Gearing - up-changes are later than I'd expect

jeremy156

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I've just moved from a V6 petrol E320 (W210) to a I6 diesel E320 (W211).

In the old petrol car, the revs were always low around town, idle at 600rpm, gentle acceleration from standstill would see it drop into second at around 1200-1500rpm, all very very relaxing. Naturally with a bit more push with the right foot the revs went as high as needed, but I always liked the low revs when pootling.

In my new diesel, I've noticed it's a harsh sounding engine (no surprise following a V6 petrol) - but what particularly stands out is how much higher the revs climb before changing to the next gear. The same gentle throttle away from standstill now sees the car grinding away to 2-2500rpm before changing to second.

Just curious whether this is normal. I thought a diesel engine would drive more on low-rev-torque rather than rely on higher revs.

Both are 5-speed auto, by the way.
 
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jeremy156

jeremy156

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Ah, ok interesting - naturally it's when it was cold and noisy that I noticed this - I'll consiously take a look when it's warmed up next trip.
 

wemorgan

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I think diesels also take longer to warm up than petrols....might be wrong on that though.
 

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Just out of interest, is the same coolant sensor used for display and feedback to the ECU?
 

c240yaz

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I've just moved from a V6 petrol E320 (W210) to a I6 diesel E320 (W211).

In the old petrol car, the revs were always low around town, idle at 600rpm, gentle acceleration from standstill would see it drop into second at around 1200-1500rpm, all very very relaxing. Naturally with a bit more push with the right foot the revs went as high as needed, but I always liked the low revs when pootling.

In my new diesel, I've noticed it's a harsh sounding engine (no surprise following a V6 petrol) - but what particularly stands out is how much higher the revs climb before changing to the next gear. The same gentle throttle away from standstill now sees the car grinding away to 2-2500rpm before changing to second.

Just curious whether this is normal. I thought a diesel engine would drive more on low-rev-torque rather than rely on higher revs.

Both are 5-speed auto, by the way.
All diesels require a higher RPM or the they cannot reach the required torque to pull the car / truck. This is normal.
 

Dieselman

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All diesels require a higher RPM or the they cannot reach the required torque to pull the car / truck. This is normal.

How does that work out given that peak torque is reached much lower down the rev band. Max torque is 1900rpm.

My 300TD happily changes up a gear at 1500rpm hot or cold.

The only thought I have is that the O-P is pressing the accelerator as far as he used to in the petrol car and is exploiting the quicker acceleration so the gearbox holds for longer. Also it's worth remembering the diesel is running longer gear ratios.

Higher change point indicates lack of torque, possibly a MAF failing.
 

c240yaz

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How does that work out given that peak torque is reached much lower down the rev band. Max torque is 1900rpm.

My 300TD happily changes up a gear at 1500rpm hot or cold.

The only thought I have is that the O-P is pressing the accelerator as far as he used to in the petrol car and is exploiting the quicker acceleration so the gearbox holds for longer. Also it's worth remembering the diesel is running longer gear ratios.

Higher change point indicates lack of torque, possibly a MAF failing.
All diesels require a higher RPM or the they cannot reach the required torque to pull the car / truck. This is normal. It is a fact that a diesel engine requires a higher RPM to pull. Any diesel mechanic / quailfied tech knows this. I thought with your user name you would be in agreement ?

I have done numerous course which taught me this, namely Cummiings, Gardner, Volvo, Mercedes and most recently, Detroit Diesel. on Airport Fire trucks in Linz, Austria.

Maybe they were all wrong ?
 
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c240yaz

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Hmm..maybe. Especially given that most lorry engines only rev to about 1800rpm max.

Typical Actros engine.

max rpm = 2000, max torque at 1080 rpm.

An abundance of low revs torque is diesels biggest feature.
dieselman, I agree with that, fully.

Are you still running veg oil ? i am still curios about the diluting percentage.
 

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Dieselman

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Are you still running veg oil ? i am still curios about the diluting percentage.

I am at the moment but am likely to not continue.

The veg oil has a greater lubricity than engine oil but has a greater risk of polymerisation when cold which bothers me.

I've been checking the oil on the dipstick to see how it's coping and being a proper diesel specific oil it has a high TBN so is ok.

I've only been doing longer journeys recently so the engine has been hot all the time.

I'm going to change the oil and possibly install a bypass filter anyway.
 
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jeremy156

jeremy156

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Well, all warmed up and you're right it was holding the gear for longer when cold - but still I'm seeing it climb over 2000 rpm before changing up and I would say I drive with a *very* light foot most of the time, through being tight of wallet and not wanting to spend on fuel ;)

Good to hear reassuring sounds of "that's normal" and that it will adapt to my driving style over time. There's every chance the previous owner conditioned the car to full throttle driving? I know certainly that the dealer wasn't shy when we took the car out for a test drive!
 

PJH

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I suspect the gear change points are later so that the Turbo-Diesel stays ON Boost after the gear change.
My Colt 1.5 Di-D changes down at about 1,600 rpm, the revs are then approx 2,000 rpm in the lower gear. The 280E will poodle along at 1,200 rpm in top.
 
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