Most Economical Rpm For Diesel Motors

[jaideeguy]

I drive a 3 ltr Chev Colorado commonrail diesel automatic trans and am looking for the 'sweet sopt' for fuel economy now that I'm paying 3x what i paid 3 yrs ago. At 2k rpm, i can cruise at 100 kph on flat land and am wondering if that is the 'sweet spot' for economy. I am sure that any faster and i will consume more diesel, but am I pushing it at 2k rpm or should i slow down for optimum economy of our precious fuel?? what is the 'sweet spot' for diesel [truck] engines in rpm's or kph??

a couple of weeks ago, i did a economy check and determined that my fuel costs were just over 3 baht/kilometer....now it's more.

[wangsuda]

Back in "the day," when I had a Cummings 400, the sweet spot was between 1500-1700 RPM. Of course, it redlined at 2300 RPM. It all depends on your redline and your load. If you can stay 500-1000 RPMs below your redline, then that should be sweet (or the sweet spot).

[torrenova]

I've given up trying to get more out of my D-Max 3.0L auto 2WD as it does little more than 8km/l around town and 11/12 on a run. I reckon the aircon must be eating a lot as well but for me it's about Bt4 a km.

[Lickey]

I just done a quick search on the Chevy colorado, it gives an urban figure of 15 and 17 on motorway, you have a pick-up so of course you carry loads of 1750 lbs most of the time, why else would you want an automatic pick-up?

[jaideeguy]

Dmax and Chev = same engine and I get around 10-11 with mostly hiway driving. average speed on hiway is 100-110kph. How much could be saved by driving at 80-90kph??

and minimal load on pickup unless wife's family is visiting....then overloaded.

[initiala4]

Probably to reduce your fuel consumption is to check your tires and while driving it avoid doing wide open throttle. RPM wise, you will always want to shift half of the rpm tach with light load on the throttle.

[Jefferson]

Wait a minute, there's more going on here than the sweet spot for the engine rpm.. That sweet spot is important to know when switching gears, but for continued driving the major factor is wind resistance. So when you're driving at 100 km/h you use quite a lot more fuel.

I believe the sweet spot is actually closer to 60 km/h, in the highest possible gear of course. It varies per car, the taller the vehicle (4WD) and the more kit on it, the more wind drag is a factor. Rememebr that Isuzu often does those 'economy runs' where they drive from Hua Hin to Chiang Rai on one tank of fuel. People who win that do so by sticking it in 5th gear, going 60 km/h constantly and never ever hitting the brakes. ( They probably keep the aircon switched off and the windows shut as well. )

I've given up trying to get more out of my D-Max 3.0L auto 2WD as it does little more than 8km/l around town and 11/12 on a run.

That's really, REALLY high fuel consumption for that vehicle.. With that same engine I get 16-17 km out of a liter, and that's in a 4WD version! (When trying VERY hard, admittedly, so 60km/h, never hitting the brakes.

But anyway, as for optimum rpm when switching gears, for a modern common rail diesel engine this is basically 'as low as possible'. So that means switching gears real quick, WELL below 2000 rpm. Then once it's in top gear, try to never ever take it out of there again. So to get maximum fuel economy, you're not stopping for red lights and do corners pretty much like a F1 racing driver using every available square inch of the road, just a lot slower.

[Hog Head]

Max economy is usually at the torque peak of the engine.

[Carib]

Max economy is usually at the torque peak of the engine.

Yup, that is the answer. Check the powergraphic of the engine and you will find the max torque rpm.

Ofcourse a normal drive style will be important too.

[Tony121]

I have driven to malaysia a few times now, last time i went i sat the car at 100kmh and stuck to it, downside boring as f@#k upside saved a lot of fuel.

I filled my car up at the malaysian Thai border and got to koh samui with half a tank left !

[PattayaParent]

Dmax and Chev = same engine and I get around 10-11 with mostly hiway driving. average speed on hiway is 100-110kph. How much could be saved by driving at 80-90kph??

and minimal load on pickup unless wife's family is visiting....then overloaded.

On my petrol driven saloon I got 20% more distance dropping from 100 to 80kph. Just give iot a go on one tank of fuel and find out for yourself.

[Birdman]

[Rememebr that Isuzu often does those 'economy runs' where they drive from Hua Hin to Chiang Rai on one tank of fuel. People who win that do so by sticking it in 5th gear, going 60 km/h constantly and never ever hitting the brakes. ( They probably keep the aircon switched off and the windows shut as well. )

...and choose the day with most tail following wind, least traffic and the smallest driver without clothes and without...äh...everything which is unnecesary...to reduce weight.

Because my 4 month old 4x4 D-Max 3.0 LS auto makes 8-9 km/l. But it has a carryboy sportlid. (Actually it should help to save petrol according to their webpage. Before it was appr.10 km/l.)

BUT anyway I like the D-Max...

[Gary A]

Check your tachometer at 90 KPH when in high gear. I think the manufacturer has optimized fuel economy at that range. Some diesels red line at 3,000 rpm and others at 5,000 rpm.

[Ground Engineer]

About 2000 rpm on my old Tiger!

[Lickey]

Get to know your engine, when its crusin and happy, you wont hear it, try some gear skipping, pulling away in 2nd, roll it downhill, turn off air-con and roll down the rear windows, try to park it in shade and leave windows down i/2 inch, when its empty, pull away in 2nd, put in 4th, gather speed slowly, then 5th, feather the throttle all the time, till you reach the speed you want, learn to listen to your engine, when its happy, you are saving money.

[Hog Head]

About 2000 rpm on my old Tiger!

Must have had the orignal 2:88's

After 36 years, I still have my Tiger but left it in Canada as at the time, I could bring myself to sell it.

May do so now however.

[Lancashirelad]

Jaidee, several posters appear to have missed that your truck is auto.

Dropping your speed to 90kph will make a noticeable difference, yet at that, you are still making good progress.

I'd guess the revs will then be in the 1500-1700 range.

If it has cruise control, use it, that will help a lot.... it will make you concentrate on your driving more & maintain a constant speed. Remember, every time you slow down, you use more fuel to re-attain the cruising speed.

Look well ahead & lift off the gas early (or manually cancel the cc) when there is need to slow.

Releasing the gas pedal slightly when accelerating away will encourage it to change up at lower revs.