finding right cruising speed for economical gas mileage
We just purchased a used 2008 Winnebago View with 5400 miles. Does anyone know a good speed to travel at to get the most out of the mileage? It is a V-6 diesel motor.
Forum Discussion
Shark, I assume by "V-6 diesel motor" you are referring to the Mercedes Benz Sprinter 3.0 liter V-6 turbocharged engine (OM-642) and the five speed automatic transmission. Everything, including the variable output turbocharger is electronically controlled.
First... this engine does not have a 'torque peak'.... it generates the same torque from about 1700 rpm to 3700 rpm. There is no 'peak'.... so forget references to running at, above, or below peak torque.
Second.... the Sprinter drive train tends to keep the transmission up shifting sooner and keeps it in a higher gear... longer, when slowing .... than conventional automatics. I don't do a lot of shifting and just let the engine/drive train management pick the right gearing. On occasion you can get on the back side of the power curve...too slow, gear to high, rpm too low.. like going up a hill and the trans wants to stay in a higher gear than I sense is appropriate or slowing and making a turn in town... you step on it and it wants to bog down and then downshifts. When it's 'boggy,' I shift it down to keep the rpm up in the middle of the torque band. That is not often.
The concept there... without using add on engine monitors and getting more wonky and complicated or increasing the cockpit workload is to keep the engine rpm within the 2200 to 3500 rpm band. Or, simply... keep the tach needle between 11:00 and 12:00 o'clock on the tach. Anywhere in the 'band' is fine and that depends on grades, speeds and headwinds, etc., etc.. It's a balancing act....
As far as the old saw about not running in OD (5th)... that is non-sense that started 30 years ago and just doesn't seem to go away. There were reasons 'back in the day' for not running OD... among which was that the american transmissions were weak designs and just couldn't handle it. Unless your operator manual specifically recommends not running OD under some conditions keep it D. With the Sprinter... it will run all day in 5th at highway speeds. Running OD reduces... most of the time the fuel burn. There are occasions when you might want to go to 4th... you are battling a 30 mph head wind. Put it in D and forget it... unless the rpm drops.
Our VP and old "B" with the Sprinter chassis seems to run most efficiently around 2400-3200 rpm. In the VP 2400 is about 63 to 65 mph .
The three things that increase fuel burn, IMHO, are: weight, high speeds, headwinds. Reduction in weight carried will improve your fuel burn. Moderate speeds will improve your fuel burn. Headwinds increase your fuel burn but you can manage that by adjusting your speed downward (still keeping a safe speed)to avoid 'fighting' the headwind. Got a tail wind...? Yeah... push it up a bit.
The problem here is the shape of the rear of the RV. It's a box. Not good for aerodynamics. The faster you go the higher the drag due to the low pressure 'bubble' that forms behind the square box back of the vehicle. Not a heck of a lot to do here other than to keep the speeds reasonable.
ALSO.... since it is a new to you Benz with the beautiful OM-642 direct injection turbo diesel.... you need to follow the MB recommendation of using ONLY MB specification 229.51 oil. NEVER>>>EVER>>>EVER a non 229.51 spec oil in your engine. Not a single drop!!!! 229.51 is required to keep the diesel particulate filter and egr systems from clogging up. Mobil Formula M is what MB stores use. Valvoline has one. Lubri-Moly 229.51 is available from NAPA. And there are on line stores who carry it.
If you are a DYier .... use only Hengist or Mann filters (NAPA).
First... this engine does not have a 'torque peak'.... it generates the same torque from about 1700 rpm to 3700 rpm. There is no 'peak'.... so forget references to running at, above, or below peak torque.
Second.... the Sprinter drive train tends to keep the transmission up shifting sooner and keeps it in a higher gear... longer, when slowing .... than conventional automatics. I don't do a lot of shifting and just let the engine/drive train management pick the right gearing. On occasion you can get on the back side of the power curve...too slow, gear to high, rpm too low.. like going up a hill and the trans wants to stay in a higher gear than I sense is appropriate or slowing and making a turn in town... you step on it and it wants to bog down and then downshifts. When it's 'boggy,' I shift it down to keep the rpm up in the middle of the torque band. That is not often.
The concept there... without using add on engine monitors and getting more wonky and complicated or increasing the cockpit workload is to keep the engine rpm within the 2200 to 3500 rpm band. Or, simply... keep the tach needle between 11:00 and 12:00 o'clock on the tach. Anywhere in the 'band' is fine and that depends on grades, speeds and headwinds, etc., etc.. It's a balancing act....
As far as the old saw about not running in OD (5th)... that is non-sense that started 30 years ago and just doesn't seem to go away. There were reasons 'back in the day' for not running OD... among which was that the american transmissions were weak designs and just couldn't handle it. Unless your operator manual specifically recommends not running OD under some conditions keep it D. With the Sprinter... it will run all day in 5th at highway speeds. Running OD reduces... most of the time the fuel burn. There are occasions when you might want to go to 4th... you are battling a 30 mph head wind. Put it in D and forget it... unless the rpm drops.
Our VP and old "B" with the Sprinter chassis seems to run most efficiently around 2400-3200 rpm. In the VP 2400 is about 63 to 65 mph .
The three things that increase fuel burn, IMHO, are: weight, high speeds, headwinds. Reduction in weight carried will improve your fuel burn. Moderate speeds will improve your fuel burn. Headwinds increase your fuel burn but you can manage that by adjusting your speed downward (still keeping a safe speed)to avoid 'fighting' the headwind. Got a tail wind...? Yeah... push it up a bit.
The problem here is the shape of the rear of the RV. It's a box. Not good for aerodynamics. The faster you go the higher the drag due to the low pressure 'bubble' that forms behind the square box back of the vehicle. Not a heck of a lot to do here other than to keep the speeds reasonable.
ALSO.... since it is a new to you Benz with the beautiful OM-642 direct injection turbo diesel.... you need to follow the MB recommendation of using ONLY MB specification 229.51 oil. NEVER>>>EVER>>>EVER a non 229.51 spec oil in your engine. Not a single drop!!!! 229.51 is required to keep the diesel particulate filter and egr systems from clogging up. Mobil Formula M is what MB stores use. Valvoline has one. Lubri-Moly 229.51 is available from NAPA. And there are on line stores who carry it.
If you are a DYier .... use only Hengist or Mann filters (NAPA).
