Service Issues: XC90 D5 engine DPF (Diesel Particulate Filter)

[RoyMacDonald]

Originally Posted by Timbo_1975

In reply to RoyMacDonald- you may like to drive for max mpg, but it is really not good practice, with any engine to not work them hard now and then.

Tim.
.

I'm not really driving for max mpg. I try to stick to the speed limits and the XC90 is only doing about 2200 rpm at 70 mph, and the max torque is at approx 2200rpm. Maybe I should go to Germany every month. :-)

Roy

[Timbo_1975]

Just hold it in 2nd or 3rd gear at 3000rpm+ with some bursts of full acceloration and the regen will occur as the exhaust gets hot enough - provided the journey is long enough...

Tim..

[RoyMacDonald]

Originally Posted by Timbo_1975

Just hold it in 2nd or 3rd gear at 3000rpm+ with some bursts of full acceloration and the regen will occur as the exhaust gets hot enough - provided the journey is long enough...

Tim..

If that's for me timbo I don't have a DPF thankfully.

One thing that occurs to me is won't the car accelerate slower if you'r not in the max power/torque band, which you won't be over 3,000 rpm?

Roy

[oilburner]

Roy, it doesn't quite work like that.

Power = torque x revs. So even though max torque has been passed beyond 3000rpm, the amount of power available will still increase right up to around 4000rpm, or so.

After that point, the revs don't increase enough to outweigh the drop in torque, so power drops off.

This means two things: 1) turbo diesels have lots of low down BHP because the torque kicks in very early (hence why they shift so quick at low engine speeds) and 2) diesels don't have as much BHP has a petrol engine with the same torque because petrols rev much higher.

Hope that clears it up a bit!



The formula to calculate power is: (Torque in LB/FT * RPM) / 5250 = BHP. That means that at 5250rpm (if your engine will rev that high, most diesels won't) the power and torque figures will always cross on a graph.

[RoyMacDonald]

Originally Posted by oilburner

Roy, it doesn't quite work like that.

Power = torque x revs. So even though max torque has been passed beyond 3000rpm, the amount of power available will still increase right up to around 4000rpm, or so.

After that point, the revs don't increase enough to outweigh the drop in torque, so power drops off.

This means two things: 1) turbo diesels have lots of low down BHP because the torque kicks in very early (hence why they shift so quick at low engine speeds) and 2) diesels don't have as much BHP has a petrol engine with the same torque because petrols rev much higher.

Hope that clears it up a bit!



The formula to calculate power is: (Torque in LB/FT * RPM) / 5250 = BHP. That means that at 5250rpm (if your engine will rev that high, most diesels won't) the power and torque figures will always cross on a graph.

Thanks but no it dosn't. The power graph shows the max at the same point as the torque max. After 2,200 revs it shows it dropping off considerably. Does it mean that the car will go faster even though it has less power, but more revs?

Roy

[oilburner]

Originally Posted by RoyMacDonald

Thanks but no it dosn't. The power graph shows the max at the same point as the torque max. After 2,200 revs it shows it dropping off considerably. Does it mean that the car will go faster even though it has less power, but more revs?

Roy

Sorry I disagree. Which power graph are you using? I'm using the one from the Volvo tech specs.

Have a look at:
http://www.volvoclub.org.uk/tech/XC90_Feb_2003.pdf

Torque is flat between 1750 - 3000 rpm, but power (the darker line) increases all the way to 4000rpm.
Bear in mind that graph is expressing torque in newton metres rather than pounds foot. The power and torque figures will cross at 5250, if the engine can rev that high, which the D5 obviously can't.

Honestly, power = torque x revs. Therefore higher revs = more power until torque drop off accelerates faster than revs are increasing.

Also see this for a more detailed explanation:

http://www.carkeys.co.uk/features/technical/636.asp

HTH!

[oilburner]

p.s. Roy, I don't mean to be patronising at all. Although it probably comes across that way!

I thought exactly the same as you until quite recently, and even when I'd read about how it really works, it still took me a week or two to get my head round it...

[RoyMacDonald]

Originally Posted by oilburner

p.s. Roy, I don't mean to be patronising at all. Although it probably comes across that way!

I thought exactly the same as you until quite recently, and even when I'd read about how it really works, it still took me a week or two to get my head round it...

No that's fine Pete...I was looking at the wrong graph. The Volvo one's clearer as it has both curves on the same graph. Now I understand the D5's power/torque relationship.

Wonder what the 185 hp and the V8 are like?

Thanks Pete.

Roy

[oilburner]

Originally Posted by RoyMacDonald

Wonder what the 185 hp and the V8 are like?

Roy

Only one way to find out...best way to feel how they drive is to find one... Must be a friendly Volvo dealer with a nice V8 on the forecourt somewhere...

[RoyMacDonald]

Originally Posted by oilburner

Only one way to find out...best way to feel how they drive is to find one... Must be a friendly Volvo dealer with a nice V8 on the forecourt somewhere...

I meant the power and torque curves. Guess I should have been more specific.

Roy