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Old 05-14-2019, 03:52 PM   #1
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5th Wheel Diesel Towing at What RPMs?

We're new to towing something this big and heavy and was wondering, at what rpm do you tow at and what gear? The 5th wheel was right at 13,500 lbs. Our TV as you can see below is the CTD 6.7, 6 speed, 3.42 rear axle. At 65 mph, 6th gear, we're at about 1800 rpms. It would downshift to 5 occasionally, but not unnecessarily. It felt like it was "lugging" in 6th, and getting around 10 mpg. I downshifted to 5th gear and left it there the remainder of the trip. It stayed around 2,000 rpms and seemed to like that better. Gas mileage on the "lie-o-meter" continued to say around 10 mpg in 5th, same as 6th gear. All the numbers on the truck remained just about the same, oil pressure, trans temp, oil temp, etc. So am I right in towing around 2000 rpms in 5th gear?
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Old 05-14-2019, 05:10 PM   #2
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For that load, you should be engaging Tow/Haul which locks out 6th gear. You should be fine.
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Old 05-14-2019, 05:11 PM   #3
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I'm not sure what others will say, but don't I think it's possible to really 'lug' an automatic transmission diesel pickup.

The down side of down shifting would be the transmission oil temp. I don't know about your Ram's factory gauges, but my Ford OEM dash gauges are abysmal - they may be accurate (even though I don't trust them) but they respond too slowly, IMO! I have a ScanGaugeII with a digital readout that I use to display engine oil temp, engine coolant temp, trans oil temp, and the engine fan RPM.

Long story short, I was driving into a VERY stiff headwind and could stay in 'high gear' (torque converter lockup) at about 60mph ONLY when behind a big truck or on a downgrade. When heading uphill or the truck ahead of me got too far ahead, the trans would downshift and I could watch the trans temp climb. That made me nervous. I have no idea how high the trans temp might go, but when the trans shifted back into high gear (torque converter lockup) I could watch the trans temp drop.

So if you can keep an eye on your transmission temp, then downshifting is probably fine.
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Old 05-14-2019, 05:13 PM   #4
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Quote:
Originally Posted by NewBlackDak View Post
For that load, you should be engaging Tow/Haul which locks out 6th gear. You should be fine.
6th doesn't get locked out. Only increases road speed needed for it to go into 6th. It's not an overdrive lock out. It changes shift points. 5th and 6th in that trans are both overdriven.


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Old 05-14-2019, 05:24 PM   #5
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I run in tow/haul with the exhaust brake on at all times. I let the "auto"matic do it's thing. I don't lock a gear out unless it started hunting. Or if I'm in a hilly curvy area and wanted to hold some revs when I come in and out of the throttle. 95% of the time I let the trans do it's thing.
But yes, the 3.42s and the Aisin can lug at times with a good load. I'd rather of had 3.73s but not an option from the factory.


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Old 05-14-2019, 06:02 PM   #6
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Originally Posted by oldmanAZ View Post
I'm not sure what others will say, but don't I think it's possible to really 'lug' an automatic transmission diesel pickup.

The down side of down shifting would be the transmission oil temp. I don't know about your Ram's factory gauges, but my Ford OEM dash gauges are abysmal - they may be accurate (even though I don't trust them) but they respond too slowly, IMO! I have a ScanGaugeII with a digital readout that I use to display engine oil temp, engine coolant temp, trans oil temp, and the engine fan RPM.

Long story short, I was driving into a VERY stiff headwind and could stay in 'high gear' (torque converter lockup) at about 60mph ONLY when behind a big truck or on a downgrade. When heading uphill or the truck ahead of me got too far ahead, the trans would downshift and I could watch the trans temp climb. That made me nervous. I have no idea how high the trans temp might go, but when the trans shifted back into high gear (torque converter lockup) I could watch the trans temp drop.

So if you can keep an eye on your transmission temp, then downshifting is probably fine.
His trans will lockup in 2 through 6 gears. The Aisin has dual coolers as well.


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Old 05-14-2019, 06:07 PM   #7
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Yep, I would and do put it in Tow/Haul more and let it do it's thing.
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Old 05-14-2019, 07:31 PM   #8
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Originally Posted by NewBlackDak View Post
For that load, you should be engaging Tow/Haul which locks out 6th gear. You should be fine.
Yes, we always engage tow haul mode but it does not lock out 6th gear. You have to manually drop it to 5th. I think we're fine too, just wanted to hear from others. Thanks.
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Old 05-14-2019, 08:26 PM   #9
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Quote:
Originally Posted by rkymntsno View Post
We're new to towing something this big and heavy and was wondering, at what rpm do you tow at and what gear? The 5th wheel was right at 13,500 lbs. Our TV as you can see below is the CTD 6.7, 6 speed, 3.42 rear axle. At 65 mph, 6th gear, we're at about 1800 rpms. It would downshift to 5 occasionally, but not unnecessarily. It felt like it was "lugging" in 6th, and getting around 10 mpg. I downshifted to 5th gear and left it there the remainder of the trip. It stayed around 2,000 rpms and seemed to like that better. Gas mileage on the "lie-o-meter" continued to say around 10 mpg in 5th, same as 6th gear. All the numbers on the truck remained just about the same, oil pressure, trans temp, oil temp, etc. So am I right in towing around 2000 rpms in 5th gear?
I'm surprised at the 10 mpg with a 3.42 gear. I have an older F-350 with a 5sp and 4.36 gear towing 16,000 lbs at 70 mph and get 11.2 and 9.5 in mountains.
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Old 05-14-2019, 08:32 PM   #10
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I'm surprised at the 10 mpg with a 3.42 gear. I have an older F-350 with a 5sp and 4.36 gear towing 16,000 lbs at 70 mph and get 11.2 and 9.5 in mountains.
I know. It was windy all four days of travel, from crosswinds to headwinds. But coming from a Ram 1500 hemi towing a 34' TT weighing 6400 lbs getting 7 and 8, I'll take 10 anytime.
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