Diesel juddery at 30 in 4th

bigjl

Strider590 wrote: »

Diesel or not, 30 is too slow for 4th gear..........

Labouring an engine is worse than revving the nuts off it, both for engine wear and fuel economy.

I was driving home a couple of hours ago and noted that at 30mph the engine was revving at a perfectly adequate number of revs in 3rd and 4th. If you were not overly interested in acceleration and on flat ground it could pull 5th gear without complaint.

And this is in a 1.4i Berlingo Multispace which is not overly blessed with power or torque.

It depends on the car and the gearing.

A Vectra might struggle as they are pretty long geared.

I don't know which gearbox is in a 1.6hdi C5 but I doubt it has the hearing of a Vectra, probably more like he gearing of my Berlingo.

gilbert_and_sullivan

If its never had an air filter then doubt its seen a fuel filter either, sounds like a decent service wouldn't do it any harm.

Regular oil and filter changes? this is not an engine to neglect in any way or it will bite back.

I'd be inclined to run some injector cleaner of your choice (unless you subscribe to the camp who say they are all snake oil) though the system too.

Retrogamer

Strider590 wrote: »

Diesel or not, 30 is too slow for 4th gear..........

Labouring an engine is worse than revving the nuts off it, both for engine wear and fuel economy.

Depends on the gear ratios on the car itself. My dad's 106 1.5 diesel 30mph in 4th is perfect (3rd is a bit revvy) and 5th is fine as well if it's flat.
Same with my old Corsa 1.5TD i had.

But with more modern cars, the gear ratios seem to be a bit longer and 3rd is usually better.

BeenThroughItAll

Retrogamer wrote: »

Depends on the gear ratios on the car itself. My dad's 106 1.5 diesel 30mph in 4th is perfect (3rd is a bit revvy) and 5th is fine as well if it's flat.
Same with my old Corsa 1.5TD i had.

But with more modern cars, the gear ratios seem to be a bit longer and 3rd is usually better.

Exactly this.


I have a colleague who I was in a car with recently, who was religiously dedicated to the idea that at 20MPH you change to 2nd, at 30MPH to 3rd, at 40MPH to 4th and at 50MPH to 5th - because that's what her driving instructor had taught her in his car.


I pointed out to her that different cars have different needs, but she was unable to get her head around the idea, and the whole concept of gear ratios.


My old diesel workhorse of a ZX would happily trundle along at 30MPH in 3rd, 4th, or 5th without labouring. Equally, my old diesel V40 would have a fit at 30 in 4th.

onomatopoeia99

Strider590 wrote: »

Diesel or not, 30 is too slow for 4th gear..........

Labouring an engine is worse than revving the nuts off it, both for engine wear and fuel economy.

My diesel (Audi A6 with the 2.5tdi 24v engine that has chocolate camshafts) is fine in 4th or indeed 5th on the flat at 30mph, but 6th is best avoided. It depends on the gearing and engine torque characteristics. For whatever reason, Audi geared that model quite short compared to many diesels

I agree with your point about avoiding labouring the engine and am certainly not afraid of using all the revs, once everything is up to temperature. You won't find me banging a cold engine up against the rev limiter though.

bod1467

I had a Merc C220D (16 plate) hire car recently ... gearing on this was longer compared to my Golf (12 plate), so 3rd for 30MPH made sense in the Merc as this was about 1200 revs. In my Golf 30MPH in 4th is about 11-1200 revs.

neilmcl

bod1467 wrote: »

I had a Merc C220D (16 plate) hire car recently ... gearing on this was longer compared to my Golf (12 plate), so 3rd for 30MPH made sense in the Merc as this was about 1200 revs. In my Golf 30MPH in 4th is about 11-1200 revs.

The optimum power band for most diesel engines is around 1800-2200, driving around 1200 rpm and you will be labouring the engine and not doing a great deal for fuel efficiency.

bod1467

neilmcl wrote: »

The optimum power band for most diesel engines is around 1800-2200, driving around 1200 rpm and you will be labouring the engine and not doing a great deal for fuel efficiency.

If that's true, why do the manufacturer's themselves (via the car display) suggest an optimal gear for engine loading that puts the revs around 1200?

Retrogamer

neilmcl wrote: »

The optimum power band for most diesel engines is around 1800-2200, driving around 1200 rpm and you will be labouring the engine and not doing a great deal for fuel efficiency.

It'll cause premature wear on the DMF as well.
I found with my last car, 30mph in 4th gear felt ok at 1400rpm. I didn't feel it labouring.

Now i have a very similar car, same engine /gearbox but it has a SMF conversion and you can really feel it labouring on even the slightest incline / or change in speed. It seems on my old car, the DMF absorbed most of that so didn't notice it.

neilmcl

bod1467 wrote: »

If that's true, why do the manufacturer's themselves (via the car display) suggest an optimal gear for engine loading that puts the revs around 1200?

Mine doesn't. If driving in ECO mode, for example, it would be around 1500 rpm when prompted to change gear, certainly not as low as 1200. Driving with the rpm between 1500 and 2400 is the most economical for practically all diesel engines.