labour.

Very True! .... and don't forget the stress on those higher gears in the box. Listen to your vehicle when you drive - you can hear (and even feel sometimes) when the motor or box is coming under strain. Your noise pedal position in relation to your speed is in itself already a good indicator when to shift.

[Johan Kriel]

And don't let in labour in 5th either. Gear down.