Thread: Who can tell fuel consumption of TD5 Auto when idling + AC on?

Lets do some rough Maths. No guarantees but should be ballpark-ish.

Rough average performance:
12 L/100 km at an average of 70 km/h and 2200 rpm and boost of say 0.8 bar.

That's the same as 0.7 x 12 = 8.4 L/h at average of 2200 rpm and 0.8 bar boost.

Assuming fueling is roughly proportional to boost (it isn't, but this is envelope maths) 8.4 / 1.8 = 4.7 L/h at no boost and 2200 rpm.

Idling at 750 rpm = 4.7 x 750/2200 = 1.6 L/h

Maybe 10% extra loading for A/C.

I would say 2-3 L/h is a fair value to do some estimation. Would be interested if anyone does the actual experiment.

Originally Posted by ScotchRocks

Lets do some rough Maths. No guarantees but should be ballpark-ish.

Rough average performance:
12 L/100 km at an average of 70 km/h and 2200 rpm and boost of say 0.8 bar.

That's the same as 0.7 x 12 = 8.4 L/h at average of 2200 rpm and 0.8 bar boost.

Assuming fueling is roughly proportional to boost (it isn't, but this is envelope maths) 8.4 / 1.8 = 4.7 L/h at no boost and 2200 rpm.

Idling at 750 rpm = 4.7 x 750/2200 = 1.6 L/h

Maybe 10% extra loading for A/C.

I would say 2-3 L/h is a fair value to do some estimation. Would be interested if anyone does the actual experiment.

Sounds quite logic with your calculation. I guessed it would be about 2.5- 3L /h from my TD5 when doing this. But I think my car is running idling at 670rpm (spot on 2nd arrow of 3 ones between 0 - 1000rpm in the dash) rather than 750rpm. Am I correct?

BTW, I always close windows and run Auto Aircon around 17-19 degree at 1-3 fan level whenever is in the car so the fuel consumption is not that really great around Sydney city with short trips (~13.8 - 14L/100kms). Still very happy though

What you need to know( around town especially) is at 690 rpm your auto is dragging first,,
Mine needs to do this a precaution, but I'm not idling around town for hours.

Originally Posted by Pedro_The_Swift

What you need to know( around town especially) is at 690 rpm your auto is dragging first,,
Mine needs to do this a precaution, but I'm not idling around town for hours.

Mine had that ~670rpm since the day I got it and it was slow. However, it has not changed rpm after I replaced MAF sensor and fitted CS2 tuning box then I never feel slow again from the red light unless the red light is at the bottom of a steep hill, and acceleration now is simply great.

I really never notice the rpm at idling until now, always thought it was a kind of 750rpm until I just found out there are only 3 arrows (333rpm interval) instead of 4 arrows (250rpm interval).

The rpm dial should be most accurate in the centre of it's range, when the ratio between signal and reference voltages is close, for rpm detection, signal loss to the instrument pack and accuracy of the dial itself. I wouldn't trust the accuracy under 1000 rpm. 750 could be 680 could be 500 could be 820.

That said I am not sure how complex the testing and validation of the equipment is at the factory. We see individualised algorithms for the unit injectors, so perhaps there is actual calibration of the rpm display before the vehicle left the production line.... 15 years ago.

From memory a Cummins signature 580 hp uses 4 lts an hour at idle, not that it's a td5 thou, just saying

Idling a diesel motor for long periods of time is Not a great idea, It tends to stuff them up

I had one of the Scanias today(G440), and it sat at 1.7lt/hr while warming it up.
So that's a 12+ lt motor.

Using that as the estimate, one quarter of 1.7lt = about 0.5lt(or thereabouts) .. so I'm guessing 0.5lt /hr.

Oh! ... I didn't have A/C running tho.