Low RPM's an issue?

cjaama

TJ Enthusiast
Joined
Jan 3, 2018
Messages
303
Location
Troy, NY
I have an ’04 LJ on 305/16’s (33x12), auto trans and stock gearing. Pretty much everyone online says that’s a lethal combination. However, I find it completely fine. Acceleration is fine, maintaining speed is fine… no, it’s not a hot rod, but it’s exactly as fast as I want it to be for street driving in a tin can. If I was offroading it I’d definitely want it regeared, but again, I have no problem with it.

So, my only concern is driving with it in OD and doing about 50mph on level ground I’m only at about 1,400 RPM. Is this bad for the motor? Are there any other issues I should be aware of?
 
These things do perform best with higher RPMs in terms of power, fuel economy, and in regards to keeping the engine cleaner. Still, you don't need to worry about re-gearing it if it doesn't bother you, but if it was me, I'd probably re-gear it in the long run.
 
1,400 seems a little low. If you're commonly operating at that RPM (e.g., lot's of highway driving) then you are also going to want to burn carbon build up out of the motor by running the RPMs very high periodically.
 
1,400 seems a little low. If you're commonly operating at that RPM (e.g., lot's of highway driving) then you are also going to want to burn carbon build up out of the motor by running the RPMs very high periodically.
Got it, lots of red light redlining.
 
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If you were to re-gear to 4:88, or 5:13, your fuel economy would improve, as would performance. Running taller tires and not re-gearing to compensate is tough on the entire driveline. It is like towing a trailer. Your Jeep wasn't geared to go 1400 rpm at 50 mph for a reason.
 
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1400rpm at 50mph sounds awful for anything more than a downhill and can't be good for the engine.

This idea that a street driven Jeep doesn't need to be regeared is confusing to me. It isn't completely fine...

2003 Rubicon
 
I guess my next question is, if the low RPM's is a problem, what is the problem with leaving it with the O/D off?
 
Leaving the od off may take care of the highway part of it. But it doesn't change the fact that all the other gears are still too tall. When taking off from a stop, the torque converter has to slip more to get going..... almost like starting off on second gear. The taller gearing also means that there's a bigger jump to the next gear. All of this makes the transmission run hotter, and heat is the biggest killer. I know two friends that lifted their pick ups, and went to 37,s. They just turned off they're overdrives , and neither of them reached the 70,000 mile mark before their transmission s puked.
 
I guess my next question is, if the low RPM's is a problem, what is the problem with leaving it with the O/D off?

I leave the OD off for everything but highway speeds 65-75....it's the first button i hit after starting the Jeep.