A question about speed...

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Here's a seriously newbie question for you. We picked up the MB and immediately drove 30 hours - so it was kind of a jump-in-and-try-to-swim sort of trip <g>... Once we were east of the mountains, we found that the van handled pretty well for its size and bulk, that it had reasonable acceleration, and that it seemed very happy cruising anywhere in the '70's. But when we had our flat tire, the guy who did the tire swap said, "Oh, I'd never think of going that fast in a rig like this - I wouldn't want to take it over 60-65." That was a surprise - I never gave speed much thought, since the rig didn't feel uncomfortable at any speed I drove it.

So - what speed do you cruise at, and do you have any speed that you consider a max? My impression is that the rig has its own max, in the low '80's, and I didn't push up there, after trying it once. But I'm curious whether anybody considers that the low to high '70's is too fast for this rig, lightly loaded, with 2 aboard.
 

pfflyer

Well-known member
Depends on what I have loaded but in your scenario lightly loaded (everything secured as well) and 2 aboard have felt safe in the mid 70's -80 but I leave a larger gap all around than I would in a car. I took a defensive driving course long ago and that is one of the things that stuck with me. I usually try to find a large gap in traffic and go with the flow trying to maintain that gap which is usually in that speed range. As far as max with no traffic and above scenario I would probably push 90-95 if she would go that fast and still feel safe.

Just looked at your profile and I need to clarify that mine is a cargo lightly loaded or semi-conversion (light camper <1000lbs) not a full blown conversion.
 
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chromisdesigns

New member
Here's a seriously newbie question for you. We picked up the MB and immediately drove 30 hours - so it was kind of a jump-in-and-try-to-swim sort of trip <g>... Once we were east of the mountains, we found that the van handled pretty well for its size and bulk, that it had reasonable acceleration, and that it seemed very happy cruising anywhere in the '70's. But when we had our flat tire, the guy who did the tire swap said, "Oh, I'd never think of going that fast in a rig like this - I wouldn't want to take it over 60-65." That was a surprise - I never gave speed much thought, since the rig didn't feel uncomfortable at any speed I drove it.

So - what speed do you cruise at, and do you have any speed that you consider a max? My impression is that the rig has its own max, in the low '80's, and I didn't push up there, after trying it once. But I'm curious whether anybody considers that the low to high '70's is too fast for this rig, lightly loaded, with 2 aboard.
I've driven our Coach House at least a few thousand miles at 65-70 with no problems. I usually try to stay at 65 for fuel economy, but she's very stable up through 70 mph. It begins to feel a little pushed in the handling department as it gets much over 70, not unsafe but just less stable. I've never had it up to the limiter.

One thing to watch is downhill grades, though -- you don't really feel the weight driving normally (one of the things I love about the Sprinter chassis), but when you hit a downhill curve at speed, you know it's there! I do try to heed the caution signs on grades, which I normally wouldn't care much about driving the car.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
I completely agree about downhills and curves - and I like the down/upshift setup on the shift lever - very easy to use - I'm a big fan of engine braking and not heating up and wearing out the brakes. What sort of mileage are you getting? When we came across from Nevada to Florida we were under some time pressure, and I was driving high 70's - mileage was between 14 and 15 mpg, usually about 14.5. Is that pretty much what you expect for mileage?
 

NelsonSprinter

Former Nelson BC Sprinter
I wouldn't go over 70, not high 70s, but 65-70 MPH in such a heavy rig.
Maybe 75 if it was an empty and straight freeway with no deer to hit, but as a rule max 70.
 

Old Crows

Calypso 2014 View Profile
Peter, IIRC, you have a newish LTV Unity 24MB....

We had a Ventura (class B) and it was comfortable and predictible around 63 (100kph) to 68, give or take. Between 17.5 and almost 21 mpg on many occasions. It would do fine at 70 on a smooth flat road and little wind. What I do... And have gotten my wife to do ... Is to constantly adjust your speed depending on road and wind conditions so that you give yor passengers a comfortable ride and you don't beat yourself to death trying to "herd" it down the highway. My upper limit is about 68-70 to avoid un-necessary stress on the equipment... Especially the tires. In the SW, it can be 100+ and the road surfaces 130+. High speed and heat kills tires and transmissions... So why push it if you don't have to?

Taking another view... To make a high average speed, you have to go very fast and not stop... Pushing over 65 just doesn't pay back in terms of miles made good or higher average speed. Then there's the cost in wear and tear and fuel consumption.

We're looking forward to travel in our View Profile. It should be a little more stable in winds, more challenging on rougher roads, and get 17 or 18 mpg. Still, it's about adapting to the conditions...
 

sailquik

Well-known member
Peter,
Since you are new to the Sprinter you may think that 14-15 mpg is pretty good. It's not! I get that kind of mileage towing a great big 7'wide V-Nose trailer @65-70 MPH. The trailer weighs ~4,500 lbs. but it's nearly as tall as the Sprinter and not tucked in at the top like the Sprinter so the aerodynamics is not good and the wind drag really kills the mileage.
If you want to get better mileage, and be able to monitor how hard you are really driving your Sprinter, get a Scan Gauge II (or similar).
It will tell you in real time what your % of engine load is, as well as your actual fuel consumption (fuel flow in GPH).
Little things like headwinds or slight uphill grades can double the amount of fuel you consume. Often you can manually downshift, increasing the RPM up into to the more powerful/more efficient 2600-3000 RPM range and get much better mileage and place a lot less stress on your Sprinter's engine and transmission.
We all like to downshift going down hills, but you have to understand your Sprinter has virtually no "engine braking".
If you had a Scan Gauge II you would see that the % engine load goes to zero (0); your fuel flow goes to zero (0); and your turbocharger pressure (MAP= Manifold Absolute Pressure) goes to ambient atmospheric pressure corrected for your altitude. If you choose BST (Turbo Boost in PSIG (Gauge)) you BST will drop to near zero (0) as well.
There is no real negative or braking effect here. Diesels make power when they get fuel so more power = more fuel. If you shut the fuel off, the engine is just spinning and that is all the engine braking effect you really get, but it's often enough, if you manually downshift and keep the RPM in the 2600-3000 range to hold your speed on downhill grades as you have a lot of wind resistance as well.
We need to get you to put your Sprinters description into your signature or take a photo and show us in your Avatar as there are so many different classes of Sprinter RV. Some are simple cargo van conversions....some have a lot of added up fitter bodywork, so what you may think is lightly loaded with 2 persons on board could be in a Cargo conversion weighing 7,500-8,000 lbs, or it could be in a fully upfitted with wider body class C that weighs 11,000-12,000 lbs.
Hope this helps,
Roger
 
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chromisdesigns

New member
I completely agree about downhills and curves - and I like the down/upshift setup on the shift lever - very easy to use - I'm a big fan of engine braking and not heating up and wearing out the brakes. What sort of mileage are you getting? When we came across from Nevada to Florida we were under some time pressure, and I was driving high 70's - mileage was between 14 and 15 mpg, usually about 14.5. Is that pretty much what you expect for mileage?
Mileage started out 14-15 mpg, occasionally high 13's. As it has broken in and I have learned how to drive it better, we are seeing high 15's to 16+. May see a little more improvement in the next 10K miles, too. I don't have a ScanGauge (SWMBO doesn't like gadgets, in general), but I do pay a lot of attention to RPM, how the rig feels, and grades. Basically, I drive it like I would a stick shift.

Interestingly, I invariably get better mpg on Shell Diesel, as opposed to the other major brands.
 

Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Thanks to all - lots to absorb here. First, I think I should now have a signature and an avatar of a sort <g>... - I thought I'd posted a signature already, but obviously not.

I have a tach, of course, but had no idea I should aim for a particular RPM range - I'll give it a try. It would be interesting to install a scan gauge - probably not in the cards immediately, as we're pretty maxed out from buying the rig, flying to Nevada to pick it up, and driving home. But Jean will be on board about trying to drive it as efficiently as possible. It's funny you should mention the scan gauge - I just spent several weeks trying to get an old car working with a modern fuel injection system, and spent hours looking at various maps and sensor readouts.

Thanks also for the advice on highway speeds - I think I was pushing the rig pretty hard, from what you're saying - we'll be looking for a comfortable speed range - fast enough to get there, slow enough to be safe and efficient - and it sounds like that range isn't going to take us much over 70...

I've had my head into the various RV manuals, trying to figure out all the RV equipment - but it sounds like I'd better start reading the Sprinter manual too - I'm new to diesels, lots to learn.
 

OrioN

2008 2500 170" EXT
Mileage started out 14-15 mpg, occasionally high 13's. As it has broken in and I have learned how to drive it better, we are seeing high 15's to 16+. May see a little more improvement in the next 10K miles, too. I don't have a ScanGauge (SWMBO doesn't like gadgets, in general), but I do pay a lot of attention to RPM, how the rig feels, and grades. Basically, I drive it like I would a stick shift.

Interestingly, I invariably get better mpg on Shell Diesel, as opposed to the other major brands.
I can get up to 25% less MPG with USA fuel, if I do not use a cetane improver.
 

mumkin

New member
I try to never be in a hurry to get anywhere, and accordingly set my cruise control at 65-68 mph. If I'm not using the cruise, I find myself getting up to 75-80 easily as it handles so well. But, common sense says that it isn't terribly smart as the margins for error aren't the same as one's car.
 

Old Crows

Calypso 2014 View Profile
Peter Tourin;273873 I'm a big fan of engine braking and not heating up and wearing out the brakes. [/QUOTE said:
Hi Peter... Re-reading the thread you started...

You might like to reconsider your technique.... Sprinter brakes are far, far less expensive than a transmission.... Also, the brakes can shed more heat, more quickly than the transmission's cooling system due to the excess slippage in the torque converter. What we are talking about is converting the stored energy of couple elephants on a sled into heat generated by the friction of the brakes. Yes, you could cook a Texas sized brisket with all the heat generated coming down a good hill! Best not to put that heat into the transmission. Better to let that energy be used up through the brakes. :thumbup:

Also, recall that engine braking in a diesel (except when equipped with a "Jake Brake") is near nothing, zip, nada, zero because of its design... Gearing down is useless in a diesel. All the effective deceleration is in the brakes. :thumbup:

Keep your speed low... Set a comfortable speed... Let's say 25 or 30. A speed that's just fast enough to not have to over use the brakes.

Keep an eye on the speedo... If it gets up to 35, apply the brakes firmly and just long enough until it gets down to 30. Do not ride or pussyfoot the brakes! On! and gradually press harder till you get to your comfort speed. Then off. Let the brakes cool....

Repeat as necessary to keep your speed under control. Never let your speed build up...

I try to brake on the straights to keep the rig balanced and slow to what I think is a safe speed to enter a corner with my slowest speed at the apex. If I have to jab the brakes in a last second adrenaline rush attempt to kill my speed as I'm entering a turn, I'm going way too fast. Everything should be nice and gentle as you come through the bend brakes off.

If you're still heading down hill, just let gravity work for you and let your speed build up to your comfort level. If you are exiting up hill this is where locking the transmission into a lower range 4, 3 or 2 will help... It lets you make a smooth transition from power off to power on... The transmission doesn't "hunt" for the right gear as you get on the power easing the shocks from hard shifting. :thumbup:

Just for fun, watch the brake lights of the guy in front of you..... They usually fly away on the down hill and then jam the brakes into and around a bend until they scare the pee out of themselves or passengers. Or, they ride the brakes down a long steep hill. They are doing it wrong!
 
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sailquik

Well-known member
Peter,
Your Avatar and signature are not posting very nicely!
Thanks!
I'm pretty sure the Sprinter-Source server software has gone back and put your current
Avatar and signature on everything you've posted since your first post.
Now we have a much better idea of what Sprinter you have!
Roger
 
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icarus

Well-known member
Hi Peter... Re-reading the thread you started...

You might like to reconsider your technique.... Sprinter brakes are far, far less expensive than a transmission.... Also, the brakes can shed more heat, more quickly than the transmission's cooling system due to the excess slippage in the torque converter. What we are talking about is converting the stored energy of couple elephants on a sled into heat generated by the friction of the brakes. Yes, you could cook a Texas sized brisket with all the heat generated coming down a good hill! Best not to put that heat into the transmission. Better to let that energy be used up through the brakes. :thumbup:

Also, recall that engine braking in a diesel (except when equipped with a "Jake Brake") is near nothing, zip, nada, zero because of its design... Gearing down is useless in a diesel. All the effective deceleration is in the brakes. :thumbup:

Keep your speed low... Set a comfortable speed... Let's say 25 or 30. A speed that's just fast enough to not have to over use the brakes.

Keep an eye on the speedo... If it gets up to 35, apply the brakes firmly and just long enough until it gets down to 30. Do not ride or pussyfoot the brakes! On! and gradually press harder till you get to your comfort speed. Then off. Let the brakes cool....

Repeat as necessary to keep your speed under control. Never let your speed build up...

I try to brake on the straights to keep the rig balanced and slow to what I think is a safe speed to enter a corner with my slowest speed at the apex. If I have to jab the brakes in a last second adrenaline rush attempt to kill my speed as I'm entering a turn, I'm going way too fast. Everything should be nice and gentle as you come through the bend brakes off.

If you're still heading down hill, just let gravity work for you and let your speed build up to your comfort level. If you are exiting up hill this is where locking the transmission into a lower range 4, 3 or 2 will help... It lets you make a smooth transition from power off to power on... The transmission doesn't "hunt" for the right gear as you get on the power easing the shocks from hard shifting. :thumbup:

Just for fun, watch the brake lights of the guy in front of you..... They usually fly away on the down hill and then jam the brakes into and around a bend until they scare the pee out of themselves or passengers. Or, they ride the brakes down a long steep hill. They are doing it wrong!

I respectfully disagree! Coming down a long mountain grade, use the old truck driver rule; go down in the same gear you would use to go up the same grade. While compression braking is less than a throttled engine, and way less than a Jake engine, the Sprinter does just fine by selecting the proper gear, and using brake judiciously. 30-50% of my driving is mountain grades, and I almost never touch the brakes.

Even using Crows technique, the heat will build up, and can glaze the pads and rotors. If you choose a lower gear, at the summit, the trans doesn't have to shift down hard or suddenly, som IMHO there is little if any added strain on the tranny. I would defer to tranny experts on that subject however.

Icarus
 

sailquik

Well-known member
Old Crows,
We have a bit of a difference of opinion here.
Manually downshifting and allowing the engine compression (without fuel or boost) hold a Sprinter back going downhill
does not cause a whole lot of torque converter slippage....in my experience.
So, downshifting on downhill grades does not cause trans fluid overheating.
Far more Sprinter NAG-1 (5G-Tronic) transmissions are "cooked" by lugging uphill at too low an RPM for the engine to
develop optimum power and fuel mileage.
When the engine is pulling hard @ < 2000 RPM, a limited amount of coolant is being circulated through the engine and the
transmission fluid heating and cooling coils in the lower radiator tank. So the engine temperature rises rather quickly.
Put a heavy trailer on the back of your Sprinter or put two tons + (4,500 lbs.) of cargo inside and lug up a hill sometime.
The coolant temp will increase from normal 180-190 deg. F to well over 210 deg. F in a couple of minutes.
If you manually downshift and get the RPM up in the 2600-3000 RPM range, you will see the temp come back down significantly.
If you get "over the top" of the uphill grade, and start down the downhill grade on the other side, and leave the transmission in 3rd or
4th gear, the temperature will drop back to the thermostat (normal) temp even faster than it went up due to lugging up the uphill grade.
There is some "resistance" with these little turbo diesels when coasting downhill @ 2600-3000 RPM because there is still compression
in each cylinder (only air being compressed here as no fuel/turbo boost is being added to create power).
As you suggest, Sprinters do not have any sort of "Jake Brake" to create negative power like the big 18 wheeler trucks.
A Jake Brake (short for Jacob's brake) actually changes the camshaft and injection timing in an engine to create negative power to
slow the truck down.
I wrote to Garrett Turbochargers (OEM equipment on all Sprinters) and they confirmed that there is NO provision for "engine braking"
in the turbochargers they supply to Mercedes for Sprinters.
Hope this helps,
Roger
 
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Peter Tourin

2020 Unity RL, ex 2012 Unity MB
Hey Roger - I don't understand this whole signature/avatar thing. I don't see my signature/avatar on any of my posts, so I can't tell what they look like. And I don't see anybody else's either. How come? - I must not be viewing the forum the same way you do. I've been going to "Sprinter-Forum > Sprinter-Based RV's & Conversions > Sprinter-Based RV Brands > Leisure Travel Vans > Unity" for all my posts.

Another thing - many of the replies to my posts seem to come from non-Unity people. How do they see my posts if they're not specifically looking in the Unity section? Are you guys getting posts by email or something?

I have to be missing something here...
 

Old Crows

Calypso 2014 View Profile
I respectfully disagree! Coming down a long mountain grade, use the old truck driver rule; go down in the same gear you would use to go up the same grade. While compression braking is less than a throttled engine, and way less than a Jake engine, the Sprinter does just fine by selecting the proper gear, and using brake judiciously. 30-50% of my driving is mountain grades, and I almost never touch the brakes.

Even using Crows technique, the heat will build up, and can glaze the pads and rotors. If you choose a lower gear, at the summit, the trans doesn't have to shift down hard or suddenly, som IMHO there is little if any added strain on the tranny. I would defer to tranny experts on that subject however.

Icarus
That's what I'm saying Vic. :thumbup: Same gear up as down. Stick it a gear and leave it. Diesels just don't have a lot of compression braking... You have to rely on the service brakes. I differ in the cause of glazing... Firm, periodic applications should not produce glazing. Pussyfooting, light long applications, will eventually polish the pad surface.
 

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