Fuel economy and odd auto tranny behavior gen 3 montero

coffeegoat

Adventurer
Oh, and based on this thread I said screw it and ordered 4 new O2 sensors, because if they can improve my gas mileage by 1 MPG, they'll pay for themselves in ~10k miles, and 2 MPG will do it in ~5k miles.
 

jasonsuperb

Observer
The flush is different than changing the fluid. Flush will always put the same worn fluid back into the transmission. Most shops are against replacing fluid because of the cleaning detergents in some fluids causing more damage. However, changing to new fluid and filter with the correct SP-III fluid should not cause any problems for this transmission. I changed it at 170K on my '01, 110k on my '05 and I will do it again on my '05 when I get a chance.

As the fluid gets old, it loses its friction properties which causes slippage in the clutches and odd torque converter behavior. My 01 had multiple flushes done for what felt like a rumble strip/gravel road as I accelerated under light load up hills and around 40mph once it got to 150k miles. The flush would help for a few months before the symptoms returned, only worse each time. At 170k miles I found someone else describing the same problem and the fluid change procedure. I didn't change the filter that time, but I cycled the engine to pump the fluid through the cooler hose 2qts at a time, shutting the engine off when flow stopped to add more new fluid until it was all the same deep red color. Afterwards, the truck drove like new. No more shaking, rumbling or odd transmission behavior.

I drove my 05 in manual mode in 5th to confirm what you are seeing and they seem to unlock the converter when decelerating in the calibration. When I shift to 4th manually at the same speed, it locks and holds the engine speed until I shift back to 5th. To tell if the converter is locking in 5th, you will see the rpms rise then drop slightly as the converter clutch grabs. You may also hear a change in noise as the engine loads up with this.

@MoabRefugee , I would say the qt low is caused by the fluid entering all the passages in the transmission while warming up. The Torque converters also take some oil as they fill. But as you saw, low fluid/old fluid/too much fluid/wrong fluid can all make this transmission act abnormally. This is especially true for the torque converter.

So I think what you are saying is my transmission is behaving normally and just unlocking the torque converter when I take my foot off the gas.


I checked the fluid cold and hot and it was over an inch past the hot mark. About halfway up the do not overfill writing. Sucks the dealership overfilled it. I hope these have a simple drain plug and I don’t have to drop the pan to drain some out.


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jasonsuperb

Observer
Mpg update. Last full tank I got 11.5mpg. After I filled it I drove 150 miles in one day to a state forest to explore trails and back home. Probably 50 of those miles were dirt and 15 miles trails 5-10mph max. I filled up again when I got home and somehow managed 20mpg! So either the pump kicked off way too fast or I got way better mpg on the day trip and people are right in that short trips kill fuel economy and longer trips are ideal. But I figured the trails would have hurt the mpg a lot
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Inyo_man

Don't piss down my back and tell me it's raining.
I checked the fluid cold and hot and it was over an inch past the hot mark. About halfway up the do not overfill writing. Sucks the dealership overfilled it. I hope these have a simple drain plug and I don’t have to drop the pan to drain some out.

Be sure your rig has been driven before you check your transmission fluid. The rig must be at normal operating temp.
Right when you stop your rig, place the vehicle in Neutral and immediately check the level of the fluid with the engine running.
This is how the FSM directs one to check the transmission fluid.

Cheers
 

Michael Brown

You followed me, so now we're both lost
That is way too much fluid. Pull the cooler hose at the front of the vehicle like it shows in the FSM and that instruction I linked. Started in N, the pump will push out ~2L of oil. Shut off the engine when the flow stops. Check the dipstick and add fluid until it is at the right level.
 

pwjazz

Member
To get a good bead on your mpg woes you'll need to check your fuel trims. You may be running rich, in which case you can then start chasing gremlins in the MFI system. Healthy fuel trim numbers should give you 16-19 mpgs.

I'm late to the party, but ... what do you use to monitor trims? I'm using the Torque app with a bluetooth OBD2 adapter, and the fuel trim option is unavailable with my 3.8 Gen 3. Are there better apps for our rigs?
 

Inyo_man

Don't piss down my back and tell me it's raining.
(This is a very old thread, but it may still assist others...)
I've been using an Ultra Gauge to keep a eye on things in the Montero.

Cheers
 

MontySquareo

Active member
I've only ever got 13-14 mpg in my Montero, and that's all between 40-80 mph and rarely less than 10 miles. I do have a bad intake manifold gasket though, so fuel trims stay around +6%
Injector cleaner has helped with the fuel trims, they were around 12% a few months ago
 

alanymarce

Well-known member
We get 14 mi/US gal in our Montero in "day to day" use. On long runs at steady speeds we've achieved 16 mi/US gal, and in soft dunes consumption goes up to 10 mi/US gal (or even more if battling really soft sand). Your consumption is normal.

The drop in revs is normal too, at least in our experience.
 

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