RAM123

I pull a 11k, 5th wheel RV, mostly in the southeast & southwest ~5-7k miles per year. Over the next year we will be doing a lot of western mountains at higher elevations.

My question is what is the best RPM range on hills for this engine that balances MPG, TEMPS, & engine/tranny Reliability. With the EDGE EZ I have +65hp & +165torque. (see my sig below) My only gagues are tranny temp & fuel pressure.

I run while towing ~ 62-65mph (maybe 70 downhill approaching next hill up). With 3.55 gears I tend to let it run in OD till it gets down to 50/55mph or 1500RPM on stteper hills. It then downshifts to 3rd, or I lock out OD and it shifts to 3rd.

So on hills am I better running 2400/2600 rpm in 3rd gear locked or 1500/1700 in OD???????

HOHN

Keep the rpm up in 3rd when climbing hills.

You need to keep engine RPM up so that the trans pressure will be high enough to support the heavy load.

High loads at low RPM is a bad deal for an auto trans.

A pyrometer might be a good idea for towing in thin air. Even stock trucks can get pretty toasty when the air is rare.

I'd recommend locking out O/D before the truck tries to downshift on its own. Your EZ shows the trans a lot more grunt at lower RPM than on a stock truck, so keep the RPM up and the trans will thank you.

jh

Totallyrad

There are so many factors that affect towing, especially in the mountains. Your best bet is to get a pyro and keep your eye on it. If it starts climbing above 1100* drop a gear and slow down a little.

chainzaw

I thought 1,250* was about the maximum safe temp to drive with and about 1,400* being close to the danger zone. Correct me it I'm wrong.

Totallyrad

Chainzaw, there are sooooooo many things affecting egt that I would rather start looking for another gear a little sooner, especially in the hills. There is also a small delay in most pyros. When you see 1100* on the gauge you may actually be past it by 100* or more.

HOHN

It's not the EGT your concerned about, per se-- it's what it means for piston and cylinder head temps.

Cummins says 1250 is safe all day long. I'd bet that's valid. But that's also for a stock truck-- any modification to timing especially can change that number (more timing raises piston temps).

Moreover, it's not just a temp, but how long the engine is exposed to that condition. Just like you can pass your finger though a flame and not get burned, you surely wouldn't want to leave it there. Heat transfer takes time.

I don't think there's any harm in a very brief flash to 1400 or even higher. But I'd never consider sustaining anything higher than 1300.

jh

nkennedy

I would run in 3rd @ 2200 to 2400 RPM's before lugging it in OD. I have a 6 speed, and have to downshift to 5th on hills when pulling my 11k lbs fifth to keep my EGT's in a acceptable range.

xp8103

RAM123,
I'm in a similar boat only I haul a 3500# truck camper and occasionally haul a small trailer. With 3.55's I can't drop below 60 without getting uncomfortably low in revs and boosting egt's. I rarely let my egts get much over 1000-1100 when hauling just for the reasons stated here. I haul in OD until I drop to between 55 and 60.