Road trippin in the CRD

CRD Joe · **Posted:** Fri May 28, 2010 11:06 pm

Yesterday I left Phoenix bound for Seattle via the Grand Canyon, Bryce canyon and Zion. So far Im in Page AZ. The trip meter is reading 445 miles and Im still above half a tank!

Gotta love them CRD's.

Cowcatcher · **Posted:** Sat May 29, 2010 12:07 am

You won't need your passport after you cross the AZ line unless you plan a short road trip to Canada while you are here. :SOMBRERO:

LibertyCRD · **Posted:** Sat May 29, 2010 11:47 am

You should have reset the trip meter when you filled the tank.

CRD Joe · **Posted:** Sat May 29, 2010 12:03 pm

Everybodys a wise guy. Looking for 700+ miles on this tank.

BVCRD · **Posted:** Sat May 29, 2010 1:54 pm

CRD Joe wrote:

Yesterday I left Phoenix bound for Seattle via the Grand Canyon, Bryce canyon and Zion. So far Im in Page AZ. The trip meter is reading 445 miles and Im still above half a tank!

Gotta love them CRD's.

Wow. You are getting 45 mpg. Good job! :roll:

litton · **Posted:** Sat May 29, 2010 4:27 pm

It's only about 250 miles from Phoenix to Page....something doesn't quite compute.

LibertyCRD · **Posted:** Sat May 29, 2010 10:54 pm

Everytime he gets to any sort of downhill grade at all, he's shutting the engine off and coasting. And he's got those special Goodyear tires that really do sprout wings like the logo.

geordi · **Posted:** Sun May 30, 2010 5:58 pm

LibertyCRD wrote:

Everytime he gets to any sort of downhill grade at all, he's shutting the engine off and coasting. And he's got those special Goodyear tires that really do sprout wings like the logo.

He doesn't need to shut the engine off, just push it into neutral. I do the same thing on any serious downhill or when I am coasting up to a light or sitting at the light. It does help.

At the same time... He is possibly also counting mileage where the CRD is on the back of a truck and getting pulled. 45mpg? Lying is a sin there Joe. :goink:

stoutdog · **Posted:** Sun May 30, 2010 10:52 pm

geordi wrote:

LibertyCRD wrote:

Everytime he gets to any sort of downhill grade at all, he's shutting the engine off and coasting. And he's got those special Goodyear tires that really do sprout wings like the logo.

He doesn't need to shut the engine off, just push it into neutral. I do the same thing on any serious downhill or when I am coasting up to a light or sitting at the light. It does help.

At the same time... He is possibly also counting mileage where the CRD is on the back of a truck and getting pulled. 45mpg? Lying is a sin there Joe. :goink:

geordi, honest question: Any concern about the transmission when shifting into neutral at such high speeds? Aren't you forcing it out of lockup?

geordi · **Posted:** Mon May 31, 2010 12:37 am

I wouldn't think so, because of two things. Maybe I'm totally wrong about this, but this makes logical sense to me and I haven't lost a transmission yet doing it. Over 150k miles on my Jetta TDI, and now 50k so far (since I bought it) on the CRD.

So, the two things:

1: The transmission's natural state is to be unlocked and disengaged.
2: The torque converter needs fluid pressure to compress the clutch surfaces together, just as the rest of the transmission needs fluid pressure to engage the gearsets.

Under full lockup, the torque converter is applying maximum pressure to the clutch plates, "locking" them and reducing the slip to zero. If you don't have sufficient pressure for whatever reason... You don't get lockup.

The pressure in the system is routed around by the solenoids in the valve body, which are electronically activated according to the commands from the TCM. FWIW, the transmission selector could be located on the driver's door or as an infrared remote control... It is a fly-by-wire system. You aren't shifting anything even as simple as a cable to the linkage anymore. So when I push it into neutral at any speed, I am simply issuing a command to the computers to change the solenoids around. This is a LOT different than the gear-on-gear meshing that has to happen in the transfer case. THAT, I don't ever mess with at-speed, unless I absolutely have to... And then, that speed will be no more than 35 or 40, with my foot OFF the pedals.

So my thinking is that since I don't have my foot on the throttle anyway, under lockup with GDE's new TCM program (Yea, I've been beta testing it for a while too) OR even with the stock system, the transmission and the engine are rotating at the same speed b/c the torque converter is holding them together. When I command the solenoid to release that line pressure, the clutch plates release from each other and the rotating mass of the engine is no longer being forced to a higher RPM by "reverse power flow" from the wheels to the torque converter.

To my thinking, this releases not only the pressure on the torque converter, but also on the transmission gearsets, while retaining the lubrication of having the engine running. I *DO* believe that shutting off the engine with the transmission engaged WILL cause serious damage b/c the transmission pump is now no longer pumping lubrication through the system. The pressure in the TC is held by the solenoid OR by the clutch plates being locked together with friction as the vehicle slows down... And will unlock in an uncontrolled manner (possibly causing damage) when the wheels slow enough that the input force starts to balance with the weight of the rotating mass of the engine. Not good.

Now I don't know if Joe (or anyone else) tries to hypermile by shutting the engine off with the transmission engaged... But I won't do that. I tow my vehicles (including the CRD and that Jetta) and know how to do it safely without wrecking the transmission from lack of lubrication. The Jetta had to be on a tow-dolly or trailer, OR I would have needed to buy a separate transmission fluid pump to keep the rotating gearsets lubed while the engine was off. For the CRD, the instructions are to put the transfer case into neutral (totally unlocked wheels) BUT because the rotating driveshafts will STILL create liquid movement in the transfer case... The transmission must be left locked in PARK to keep the gearsets from being spun by the turbulent force in the transfer case.

Cowcatcher · **Posted:** Mon May 31, 2010 4:49 pm

I am not sure that it is load or RPM's that add to fuel consumption but you will note that should you shift to neutral on a long dowmhill run your rpm's are typically higher than if you let it coast engaged. Unfortunately the CRD is not free wheeling (except perhaps after a GDE upgrade) so you are fighting that on the downhill with the tranny engaged.

Sir Sam · **Posted:** Mon May 31, 2010 6:42 pm

Cowcatcher wrote:

I am not sure that it is load or RPM's that add to fuel consumption but you will note that should you shift to neutral on a long dowmhill run your rpm's are typically higher than if you let it coast engaged. Unfortunately the CRD is not free wheeling (except perhaps after a GDE upgrade) so you are fighting that on the downhill with the tranny engaged.

Its load that determines MPG.

stoutdog · **Posted:** Mon May 31, 2010 6:56 pm

Sir Sam wrote:

Cowcatcher wrote:

I am not sure that it is load or RPM's that add to fuel consumption but you will note that should you shift to neutral on a long dowmhill run your rpm's are typically higher than if you let it coast engaged. Unfortunately the CRD is not free wheeling (except perhaps after a GDE upgrade) so you are fighting that on the downhill with the tranny engaged.

Its load that determines MPG.

If that's the case, and I'm following what geordi said correctly, this means that throwing it into neutral on long downhills will actually help your mpg.... Although RPMs might go up, you would be eliminating load. Correct?

Sir Sam · **Posted:** Mon May 31, 2010 10:51 pm

stoutdog wrote:

Sir Sam wrote:

Cowcatcher wrote:

I am not sure that it is load or RPM's that add to fuel consumption but you will note that should you shift to neutral on a long dowmhill run your rpm's are typically higher than if you let it coast engaged. Unfortunately the CRD is not free wheeling (except perhaps after a GDE upgrade) so you are fighting that on the downhill with the tranny engaged.

Its load that determines MPG.

If that's the case, and I'm following what geordi said correctly, this means that throwing it into neutral on long downhills will actually help your mpg.... Although RPMs might go up, you would be eliminating load. Correct?

Yes.

Just because its at a higher RPM doesn't mean its burning more fuel.

It's very easy to rev the engine at idle, not easy to rev the engine when in drive(IE load attached).

CRD Joe · **Posted:** Mon May 31, 2010 10:58 pm

First fuel up was a trip from Phoenix to the Grand Canyon to Page then on to Bryce Canyon.

Stats: 625 miles 19.1 gallons 32 MPG

Second fuel up was from Bryce canyon to Boise.

Stats: 648 miles on 19 gallons even 34 MPG

Third day Boise to Seattle 475 miles just past half left.

Not as good as the mileage I got driving from Tennesse home but then that was on BALD goodyears and not Firestone Destination LE truck tires.

Im happy.

stoutdog · **Posted:** Mon May 31, 2010 11:13 pm

CRD Joe wrote:

Stats: 625 miles 19.1 gallons 32 MPG

Okay, that I believe. If you were driving 60mph or less. I've made that trek a number of times myself and netted close to the same mpg.

CRD Joe · **Posted:** Mon May 31, 2010 11:20 pm

I never claimed more than that. Hell, name me a US SUV that gets close to what we're getting. There arent any.

Not realy 4x4 SUV's. I can sleep in the back of my KJ.

geordi · **Posted:** Tue Jun 01, 2010 12:49 am

Cowcatcher wrote:

I am not sure that it is load or RPM's that add to fuel consumption but you will note that should you shift to neutral on a long dowmhill run your rpm's are typically higher than if you let it coast engaged. Unfortunately the CRD is not free wheeling (except perhaps after a GDE upgrade) so you are fighting that on the downhill with the tranny engaged.

I have to disagree here. On my 97 Grand Cherokee, Yes, this is the case that for some stupid reason the computer keeps the engine revving when it is out of gear, to the same RPM that the engine was at with it engaged. Blip the throttle, and it will rise... But return to whatever the RPM was at the same speed. You can re-engage without feeling anything, since both sides are still spinning the same speed.

Now, on my CRD and on my Jetta TDI - When I push it into neutral, the engine RPM drops to 800 rpm. If I had been doing 2000 before (~60mph) then I am now coasting at 800 rpm.
If I want to re-engage the transmission, I can just push it back into drive... But I don't b/c I know the engine will be (possibly violently) dragged UP to the current transmission RPM. This is bad for the transmission and torque converter. I will blip the throttle to run it up to about 2500 RPM, THEN put it back in Drive. The transition then is completely transparent.

Do your CRDs not behave in this way? This has NOTHING to do with the GDE transmission tune, my CRD has always behaved like this. The 97 GC is the only vehicle I have ever owned that keeps the engine at-speed when you kick it into neutral... OR even raises the RPM more. I don't like that behavior at all, especially on a gasser that struggles to get 15mpg on a good day... Downhill in a hurricane.

CRD Joe · **Posted:** Tue Jun 01, 2010 1:12 am

As I understand it the engine uses the LEAST amount of fuel if left in gear while going down hill and simply lifting your foot off the accelerator.

Or, taking her out of cruise while going down hill.

dieseldoesit · **Posted:** Tue Jun 01, 2010 2:03 pm

Sir Sam wrote:

Yes.

Just because its at a higher RPM doesn't mean its burning more fuel.

It's very easy to rev the engine at idle, not easy to rev the engine when in drive(IE load attached).

Don't you have your own thread?? :goink:

Road trippin in the CRD

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