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Moxxi · 02-22-2018, 03:58 PM

Quote:

Originally Posted by cruzbill

... gearing is the trick on the downhill, that's where you can get into trouble.

But motor home trannies are automatic.
Do you manually shift to a lower gear?

Moxxi · 02-22-2018, 04:01 PM

Why is it that DIESEL engines have engine retarders, but GAS engines do not?

Is it because of the way that the fuel is ignited?

cruzbill · 02-22-2018, 04:02 PM

If I needed to, I would (and have), but by using the engine compression brake, the tranny downshifts by itself (Allison 4000). The easiest way is just to leave the trans in the same gear it was in on the uphill, for your downhill run.

l1v3fr33ord1 · 02-22-2018, 04:16 PM

Quote:

Originally Posted by Moxxi

But motor home trannies are automatic.
Do you manually shift to a lower gear?

You may downshift, if you wish. Or, you can use the Ford Tow-Haul feature to downshift for you. See my post #8.

The old rule-of-thumb was to come down the hill in the same gear you used to go up.

Quote:

Why is it that DIESEL engines have engine retarders, but GAS engines do not? Is it because of the way that the fuel is ignited?

Correct.

twinboat · 02-22-2018, 04:18 PM

Quote:

Originally Posted by Moxxi

Why is it that DIESEL engines have engine retarders, but GAS engines do not?

Is it because of the way that the fuel is ignited?

Gas engines have throttle plates that close, so there is very little exhaust flow to block. Diesels have open intakes and engine speed is controlled by fuel.

You use Tow/Haul or manual downshift while going downhill. The engine will hold you back.

Thor29.3inAZ · 02-22-2018, 04:50 PM

Quote:

Originally Posted by Moxxi

Do all Class A “Gas” MHs have to struggle, when it comes to climbing hills & mountains?

Are there any gas MH engine/transmission combinations that are better than others?

I realize that, not driving a diesel MH, going DOWNHILL, you will not have the benefit of having a “jake brake”. But, at this point, I’m more concerned about the struggle to get up the mountain.

Also, pulling one up a mountain, what about overheating?

I must have a exceptional MH. A 2017 gas Ford V10, 6 speed trans, Thor 29.3 (30' long). Weighting in a 18,000 lbs. We live in AZ and no matter which way we travel we end up climbing around 3 to 4K feet. Ending up around 7K feet AGL. So we do a fair amount of up and down climbing. We can pass pretty much any 18 wheeler or diesel MH. We did our research on diesel engines and wanted to go the route but cost was was more than we wanted to invest in. AND not to mention all the maintenance involved. We don't regret at all getting a gas engine MH.

nothermark · 02-22-2018, 05:43 PM

The big problem with gas motorhomes is the nut behind the wheel.

There are folks who try to drive them like a diesel with low RPM's because of the sound they make. These folks think they are screaming in pain when the rest of us know they are singing with joy at being at the peak of their power curve. As a side effect of running low RPM's they also do not get enough cool air or coolant circulating to keep the engine cool. The same system cools the transmission. The race is then on to see who fails first.

The biggest benefit I find with tow/haul is that it lets me change gears just by tapping the brakes on a downhill. I actively manage the engine RPM by forcing shifts where I want them with the engine up in the power curve. Folks who depend on the automatic knowing what to do are the one's complaining about the transmission. It has no way of knowing what the terrain conditions are so it responds when it is too late. Manually forcing shifts lets me allow for conditions. Engine braking works quite well as long as one manages the speed of the engine.

Just to build a bit on the question of ignition differences...the diesel depends on packing as much air as possible into the high compression cylinder because the heat liberated by compressing that air ignites the fuel. That is why there are no significant restrictions and often some kind of supercharger to pack in more air. That requires some kind of restriction be added to get engine braking. Gas engines use a throttle plate to restrict air flow so they can control the amount of air they are injecting fuel into as a way to set the power level of the explosion that happens when the spark plug ignites the fuel. That gives them a restriction to work against. Engine braking in both cases is done by pumping air against a restriction. When somebody talks about a diesel having an engine brake and gas engines not having one it tells you they don't have a clue.

Hope This Helps
;-)

Vacay Wheels · 02-22-2018, 05:50 PM

Quote:

Originally Posted by Moxxi

Do all Class A “Gas” MHs have to struggle, when it comes to climbing hills & mountains?

Are there any gas MH engine/transmission combinations that are better than others?

I realize that, not driving a diesel MH, going DOWNHILL, you will not have the benefit of having a “jake brake”. But, at this point, I’m more concerned about the struggle to get up the mountain.

Also, pulling one up a mountain, what about overheating?

Huh... We have climbed up and down the Rockies through BC, AB, ID, MT & WY, plus Cascades (OR,WA) & Sierras (CA). As long as we're willing to open up the throttle, we're up anything with no struggle or overheating. This is a run-of-the-mill Ford gasser, pulling 22klb combined.

The problem is the absolutely unbearable noise. So maybe I'm struggling to cope with the noise, but the engine is never struggling.

Downhill is equally no problem. Tow/Haul keeps the gears down, or manual downshifting will do it as well. The worst case for us was coming down from Yosemite into Mono Lake, and I'm literally going 15mph in 1st gear, with the occasional full stops to bleed off speed. Still, the coach handled it no problem. Just needed patience here.

Quote:

Originally Posted by nothermark

The big problem with gas motorhomes is the nut behind the wheel. There are folks who try to drive them like a diesel with low RPM's because of the sound they make. These folks think they are screaming in pain when the rest of us know they are singing with joy at being at the peak of their power curve.

The biggest benefit I find with tow/haul is that it lets me change gears just by tapping the brakes on a downhill. I actively manage the engine RPM by forcing shifts where I want them with the engine up in the power curve. Folks who depend on the automatic knowing what to do are the one's complaining about the transmission. It has no way of knowing what the terrain conditions are so it responds when it is too late. Manually forcing shifts lets me allow for conditions. Engine braking works quite well as long as one manages the speed of the engine.

Totally concur with this! Except I am not "singing with joy at being at the peak of their power curve". Crying in pain is more like it. But peak of the power curve is the place to be, for sure.

Moxxi · 02-22-2018, 08:43 PM

Quote:

Originally Posted by nothermark

... When somebody talks about a diesel having an engine brake and gas engines not having one it tells you they don't have a clue...

That’s why I asked.
I don’t have a clue.

TXsurfer · 02-22-2018, 09:23 PM

Do the math on how much extra a DP cost and how many passes you may encounter. You may be shocked what the pass toll may be lol

m.elliott63 · 02-23-2018, 05:16 AM

"Do the math on how much extra a DP cost and how many passes you may encounter. You may be shocked what the pass toll may be lol"

So true! One day I may brave the passes through the Eisenhower in my gasser but we snuck up to Cortez, CO from the south at Gallup, NM then on up to arches. Not only the up front costs but maintenance and repair costs for a DP.

Sent from my SM-G930V using iRV2 - RV Forum mobile app

nothermark · 02-23-2018, 05:23 AM

Quote:

Originally Posted by Moxxi

That’s why I asked.
I don’t have a clue.

That's why I wrote the longer answer. ;-)

I was trying to give you a way to measure other answers. You will read a lot of stuff in any discussion group about how things work or what is best. If you learn how any particular thing works you will find a few basic questions and answers about anything that you can use to judge whether or not the author knows what they are talking about. Engine braking is one of mine for the gas vs diesel issue.

boatman10 · 02-23-2018, 05:51 AM

My 4 speed, 25" 8.1L GM class A gasser has TOO much power......I wish it had a taller gear ratio.....seems stupid they put the same 4.63 rear end in all the different weight MHs.

wa8yxm · 02-23-2018, 06:36 AM

I have a 38' Class A. workhorse chassis, 8.1L Vortgec and Allison.

Very rare is the hill it labors to climb, Oh it will "Speak to me" going up hills. and occasionally downshift a gear or two. but if I'm doing less than 45 MPH going up hil the reason is in front of me (I do not wish to rear end the semi in front of me).