[Airbird]

I'm looking at buying a new WK and I cant make up my mind on a CRD or a Hemi. I'm tired of researching and hoping some of you guys can shed some light on the ups and downs of both...

Thanks

[no-blue-screen]

It depends on what kind of driving you will be doing. If you do a lot of short trips, then I would recommend against the CRD. Otherwise, the CRD is the way to go...especially now that diesel is below regular unleaded in a lot of areas.

Downsides to the CRD would be oil changes cost a little more, tougher to get service from most dealers because they don't understand the new diesels...but the pros far outweigh the cons IMO. Lots of torque, I average 25 mpg over the last 14k miles, highway driving pleasure (no downshifting needed), towing ability, etc.

[Robert J. yates]

The Hemi wasn't even considered in my purchase decision and I am still very satisfied with the CRD with about 19,000 miles under the tires so far. Its a nice truck....period.

[chadhargis]

I wouldn't even own a Jeep if it wasn't for the diesel option.

I LOVE, LOVE, LOVE diesel engines. I do my own oil changes, so that's not a consideration for me.

Sure, a big V8 is fun, but also very thirsty.

[Spider-One]

I chose the CRD. One downside is the lack of aftermarket support, but that's about it in my opinion. Sure the oil changes are a bit more but you get more mileage per oil change, not sure what the interval is on the Hemi but with the CRD's the severe oil change interval is 10,000km.

I don't see why the CRD would be a negative with short trips, short enough and the engine wont fully warm up but really if it's that short you should just walk. It only takes a few minutes of city driving to warm it up plus the CRD has a ceramic (electric) heating element to warm up quickly even at idle.

I didn't even look at the Hemi honestly. Were it not for the CRD I never would have even considered a Grand Cherokee, I probably would have waited for the half-ton diesel trucks to come out.

The CRD has a good amount of torque even when compared to the Hemi, more than enough for most. If you tow anything the CRD will kill the Hemi in mileage. It beats the Hemi for mileage pretty much everywhere, the only time the Hemi comes close is on the highway with MDS.

[chadhargis]

And I just did the InMotion tune on my CRD. 443ft/lbs of torque baby!

[no-blue-screen]

Let me define what I mean when i say short trips. A short trip is any trip where the engine doesn't get up to operating temp. Short trips are bad for any engine, but some things that come to mind are what is call wet stacking and then there are the implications on the DPF. Not a big deal if you have a decent run with it once a week or so. You are running slightly rich until the engine gets to operating temp and closes the loop...so soot in the DPF and EGR as well as more combustion byproduct in the oil (oil dilution). The oil would not be so much of an issue if you follow the severe service interval but soot in the intake and EGR could be a problem down the road. There may also be issues with DPF regen.

[ctate]

Diesel power!!!!

[Spider-One]

I doubt there would be issues with the DPF and short trips. It would require at least a bad sensor to have an issue with it. It only takes a few minutes of regen to clear it out, on top of that guys have used DashHawks and such to read the EGT's and even on idle the ECU injects enough fuel to heat up the exhaust to the required temp. If you shut down during a regen it begins once you start back up.

I do agree with the soot situation and oil change interval especially with the EGR systems, but I doubt it would cause any major issues so long as you stuck with the severe schedule. If you read the description in the owners manual I don't think there's anyone in the world who doesn't fall under the severe section so everyone should use that schedule as far as the manual is concerned.

And like I said it only takes a few minutes to get up to operating temp and if somebody was using the Jeep for trips that don't allow for that there's seriously something wrong with the person for being so stupidly lazy. Even in serious stop and go it can easily get up to and maintain operating temp in all but the coldest scenarios.

[oldmac1]

I just picked up a 09 Wk with the Hemi two weeks ago and so far I love it. On short trips with the air on I am getting around 15.4 mpg with 1200 miles on the Jeep. I do not expect to get much better mileage around town with it. I knew this when I bought it so if mileage is important maybe the diesel is the way to go for you. I had a 07 Chrysler Hemi that I traded for this and the 09 Hemi with VVT will take the previous Hemi easily. I have not heard anything bad about either engine so good luck with your choice.

[no-blue-screen]

Originally Posted by Spider-One

I doubt there would be issues with the DPF and short trips. It would require at least a bad sensor to have an issue with it. It only takes a few minutes of regen to clear it out, on top of that guys have used DashHawks and such to read the EGT's and even on idle the ECU injects enough fuel to heat up the exhaust to the required temp. If you shut down during a regen it begins once you start back up.

I do agree with the soot situation and oil change interval especially with the EGR systems, but I doubt it would cause any major issues so long as you stuck with the severe schedule. If you read the description in the owners manual I don't think there's anyone in the world who doesn't fall under the severe section so everyone should use that schedule as far as the manual is concerned.

And like I said it only takes a few minutes to get up to operating temp and if somebody was using the Jeep for trips that don't allow for that there's seriously something wrong with the person for being so stupidly lazy. Even in serious stop and go it can easily get up to and maintain operating temp in all but the coldest scenarios.

Oil change interval will have no affect on soot formation. It may not cause a problem right away, but eventually excess soot and condensation can cause passages to become narrow and will affect performance. Then you will need an intake cleaning.

On the DPF, I was under the impression it will not do a regen unless it is at operating temp...but I am not able to confirm that.

Lastly, it has been my experience that it takes more than just a few minutes if temps are below 50F. 11 miles to work in the winter and the engine would just be getting to operating temp and this is after driving it on the highway for 10 of those miles....idling I found it to be even longer with the temp gauge usually only able to get 1/4 of the way. When it is 80F, it is at operating temp within 2 or 3 minutes.

Not trying to start a battle over the subject or otherwise hijack the thread, but just trying to save someone some hassle down the road.

[Spider-One]

You may be right on the DPF not doing a regen until at operating temp. I'm not sure either way. That would bring up the question what does the ECU consider a good temp to start the regen.

When you said soot I thought you meant the accumulation of soot in the oil due to the EGR process. Hence the reason most new diesel oil turns black very quickly. I will say I think you're absolutely right about the soot causing a blockage in the intake and that's something I didn't think about. You see a lot of the big diesels that go on a lot of short trips that need frequent EGR valve cleanings and such. It seems you need those good bursts of power to clean everything out every once and a while.

As for the time it takes the engine to get up to operating temp I generally haven't noticed it take all that long, my typical drive to work is about 7km and it's never had trouble hitting the operating temp with plenty of heat by the time I get there. Unless it's -40°C/F out or the wind chill is exceptionally bad. Then again until I made up a winter front for myself it was stupid how long it took. Amazing what a few pieces of black cardboard can do, lol. I just need to figure out something that looks nice for next winter.

[chadhargis]

I didn't think diesels had a air/fuel mixture, so they couldn't run rich or lean. In a diesel, doesn't air intake stay wide open and the throttle controls fuel only?

[nostaw22]

Originally Posted by chadhargis

I didn't think diesels had a air/fuel mixture, so they couldn't run rich or lean. In a diesel, doesn't air intake stay wide open and the throttle controls fuel only?

Modern diesels have an air/fuel mixture map and the air and fuel is controlled by the computer... This doesn't mean they regulate it like a gas engine does (as you point out, diesel engines are fuel throttled). In order to keep the EPA happy they optimize the mixture to reduce emissions.

The CRD's turbo doesn't run at full boost all the time... I've been watching the boost pressure on my DashHawk for about a week and it generally runs 6-8 PSI during normal driving (e.g. on the highway ~65-70mph on "flat" road) and I've seen it spike up to ~20-24 PSI for short periods (>1s) during heavy acceleration if I put my food down, but generally it runs in the mid-teens when I'm accelerating.

JW

[no-blue-screen]

In most diesel engines that is true that there is not a throttle. In this engine, there is a throttle and it is electrically controlled. Many refer to the accelerator as the gas or throttle...but now that there is no mechanical linkage that really isn't correct. In this engine both fuel quantity and throttling are controlled by the ECU based on how much acceleration you are requesting and the input it received from all the other vital sensors. Maybe running rich is the wrong term to use. Soot + condensation and you have a gooey mess of a clog in your intake.

If you are considering the diesel this is a cool document all about the OM642.

http://www.ourexcellentadventures.com/wp-content/documents/OM642.pdf