I OWN A 99 F-250 SD POWERED BY A 5.4L, AUTO TRANS AND 4.10 REAR END. WHILE TOWING MY 5000 LB. TRAVEL TRAILER WITH THE OVERDRIVE OFF, THE ENGINE RUNS AT ABOUT 3200 RPM WHEN GOING 70 MPH. CAN ANYONE TELL ME IF THIS IS TOO HIGH OF AN RPM FOR THIS ENGINE.(AT 65 MPH THE RPM IS ABOUT 3000)
THE TRUCK LACKS POWER WHILE TOWING IN OVERDRIVE AND HUNTS FOR A LOWER GEAR SO I CAN'T TOW WITH IT ON. MOST HIGHWAYS IN MY REGION ARE 75MPH BUT IF I HAVE TO SLOW DOWN TO PROTECT THE ENGINE, I WILL.

 

To me, it makes sense that running at 3200rpm is harder on the engine than running 2500.
I'm sure the engine can 'take it', but you'll have to do more maintenance on it in the long run if you want to get several hundred k miles out of the engine.

Also, does the tranny 'search' for gears if you try to do 60 or 65 in OD?

If it were me, I'd back off the speed some and keep it under 3000, but I'm a conservative driver and expect to get 200K miles from my engines..

 

Even at 60-65 if I encounter the slightest grade or headwind....forget it. Either I or the cruise control has to get into the throttle to the point where the tranny downshifts and then hunts back and forth out of O.D.(which will ruin a trans pretty quick)
I'm with you, I plan to get many years and miles out of my truck and don't want to compromise my engine just to get somewhere a little faster. Probably better to keep the speed below 65(3000 rpm). The truck pulls like a mule with the overdrive off.

 

My '99 f250 sd sc 5.4 5 spd 4.10 is turning the exact rpm in fourth gear as your 3rd in the automatic. Both gears are direct drive thru the transmission (1 to 1). I haul a 3000 lb camper on mountainous and sometimes flat terrain. Sometimes hunting in the hills or sometimes on the freeway to the coast. I almost always use 4th gear and find it very efficient. The only exception is when the highway is very flat, I will use 5th.

My 4th gear at 60 mph is 2700 rpm as I am sure yours is in 3rd. I prefer this speed and gear for a few reasons. 1) The rpms are high enough that most hills are overtaken with no shifting and the cruise control doing the work. If I see a big hill coming up I might hit the gas a little to bump up the rpms and take the hill, then let the cruise take over again. 2) I feel this rpm will have no long term effect on the engine, even when running for hours. 3) My 4th gear is direct drive straight thru the transmission - no meshing gears to rob efficiency and horsepower, less wear, less heat. Your 3rd gear on the auto should be the same with a few exceptions inherent with an auto.

One thing to keep in mind regardless of your rpm is that the faster you go, the harder the engine has to work in general and the less efficient your travel is. At faster speeds your oil will deteriorate faster, and things will run hotter.

As a sd owner with the 5.4, I had efficiency in mind from the start.

To answer your question; No, the 3200 rpm will not "hurt" your engine, but if you cut it down to 60 or 65 every thing will last just a little bit longer, and you will stretch a little bit further between filling stations. Besides, if you have an rv on, isn't it all about sitting back and enjoying the scenery??

PS My 3000lb camper is very tall so it is probably a similar tow to your rv considering the wind resistance I pick up.

It is a pleasure to drive with it on. I get 12mpg on the hwy, 11 thru the mountains (big mountains). Empty I get Hwy: 14mpg at 75mph, 15mpg at 70mph 16mpg at 65mph, and 17mpg at 60mph.
City and country roads mixed runs 13 to 15mpg.

I am curious as to what mileage you are getting towing at those higher speeds??

Dean

 

On a trip from Las Vegas to Santa Fe N.M. for instance, I averaged 9-10 mpg towing while turning 3000-3200 rpm @ 65-70mph. Recently when driving solo from Vegas to Phoenix while going the same speed in overdrive, I averaged about 14 mpg.

 

Your correct, the 5sp is more efficient than the auto, and 3rd in the auto is 1:1, and 4th in the 5sp is 1:1.

However, 4th in the 5sp (1:1) has the same number of gears meshing as 1st through 5th. Not the 'direct drive' as you described.

Also, the OD on the auto (4th) is .72, and on the 5sp its .76. So the 5sp might have a little extra capability to tow in OD.

Y2K F250 XLT 4x2 SC 5.4L 5sp 4.10LS

 

Crittergetter: Wow, that is a big mileage difference with the OD. I just remembered seeing a TSB about auto trannys that hunt between 3rd and OD when towing, I think they have a fix for it if that is what is effecting yours. I have heard of v-10s having the same problem and getting it fixed.

Roger_B: I have the shop manual for the '99 Sd with a diagram of the 5spd tranny operation. In 4th gear it splines the input shaft to the output shaft straight thru. The gears mounted to the shaft are turning, but they are out of contact position from the 3rd shaft. The shop manual description of operation seems to confirm this as I read it.

Unless I am missing something, I am pretty sure that 4th is direct drive straight thru the 5 spd without gear meshing. This is un-scientifically confirmed by the fact that 4th gear is the only gear without a hint of gear whine.

PS

The shop manual is great - one of the best uses I could of had for $140.00. For a SD enthusiast, it makes good reading.

 

Thanks for the info on the SD 5sp tranny.
I've not seen that type of configuration where they figure a way to spline the input/output shafts directly together..

 

Thanks to both of you for all the usefull info. I've learned alot.

 

Crittergetter: Here is the tsb:

Service Bulletin Number: 99-16-9
Bulletin Sequence Number: 765
Date of Bulletin: 9908
NHTSA Item Number: SB60766
Make: FORD TRUCK
Model: F SUPER DUTY
Year: 1999
Component: POWER TRAIN:TRANSMISSION:AUTOMATIC:OTHER PARTS
Summary: SOME VEHICLES MAY EXHIBIT A NO 3-4 UPSHIFT, OR A 3-4 / 4-3 SHIFT HUNT ONLY WHILE THE CRUISE CONTROL IS IN USE. *TT