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Old 07-06-2017, 05:21 PM   #1
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Default Irritating downshift reduction-Scangauge

Our 07 C190P Roadtrek with the 6.0 engine and 4L80E transmission, like all heavy stuff, downshifts under full power a lot while climbing hills. High load, high rpm downshifts are fairly hard on a transmission compared to normal driving and shifting, so minimizing them has always been something I try to do.

It downshifts the most when on cruise in the rolling hills, so I normally will take it out of cruise for the hill or if it is really rolling hills, just drive it all the time. Building some speed on the downhills and flats before a hill, and letting it slow a little on the upgrade can mostly stop the downshifting. Even driving it without cruise, it would sometimes surprise me and downshift, though, especially if there was a headwind, though.

On our last outing, I set the Scangauge to read the engine load (LOD on the Scangauge). I wasn't sure what it really read from the description, but it got pretty obvious in use. It is actually seems to be reading the % of horsepower the engine is making, compared to the maximum amount of horsepower it could make at that rpm and other conditions like altitude and temperature.

Having it read that way makes using it to control downshifts really easy in most cases with the Chevy. It will not downshift until it gets to 99-100% load, so all you need to do it back off the throttle to be less than that and it won't downshift unexpectedly. Worked very well for me over our about 3K miles.

The only time it I got fooled was if the load was changing very rapidly. I had it downshift at 97-98% a couple of times. I think it is because of the update lag of the Scangauge. If the load was climbing quickly, I just stayed at 96% or lower and then had no problem, but still would go to 98% for slow changing load.

A bonus is that preventing the downshifts can increase fuel mileage quite a bit in rolling hills, maybe 1 mpg. If you have the Scangauge showing the mpg, either instantaneous, or trip, you can actually see how much it changes at a downshift.

Plus, it keeps me amused on long drives
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Old 07-06-2017, 10:05 PM   #2
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The Scanguage is a useful tool to maximize engine efficiency, to keep the engine in the optimal rpm range, to reduce long term engine wear and to improve fuel economy. They are not even very expensive. It is most useful though with a vehicle that can be manually shifted like a Sprinter.

On the Sprinter forums, the recommendations are usually to keep the % LOD below 70% and an optimal rpm of 2600-3000 (for the 6 cylinder) to achieve the above.

Here is a good post that discusses optimal rpm and the use of manual downshifting to help achieve this. These gauges illustrate problems with most transmissions in achieving optimal engine efficiency.

https://sprinter-source.com/forum/sh...ad.php?t=31275
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Old 07-07-2017, 04:26 PM   #3
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in a similar situation on the same chassis ( PW), I might use tow/haul or shift to 3rd and keep it there and modulate speed with my foot- this will result is a lower avg speed. I'm ok with that

the 4.8 in my pickup is horrible for "hunting" gears...the 6.0 is much better.

i bet the newer models are better

Mike
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Old 07-07-2017, 05:28 PM   #4
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Quote:
Originally Posted by mkguitar View Post
in a similar situation on the same chassis ( PW), I might use tow/haul or shift to 3rd and keep it there and modulate speed with my foot- this will result is a lower avg speed. I'm ok with that

the 4.8 in my pickup is horrible for "hunting" gears...the 6.0 is much better.

i bet the newer models are better

Mike
I have tried tow/haul quite a bit, including the last trip using the LOD function. I can tell you for an absolute fact, or as close to it as possible, that it uses much more gas in the 3rd than 4th, more in tow/haul than with it off (letting it shift itself), and the two/haul will make the trans run hotter also which really surprised me. Keeping the trans in four/lockup as much as possible gives the best mileage and lowest temps. In the situation I described, there would be almost no downshifts happening, but if it was on cruise it would downshift on at least 50% of the hills, which is a lot of gas and wear and tear.

As near as I could tell, all tow/haul does is delay the shift points going up, and makes the downshifts happen sooner going down.
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Old 07-07-2017, 07:02 PM   #5
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Ours - 2013 w/6.0 & 6spd trans it shifts down rather violently when descending hill at low spd. I try to modulate brakes & throttle to prevent shifts & usually use manual shifting mode on long hills. But occasionally caught off guard. Perhaps the "scanguage" would help?
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Old 07-07-2017, 09:18 PM   #6
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Originally Posted by AZ ADVenturist View Post
Ours - 2013 w/6.0 & 6spd trans it shifts down rather violently when descending hill at low spd. I try to modulate brakes & throttle to prevent shifts & usually use manual shifting mode on long hills. But occasionally caught off guard. Perhaps the "scanguage" would help?
Interesting that it downshifts on downhills, the 4L80E doesn't seem to do that. With essentially zero load, I don't have a clue to what you would see on the Scangauge.

Does the six speed give you the option of full manual shifts? I would really, really, like that option.
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Old 07-07-2017, 10:29 PM   #7
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Yes, our 6spd does have Full manual mode. With "paddle" type shift button to control up/down shifting. As I said, it is very nice & I use it to control shifts on long down hill descents. But sometimes neglect to lock it in on short hills.
That's when I sometimes get the surprise-sudden down shift - feels like 4th to 3rd or even 3rd to 2nd!
BTW- when using cruise control, I always try to do as you describe at approach to an uphill climb. I'm an 'old' manual transmission guy. Prefer to be in control!
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