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Old 02-12-2010, 09:39 AM
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mileage decrease / transmission ?

Last year, my Jeep dealer flushed my transmission, and almost immediately, I noticed about a 10% drop in mileage, longer transmission warmup times, and less "coasting" when getting off the accelerator.

Basically it feels like the transmission fluid is thick (in warm or cold weather, but obviously worse in cold weather)

Today, my 04 Grand Cherokee 4WD 4.7 V8 is in the shop for inspection and 75k service. I asked them to look at the transmission again. They just called and said the only thing they notice is a noise coming from the transfer case and they recommended a flush of that as well.

Does anyone have any other suggestions ?

Thanks,

Doug
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Old 02-12-2010, 10:38 AM
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Re: mileage decrease / transmission ?

Have you noticed the noise from the Transfer-Cass? If your looking to increase gas MPG try changing you spark plugs also.
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Old 02-12-2010, 11:48 AM
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Re: mileage decrease / transmission ?

I would try the plugs too. I've just done mine, as it wasn't starting first time and the reduction in mileage was pretty noticable (not funny with UK fuel prices). Anyway 80 spent on new plugs and an hour and a bit of me fumbling and swearing and the problems was sorted.
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Old 02-12-2010, 12:24 PM
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Re: mileage decrease / transmission ?

I may try the plugs, but that won't change the fact that it feels like I have pudding for transmission fluid. (or that I'm always driving into a 20 mph headwind)

I'll make a post tonight after I pick the Jeep up from the garage. It won't take but a few miles to see if the transfer case flush helped. at all.

I'll have to go over my records to see if the plugs have been changed sine I bought it.


Thanks !

Doug
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Old 02-12-2010, 02:58 PM
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Re: mileage decrease / transmission ?

As far as I know the sluggish feeling may come from the plugs not firing correctly. I don't the exact in and outs, but mine did feel sluggish on and off until I sorted the problem. The other possibility could be what I think is called the transmission speed sensor.

Just a suggestion. I'm still learning lol

All the best Doug

Aaron
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Old 02-21-2010, 02:13 PM
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Re: mileage decrease / transmission ?

I just took a trip of 160 miles, and about 80% wash highway at about 65-70 MPH. I ended up with 16.5 MPG. I'm going to try new plugs either this coming week or in earlier March when the wife's car will be out of the garage for a few days.

Thanks again all .

Doug
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Old 02-22-2010, 10:09 PM
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Re: mileage decrease / transmission ?

I changed the plugs per so many suggestions. The old plugs didn't look too bad. *maybe* gapped just a tad small but they seemed okay.


Holy crap though !

<sarcasm> Thanks for warning me about those last two plugs on the passenger side of the engine. </sarcasm>


The last one must have taken at least twice as long as any of the others. I'll see if I can take it on a trip this weekend to see if changing plugs helped the mileage. At least it started back up after I changed them. I consider that a moral victory anyway.


Doug
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Old 02-22-2010, 10:46 PM
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Re: mileage decrease / transmission ?

Well...Wait about a week and see what going to happen. Just wondering have you changed your Air Filter yet? Check that. That would help increase gas MPG also.
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Old 02-23-2010, 08:47 PM
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Re: mileage decrease / transmission ?

Yes, I changed the air filter when I first noticed the problem (at 60,000 miles) and again this week (75,000)

The garage wanted to charge me $32 to change the filter and about $100 to replace 2 hood supports. Doing both of those myself cost about $50 and 20 minutes.

I'll post back after I put some highway miles on the new plugs.
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Old 02-24-2010, 12:59 AM
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Re: mileage decrease / transmission ?

Hi. First post here. Just a different direction, but sounds like you have a brake dragging.
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Old 04-26-2010, 08:31 PM
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Re: mileage decrease / transmission ?

Sorry it took so long to follow up, but shortly after I changed plugs, I tried to reset the Adaptive Engine Memory system I went from a trip of 90% highway miles (16.5 MPG) to a trip of about 90% highway miles producing 18 MPG. My next tankful was about 50% highway miles and still gave me almost 17 MPG. The two big changes were resetting the computer and the weather getting slightly warmer.
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Old 04-26-2010, 08:57 PM
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Re: mileage decrease / transmission ?

just something to throw out there do you have a tune ? or have tried one ?
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