5th gear/2400RPM or 6th gear/1700RPM???

[Radshooter]

We are currently pulling our big (17,700 lb) fiver through Illinois. A lot of our route is on 2 lane hiways at 55 mph. I tried 6th for awhile at 1700 rpm, but it seemed like the engine was working pretty hard on some of the hills to maintain speed, and the EGTs crept up pretty quickly. After an hour or so, I downshifted to 5th and just left it there the rest of the day. EGTs went down a couple hundred points. RPMs were holding at 2400.

I seem to remember reading somewhere that the power band starts at 1600 rpm for the 5. 9 HPCR. Is 1700 lugging the engine too much? It struggles to accellerate in 6th, while it seems to have lots more pep in 5th. Is 2400 too high for driving all day?

When we get to Interstate and can run 65+, it does fine in 6th, but RPMs are up around 1900-2000 also. My personal speed limit with that big trailer is 65 MPH, so I don't like running 70 just to get the rpms up.

Thanks for any advice you can send my way!

Steve

 

[steved]

5th with just enough input to hold that speed... don't try to race up hills.



I found the EGTs are almost uncontrollable in a stock truck when in 6th (towing) at lower RPMs in hills... running it at a higher RPM in 5th will still cause heat, but if you "level off" at a constant speed, EGTs will stay manageable.



steved

 

[Radshooter]

Thanks steved. The hightst EGT I saw all day, even in 6th, was only 1000 or 1100. When I dropped to 5th, they hung around 600-900 depending on the hills. I try to keep the speed as steady as possible, and try to squeeze out another mile or two per tankful. At $3. 40/gal, I try to stretch it as far as possible. That is why I was trying 6th, but the difference saved was not worth the extra work for the engine.

Thanks again... . Steve

 

[sfr1047]

I have noticed that the transmission temps on my 5600 are 20 to 30 degrees cooler towing in 5th rather than 6th.

 

[steved]

I have noticed that the transmission temps on my 5600 are 20 to 30 degrees cooler towing in 5th rather than 6th.

For several reasons... probably the main one is less load. But you aren't turning planetaries in 5th (and it is direct drive)...



steved

 

[JasonCzerak]

For several reasons... probably the main one is less load. But you aren't turning planetaries in 5th (and it is direct drive)...



steved

There are plantaries in a manual?

 

[JCasper]

I have noticed that the transmission temps on my 5600 are 20 to 30 degrees cooler towing in 5th rather than 6th.

I have heard that from quite a few people also.



I would go with 5th gear. I will run 5th at 62 on the Interstate when I am hauling a load of hay with a weight of 13,000lbs or so. It just seems to be easier on the truck.

 

[RVTRKN]

My personal preference when pulling heavy is 6th until I start to climb any grade at which time I will drop down to 5th to keep up the RPM's for a better EGT. I don't have a pyro gage and I don't know what my temps are, that being said, my Diesel tech told me "the stock configuration of the CTD will not go over the ratings of the EGT when your within the GCWR". Now I don't believe all of that but level towing should be fine, thats why I drop down to 5th and about 24-2500 RPM's when climbing. The first thing you should do if you bomb (become your own warranty station) your rig is get the gages with your pyro being the highest priority and then all bets are off.



With your truck and your 17K 5ver, you should be over the GCWR and may warrant the 5th gear running at any time, and a watchful eye on that pyro gage would be recommended. Because of your heavy GCWR the trany will get hot as well and you should get the trans cooler that Geno sells and add the trans temperature sending unit to the pyro gage.

 

[SBeretz]

My truck really likes to run at 1900-2100 when fully loaded with 5ver in tow. Seems like the sweet spot for mine. On the level, I can run at 55 at 1700 RPM's but I still keep a close eye when hitting larger hills. I don't think you can hurt your truck by running it at 2400 all day long. My truck ran at 2250 at 70MPH before I went to a larger tire. Scotty

 

[jmadison]

no plantaries in a manual trans.

 

[steved]

There are plantaries in a manual?

I was half asleep... sorry.



But my other statement holds... more load in OD.



steved

 

[steved]

... my Diesel tech told me "the stock configuration of the CTD will not go over the ratings of the EGT when your within the GCWR"...

I was well under my GCWR (probably around 10k total), and could easily sail past 1450*F without even trying. Especially out in the rockies... must be an altitude dependent thing (less air)?



steved

 

[Radshooter]

Update

Thanks for all the input guys. We made it out of Illinois, through 80 some miles of Missouri, and are sitting in Arkansas tonight. (Eventually we are going to wind up in Houston. )

That 55 speed limit for trailers in Illinois sucks a big one. I kept the truck in 5th most of the day today, except for a few long downhill runs I slipped it into 6th and let it coast downhill, downshifted back to 5th to pull up the hill ... ...

In 5th gear the EGTs hung around 700 on the flats instead of the 900 yesterday in 6th. I liked that better. The 2400RPM did not seem to bother the engine at all.

After we cleared Illinois, the speed limit went up to 70MPH, so I kicked it up to 65 in 6th gear at 1900 RPMs. EGTs stayed pretty cool, around 800 on the flats. Funny how just a few hundred RPM can make that much difference.

Thanks for the info on transmission temps. I do not have a temp gage on the transmission yet. I would not have thought 5th gear would run cooler than 6th.

About the stock EGTs not getting too high... That is bull. . Before I got the AFE intake, I could run the EGTs up to 1400 or even 1500 without even trying when pulling the trailer. The point about mountain air may have some validity, because back then, we were in the western USA. I really noticed it out west. After the AFE, I still could still run up the EGTs, but it seemed to take a longer, harder, steeper pull to do it. This is our first real trip east of the Mississippi River. The highest EGT I have seen on this trip is 1100 pulling a hill in 6th gear. I dropped to 5th and the EGTs dropped to 900 for the rest of the way up the hill. We never got far enough east to hit any of the Applachian mountains, pretty much stayed in the flats. Basically, from Nebraska to Wakarusa, Indiana, then south to Houston. No real hills on this trip.

OK... enough babbling. I will let someone else talk now. Thanks again... ... Steve

 

[DavidGardner]

You are not going to hurt your engine by reving it up. On my engine(12 valve) The rpm is governed by the fuel pump. I can run my engine wide open all day and it will not hurt it. Will not rev past the red line. Of course we are talking 95 12 valve here. Yours might be different but I dought it that Cummins is going to allow your engine to self destruct in stock configure .



My 2 cents worth.

Dave Gardner

 

[Ragain]

I've been pulling Air Force Mobile Lab trailers out of KS that weigh 23,000 lbs with a pintle hook coupler. 13'6" tall and 35' long..... just like pulling a parachute! With only 1,200# tongue weight, they can get away from you really quick. I keep it in 5th (direct) and 59 mph @ 2250 rpm (3. 54 rears). The EGT's will stay 800° on the flat and climb to 1000° on a hard pull. I do not allow the EGT's above that! These trailers move so much air that dropping down a 6% grade will not increase in speed while coasting. So that means, on a flat run they are like PULLING up a 6% grade. I feel that because I keep my EGT's down, RPM's up (2,400 max) and boost at or below 20 psi is how I've been able to get the nearly half million miles out of "Ol' Shep"!

 

[MA2LA]

Don't worry about the rpms mine has spent hours on end at 2400. As for the fuel mileage you will proble see better numbers using 5th in situations like that and you motor will thank you. As for the EGTs I have the auto and I have tried to see how high the egts will get and with out the boost fooler the highest was 1250 and with it about 1150 so if you are having issues thaat little $70 piece is a nice option.

 

[RVTRKN]

I was well under my GCWR (probably around 10k total), and could easily sail past 1450*F without even trying. Especially out in the rockies... must be an altitude dependent thing (less air)?



steved

You are not going to hurt your engine by reving it up. On my engine(12 valve) The rpm is governed by the fuel pump. I can run my engine wide open all day and it will not hurt it. Will not rev past the red line. Of course we are talking 95 12 valve here. Yours might be different but I dought it that Cummins is going to allow your engine to self destruct in stock configure .



My 2 cents worth.

Dave Gardner

I did say that I don't believe everything he said and is the reason I drive the CTD the way I do. The reason for the high RPM is for more air to fuel ratio to keep it cool, and that same tech did say I could run the CTD at the governed RPM all day long, which I would not do, but its comforting to know it would not effect warranty for both points per the conversation with the tech. (There were other techs that heard him, for the proof if he were to deny it later. )