I just took a road trip and I know it’s an older jeep and not great with gas but I didn’t really a big improvement on mpg when driving on the highway vs city. And it’s a 4 speed automatic transmission with 31inch tires and when I do 70mph I am sitting around 3000 to 3250 rpms and didn’t know if this was normal. And on the road I decided to drive slower at 60 mph around 2750 rpms and only got 15 mpg. It’s the stock transmission with 3.77 axles. Is there anything wrong/I should check for or anything I can do to improve the rpms and mpg?
Highway speed with rpms
- Thread starter DS TJ 1998
- Start date
deserteagle56
Member
Running those rpms at 70 mph tells me your tranny is not shifting into overdrive, maybe not even into 3rd gear.
Exactly what gas mileage are you getting?
Have you monitored live ODB data? Fuel trims, O2 sensor voltages, vacuum. Data will help pinpoint the problem.
-Mac
Have you monitored live ODB data? Fuel trims, O2 sensor voltages, vacuum. Data will help pinpoint the problem.
-Mac
I believe your 1998 would have the 3 speed 32RH auto which doesn't have an overdrive. 15mpg at 55-65mph sounds reasonable though perhaps a little low on 31s. I see about the same at 55-65 with a 5speed, 33s and 4.56 gears and about 1.5mpg lower at higher speeds.
The 1998 had a 32rh, which is a 3 speed without overdrive.
Your rpms look about right. So does your mileage.
32rh/29.5"/3.73=3186rpm @75mph
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