RPMs, Speed and the 3.7 Engine

arturo · **Joined:** Tue Jul 11, 2006 5:21 pm **Posts:** 9

Hello Folks :

I just got my brand new 2.006 Liberty Renegade (6 speeds) and so far I'm preaty happy about it (my 2nd jeep since my old 1.995 Wrangler). In the mean time I got used to drive cars like HONDAs and TOYOTAs, where the RPM range of 3.000 - 5.000 is considered normal and not harmfull ...

I have no information from the dealer except "don't go beyond 2.500 RPMs", but I was wondering what RPM range is considered "normal" "peak" "excesive" and it's relation with torque ...

I'm not planning to make it to NASCAR

but I like to know the speed limitations vs RPM involved ... I have the feeling that going over 70-80 mph could be bad for the engine ... (with my old Jeep the 100mph limit was top !!!)

Saludos

Arturo

Jeepjeepster · **Posted:** Wed Jul 12, 2006 5:37 pm

2.5rpms? I hit 4k today for about a mile while pulling a boat up a hill on the HW. I Just put it into 2nd and did about 55mph until I got over the top. I believe the redline is 5600rpm, I wouldnt be bouncing on that all day but Im sure around 3-3.5rpm wouldnt hurt a thing to hit everyday. Just make sure the engine and tranny is warmed up before you go laying it to the floor. Wouldnt be a bad idea to use syn if you plan on being hard on it. Keep the tranny and rear diff changed too.

Edit: Im sure you could go over 80mph without hurting the engine, but its not a good idea to do in the libby.

tjkj2002 · **Posted:** Wed Jul 12, 2006 5:46 pm

As long as your tach needle stays out of the red you are fine,under full throttle accels your tach will go right up to redline and should shift so you will be fine.When I tow my 3500lb trailer I lock out OD so going 60-65mph my tach is reading 2900-3200 rpm's.The only thing is if you hold a very high rpm,say 4000 to redline for extended periods of time then you may have a chance of doing some damage but unlikely.The bad thing about high rpm's in the KJ is very decreased gas mileage,the factory has done many endurance tests to make sure these engines can take those high rpm's also.Not to sure on exact tests but have read about a plastic engine built by Ford(all plastic execpt clinder liners and pistons)ran at full throttle(6500rpm's)for over 200 hours with no damage(read in moter trend mag a couple of years ago).Who ever told you that is feeding you a line of crap.

chefdab · **Posted:** Wed Jul 12, 2006 5:50 pm

There have been a few owner who previously tested the top mph limit. They found that there is limiter that cuts in at 114 mph. I personally wouldn't want to try that though. As for rpms, mine has only kicked over 4000 once or twice when I was driving through the mountains with the cruise on and had forgotten to turn off the overdrive. I wouldn't test the rpms out though until you've got a few thousand miles on the clock to make sure the engine is sufficiently broken in.

Jeepjeepster · **Posted:** Wed Jul 12, 2006 6:24 pm

Ive heard of the guys out in moab hitting 5200rpms pulling a loaded trailer up a hill for many miles and doing about 45mph. Must be some rough mountains! I do not believe the 3.7 will let you hurt it, it just shifts no matter what. Ive had it in 1st gear(pulled the shifter back) and it still shifts when it needs to so you do not over rev it. Its a smart little thing. The engines with the electronic throttles are even better.

PitViper · **Posted:** Wed Jul 12, 2006 7:03 pm

read your book
Part of the break in procedure says at highway speeds run at full throttle for a few seconds.

I wouldn't do this untill after you have about 1000miles on the motor and do a oil change.

smitty1938 · **Posted:** Wed Jul 12, 2006 8:11 pm

I just put it to the floor when I left the dealers the first time and keep it there quite often. If it is going to break I want it to do it under warranty. I never baby any engine. I just do regular maintenance when it is due. I had a 2004 Dodge Quad cab before the jeep and it had the 4.7. Drove it like I was going to a fire and never had a minutes problem.

jeepkj02 · **Posted:** Wed Jul 12, 2006 8:29 pm

I'm sure you already knew this, but...the heavier your right foot, the emptier your wallet is going to be! :wink:

smitty1938 · **Posted:** Wed Jul 12, 2006 8:33 pm

I bought my jeep to have fun with. If I had wanted fuel economy I would have bought a Honda.

gopherbeats · **Posted:** Wed Jul 12, 2006 9:15 pm

In the words of a fellow friend:

"if i cared about gas mileage in my suv i'd get a kia.
if i got a kia i'd drive it off a cliff.
then hike down and torch it.
then bulldoze it.
then sell it to some stupid kid"

jason thompson · **Posted:** Wed Jul 12, 2006 9:26 pm

i dont know about the KJ but TJs have a revlimiter at about 5500rpm and that is a good size I6 so a V6 is probably at 6k
i see guys hit the revlimiter all the time in there TJs in fact some spots the line is a little like this
"ok as soon as your front tires start going up just find the revlimiter"

oh yeah and if you did 100mph in a YJ my hat goes off to you even stock my tj got "squerly" over 75 now its a little better but i am cranking out 3100 rpm to do 70 so to do 100 i would almost "find the revlimiter"

SavageSS27 · **Posted:** Thu Jul 13, 2006 2:14 am

I believe the "don't pass 2,500 RPM" was just for the break-in period, i hit 4K in mine on a daily basis...darn, driving a KJ is fuuuUUUn...

streetKJ · **Posted:** Thu Jul 13, 2006 3:25 am

I was doing 85 on our long bridge here and up comes roaring a BMW X5 in a mad rush. I could tell he wanted to pass me so I said the hell with it and locked out overdrive for higher rpms. He didnt have the guts to pass a Jeep doing 110. I backed off the throttle because I didnt want to use the brakes for the upcoming "wall" of cars. He slammed on the brakes and did some noob pass in the right lane to get ahead.

The 3.7 feels pretty sturdy, and I often go in the 4k to redline threshold with no problem except gas mileage. I'm running at 8k miles with Mobil 1 synthetic. I need an oil change soon.

KJ_Dave · **Posted:** Thu Jul 13, 2006 5:40 am

I cruise at 80 - 85 on a daily basis and never have had a problem, except when the mid-life crisis rejects in thier BMW and MBs come flying up. That is when I go faster and block them in behind slower traffic.

Se7enLC · **Posted:** Thu Jul 13, 2006 9:08 am

The manual transmission liberty has the same engine as the automatic, and I usually stay in a gear from 2k all the way up to 3k, maybe a little higher, depending on my mood :-P

Jeepjeepster · **Posted:** Thu Jul 13, 2006 9:51 am

Ohh, I forgot he has a 6speed. Look over my threads where I said it protects itself, it cannot with a 6speed.

RPMs, Speed and the 3.7 Engine

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