Best torque converter for mileage?
 

All,

I have a mostly stock 2002 Jeep Grand Cherokee Overland with 4.7HO and 545RFE transmission. The previous owner must have been in Florida. I suspect they were towing a boat which was too farfegnugan heavy on a regular basis because I had to replace the UpCountry coil springs. Inside of 120K miles, that's the only way I know of you could wear out coil springs.

Been throwing a code about the torque converter for a bit now. I can tell it is not locking up by the tach and the massive drop in mileage. Had tranny fluid changed twice recently, second time having them add Lucas hoping there was just something clogging up the flow. Debated about replacing the entire transmission, but have put nearly 1000 miles on the transmission as is and am having second thoughts about that. Seems pretty solid.

A few times each summer I have one 18 foot trailer we put either one or two zero turn mowers on to transport between farms. That's the extent of towing. This Jeep spends the rest of its life on-road.

Previous owner did "some" mods to it. K&N intake system. I think He/She had it chipped as well. The reason I think that is I could get 25 MPG on the Interstate with base gas. Not just a one time thing. As long as I set the cruise control after merging on, that was a pretty consistent ocurrance.

So. If I'm going to replace just the torque converter, what is the best one for mileage? I don't care about mudding, crawling or any other abusive Jeep activities. This is close to stock (but might not be the original/stock transmission or TCU). When I get the repair done I just want to be able to get 25MPG again. Right now I'm getting the 12-14 MPG Jeeps are famous for. Even on its worst week, local driving lots of idling due to winter, this used to get over 16 MPG.

Thanks,

It might be helpful to complete the diagnostics to fully identify the fault, prior to disassembly / replacement / reassembly.

The torque converter lockup is an electrical / hydraulic function. It is possible that the problem is not the torque converter, but instead the control / actuation for the lockup.

Follow the FSM or the ATSG manual for testing prior to disassembly.

Just as a point of reference, my 2000 WJ 4.0 with 3.55 gearing and the 42re transmission got me 27.5 mpg on a long run on the highway to Rochester and back from Syracuse at 70 mph with 90*F air temp, no converter clutch, no A/C, and all the windows down ONE TIME! It's never gotten that kind of mileage before or since, and this on 87 octane fuel. The Thruway is basically flat between those destinations and there was hardly any wind, but the 2-way run should have cancelled that concern out. This mileage was calculated by actual gallonage pumped and recorded odometer mileage. I used the same pump at the same station at the start and finish of the trip. This vehicle usually gets me 16 mpg around town and 12-14 in the winter with warmups.

In my estimation, all the converter clutch does is reduce most of the heating of the fluid by the slipping in the converter, prolonging the life of the transmission. Towing anything heavy, you should be in 3rd gear anyhow and with O/D eliminated electrically, the converter clutch will still come on in 3rd gear. The only different torque converter you can get will have a different stall speed which is not useful for towing.

You aren't going to get better fuel mileage by changing torque converters, unless the lockup clutch in yours is burned up. If that's the case a factory replacement would be fine.

I thank you for your input. I did take this to my mechanic twice for the fluid change. Their diagnostics software says to replace the torque converter. Mine erroneously told me to replace the TCU inside of the transmission. Even RockAuto listed an electronic module for it. It appears the cheaper diagnostic units and RockAuto all assume the 42re instead of the 545RFE. I will poke around a bit more online. I have found some decent links, but they also tend to be a bit general.
https://www.transmissionrepaircostguide.com/p0740/
https://www.jeepgarage.org/threads/y...y-issue.31703/

The lockup isn't happening. I can see the higher RPMs on the tach.

Ah! I might have found the answer. Video explaining the fix.
Kit: https://www.cascadetransmissionparts...icekit4wd.aspx

Mine is a 2002 which falls into the range of 1999-2003 "which must be updated."

Yeah, I've sunk a lot into this jeep, but it rides nice, handles great, and until this issue would routinely get 25MPG on the Interstate. I've had pretty good luck with the mileage of my last two Jeeps. Prior Jeep was 1990 Wagoneer Ltd. 4.0 with AW4. I used to get 23 with "local" driving and a bit higher on Interstate. Of course that Jeep was so light Interstate driving could get hairy on really windy days.

Thanks for forcing me to dig into this a bit further.

Ah! Actual instructions.

https://www.instructables.com/id/Dod...k-Replacement/

Another way to remove the pan (different than the linked instructions) is to have the last two bolts be on either side of a corner, making it possible to have the opposite corner drop down, making a pour point. It is a mess regardless. I like to use both my large flat sheet pan and my large oil pan for this task.

The instructions don't mention that lots of fluid will pour out once the valve body is loosened. Again, have the pan(s) in-place prior to unscrewing.

Thanks! I've gotten really lazy in my old age. While I could potentially do this, I'm going to let my mechanic do it once the parts get here. I found someone on eBay selling the upgrade kit. The only parts I really needed.

https://www.ebay.com/itm/Genuine-Mop...72.m2749.l2649

Since this was just a technical service announcement and not a recall, I feel it rather safe to assume my Jeep never had it done. Another thing I learned while researching is the Detent Plate (TRS Cam Plate) is supposed to be replaced around 120K.

Thanks for everyone's help. Sometimes all a person needs is the right nudge to research something properly.

There may be other "bolt on" upgrade parts appropriate for that transmission to do while the pan is out, like a shift kit or the accumulator spring.

The Sonnax parts are designed very well and have excellent construction.