Lower LOD when cruising in 4th rather than D

Thanasis

Active member
On my most recent trip, I noticed that when traveling at speeds between 55 to 65 mph with everything else (grade, wind) being almost equal, and downshiftingt from D to 4th, the LOD will drop by as much as 20%. The only exception was in downhill driving.
I have been routinely downshifting on steep uphill driving when my LOD would go over 85-90, but now I wonder if I should be doing so more often to archive lower LOD and better mileage.
This is not the behavior i would have expected...What you folks think?
 

TQUIN45

TQUIN45
Would you mind defining LOD???

Sorry I am so inexperienced but what does L O D stand for??? I understand he is down shifting which raises the engines RPM. Is he doing it for braking or to improve his fuel economy???
 
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autostaretx

Erratic Member
Downshifting does two things:
(a) gives the engine more mechanical advantage due to the lower gear (less engine energy needed to turn the tires)
((added: as sailquik is about to say, the overdrive (0.83:1 Ratio) -to- 4th's 1:1 is a 20% change))
(b) at certain speed ranges, may bring the engine RPMs up to a more efficient spot on the torque/power curve.

For my T1N with OEM 15 inch wheels, 5th gear at 65 mph is 2553 rpm
Downshifting to 4th raises that to 3076. (the numbers for 55mph are 2160 and 2603)
(16 inch wheels will lower all of those numbers)

... and at the moment, i can't find an image of the T1N power curve... i'll come back and edit that in when i find it...

--dick
 
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sailquik

Well-known member
TQUIN45,
LOD is an acronym for percentage of engine LOAD at the current RPMs.
As suggested, in the 55-65 mph range, some significant gains in fuel economy can be realized if you are pushing into
headwinds, going up a grade, towing a trailer with significant wind drag (outside the profile of the Sprinter), or heavily loaded in the interior.
It's very easy to see if you can get better fuel mileage with a manual downshift.
Set the PID (Parametric Identification) LOD in the upper left readout on your Scan Gauge II... set the the PID GPH (or MPG) in the lower left readout.
When you make the manual downshift out of overdrive and into 4th gear (1:1 ratio), you will see the % LOD change (normally slightly to significantly lower).
Then take a look at the your GPH reading.
If you are using a significant amount less fuel...leave it in 4th gear (1:1 Ratio through the transmission).
If the change is < -5% LOD or <-0.3 GPH, might be worth while to shift back into OVERDRIVE (D... 5th gear in a NAFTA Sprinter with the NAG-1 transmission is always an overdrive (0.83:1 Ratio).
If you set MPG, the mileage may improve/increase when you downshift, but I have found that GPH is easier to understand, read and follow while driving.
Hope this helps,
Roger
 
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Boater

New member
I'm going to have to get me one of these gauges eventually, I have been trying to work out for ages whether or not I upshift too soon (all my gear shifts are manual) and just trying to change gear at different points on the rev counter for a whole tank of fuel doesn't cut it - mainly because I forget my plan within 5 minutes of starting a journey.....
 

sailquik

Well-known member
Boater,
The Scan Gauge II or similar performance monitoring gauge systems/packages would show you very quickly where the sweet spot
in the power curve really is, and once you determine where to upshift and downshift, you will be able to realize some savings at the fuel pump. How much....varies with the driver, the loads, all sorts of factors, but the SGII will allow you to monitor what's happening in real time an make smart adjustments to the current situation.
The "conventional" wisdom is to up shift at the peak torque RPM.... but that is for engines where the peak horsepower RPM is nearly the same as the max torque RPM......Not 800-1200 RPM higher.
IMHO, the NAFTA 5 cylinder (OM-612 & OM-647) Sprinters get the best mileage @ ~ 2800-3250 and the NAFTA V6(OM-642) Sprinters get the best performance/efficiency @~ 3000-3400 RPM.
Both of these figures are well above the 2400 peak torque RPM, so perhaps the "conventional wisdom" does not apply quite so universally to the smaller higher revving emissions controlled common rail turbo diesels found in Sprinters.
And, if my research is correct the even smaller OM-651 dual turbo (larger and smaller) will continue this trend in 2014 with a much smaller 2.1 liter package that puts out max. torque @ 2400 RPM and peak horsepower @ 3600 RPM.
It will be very interesting to see what the US government EPA testing does to the performance of the EURO 6 OM-651.
Roger
 
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Old Crows

Calypso 2014 View Profile
Prover, I think the "conventional wisdom" only applies to gas motors. It's a long held "truth".... OTH, it's also a "school solution to "short shift" the up shift at as low rpm as you can and to get into the highest gear as soon as you are able. Don't think that applies to diesels either.

Diesels and some turbo gas engines have flat torque curves from off idle to near max RPM... The intersection of the torque non-curve and the horsepower curve become meaningless, IMHO. Rethinking it... best to stay in the middle of the torque "plateau" with a light foot and forget about the horsepower..

Adding more fuel to a diesel makes more power but consumes more fuel. Maybe another way of looking at your LOD theory is to consider that the van is sometimes over geared for the load, speed, road conditions. While you are not lugging the engine you are deeper into the fuel map to make the power you need for that situation. Down shifting puts less of a load on the engine (better mechanical advantage by being in a more appropriate gear) and the engine management computer lessens the fuel used accordingly. Appropriately, the LOD drops.

Have you considered using Lbs/Hr fuel burn as an alternative indicator? It would seem that LOD would change too rapidly to be useful. Fuel burn might be more representative of the actual load on the engine. Higher burn rate = deeper fuel mapping = more load.... And it's direct reading.
 

owner

Oz '03 316CDI LWB ex-Ambo Patient Transport
%LOD is really just the percentage of available power you are using at that particular rpm/load point. It doesn't mean you have less load, the van is still doing the same amount of work in the real world. In your case by dropping to 4th its just doing less work more often.

The biggest difference in what you're doing by dropping into 4th, is changing to a 1:1 gear ratio in the box. This is only relevant when you are under real load, not when cruising.

When cruising you want to minimise friction and pumping losses, which means lower rpm.
 

Thanasis

Active member
Thank you all of you for taking the time to comment. What I concluded from discussion so far, is that overriding the transmission is advisable ANY TIME metrics like GPH or LOD favor a shift up or down.
This , then, brings up the question of what were the criteria the MB engineers used in designing the transmission's automatic shifting "policy" so to speak. And if the transmission design was not driven by less stress on the engine and energy/fuel efficiency , then what was it driven by? Or am I missing something?
 

220629

Well-known member
...
This , then, brings up the question of what were the criteria the MB engineers used in designing the transmission's automatic shifting "policy" so to speak. And if the transmission design was not driven by less stress on the engine and energy/fuel efficiency , then what was it driven by? Or am I missing something?
I think that you bring up a very good point. I can't really answer your question.

First off let me say that I don't have a performance monitor unit of any type. I do have the OEM engine water temperature gauge, an added mechanical boost pressure gauge, and an added voltmeter.

I tow my 2600# (all up) sailboat quite a bit. Except for that, and our annual pilgrimage to the Florida Keys most of the times my Sprinter is at medium load.

I feel that when I tow my boat it is often necessary to manually downshift on longer uphill climbs. I watch the boost pressure and water temperature. Generally when the engine needs tp supply more power my gauge will spike slightly above 20# and then settle back to maybe 17 or 18#. If my mechanical gauge boost pressure rises closer to 20# and holds there then I know for certain that I need to downshift. I also will often downshift as a pre-emptive strike when there is an obvious long climb ahead.

I know that many times the torque curves are cited for why you need to intercede, or override the TCM program, and downshift. Around 2800 rpm is often cited as the lower number for T1N's. My observation is that my Sprinter engine also has very good torque and performance in a band below that.

The difference in engine speed between 2800 rpm and 2300 rpm is over 10%. Generally speaking, you can run back and forth across the country many more times without engine troubles at 55 mph as opposed to 75 mph. Less RPM is less wear and tear. Ciprian has over 500,000 ... 770,000 miles on his T1N by using his CSS method.

I watch my boost gauge and my engine temperature. Lately I find that I don't override the transmission program as much as I once did. I do use cruise control fairly religiously. Not even time will tell if what I'm doing is correct or not because my one vehicle being driven by one driver does not a study make.

FWIW. vic
 
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Boater

New member
When it was first released in Europe the Sprinter was without a doubt the fastest 3.5 tonne vehicle on the roads (If it wasn't it certainly managed to make people think it was). My first gear is pretty much irrelevant unless heavily loaded or on a steep incline, I can pull away in 2nd in any other situation (or drive it around in 1st without touching the gas pedal). The top gear (may be a 0.78:1 overdrive, not sure if that includes the axle ratio) lets the sprinter outrun any contemporary van on somewhere like for example the German Autobahn network which generally has no speed limit (but where they have applied speed limits you better stick to them!). Now that's in a manual but I suspect the contemporary auto was geared similarly.

I think it is clear that at it's conception, what Mercedes geared the Sprinter for, was to be a heavy flying machine, not to be easy on engine load or light on fuel, presumably the upshift policy on the auto boxes was in line with this, and whilst priorities have changed a little over the years, I suspect somewhere in the design criteria for the Sprinter is that it should still drive like a cargo rocket and maintain it's niche position......

Now I think about it, it's a boy racers white van!

Ironically in the UK there is/was also a train called a Sprinter, which even when it was introduced was about the slowest thing on the network. Not sure how many are left now, I think the regional rail companies still use them, nasty slow trains with a really bouncy ride, on the plus side they usually have space for a couple of bikes below the luggage rack.....
 

sailquik

Well-known member
Thanasis,
I don't have the answer to what the MB engineers who developed the transmission ratios and shift points had in mind.
I've asked myself that question on a daily basis since I purchased my first Sprinter.
In my experience not all Sprinters are fuel mapped quite the same, even when considering only those imported into the USA (all with basically identical engines and transmissions).
Also, the sensitivity thresholds on the cruise control have seemed to vary and this seems to make a significant difference in how the engine management systems increase the fueling rate as the sensed % of LOAD increases.
Yes, I totally agree.....what were they thinking?
But then again, it's uncertain how much of the original MB design and performance has been modified to get the Sprinters to pass all the EPA/CARB requirements for importation into the USA. I'm sure they take the same basic engine and alter the fuel map characteristics significantly.
Roger
 
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Graphite Dave

Dave Orton
The transmission needs to be reprogramed. The current design does not function correctly. A driver should not have to manually shift an "automatic" to make it match the driving conditions. It is not even close to correct. We would not be having this discussion if it was close to correct. Interesting how many drivers in different operating conditions are compensating for the poor selection of shift points by manually shifting. If I need to shift manually, then please give me a true manual transmission.
 

220629

Well-known member
The transmission needs to be reprogramed. The current design does not function correctly. A driver should not have to manually shift an "automatic" to make it match the driving conditions. It is not even close to correct. We would not be having this discussion if it was close to correct. Interesting how many drivers in different operating conditions are compensating for the poor selection of shift points by manually shifting. If I need to shift manually, then please give me a true manual transmission.
Dave,
Contrary to what many people indicate in these threads, I don't find myself shifting manually very often when I'm not towing. I don't find the TCM control of the transmission bad for most of my use. I hear what you are saying, but many of the vehicles which I have used to tow trailers have needed operator input under some conditions. The answer in the operator manuals for towing is often to not use overdrive at all, unless they have a tow/haul button to enable. FWIW. vic
 

Graphite Dave

Dave Orton
Maybe it is much more obvious when you are close to the maximum load rating. I have not recently weighed the Sprinter when it is full of water for a trip. I believe it is about 8000 lbs. The ScanGage makes the need to shift very clear. I hate automatics anyway so one that does not work correctly just adds to the pain.
 

Thanasis

Active member
Interesting point Owner. If I understand correctly, what you are saying is that it makes sense to manually downshift only when you are running out of available power (LOD approaching 100%) , and that otherwise lower LOD at higher rpm means less fuel to the engine but at a higher frequency, and therefore not overall improvement of mileage.

%LOD is really just the percentage of available power you are using at that particular rpm/load point. It doesn't mean you have less load, the van is still doing the same amount of work in the real world. In your case by dropping to 4th its just doing less work more often.

The biggest difference in what you're doing by dropping into 4th, is changing to a 1:1 gear ratio in the box. This is only relevant when you are under real load, not when cruising.

When cruising you want to minimise friction and pumping losses, which means lower rpm.
 

autostaretx

Erratic Member
vic said:
I don't find the TCM control of the transmission bad for most of my use.
graphite said:
I hate automatics anyway so one that does not work correctly just adds to the pain.
The automatic does a fairly decent job... if you drive blindly with no additional gauges, you'll still get far better mileage than your E350 or Savanna.
But no automatic (yet) can look ahead up the road and see that the hill is going on forever, or that it's getting steeper or that you're about to be sniffing the butt of a truck that's crawling up the hill.

There's even the distinct possibility that the transmission stays too high to lower the engine noise
(when it comes to trying to shift for maximum MPG on hills, i frequently hit the wall of my co-pilot complaining about the high whine of the Sprinter exceeding 2900 rpm)

--dick
 

autostaretx

Erratic Member
it makes sense to manually downshift only when you are running out of available power (LOD approaching 100%) , and that otherwise lower LOD at higher rpm means less fuel to the engine but at a higher frequency, and therefore not overall improvement of mileage.
As others have posted (and i have certainly seen) 70% is the easiest-to-remember downshift spot.
You will see your MPG improve by quite a bit by avoiding higher LOaDs.

The question then becomes: when should i shift back *up*?
(my own answer is when i see the MPG peak, or start to droop, at a near-constant speed)

--dick
 
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owner

Oz '03 316CDI LWB ex-Ambo Patient Transport
Yes thats the physics of what I'm saying. But each vehicle will have its own sweet spot and I certainly wouldn't wait until 100% lod. There will be compromises and limits approaching 100% lod that would have an adverse effect on fuel economy. Such as IAT for example.

The early downshift sweet spot depends on many many variables, many of which the ECU has no way of knowing, eg you might be just about to crest the hill etc. or pulling up to slower traffic.

I'd far rather have to knock the stick left once in a while, than constantly have it auto shifting into a far too low a gear all the time.

I will concede that the sprinter is quite an aggressive upshifter, but that is preferable to an aggressive downshifter for me.

Interesting point Owner. If I understand correctly, what you are saying is that it makes sense to manually downshift only when you are running out of available power (LOD approaching 100%) , and that otherwise lower LOD at higher rpm means less fuel to the engine but at a higher frequency, and therefore not overall improvement of mileage.
 

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