42RLE Four Speed Automatic Overdrive

Speartip

Speartip

JK Addict
Supporting Member
Joined
May 8, 2022
Messages
1,074
Location
Victoria BC , Canada
Doing some research last couple days many are commenting on leaving OD off in the older 4 speed autos when on hilly roads as the trans searches for gears a lot and will struggle.

Users were saying it can lead to heating up trans etc and undue stress on engine .

I’m running an after market trans cooler so haven’t experienced the “hot oil” warning . But even after all the work recently done still hunted for gears and sluggish on hills at hwy speeds with OD engaged .

Decided to test it out with OD off yesterday .To be clear when off road it’s always off and put in 2nd .

On the hwy sections that were really curvy and hilly with a speed of 60-80 KPH it was great . Literally stayed in 3rd the entire drive hovering around 1700- 2K rpm.

On the way back crossed Island to east coast . Relatively level at 100kph engaged OD and was good . RPM 1700.
Once on the other hwy heading back to Victoria , hilly , curvy and 80-90 KPH took off OD. Stayed in 3rd . No lugging of engine . 2- 2.3 K rpm . Drove really well .

If you’re driving a 2007-2011 JK auto try it without OD and you will be pleasantly surprised how much smoother it runs .
33” tires
3.73 gears .

60KPH = 37MPH
80KPH = 50MPH
90KPH = 56MPH
100KPH = 62MPH
 
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As long as the torque converter is locked, your transmission temperature should remain in the normal range. These 3.8 and 3.6 engines run better at 2k rpm's and up. Have you adjusted your tire size with Jscan?
 
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Rich1961 said:
As long as the torque converter is locked, your transmission temperature should remain in the normal range. These 3.8 and 3.6 engines run better at 2k rpm's and up. Have you adjusted your tire size with Jscan?
Click to expand...

I've heard that 3k RPM is the sweet spot for 3.8s. I have an '07 auto with 4.10 gearing and 33s and my RPMs are always dead on 2k at highway speeds. 60 to 75 mph.
 
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Rich1961 said:
As long as the torque converter is locked, your transmission temperature should remain in the normal range. These 3.8 and 3.6 engines run better at 2k rpm's and up. Have you adjusted your tire size with Jscan?
Click to expand...

Yup . Been using JSCAN for awhile . It’s an awesome tool !
 
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