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Old 01-30-2014, 01:24 PM
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Shimmy at Highway Speeds and Cool Down Time

Hi All

Seriously thinking about the ecodiesel, but two questions vex me.

1. Anyone having vibration/shimmy problem at highway speeds that other JGC models are reporting in such large numbers, especially with the Summit model?

2. What's up the having to let the diesel idle to cool down before turning it off as indicated in the manual? Depending on how hard you've been driving, they recommend up to five minutes of idle before turning the engine off. Is this normal for diesels? Is everyone doing that?

Thanks in advance...
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Old 01-30-2014, 01:32 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

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Originally Posted by gme2815 View Post
Hi All

Seriously thinking about the ecodiesel, but two questions vex me.

1. Anyone having vibration/shimmy problem at highway speeds that other JGC models are reporting in such large numbers, especially with the Summit model?

2. What's up the having to let the diesel idle to cool down before turning it off as indicated in the manual? Depending on how hard you've been driving, they recommend up to five minutes of idle before turning the engine off. Is this normal for diesels? Is everyone doing that?

Thanks in advance...
1. WTH are you talking about "reported in large numbers"? Mine doesn't and neither do several others in my area. There was an "old" problem where SOME units need a thrust alignment - but I thought it was fixed quite a while ago??????
2. Cant help you with the diseasil as I have a gasser!
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Old 01-30-2014, 01:40 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

See this link...

Vibration in the 2014 grand cherokee summit

and this one...

2014 GCs that have steering shimmy over 60MPH

I test drove a Summit a while back and took it on the freeway and got the shimmy, so I know it's a real problem. Just wondering if it's sorted out in the diesel.
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Old 01-30-2014, 02:15 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

OK that's 6 months ago and was sorted by thrust alignment IIRC...

FWIW My summit was built in August and doesn't have that problem at all and never did - so its not "all summits"
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Old 01-30-2014, 02:22 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

As for the diesel cool down times, I believe it has to do with giving the turbo time to cool off. I've had several turbo diesels before and never really give it any thought unless I'm driving it hard or towing. Usually the casual stroll through my neighborhood has been plenty of cool down. There have been a couple of threads on here discussing it, but my take away is that it's not that big of an issue unless you are driving it hard or towing.
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Old 01-30-2014, 02:54 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

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Originally Posted by dsears00 View Post
As for the diesel cool down times, I believe it has to do with giving the turbo time to cool off. I've had several turbo diesels before and never really give it any thought unless I'm driving it hard or towing. Usually the casual stroll through my neighborhood has been plenty of cool down. There have been a couple of threads on here discussing it, but my take away is that it's not that big of an issue unless you are driving it hard or towing.
Thanks...
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Old 01-30-2014, 05:11 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

My 2 December build has no shimmy. As to idling before shut down it's extremely important but also something that seldom applies to us. I've got more than 100k hours of logged diesel operation and have temp both pre and post turbo on most of my engines and I can tell you without question that cooling occurs very quickly. Even on the main engines where the turbos weigh more than our cars the turbos will have cooled down to a 50 degree delta just in the time it takes to get tied to the dock without any directed cool down time. On the power generation side you can be running an engine at rated power, switch over, and then turn it off immediately. This would be mucho bad of course so I don't but this is kinda getting to my point. You don't really have this as an option with your jeep.

Even when towing a trailer on the freeway your temps will be down significantly just in the time it takes to get down the off ramp at a rest area. With my truck (Cummins) the oil temp post turbo would be down to shut off temps in around one minute in this situation. Around town the temps were usually good to go before I even got the truck parked. This because driving around town is a lark to the engine and the same is true here. This thing is loafing most of the time and I shut mine down as soon as I'm parked in most cases and losing no sleep.

What I know tells me I should give the car a minute or so when I'm towing. I should be aware that under unusual circumstances I should not immediately shut my engine down. Something like driving down the freeway with tow and deciding I'm not going to make it without an emergency pee stop. I'll leave it running instead of shutting it down right away after getting to the side of the road. Use a little common sense and you won't have a problem with turbo bearings and such.
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Old 01-30-2014, 05:31 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

Quote:
Originally Posted by gme2815 View Post
See this link...

Vibration in the 2014 grand cherokee summit

and this one...

2014 GCs that have steering shimmy over 60MPH

I test drove a Summit a while back and took it on the freeway and got the shimmy, so I know it's a real problem. Just wondering if it's sorted out in the diesel.
Diesel would do nothing to deal with a small number of vehicles with crappy tires/balance issues that some dealers have the willingness and brains to solve--and some don't.

As for cool down, suspect it would be to cool down the turbochargers, as that used to be required on pretty much every turbo vehicle until some makers started putting in post shut-off oil circulation/cooling systems. Dunno if the ecodiesel has one or not...
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Old 01-31-2014, 12:38 AM
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Re: Shimmy at Highway Speeds and Cool Down Time

Quote:
Originally Posted by crabman View Post
My 2 December build has no shimmy. As to idling before shut down it's extremely important but also something that seldom applies to us. I've got more than 100k hours of logged diesel operation and have temp both pre and post turbo on most of my engines and I can tell you without question that cooling occurs very quickly. Even on the main engines where the turbos weigh more than our cars the turbos will have cooled down to a 50 degree delta just in the time it takes to get tied to the dock without any directed cool down time. On the power generation side you can be running an engine at rated power, switch over, and then turn it off immediately. This would be mucho bad of course so I don't but this is kinda getting to my point. You don't really have this as an option with your jeep.

Even when towing a trailer on the freeway your temps will be down significantly just in the time it takes to get down the off ramp at a rest area. With my truck (Cummins) the oil temp post turbo would be down to shut off temps in around one minute in this situation. Around town the temps were usually good to go before I even got the truck parked. This because driving around town is a lark to the engine and the same is true here. This thing is loafing most of the time and I shut mine down as soon as I'm parked in most cases and losing no sleep.

What I know tells me I should give the car a minute or so when I'm towing. I should be aware that under unusual circumstances I should not immediately shut my engine down. Something like driving down the freeway with tow and deciding I'm not going to make it without an emergency pee stop. I'll leave it running instead of shutting it down right away after getting to the side of the road. Use a little common sense and you won't have a problem with turbo bearings and such.
Thanks...!
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Old 01-31-2014, 10:43 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

As reported unless you pull right off the interstate after running your SFU hard and shut if off you will not have any issues coking the turbo issues in normal use. My Super Duty has a turbo the size of a good size watermelon and in 180K miles of use in Florida I never had problem one. If I do run it hard and need to pull off quick I will let it idle for a minute or two to cool the turbo down.

Many new turbo designs are both oil and coolant cooled and those coolant cooled with an electric water pump run for a few minutes if needed to cool the turbo down with no input from the operator...

I expect the turbo to last the life of the engine. In all my years of flying and driving turbo engines never had but one failure and that was in a high performance twin engine aircraft...
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Old 02-01-2014, 03:51 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

Actually, oil- and water-cooled turbos are not new. Every Mopar 2.2/2.5 turbo since the 80s has had oil/water cooled turbochargers. I believe all the Cummins Dodges have also been oil/water cooled, for at least as long.

Simply adding a coolant passage does not eliminate the need for a short cool-down period. What happens if the oil circulation is stopped when the turbo is too hot is, it turns into carbon. Dry, pencil-lead carbon. This is called "coking", and as you can imagine it is a bad thing for the turbocharger.

I spent quite a bit of my youth drag racing the 2.2's. 11 second cars with EGT, boost, air/fuel, and oil temp gauges. By the time I'd finished my run, made it back down the return road, gotten my timeslip, and got back to the pits...the turbo was cooled down just fine. I'd idle it for about 30 seconds just to mental-log the gauge readings...then shut 'er down. Popped plenty of headgaskets ("the ten second fuse"), but never a turbo.

And if any of you doubt the existence of an 11 second 2.2...check out my friend Pat's car. It's gotten quicker since '12 (added nitrous)...but to my knowledge he hasn't popped the turbo yet.

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Old 02-01-2014, 04:05 PM
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Re: Shimmy at Highway Speeds and Cool Down Time

Oh, and I did get some shimmy out of my Summit...when I packed the wheels with snow by driving through snowdrifts. Mental note - the factory 20's are a very "open" design, and if you slide even the least bit sideways in a snowbank...they'll pick up and pack-in snow, and get WAY out of balance.
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