The Fast Lane Truck: 2014 Grand Cherokee diesel towing test

[kevm14]

http://www.youtube.com/watch?v=WRo4uNWCy5E

1. Horsepower ALWAYS matters for ultimate performance (i.e. power to weight). The advantage torque provides is lower rpm drivability and "effortlessness" but not actual performance

2. Thermal management is poor and it wasn't towing that much.

3. Overall impression is this is a car diesel misplaced into truck duty. Not all diesels are created equal.

Side note: Ford Ecoboost also has thermal management issues under continuous load. Turns out that just because tractor trailer turbo diesels can operate under continuous boost doesn't mean everything else is fine.

[Bob]

It looks like body on frame still has a place in this world

Being realistic about what this vehicle will actually be used for (family hauling, taking up multiple parking spots at malls), I don't think this is a bad engine choice.

[bill25]

Oh no... Don't tell Tim. He bought this to tow a boat...

[kevm14]

I would bet a large sum that GM's still-born Duramax 4500 wouldn't have had these issues. Because in the GM tradition, it has some displacement, so it's not relying solely on boost to get the power. And with ~310hp, it would have been perfect in everything from cars to 1/2 ton trucks.

[kevm14]

It's funny how people are still confused about torque vs horsepower. Lots of torque means you have a relatively large amount of horsepower available at lower rpms (relative to engines of the same power but less torque). It just means you can do more work at lower rpms than you would otherwise be able to. But as is the case with ALL engines, the MOST work is done at the horsepower peak. And at 240hp, it speaks for itself. 420 lb-ft @ 2000rpm means it has 160hp at 2000rpm. Which is pretty good for a 3.0L engine, but is still 160hp.

One of the hosts was referring to the engine's characteristics. He said the torque is great off the line but not at 50mph. The first part is correct, but at 50mph, you need horsepower. Torque would allow you to do more work without downshifting but again, ultimate work is done at horsepower peak. Always.

It also means that the Hemi would absolutely waste this thing in this tow test, unless it was stuck in a gear where it couldn't access HP peak. But with 6+ speed transmissions, that's not an issue today.

Also, this engine is a $4500 option over what I assume is the Pentastar (which probably would out-tow this on a grade but at a substantial fuel economy deficit and lots of RPMs).

Anyway, this is my issue with engines that have huge torque and modest HP. They feel extremely capable, like nothing could slow it down. Then you floor it and realize you only accessed an additional 15% of your available power. The illusion is destroyed.

For all that flogging they still got 15mpg up that grade, which is pretty amazing. But that creates a bit of a paradox. A $4500 engine option and a $46k+ vehicle...to save money on gas?

[Adam]

Reminds me of the drivability characteristics of the TPI family of engines from the '80's.

[kevm14]

Yes. But unlike a turbo diesel, those TPI engines had very snappy response. Fun to drive even with the 700R4.

[Bob]

It's too bad the SRT-8 really can't tow anything. That would probably do really well in this test.

[kevm14]

Of note, the Trailblazer SS (LS2) will tow 6,800 lbs.

[Adam]

That's almost as much as a V4P Fleetwood (7000 lbs).