Safe RPM for longer (150 mile), freeway trips

JLANEF

JLANEF

TJ Enthusiast
Joined
Jan 9, 2019
Messages
138
Location
Chandler Arizona
As many of us with the 3 speed auto transmissions know, bigger tires and lower axle gear ratios provide great power, but really run freeway RPMs up. Anyone have a thought on max RPM to cruise at on the highway for a couple hours or more? With 33s and 410s, I’m tacking over 3000 rpm at 70. In Az I get blown off the interstates at 70 and don’t like running 3000 rpm on a 4.0 with 130,000 miles Either! Am I being too conservative? Thoughts?
 
I've had 33's with 4.56 for years now. I usually run about 3000-3200 rpms on the highway. 3k is nothing to worry about for prolonged periods of time. I've done a few 1000k mile trips to king of the hammers, drove non stop with zero issues.

I do remember an old post of @mrblaine I think where he said 3200rpm max sustained, but I don't remember his reasoning.
 
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JLANEF said:
As many of us with the 3 speed auto transmissions know, bigger tires and lower axle gear ratios provide great power, but really run freeway RPMs up. Anyone have a thought on max RPM to cruise at on the highway for a couple hours or more? With 33s and 410s, I’m tacking over 3000 rpm at 70. In Az I get blown off the interstates at 70 and don’t like running 3000 rpm on a 4.0 with 130,000 miles Either! Am I being too conservative? Thoughts?
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Don't worry about it.
 
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Trevlaw said:
I've had 33's with 4.56 for years now. I usually run about 3000-3200 rpms on the highway. 3k is nothing to worry about for prolonged periods of time. I've done a few 1000k mile trips to king of the hammers, drove non stop with zero issues.

I do remember an old post of @mrblaine I think where he said 3200rpm max sustained, but I don't remember his reasoning.
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I never put a limit on it. What I said is the factory spec is 68 mph at 3000 rpm with them in full knowledge that the speed limits on our highways often exceed that speed for very long stretches at a time.
 
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Dan Carey said:
Safe and prudent are 2 different things. I like 2500 at 70. Every time the piston goes 1 cycle it is wearing out the rings and other parts, so cycle it as few times as possible.
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Bullshit. I have a TJ Unlimited that I ran a supercharger on for 2 years that has 200,000 miles + on it and it runs as good now as the day it left the assembly line. It has 32's, 4 speed auto and 4.88 gears in the diffs. I don't even let it get into OD until I'm running over 3000 rpm and I've driven it like that since I owned it.

Moderate application of the throttle (unlike you mamby pamby drivers) will shoot it past 32-3400 rpm at every shift.
 
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Most large generators run at 3600RPM their whole life and that's considered low rpm for an internal combustion engine as far as I know. 3K all day wouldn't bother me one bit, not just extended periods on the highway, years all day long.
 
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mrblaine said:
Bullshit. I have a TJ Unlimited that I ran a supercharger on for 2 years that has 200,000 miles + on it and it runs as good now as the day it left the assembly line. It has 32's, 4 speed auto and 4.88 gears in the diffs. I don't even let it get into OD until I'm running over 3000 rpm and I've driven it like that since I owned it.

Moderate application of the throttle (unlike you mamby pamby drivers) will shoot it past 32-3400 rpm at every shift.
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No wear on the motor is reserved for special people only.
 
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JKP said:
You are still cycling it the same number of times, just over a longer period of time
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I agree with that. I also know that higher RPMs wear out parts faster for most people, not all. Most would agree that 5000 RPMs is not a good number for a 4.0?
 
Dan Carey said:
I agree with that. I also know that higher RPMs wear out parts faster for most people, not all. Most would agree that 5000 RPMs is not a good number for a 4.0?
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There are also different versions of high rpm....higher rpm with less load will wear the engine less than low rpm with high load. That and the difference in wear accelerated or slowed down in relation to rpm just doesn't matter over the life of the engine. We are talking about millions and millions of rotations in either scenario and neither are dying at any time point that we can blame the rpm for with certainty.

The important part is you don't see any more dead 4.0's that had the 3 speed on them than ones that had the 5 speed on them. for this discussion, I just do not think rpm attributes to any sort of regular problem experienced by Jeep owners.

That and if you were to drive a 3 speed geared to run 2500 at 70, that thing will be a tremendous pig around town and offroad.

I guess to put what I'm saying another way, let's say you have two jeeps, both going to 250K miles. 250K miles at 70 mph is 3571 hours.

Jeep 1 is geared for 2500 rpm on the highway at 70.

2500 rpm for 60 minutes is 150,000 revs in an hour. Do that for 3571 hours and it's 535,650,000 revs. 535.6 million revolutions to 250K.

Jeep 2 is geared for 3200 rpm on the highway at 70.

3200 rpm for 60 minutes is 192,000 revs in an hour. Do that for 3571 hours and it's 685,632,000 revs. 685.6 million revolutions to 250K.

Between these two, I just don't see how Jeep 1 is really going to last longer, They both made it to 535,000,000 million revs without giving up and no signs of it happening soon. Is another 150 million going to really matter that much? Engines blowing can almost always be attributed to something other than revving too high of rpm for their lifetime.
 
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JKP said:
My 06 Rubi has been running at approx 3K RPM on the interstate since new. Just about 240K mi on it now... Just drove it 6 hrs to Nashville TN and back.
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WOw, i've wondered the same question as the OP. 3K+ feels like a lot of rotations per minute.
 
mrblaine said:
Bullshit. I have a TJ Unlimited that I ran a supercharger on for 2 years that has 200,000 miles + on it and it runs as good now as the day it left the assembly line. It has 32's, 4 speed auto and 4.88 gears in the diffs. I don't even let it get into OD until I'm running over 3000 rpm and I've driven it like that since I owned it.

Moderate application of the throttle (unlike you mamby pamby drivers) will shoot it past 32-3400 rpm at every shift.
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I go to near redline on every drive of every vehicle I have driven. I have yet to wear an engine out from too many rotations.
 
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B00mb00m said:
WOw, i've wondered the same question as the OP. 3K+ feels like a lot of rotations per minute.
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It bothered me when I got it.

But, after nearly a quarter million miles, nothing but the problematic 05/06 OEM OPDA has been changed out on the engine and it still runs great.
 
JLANEF said:
As many of us with the 3 speed auto transmissions know, bigger tires and lower axle gear ratios provide great power, but really run freeway RPMs up. Anyone have a thought on max RPM to cruise at on the highway for a couple hours or more? With 33s and 410s, I’m tacking over 3000 rpm at 70. In Az I get blown off the interstates at 70 and don’t like running 3000 rpm on a 4.0 with 130,000 miles Either! Am I being too conservative? Thoughts?
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3000 or over is nothing for the 4.0, I ran well over even that for years when I was running 4.88 with 35" tires with my 32RH. I would have rather had 4.56 but I had 4.88 from the days when I had a 5-speed, before converting to the 32RH. I'd say 4.10 is the ideal ratio for 33's.
 
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I've noticed something over the years, you can rev an engine in your driveway under no load to redline and people will get "nervous" that something is going to explode when it is extremely low load. It's just loud and scary. Those same people have no problem winding out the engine under load on the street which is much more difficult for the engine. It's all perception. These engines are run at close to redline, maybe even over, for thousands of hours on test stands before they enter production. It's no big deal, if it was the redline would be lower.
 
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