Diesel fuel questions

As I mentioned in another thread we are getting a new RV and it has a diesel engine. I am completely unfamiliar with diesel so there are a ton of questions that I have and I am hoping that people on this forum can clarify some stuff for me.

The RV has a sticker on the dash that says to use only Ultra Low Sulphur fuel. The sales guy said that all diesel fuel in the US is low sulphur. The question is whether there are multiple types of diesel fuel (low sulphur and ultra low sulphur) like there are different grades of gasoline, or if low sulphur and ultra low sulphur are the same.

Does diesel fuel need a stabilizing additive like gasoline? I live in the desert southwest of the US and during the summers the temperatures are often over 110, and if I do not add some stabilizer to the gas in our current RV it tends to leave deposits and that becomes an issue. Do I need to do the same with a diesel?

I test drove the RV and it handled really well and had plenty of power, but I noticed that the tachometer showed about 2700 rpm when I was doing 60-65mph. That seems high compared to the revs in our current gas RV which runs about 2000-2100 at the same speeds. Is that normal for a diesel?

Are there additives for diesel fuel as there are for gas engines? And, if so, are any of them worth considering?

One good thing is that the dash display on the diesel RV showed great fuel economy while I was test driving, and perhaps it will get me much better than the 13-15 I get with the Ford V-10.

Thanks for any help.

instead of mom and pops go to truck stops for fill ups---5 years down the road you'll know all ya need to know concerning that diesel

We have a diesel pick up truck. This is our first one and it's been a real eye opener as to the variety of diesel fuel out there. ULS diesel is normally identified as Diesel #2. Normally. Sometimes you have to read the fine print on the pump. There are other diesel fuels you want to stay far away from. Most of those are for farm and industrial equipment and are fairly obvious as to what they are. I'm not even sure if I can use biodiesel in my truck. It doesn't seem like it based on my research so far, so I just haven't tried it.
I don't know about additives. Ours is a 2016 truck and it lives in 4 seasons that do get over 100 in the summer and snow/ice in the winter and we've never added any sort of additive. The only thing we add is DEF, but that is a separate tank and is for the exhaust not the fuel.

    It would help if you could tell us what year the RV is and what make and model the diesel engine is, as older models and different engines do  have different needs.  While virtually all stations have switched to low sulfur, there may be still a few which still carry the older style fuel as older farm equipment can use it and it is much cheaper to produce.  All that to say, keep your eyes open at the pump.
    As for RPM or milage, it is impossible to tell you what to expect.  RPM is a result of gearing of the transmission and the rear end, but usually diesels are higher torque with lower RPM.  Milage is motor, weight to horsepower, wind, speed, and a lot more.
    There are diesel specific additives and stabilizers, but I rarely used any, including when we winterized.

Ed

All Highway-use diesel fuel sold in the USA (and Canada) is ULSD (Ultra-Low Sulphur Diesel), so no worries there.  It is frequently 5-20% biodiesel as well and that is acceptable for diesel engines made since around year 2000. If yours is older, it may be worth checkig with the engine manufacturer if you encounter fuels over 10% biodiesel.

Diesel fuel does generally not need additives of any sort, especially in a low-humidity environment. Diesel can be affected by a moisture and an algae sometimes grows in it in hot humid climates.  A full fuel tank helps avoid moisture problems, and a stabilizer never hurts if the coach will not be driven for a 3+ months.  Do NOT start the engine just for exercise.

Diesels produce their rated horsepower at lower rpms than a gas engine.  2700 rpms sounds rather high for a diesel, but you didn't identify what engine & transmission you have so its hard to judge.  My 400 hp Cummins ISL ran at 1600 rpms for 65 mph.

Mike, need more info. what were  you driving?
Bill

Hfx_Cdn said:

    It would help if you could tell us what year the RV is and what make and model the diesel engine is, as older models and different engines do  have different needs.  While virtually all stations have switched to low sulfur, there may be still a few which still carry the older style fuel as older farm equipment can use it and it is much cheaper to produce.  All that to say, keep your eyes open at the pump.
    As for RPM or milage, it is impossible to tell you what to expect.  RPM is a result of gearing of the transmission and the rear end, but usually diesels are higher torque with lower RPM.  Milage is motor, weight to horsepower, wind, speed, and a lot more.
    There are diesel specific additives and stabilizers, but I rarely used any, including when we winterized.

Ed

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2017 Winnebago ERA. The spec sheet for the current model  (which is all I can find, but which is probably the same) is

3.0L 6-cylinder, 188-hp, diesel engine, 5-speed automatic Tip Shift transmission, 220-amp. alternator

If diesels are supposed to run at lower rpms, then perhaps there is an issue here as 2700 rpm seems quite high to me for 65 mph.

There is a difference between low sulfur diesel and ultra low sulfur diesel.  Low sulfur diesel allows up to 500 ppm (Parts Per Million) while ULTRA low sulfur only allows 15 ppm.  The salesman you were talking to was just using the language sloppily.

As other's here have said, ALL highway diesel in the US and Canada is ultra low sulfur.  I'm not sure about farm, off road, or marine diesel, but you're not supposed to be using that on the highways anyway.

Mexico used to be low sulfur, which caused problems for people who went down there for the winter, but the latest reports say that Mexico is mostly switched over and will be 100% ultra low sulfur diesel by the first of the year.

I'm not sure what you would find if you pushed further south into Central America, you'd have to research the issue if it ever comes to that. 

I test drove the RV and it handled really well and had plenty of power, but I noticed that the tachometer showed about 2700 rpm when I was doing 60-65mph. That seems high compared to the revs in our current gas RV which runs about 2000-2100 at the same speeds. Is that normal for a diesel?

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You didn't indicate what RV you're talking about, but 2700 is definitely high even for max RPM on a diesel, let alone a 65 mph cruise. Perhaps you were downshifted when you checked the RPM?

My Beaver was redlined at 1800 RPM, but most that I've seen (including my Ventana) are 2200-2500 redline, with an exception here and there.

The Era has the Mercedes 3.0L V6, so yeah, they rev a bit higher than the larger diesels found in Class A coaches.  No worries, the engine and tranny have been matched to utilize the torque & Hp optimally.

Ahh, I'd not seen the other thread, I guess, so didn't know it was a Sprinter. Thanks...

Mike, when you get your new motorhome it should have manuals, not just for the motorhome such as appliances, but also for the chassis etc.  I drove the first 1,700 miles while Jerry read the stack of manuals that came with ours!

ArdraF

I too have a 2018 Fleetwood Pulse on the Sprinter 3500 chassis.  Brand new to me.  It does have the 3.0L 6 cylinder and it runs around the rpm you talking about.  I have done 1 long trip (400+) miles and averaged around 14 mpg running at 70 mph.  I think I will try 65 mph and see what the rpm is and mileage I get.

djlewis said:

I too have a 2018 Fleetwood Pulse on the Sprinter 3500 chassis.  Brand new to me.  It does have the 3.0L 6 cylinder and it runs around the rpm you talking about.  I have done 1 long trip (400+) miles and averaged around 14 mpg running at 70 mph.  I think I will try 65 mph and see what the rpm is and mileage I get.

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Your mileage is interesting.

In looking at these RVs we saw and test drove both a used 2017 with about 5000 miles and a new 2018 with about 2200 miles (from driving it from the factory according to the sales people). We first tried the used model and I noticed that the trip odometer mileage showed about 15.8 mpg which seemed to be for 3800 miles or so (so the values were never zeroed and this included all of the miles for that distance) and the new one gave me about 15.5 for the test drive on one of the local highways. I drove both on the same route with about the same speeds, and both yielded somewhere around 15.5 mpg, although the used one already had so many miles on the trip odometer that I am not sure that the final value represented my driving. That is not bad, but it is not the 18-22 mpg that people talk about.

The sales people talked about a mileage increase due to "breaking in" the engine but I do not believe that is valid for diesels. It used to be true for gas engines, but I am not sure it still is with the modern engines so I assume 15-16 is what I should expect at 65-70 mph driving on relatively flat terrain. My old class B (2005 Pleasure-Way, Ford gas V10) usually gives me about 13.5-15 on the highway so I do not see much difference between the gas and the diesel.

I would be interested in seeing any new information you get about your mileage. Thanks for letting me know.

All on-highway diesel sold in the US is ULSD.  What you want to stay away from is red-dyed OFF highway diesel for engines that are used for things like construction and farm machinery that don't go on road.  Off road use includes the diesel refrigeration units in refrigerated trucks so sometimes truck stops will have a Off Highway pump to supply them.  Off highway diesel is cheaper because it doesn't include highway taxes in the price, but there are steep fines if you're caught with red dyed fuel in your on highway tank.

It's cold weather, not hot that causes problems with diesel fuel so it comes in two grades, depending on the temperatures where it will be used.  #2 diesel is the normal grade and it's used when the temperature will stay above 32F.  Below that it forms wax crystals that will clog your fuel filter until the fuel warms back up and they return to their liquid state

Winterized or #1 diesel is sold in areas where the temperatures are expected to go below freezing.  It's thinner than #2 diesel, and continues to flow below freezing.

You can use Winterized diesel in warm weather, but it contains less energy than #2 diesel so you'll get slightly less power and MPG.

Usually diesel stations in an area will automatically switch from #2 to winterized fuel before sub-freezing temperatures hit.  But you want to be careful about filling up with a tankful of #2 fuel in a warm area, then driving into sub-freezing temperatures ... say driving from the hot desert into the mountains in the fall, then letting the rig sit there until winter.

MikeFromMesa said:

2017 Winnebago ERA. The spec sheet for the current model  (which is all I can find, but which is probably the same) is

3.0L 6-cylinder, 188-hp, diesel engine, 5-speed automatic Tip Shift transmission, 220-amp. alternator

If diesels are supposed to run at lower rpms, then perhaps there is an issue here as 2700 rpm seems quite high to me for 65 mph.

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The large diesel engines used in diesel pusher motorhomes and over the road trucks run at lower RPMs due to the larger, heavier moving parts inside them.  Smaller, lighter engines can run at higher RPMs.  For example, the smaller 1.6-1.8 liter diesels used in VW cars redline at 6000 RPM.

That engine produces 188 HP at 3,800 RPM with a 4000 RPM redline.  Peak torque is achieved between 1400 - 2400 RPM, so 2700 RPM at 65 MPH sounds about right considering it's working hard to move a heavy, boxy motorhome down the road.

https://assets.mbvans.com/Freightliner/Brochures/MY17-FTL-Sprinter-Brochure.pdf

I have driven an F350 diesel for 16+ years.  I have never been worried about the type of diesel, other than a while ago Bio diesel had some issues.  If they sell it at a pump designed for vehicles, you can use it.

Use #2 diesel for weather above ~20 degrees.  #1 diesel for when it starts to get below that.  Be aware of filling up in warm weather down south and driving north.  There are additives that can be used to prevent diesel gelling.  Most #2 diesel has additives that prevent gelling anyway.  You can mix #1 and #2 fuels without issue.  Most pumps in cold weather sell a blend anyway.

Red diesel is un-taxed.  It works fine too, if you get caught using it you can get a fine.  Pumps are clearly marked.  Even kerosene can be used in a pinch.  Kerosene is like maybe #0 diesel.

Lou Schneider said:

Usually diesel stations in an area will automatically switch from #2 to winterized fuel before sub-freezing temperatures hit.  But you want to be careful about filling up with a tankful of #2 fuel in a warm area, then driving into sub-freezing temperatures ... say driving from the hot desert into the mountains in the fall, then letting the rig sit there until winter.

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I live in southern Arizona and make frequent trips into the mountains here, Utah, New Mexico and Colorado, but never in the Winter. We try to camp when the night temperatures are not too hot, but not when it drops below about 40 F so perhaps #2 is all we will need.

Senator said:

I have driven an F350 diesel for 16+ years.  I have never been worried about the type of diesel, other than a while ago Bio diesel had some issues.  If they sell it at a pump designed for vehicles, you can use it.

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Does that mean that I do not need to worry about fuel stabilizers when storing my diesel RV in the summer? Temperatures here often get well above 110 F and I had problems with gasoline in both the engine and especially the generator during the summer if I did not run them once or twice a month unless I used a fuel stabilizer.

MikeFromMesa said:

Does that mean that I do not need to worry about fuel stabilizers when storing my diesel RV in the summer? Temperatures here often get well above 110 F and I had problems with gasoline in both the engine and especially the generator during the summer if I did not run them once or twice a month unless I used a fuel stabilizer.

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Diesel fuel lasts a LOT longer then unleaded gas.  If you are only going to go three or four months or so, you should be fine.  I do not know the actual answer, but I have run a torpedo heater with diesel fuel that was 10+ years old.