Manual Shifting Technique

Topic: Manual Shifting Technique (Read 1078 times) previous topic - next topic

Manual Shifting Technique

October 03, 2013, 06:06:12 pm

Is there a general technique that one should use when there is a need to down shift or up shift for grades. Is there a target RPM (2002 ISM 450) that should be used? I understand that engine/trans./retarder temps should be closely monitored also.
Is going slow up steep grades an issue and how concerned should I be about traffic behind me?
I would appreciate any insight.
Old Hippie

Re: Manual Shifting Technique

Reply #1 – October 03, 2013, 06:11:08 pm

Depends on your objective.

Best MPG climbing is just above peak torque RPM. That is what it says in your Cummins manual (same for Caterpillar, etc). Basically any modern turbo, after-cooled engine is most efficient at low RPM, even at high throttle positions.

Best speed climbing is just under governed RPM.

For the most control/manual shifting, select "mode" which is economy mode.

Then use the down/up arrows to "manually" shift.

Re: Manual Shifting Technique

Reply #2 – October 03, 2013, 06:22:50 pm

Quote from: Old Hippie – October 03, 2013, 06:06:12 pm

and how concerned should I be about traffic behind me?

That is what the emergency flashers, and slow lane, are for.

Re: Manual Shifting Technique

Reply #3 – October 03, 2013, 06:30:45 pm

With the ISM450 in a 36', your bigger concern is running over the folks in front of you going up mountains.

With the 4,500 lb toad, I have never been close to needing the 4 way flashers going up, sometimes I use them going down while laughing at all the wannabees I passed going up, boy do they ever fly down hill, holy smoke. I venture they could not stop in a half mile the way they fly down hill. You need to get your kicks where you can, I do laugh alot and steer clear of them.

Re: Manual Shifting Technique

Reply #4 – October 03, 2013, 06:37:05 pm

As someone suggested here earlier, I try to keep downhill RPM to 1900.

On relatively steep downhills the engine RPM dissapates the heat and Retarder controls the RPM.

Keeping the engine RPM at 1900 means I don't need the retarder that much.

best, paul

Re: Manual Shifting Technique

Reply #5 – October 03, 2013, 07:42:22 pm

Paul is correct.

Higher RPM descending uses zero fuel (throttle closed), but the water pump and fan turn faster and there is a little more engine braking, so it doesn't require as much transmission retarder. That keeps transmission fluid temperature down.

So, on long downgrades with the retarder on, if transmission temperature starts to rise, ease off the retarder and raise engine RPM. If you need more braking or temperature continues to rise, slow down and shift to a lower gear.

Brett

Re: Manual Shifting Technique

Reply #6 – October 03, 2013, 08:04:47 pm

When doing grades up or down I try to keep the engine at 1500 rpm. I use down shifting and retarder to maintain this level. I forget about the speed. Everyone else is having the same issues in front or behind me. Now, I am not in the economy mode when down shifting as I could get an increase to high rpm's if I have a steep hill to go down. Mine is a 400 HP. Brett that is some good information. DAN

Re: Manual Shifting Technique

Reply #7 – October 03, 2013, 10:14:37 pm

Don't be concerned about the people behind you if it interferes with safe operation. You will go slower than the cars, up the hill and down the hill. We have been on I-90 where the speed limit for cars was 70 mph and the speed limit for trucks was 25 mph. I tend to stick with the speed limit for trucks.

We choose a speed and gear combination that can be maintained without overheating engine or transmission. That applies to going up the hill or down the hill. If temperatures start climbing, we shift down manually and reduce speed. In general, we keep the engine at a "normal" rpm value. For our engine under normal conditions, that is about 1900 rpm. (Cummins C-8.3) For bigger engines, the rpm value is usually lower.

Re: Manual Shifting Technique

Reply #8 – October 03, 2013, 10:44:35 pm

Last time I was at Stewart & Stevenson I had the mechanic check the rpm on my radiator fan. He did it by placing a red dot on one of the fan blades and pointing an adjustable timing strobe at it. He asked me to floor the accelerator while he pointed the strobe. The look on my face told him I wasn't too sure about that. He said the DDEC wouldn't let the engine overrev. I "cautiously" floored the throttle and RPM went to 2100RPM and stayed there. Thankfully the engine stayed together too. The mechanic said the only way you could overrev it was going downhill. Also said that one trick the drivers used was when they overheating going up a hill they would pull over, put the engine in neutral and floor it. The engine would cool right down. I actually tried it on a mountain pass when I headed west this year. Engine was at 215° when I pulled over and after less than a minute at full throttle it was at 185°! I could watch the needle move on the temp gauge.

Now when I'm pulling a hill I gear down and try to keep the RPM up in the 1900RPM range. If it's a long enough hill the temp will start climbing. At that point I start using the temp gauge instead of the tach to determine throttle position. My goal is to not let the engine go over 210°

see ya
ken

Re: Manual Shifting Technique

Reply #9 – October 04, 2013, 12:43:30 am

Ken,

Part of cooling down at the top of a grade is bringing oil temperature down to a normal temp along with the engine coolant temp. Oil cools slower than the water/coolant temp. Lots of RPM at the top will bring the coolant down in a hurry but the engine will generate more heat at 2100 RPM compared to 1000-1200 RPM and will take longer to cool the oil. The turbo gets really hot, even glowing on grades and uses oil to lubricate and cool. Getting the oil temp down so if you turn off the engine, the turbo won't refine the oil into coke and shorten it's life is part of my top of the grade procedure. The oil/water heat exchanger will help but with oil spraying up into the hollow piston crowns, it drains back into the crankcase at a lower temperature if the pistons crowns are cooler. A huge amount of air goes through a Detroit 2 cycle and out the four exhaust valves. With a light load and medium RPM, internal temps come down in a hurry.

Pierce

Re: Manual Shifting Technique

Reply #10 – October 04, 2013, 11:30:03 am

Every Rv owner I sold coaches to was overly concerned about the engine and trans temps.

They would panic if the gauge moved. Be aware of it but up to 230+ I would not be too concerned for pulls up grades.

Normal. I ran our m11 up to Grand Canyon from the east floored on purpose to see what the engine would do. Never got past 215. Trans similar.

Never lifted my foot or even down shifted. Foretravel had enough radiator easily for my coach and a 3.000 pound towed.

good test to see if everything is functioning correctly IMO.

Drove dozens of older unihomes and oreds up baker grade in the summer at 110 degrees floored all the way up the hill to show the new owners that the temp gauge stopped at 230-240 and no coolant loss occurred.

Versus they were leaving before dawn so the temp gauge did not move.

Lots of owners thanked me as they got to use their coaches easier without damage.

More exciting to see the coach work perfectly.

Foretravel built the original u280's unihome with a 250 cat and with the radiator the same size as the u300 it never warmed up correctly. They Had to block part of the radiator on those coaches years later.

Bob

Re: Manual Shifting Technique

Reply #11 – October 04, 2013, 12:52:06 pm

Bob,

All of the Foretravel diesels require different operating rules. Unlike the Detroit 71 series, the 92 series has wet liners. This means an overhaul can be done with the engine in the coach but it has a downside too. Here is an excerpt from another RV site: The nemesis on the 92 Series Detroits is overheating. This is a wet liner design with elastomer (O-ring) seals at the top and bottom of the cylinder liner. If you overheat these engines, even just a bit, the liner seals will be compromised. The result will be oil to cooling system leaks, and if not caught very quickly, damage to the mains or even worse, a spun main and damaged crank. Cooling system maintenance is THE big deal on these motors. Keep them running cool and all is well. Let them get hot and you will be rebuilding them. In reading several boat forums, most operators keep the coolant temp below 200 degrees and have a phobia against overheating the 92's.

I tend to be conservative, slow and gear down to keep temps down when the gauge gets towards 200+. I can run at 2150 RPM and 82 mph all day on flat ground and stay cool or climb most any grade in mild weather and also not reach 200 degrees but in summer, I keep a close eye on the gauges. If it gets close, I turn on the dash heater to help keep it cool. The DDEC will shut it down automatically if it gets too hot but that is well over 200 degrees.

Pierce

Re: Manual Shifting Technique

Reply #12 – October 04, 2013, 02:42:39 pm

This aspect of the discussion has come up before.

While some may be comfortable running their engine coolant temperature to 230-240 degrees F, I for one would never do it.

To me it falls into the category of "what I hope I can get away with", not "best practices".

I don't think you will find an engine manufacturer who will guarantee you that engine life would be the same for an engine that one taken up to 230-240 degrees vs one that stays in normal temperature range.

But, like most other things, this is a decision each owner must make.

Brett

Re: Manual Shifting Technique

Reply #13 – October 04, 2013, 03:05:18 pm

On top of what Brett posts, imagine if you didn't get way with it, had a 30,000 RV with a spun bearing, etc. and you are half the country away from home. What do you do then? Suggest anyone with doubts should do a Google search with Detroit, 6V-92TA and boat forum as the keywords. Boat engines get worked a lot harder than ours and any problems show up much faster. These 2 cycles can be flogged and last a very long time if the correct weight oil and temperature limits are used by the operator. Hundreds of thousands of satisfied operators all over the world even today.

Doesn't do much good to say, "but he said......" after the fact.

So much space up front in a GV that a couple of tall radiators could have been installed. The grills and removable plates are already there.

Pierce

Re: Manual Shifting Technique

Reply #14 – October 05, 2013, 04:16:26 am

Quote from: Pierce & Gaylie Stewart – October 04, 2013, 03:05:18 pm

On top of what Brett posts, imagine if you didn't get way with it, had a 30,000 RV with a spun bearing, etc. and you are half the country away from home. What do you do then? Suggest anyone with doubts should do a Google search with Detroit, 6V-92TA and boat forum as the keywords. Boat engines get worked a lot harder than ours and any problems show up much faster. These 2 cycles can be flogged and last a very long time if the correct weight oil and temperature limits are used by the operator. Hundreds of thousands of satisfied operators all over the world even today.

Doesn't do much good to say, "but he said......" after the fact.

So much space up front in a GV that a couple of tall radiators could have been installed. The grills and removable plates are already there.

Pierce

Being in the desert southwest and representing five major brands with silver detroits both 6 and 8's I have had hundreds of coaches input. Told every customer to drive it harder. Offerred to buy back any damaged coach. Never a call. Rv's are fairly light. Birds were not and had small radiators and ran 230 a lot in the summer.

Maybe to boats use at 475 hp on a 6v versus the Rv at 350hp contributed to the heating issues?

Bob

Re: Manual Shifting Technique

Reply #15 – October 05, 2013, 09:05:37 am

I use VMSpc a lot when we are headed up or down an extended grade. A couple of days ago, near the end of our return trip to Asheville from Raleigh, NC, we climbed a fairly steep 6 mile grade up the eastern edge of the Blue Ridge Mountains. For normal terrain our engine runs at 183 degrees with very little variation. I try to keep the engine temperature close to this number for long climbs. Certainly below 200. I do this by downshifting and reducing speed monitoring the VMSpc "load" gauge such that it is less than 100% (say around 80%). I think we were going about 30 mph near the top, which didn't cause any traffic issues since we were behind a truck going the same speed. The temperature got up to about 190 and then quickly returned to normal after the summit. Sure, we had to power to blast over the pass at 55mph, but the temp would have been well over 220 in no time. My goal is "low stress" in life, for both me and my engine! Why push it? As my wife would say...."what are you late for?"

For down grades I follow the VMSpc retarder temp closely and keep it below 260. If it gets too high, I slow down and shift down. This reduces the rate of energy going into the retarder system and increases cooling due to increased engine revs.

Works for me.

Re: Manual Shifting Technique

Reply #16 – October 05, 2013, 11:49:54 am

Bob,

Expect you may be correct on the boat vs. RV aspect. 475hp is probably the least horsepower seen in a boat by a 6V-92TA. A lot run 525-535hp and there is a YouTube video of a fire dept ladder truck 6V-92TA showing 517hp on the dyno. With these hp numbers, the combustion pressures must be a lot higher and a lot hotter and keeping the water temp down to protect the seals is mandatory. Higher combustion chamber pressures also push harder against the cylinder head putting more stress on the head gasket. On engines that have been overhauled, the "counterbore" at the bottom of the liner has to be checked as it can cause the liner to be slightly below the engine block deck resulting in gasket failures. A special tool cuts the area and then the liner can be shimmed up to be flat with the block deck.

Interesting as Mercedes makes their liners a bit on the tall side so the block has to be surfaced after the liners have been installed. Naturally, not possible for an in frame overhaul.

It does make some sense that Detroit electronic controls (DDEC) will not shut the engine down until the temp gets above 230 degrees. They did design the controls to make driving one almost idiot proof. On the other hand, there is an override switch that I am certain has led some owners to be stranded on the side of the road.

We had mostly Detroit 8V-71s in the fire service. We did absolutely torture them going from a cold start to 2400 rpm in seconds responding to an emergency, year after year. The factory did provide seminars on keeping them healthy. Other than the an initial start up on the apparatus floor, we always used the fast idle switch that brought the revs to 1000. This keeps the oil pressure up so the pistons receive their oil stream into the piston crowns, circulates coolant to keep temp down and also keeps the top compression ring free of carbon deposits. At the scene of an emergency, we always kept the lights, radios and other accessories on even if we were not using the pump so the fast idle switch came in really handy for engine and batteries. While some Foretravels have that capability with the cruise control, the Detroit powered models don't.

The Detroit 2 cycle fuel injectors won't work past 2800 rpm but have not seen any blow up with limited time at that number so you would really have to spin the engine up on down grades to experience a failure.

I have seen big diesel pushers broken down on grades in really hot weather and tried to imagine what it must be like for the owners. A lot of areas out here don't have cell service so expect they have a bit of a wait for help to arrive and a huge bill after the tow. Never had a problem flogging Detroits in the past and use full throttle/2150 rpm all the time but watch the temp gauge like a hawk. After all, what retiree is in that much of a hurry to get up a hill?

Pierce

Re: Manual Shifting Technique

Reply #17 – October 05, 2013, 03:36:31 pm

@Pierce Just a little bit of a nit-pick. The documentation that came with my coach says that there was a fast-idle option. Not sure why it wasn't just included. Maybe because it was an additional electronic module?? Never met or heard of a 6v92 Foretravel that has the option. The high idle would be nice. Oil pressure is pretty low at idle when the engine is at operating temp. If I'm idling for more than a minute or two I shut it off. More wear and tear on the starter but that's easier to replace than the motor.

As to overreving the engine I'm pretty sure the mechanic was emphasizing that I wouldn't overrev by flooring it. Although if you really tried with a manual transmission truck I'm pretty sure you could blow up the motor with a combination of heavy enough load, steep enough hill and low enough gear.

see ya
ken

Re: Manual Shifting Technique

Reply #18 – October 05, 2013, 05:01:15 pm

Ken,

I have the DDEC manual and will do a search to see if they list an option. My original thinking was it was not offered because some might punch in a gear while at fast idle but it could have been engineered to disengage if the brake were to be released or a transmission gear engaged. All the fire apparatus had it along with my Buffalo bus.

Yes, downhill with a stick could blow up anything. The Allison should shift up before blowing the engine but have not tried it.

Pierce

Re: Manual Shifting Technique

Reply #19 – October 05, 2013, 09:36:05 pm

I seem to always be worrying about temperature during the summer. I still am not clear whether our early 90's U300's have a cooler on the diesel fuel line. I think a cooler on the fuel would help keep things cooler. If they don't have a fuel line cooler factory installed, where would be the ideal spot to install one?

Re: Manual Shifting Technique

Reply #20 – October 05, 2013, 10:15:46 pm

Guess I was one of the first to use a Hayden transmission cooler in the RETURN LINE from engine to fuel tank.

Several locations would work, but I had mine in front of the CAC. Had a cover that I velcroed on in the winter.

Used the original return line from engine to fuel tank, just moved it to cooler OUT. Had a new engine to cooler IN line made.

Brett

Re: Manual Shifting Technique

Reply #21 – October 05, 2013, 10:18:05 pm

Probably on the return line fairly close to where they join after coming out of the cylinder heads. That way, there is no place to let air in on the way to the engine. On the way from Oklahoma to California in the old days, I used to bake an chicken on the exhaust manifold but the tank on the U300 is plenty hot for that now.

Since the 2 cycles use the cylinder heads to carry both the supply as well as the return fuel, they get much hotter than the diesels with external fuel lines, pumps and injectors. After a couple of hours in warm weather, I can't even touch the fuel tank.

A lot of diesels actually run a coolant hose through a fuel heat exchanger to warm the fuel. Probably keeps the waxing/gelling down in freezing weather. Bet the huge diesels in ships really heat the devil out of the bunker oil before it gets to the injectors when they start up.

Yes, summer really tests the cooling system and nerves on highways like I-70.

Pierce

Re: Manual Shifting Technique

Reply #22 – October 06, 2013, 10:45:05 am

More laughing

, wolfe10, you are years after using a Hayden transmission cooler in return diesel fuel use, been using that idea for many years in the generator world, we stated using it on the Cat 399 and 349 series 40 years ago, I used it on my MCI using the 12v-71 25 years ago due to the heat build up in the fuel tank.
We proved the Cat 399 was able to carry an additional 80 kw electrical load using a large Hayden on the radiator guard for air flow / cooling. Heating was a big issue.
Maybe you read the Cat field reports when Virginia Tractor reported the info to Peoria.

Re: Manual Shifting Technique

Reply #23 – October 06, 2013, 12:54:55 pm

Dave,

Guess I should have qualified, I ran this by James Triana, and at that point he was not aware of anyone who had done it ON A FORETRAVEL. I then got with the engineers at Caterpillar (though DD and Cummins would have likely given the same information) who said indeed excessively high fuel temperatures would degrade performance and economy and perhaps fuel component longevity.

This is really not an issue on most RV's, as the fuel tank is external instead of buried in the basement, so lots of exposure to air.

But, glad you got a laugh out of it.

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