My wife's CRD has gotten about 16mpg the last two tanks. These were the first two tanks that she used driving to her new job, which is 4 miles from home.

For the last two tanks, the maximum speed the crd saw was 45mph and the longest trips were 4.5 miles one way. I'd say the average speed she drives going to work is 30 mph.

two tanks in a row like that and they both came out to almost 16mpg.

When we took two long trips in it we got 24 mpg. I towed my TJ 400 miles with it and got 15.5 mpg.

I guess never going fast enough to lock the Torque converter will suck down some fuel!

I'm happy with 16mpg. My GMC gets 11 mpg and i drive it the same way during the week. My TJ gets about 13 mpg at best with it's lift and tires so 16 is cool for me.

Your wife is triply cursed here on this: she is neither going fast enough to lock up the torque converter nor far enough to warm the engine up properly. Both will KILL mileage, as well, I might add, as your exhaust system, which never gets warm enough to eject all the water, so rusts out from inside.

She might try turning off the overdrive whenever she gets in to make that little short trip. That, at least, would let the torque converter lock up for part of the trip. You also would be well advised to take the vehicle out on the expressway for a 10 or 15 mile drive every couple days to help blow out that water, along with the inevitable soot and crud produced by such short-duration, low-speed operation. My guess is that the savings on maintenance later would more than pay for the extra fuel.

I usually drive it a couple of times on the weekend. My god...the amount of smoke it makes when I floor it the first two or three times is amazing!!

lol

It's pretty fun actually. I get to look forward to blowing smoke with all of the buildup she makes for me during the week

ROFL! Spoken like a real "guy." Wimmin just don't understand the joy of making smoke. And noise.

Can anyone give me info about the torque converter lockup with the overdrive off?

If were doing back road driving where we will never see 52mph to get the torque converter to look up should we leave the overdrive disabled?

What speed does it lock up when the OD is off?


Side note, also make sure your wife isnt running the heat with the knob in the last 3 positions (Floor, Defrost&Floor, Defrost), They will all run the AC and kill gas mileage. We got 21mpg to a tank then I learned about the AC coming on automatically even while in the Floor setting, I disabled it and we got almost 24mpg the next tank.

With OD turned off, the torque converter locks up at and above 38 mph, and stays locked up until you drop below that speed. No modulation, it just locks up, period.

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Mitchell Oates
'87 MB 300D Diamond Blue Metallic
'87 MB 300D - R.I.P. 12/08
'05 Sport CRD Stone White
Provent CCV Filter/AT2525 Muffler
Stanadyne 30 u/Cat 2 u Fuel Filters
Fumoto Drain/Fleetguard LF3487 Oil filter
V6 Airbox/Amsoil EAA Air Filter
Suncoast TC/Shift Kit/Aux Cooler
Kennedy Lift Pump/Return Fuel Cooler

ok, so is it safe to assume that if your driving 40-50mph you should turn the OD off? I'm trying to think of why you would want the OD on except for highway? Like why wouldn't jeep just program the ecu to stay out of OD mode util you go above 52mph?

Problem with the with the word "ASSUME" - it often makes an A## of U and ME.

Whether or not locking out OD will give you any benefit is going to depend on your driving style and conditions. Only thing I can tell you is that with OD locked out, between 40 to 50 mph the engine will be turning at 1800 to 2200 rpm, at and above the max torque point and further up in the HP band, and in the vicinity of the minimum point on the BSFC graph.

In my case, locking out OD matched up pretty well with my driving style and road/traffic conditions and helped improve my fuel economy.

Only way to know for sure, give it a try over the course of a full tank. See if it suits your road conditions and driving style, and whether it hurts or helps your fuel economy. As the EPA is fond of saying, "your mileage may vary".

_________________
Mitchell Oates
'87 MB 300D Diamond Blue Metallic
'87 MB 300D - R.I.P. 12/08
'05 Sport CRD Stone White
Provent CCV Filter/AT2525 Muffler
Stanadyne 30 u/Cat 2 u Fuel Filters
Fumoto Drain/Fleetguard LF3487 Oil filter
V6 Airbox/Amsoil EAA Air Filter
Suncoast TC/Shift Kit/Aux Cooler
Kennedy Lift Pump/Return Fuel Cooler

Yeah but why would she be using the heat in March? It's 80 degrees! We pretty much run the A/C year round in Southwest louisiana.

So lets say your traveling at 45mph with the OD disabled. If you put your foot to the floor does it downshift? I assume that with the OD enabled it would downshift to second and wind the engine up which kinda sucks because this is a torque motor and not a HP motor (Things I hate about automatic )

I wish the auto tranny wouldn't upshift to 3000+ rpms when you floor it and climb because there isnt any power to be had up there...

Amen brother! Learning to drive this auto diesel has been an interesting road for me. I have never had a vehicle with better roll-on acceleration times at 1/2 to 34/ throttle than at full throttle. The first few times I made the mistake of nailing the throttle I'm surprised I didn't cause accidents. I was trying to pull out into a little hole in traffic and *punch* (pause, pause, pause) *click* WAAAAAHHHHHHHHHHHHHHHHHHHHH!!!!!! And it didn't go any faster. I thought I'd broken something.

Lock out the OD and roll on the throttle in the exact same situation though...WHOOOOSH! Just freakin' gone! Next thing I know I'm hitting the brakes 'cause I'm going 90.

My fiancee drove my truck once and got pulled over about 20 miles down the road. She had no idea she was going 80 in a 55. Told the officer that we had just gotten the truck (I had) and that she had never driven a turbo diesel before (she hadn't) and he steps back a bit, looks left and right, looks back and me and goes, "This is a diesel?" He let us go with a warning. Nice guy. Props to the Maryland State officer that was patrolling Rt13 that day!!

Anyway, I've modified my driving style to suit this truck and my fuel mileage (and happiness quotient) has gone up from 18-20 or so to 25-27. I spend a lot of time trying to lift the front end off the ground with traffic light launches though so I could probably get better (shrug). If I wanted a fuel miser I'd be driving a Jetta Wagon TDI.

Oh! And everyone take Omniphil's comment about the air distribution knob (for lack of better name) to heart. I got another couple MPG average by turning that thing to dash vent. It doesn't matter where the temp knob is...if the air distribution knob (the one on the left) is on one of the three right-most settings, your AC is running to pull moisture out of the air and sapping your fuel mileage.

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_______________________DogDomain_______________________

The other thing that has me wondering is the two different second gear ratio's. When I look at the ratio specs it lists 2 for 2nd gear, the description for the 5 speed auto also says "multispeed automatic". When you lock out the OD maybe it uses the more aggressive 2nd gear?

Why and how is there 2 ratios for second gear?

Omniphil = Learning

If I understand it correctly one ration is for starting from a dead stop the other is for downshifts when moving

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Sold 05 CRD Patriot Blue, hole in the roof, Trailer tow, factory skids, LSD, Saris load bars, Michelin LTX M/S
Current Bright white 2010 Dakota Quad Cab 4x4 V8

The ratios listed by About, Inc. for the 545RFE-A5 automatic are:

1st: 3.00
2nd upshift: 1.67
2nd downshift: 1.50
3rd: 1
4th: .75
5th: .67
Reverse: 2.21

Don't really understand the advantage of upshifting and downshifting at different ratios (shrug). But I hope this equation is true until the day I die: Dog Party=learning. Or, in emoticon language

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_______________________DogDomain_______________________

I would guess the the downshift gear is taller so the rpms don't go as high when you nail the throttle and the tranny downshifts as you really don't need revs on the diesel... Where as the upshift is shorter to transition out of first better and to increase the acceleration from a stop.

So I wonder if there are 6 gears? or is some sort of fluid/pressure trickery used to get two variations of second gear.

In either case, I would think the CRD would be better off having a 3000-3200rpm redline and having the tranny shift appropriately, this would keep the CRD in the powerband, above 3000 rpms there is so little power it dosen't even feel like your accelerating. If the CRD had more HP, like say 200 or so, it might make sense, but I think its silly to have to accelerate using 3/4 throttle, why not cut the rpm range short instead and just let the end user floor it?

Omniphil != Car Engineer.
Omniphil = Curious however

Hmmmm, what about the ECU programmers I always see for other cars that let you raise the rpm limiter, wonder if you can lower it too?

OK, so what if OD gears are turned OFF, you are driving over 40 mph, and you hit a steep hill with 5,700 lbs. hooked on the rear?

With OD off my CRD still downshifts on hills even though I'm running 45-50 mph. So if you are over that magic 38 number is the torque convertor locked up all the time even when it downshifts??

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2005 Stone White KJ Limited CRD 4x4
Off-Road Pkg
Trac-Lok
Emu 790s/948s
Skyjacker H7088s rear/Bilsteins front
15x7 Black Rock Lobos/31x10.50 Firestones
GDE HOT Tune + TCM Tune
Euro TC
CB radio
Thrush Turbo muffler
AEM DryFlow filter

It sounds like it just takes alot more throttle input to get it to disengage. If it does downshift the torque converter pretty much has to disengage. I imagine its all based on trying to keep the tranny fluid temp under a certain threshold.

Ok, so that automatic lock-up above 38 mph with OD off only applies to 3rd gear then (the highest gear you can get to with OD off). That's what I figured.

_________________

2005 Stone White KJ Limited CRD 4x4
Off-Road Pkg
Trac-Lok
Emu 790s/948s
Skyjacker H7088s rear/Bilsteins front
15x7 Black Rock Lobos/31x10.50 Firestones
GDE HOT Tune + TCM Tune
Euro TC
CB radio
Thrush Turbo muffler
AEM DryFlow filter

Yeah, which kinda makes sense, I figure the OD lockout is mainly for towing heavy loads, and you dont want the torque converter slipping while towing, that might equal very high tranny fluid temps and alot of wasted power/fuel.