2015 Itasca Viva: Gas vs Diesel

[avanti]

Originally Posted by Davydd

the Sprinter readout is not accurate other than projected over time if same conditions were constant that would be the MPG based on that one singe moment condition.

Davydd,
My 2014 I4 Sprinter has a mode in which it shows the average MPG since the start of a trip. I assume that this should be quite accurate, since it is using the same data that the van uses to set the fuel gauge. (Yes, I know this is hard to believe, but modern Sprinters do not actually measure the amount of fuel in the tank, except immediately after a fill up). I do admit, though, that I have never actually checked it for accuracy.

[Davydd]

Originally Posted by avanti

Davydd,
My 2014 I4 Sprinter has a mode in which it shows the average MPG since the start of a trip. I assume that this should be quite accurate, since it is using the same data that the van uses to set the fuel gauge. (Yes, I know this is hard to believe, but modern Sprinters do not actually measure the amount of fuel in the tank, except immediately after a fill up). I do admit, though, that I have never actually checked it for accuracy.

I record every fill-up. I can tell you the computer is not accurate. The best thing you can get out of the computer is to readily see how speed affects your consumption.

Fuel mileage in my Sprinter is highly variable. There are many factors that go in. I am coming to believe the biggest one is the quality of diesel from around the country, whether it has bio-diesel and what percentage, what company, what refinery or who knows what. On my last trip I was hitting close to 19 mpg on three fill ups in a row driving on mostly similar conditions level freeway at a constant speed of about 65 mph. I got to Illinois and filled up with bio-diesel and the mileage dropped to 17.6. Conclusion: bio-diesel sucks and is a major consumer scam. That wasn't just this one time. I have noted it numerous times. Normally, from experience I try to drive through Illinois without stopping as I do in my home state of Minnesota as well. I fill up at the neighboring border state before going home and try to not fill again until I leave the state on a trip.

Wind definitely affects it. Mountainous or hilly driving affects it as up and down really don't even out. Obviously speed is a big factor.

[avanti]

Agree about biodiesel.

I posted because your original msg seemed to be describing instantaneous MPG readings. Have you compared your computed values with the trip-level averages that I described? I have been curious about the accuracy of the latter.

[Davydd]

Originally Posted by avanti

Agree about biodiesel.

I posted because your original msg seemed to be describing instantaneous MPG readings. Have you compared your computed values with the trip-level averages that I described? I have been curious about the accuracy of the latter.

It can be all over the board. Last week on my 1,900 mile trip the computer was not keeping up with the true average. You have to drive I think at least 200 miles for the computer to catch up to the real average. I do carefully fill not to when the automatic pump stop goes off but to the same fill level as possible each time. Of course the best average is to take it over several fills totaled together to get a reliable expected average.

In answer to your question. Get a long stretch of same highway. Drive 70 mph for a while and then drop drastically down to 55 mph. You will see the change for the better. It is more predictive than averaging previous driving results. That is also why many times the actual results will be better than the computer readouts. The computer does give you some indication of relative performance. Things like seeing the differences in fuels as I mentioned, speed, head winds, city driving, and mountainous driving.

Another factor is the computer starts all over each day or whatever time period it is set at. It has to build an average so always starts out low and needs those miles I mentioned to build. If you use your diesel fired Espar for heat or hot water that is going to mess up your average as well. Surprisingly it is not all that much unless you are camping in very cold weather and running heat pretty hard all night.

[booster]

I don't know all the little intricacies of the factory systems, but we use the trip computer part of the our Scangauge a lot.

The Scangauge has a few different calculations going on:

Current trip is since the vehicle was started and not shut off, also has manual reset to zero

Today trip is since the vehicle has been run after sitting 8(?) hours

Yesterday trip is time from the day before the 8 hours

Tank trip is since you manually reset the tank trip when you filled up with gas.

We had all the issues that have been discussed here related to not getting the tank the same amount full when comparing, low amount of miles within each test affecting accuracy, etc, etc.

We made a change in how we use it to get a huge amount of data so the accuracy is greatly improved. Last year we had the Scangauge information for 7500 miles continuous. Miles and mileage. We also had the odometer mileage and kept track of total gas for the trip.

What we do now is fill the tank as we are leaving, and reset the tank trip. After that we never touch the tank trip until we are almost home when we fill again. We are talking 500 gallons of gas fill, so good averaging. We also know exactly how far the van odometer is off as we tested it against the GPS, and the Scangauge is calibrated to be accurate for odometer. We generally match within 1%.

Averaging over lots of miles and fills is the only way you are going to get really good information. Now that we have the right correction factor in the Scangauge, it is very accurate for us.

[35603]

I have 136" wheelbase diesel Promaster that has been converted to a class B. The conversion added about 1800lbs to the van. Also this van is 18' long, about three feet shorter than the Travato. I got about 27mpg before the conversion and about 24mpg after. This is interstate driving with cruse set between 65-70. I didn't use any extraordinary measures to increase my mileage. Of course city driving will reduce this by 1-2mpg.

[papab]

I have a diesel PM 159ext campervan conversion. Driving economically & rarely over 70 I've been averaging about 25. I might be able to get 27 with good conditions, very few stops and driving less than 60. I compute it from miles/gallons. The actual mpg's are usually about 1mpg better than the van computed number.
I liked the diesel transmission better than the gasser, that's 1 of the reasons I went this way. I think it's quieter too. I think it could be a great vehicle if it becomes reliable. I can't say anything good about FCA customer service though.