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What RPMs are you reading at 65MPH?

60K views 30 replies 17 participants last post by  PitownPi 
#1 ·
My truck is a 1996 F350 4x4 CC/LB 7.3L, 5-Speed.

Now, I realize that this truck is no speed demon, but like I have said before, I live in Northern California and around here, everyone drives like an idiot and goes as fast as they can.

I usually just set my own pace and not care about anyone else and how fast they think they need to go.

But my question is, when you are driving on the freeway, going about 65 MPH, what does your tach read?

Mine reads just at 2000. And for every mile an hour faster, you get exactly 100 rpm more-meaning that at 70, I am reading 2500.

Does this sound okay, or do you guys think that the motor is turning a little too fast for the kind of driving that I do?

Just by what I have told, can you give me a guess on what gears are in the truck?

What RPM SHOULD I try to stay at when I am driving on the freeway so as not to damage the motor?

Any other suggestions?
 
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#2 ·
1994 F-350 Dually 7.3 diesel. I too have the 5 speed manual. I don't like driving much over 60 as I am told that is when I start cutting back on my fuel mileage. My son has had it up to near 80 a couple of times but he isn't driving my truck anymore. :nono::lol:

My new battery cables should be in tomorrow, hope the starter makes it's way here this week too. As soon as I can get the "Beast" running again, I'll chime in here on what I prefer for rpm's too.

cheers!
 
#3 ·
i don't believe you will hurt the engine , the faster you go the more you hurt you're mileage . at 65mph my engine is turning about 2200 to 2300 rpm , i have 410 gears and an auto trans . you're info should be on the driver's door post. unless it has been removed or painted over . it sounds like you have the same gears , lower rpm's because of the 5 speed i suspect .
 
#16 ·
I see where you say info on drivers door. But, it only shows a code for my gearing "45".

I did write down my rpm's, seems to run 1800@50 and 5mph more each 200rpm to about 2400 rpm for 65.

My question would be if I am towing a 8k# trailer on the interstate, would I need to stick in 4th gear for 60 (my planned max speed, it's a 28' sailboat) or would I be ok in 5th gear, downshifting for hills?
 

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#4 ·
I have a 96 also but with the auto, my rpm's are at 2000 at 65 mph and I have 4.10's. as far as doing damage don't worry about that I have towed thousands of miles with my rpm's between 2200-3000. You will get much better gas mileage if you can stay at 2000 or below:thumbsup:
 
#5 ·
Thanks for the responses guys.

It's at 2100-2300 going 65.

But I've gotta throw this out there-GAS MILEAGE on a diesel truck???

Sorry, I'm a product of my surroundings!!!
 
#8 · (Edited)
But my question is, when you are driving on the freeway, going about 65 MPH, what does your tach read?
Will depend on rear end gear ratio. Like you can see from previous posts a 4:10 rear will put you at about 65mph (or perhaps a hair less) at 2000rpm.
Frugalyankee has a 3:80 or 3:55 rear if I would have to guess since he is 1900 rpm at 65.
At 1900-2000rpm my automatic e40d goes 68.5 and I have a 3:55 rear gear.

For me the tach reads 70mph while doing this though. I have determined through both gps and mile markers that I have about a 3% or 1.5mph odometer error at 65-70mph.
Tire size will also skew your results a little, but point being that your speed at 2000 rpm is a pretty good indication of what rear gear ratio you have.

Way to go on your mileage frugalyankee. Ive hit close to that a few times but I am usually sub 20mpg. The difference between 70mph and 65mph is very tangible in mileage but also takes an equivalent amount of discipline to stay that slow vs going 68 to 70.
 
#14 ·
Will depend on rear end gear ratio. Like you can see from previous posts a 4:10 rear will put you at about 65mph (or perhaps a hair less) at 2000rpm.
Frugalyankee has a 3:80 or 3:55 rear if I would have to guess since he is 1900 rpm at 65.
At 1900-2000rpm my automatic e40d goes 68.5 and I have a 3:55 rear gear.

For me the tach reads 70mph while doing this though. I have determined through both gps and mile markers that I have about a 3% or 1.5mph odometer error at 65-70mph.
Tire size will also skew your results a little, but point being that your speed at 2000 rpm is a pretty good indication of what rear gear ratio you have.

Way to go on your mileage frugalyankee. Ive hit close to that a few times but I am usually sub 20mpg. The difference between 70mph and 65mph is very tangible in mileage but also takes an equivalent amount of discipline to stay that slow vs going 68 to 70.
It is possible to recalibrate your instrument cluster. I think you can do it 5 times total.
 
#9 ·
With my factory tires, 235-85R-16's & my 265-75R-16's (same rev's/mile according to Firestone/Bridgestone website) in O/D 5th gear in my ZF w/3.55 gears I run 67 mph @ 2000 rpm. I've figured it out mathmatically, counting mile posts, with GPS, everything EXCEPT my friendly local law enforcement officer with his calibrated RADAR gun.

The E4OD has a higher O/D than the ZF. Not sure of the exact difference but would make about 100 RPM lower engine speed, like running 1900 while a 5-spd manual would be running 2000. A truck w/4.10 gears would run 2310 RPM compared to a truck with 3.55's running 2000.

Those speeds & RPM's are ALL accurate with stock sized tires with factory speedo calibration. If your speedo has been recalibrated and your tires are larger or smaller than the factory tires ALL bets are off.
 
#10 ·
2350 rpm at exactly 65 miles per hour, gps confirmed. 5 speed manual transmission with 4.10 gears.
 
#12 ·
To the OP: You have 4.10 gears. The 444E is rated at 2700 rpm & is expected to run there all day every day with no damage. Since we have 444E's essentially that would be my start point. Oh yeah, don't ever exceed 3600 rpm(the only way to achieve this is by being pushed(by load downhill or other vehicle)) becuase then bad things will happen. With 35's on my truck, I'm about 2350 at 70.
 
#15 ·
You guys know more about my truck than I do lol. I finally checked the door tag and I have 3.55 gears. The way this truck tows a 10K trailer I would have thought for sure it was at least 3.80 gears if not 4.10's. But knew it wasn't 4.10's with the fuel economy. My first diesel and still getting used to difference in power and towing capacity versus a gas engine (replaced a 460 with this truck). Love it and will never go back to gas for towing.
 
#17 ·
according to the info i have , code 45 is a 410 rear end . and for you're other question about towing . i have towed in over drive with a 35' trailer but i pay attention to my temps i also have a large trans cooler with a thermostatic fan . that being said i have been told by my trans guy that you shouldn't tow in overdrive because you can burn out the od gear . so if you have a good cooler and gages you can do it but shift down if the temp gets up . or just leave it out of overdrive . if you've got hills or a windy day i would leave it out , it would be you're call . i hope that helps you decide whether you want to tow in overdrive or not . i don't like to tell people what to do when it's a judgement call .
 
#19 ·
nope i thought you had an auto trans . what you have to watch is EGT's and engine temp . if they get too high you need to down shift . thats easier to keep tabs on . you could treat it like you are lugging the engine .
 
#20 ·
I have 4.10 gears in my truck. I had to follow an oversized semi-trailer a few weeks ago as an escort. With the frost laws, we were doing between 55-60, which put me a little over 2000 rpm, for about 150 miles and I picked up about 60 miles more than usual on a half tank of fuel. Do you think that increase in mileage would be consistant if I switched to taller gears and were doing 70 mph at the same engine speed?
 
#23 ·
Everything is normal. These engines can run at the redline all day long and you have a few RPM's left after 2300 RPM's.
 
#27 ·
It is because of the rear end gears. It sounds like you have 4:30 rear gears that are made for towing a heavy load and not for a daily driver.

Smoke is a bad subject. You really don't want it to smoke since that is just unburnt fuel and is the reason for all the EPA required equipment on the new diesels.
 
#28 ·
65mph on flat = 2100-2300 rpm w/4.10 dually

65mph on flat = 2100-2300 rpm w/4.10 dually

when going downhill, I set my tune back to STOCK and enjoy the quiet glide!

(really enjoy having the stock tune available, it's nice for sneaking out of the yard)
 
#29 ·
Just removed a bunch of argumentative posts from this thread.

Keep it on-topic and civil guys, or it will be locked down. :nono:

klhansen
Moderator
 
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