Ecodiesel power derating as temps rise?

[briandmiles]

Remember my issues did not start until I hit over 7K miles but before my 1st oil change. The DPF failed to do it's job and was 92% clogged with no warning until it went into limp mode with every warning light coming on in the dash. Before that I was averaging around 25mpg. In fact at 1500 miles I did a 4000 mile trip that was 2500 miles off road thru 6 states and had averaged 23.5 for that trip. Since the fix when it all but shut down my MPG had gotten progressively worse. Around town I now get maybe 12, highway 16.5 and overall 15.1. Very disappointed. Dealer has no idea why. 37 Jeeps and my 1st lemon ?

The display of the gauges a post or two above this one is my picture after a 4 mile, 6% grade and not towing anything, I'm afraid to tow. Dealer told me that the motor will shut down above 250 something coolant temp and 270 oil temp to protect the engine. As you can see after a 4 mile grade I was not far from those numbers. On the bright side, the 4 mile grade down the other side, the temps quickly returned to normal

I had a similar situation with my JTRD on the way back from Boise. The computer said I needed a regen, but the filter was only 29% full. It still derated and went into limp mode with dash saying there was an exhaust problem and to take it to the dealer. The next 3 hours I was going between 45 and 75 mph depending on the incline or decline.

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[CrazyCooter]

Did you regear and run the same test again? If not then your reply means nothing. 4.88’s are over 30% more rpm’s with 33” tires than stock 3.73’s. IMO were the heat issue factors in the most on climbs. If the truck will climb a hill in a higher gear and not have to down shift as far it will allow for less stress on the motor and theoretically lower engine temps.

No way I would install lower gears than 3.73 on the OE 33" tires!

Just dropping to 7th gear would be a 20% change or the equivalent of 4.32's. Towing in 6th would be equivalent to 4.97's. Id rather just not use 8th while towing and tow in 6th (Direct) in the hills or 7th (0.8392) for lower heat production in the trans leaving 8th for driving unloaded on the flats.

33 vs. 37's is just an 11% change and I think it's perfect enough that I won't be changing gear in mine.

Also note this isn't even a money thing for me......I have 3+ sets of gears on the shelf and can do the gear swap for the cost of oil and crush sleeves if I knew it would make a significant difference for me. I have actually planned to swap them prior to purchasing the truck, but 10K miles of driving with various loads and conditions made me feel otherwise.

 

[Wapiti Jeep]

No way I would install lower gears than 3.73 on the OE 33" tires!

Just dropping to 7th gear would be a 20% change or the equivalent of 4.32's. Towing in 6th would be equivalent to 4.97's. Id rather just not use 8th while towing and tow in 6th (Direct) in the hills or 7th (0.8392) for lower heat production in the trans leaving 8th for driving unloaded on the flats.

33 vs. 37's is just an 11% change and I think it's perfect enough that I won't be changing gear in mine.

Also note this isn't even a money thing for me......I have 3+ sets of gears on the shelf and can do the gear swap for the cost of oil and crush sleeves if I knew it would make a significant difference for me. I have actually planned to swap them prior to purchasing the truck, but 10K miles of driving with various loads and conditions made me feel otherwise.

I agree the truck is perfect until you give it a decent load. I will post a performance update once I get my gears in. Going with 4.88’s and currently running 35’s.

 

[CrazyCooter]

I agree the truck is perfect until you give it a decent load. I will post a performance update once I get my gears in. Going with 4.88’s and currently running 35’s
I agree the truck is perfect until you give it a decent load. I will post a performance update once I get my gears in. Going with 4.88’s and currently running 35’s.

4.88's and 35's is going to be way low! Like even a bit low for the 3.6 engine....... I hope you don't drive much long distance in the flat land at high speeds.

Something to remember is that it takes xxx hp to do xxx work at a certain speed and HP=Heat. R&P gearing wont do anything except get you off the line harder unless you are stuck between transmission gears which is pretty hard to do with modern 8 and 10 speed autos.

 

[Wapiti Jeep]

4.88's and 35's is going to be way low! Like even a bit low for the 3.6 engine....... I hope you don't drive much long distance in the flat land at high speeds.

Something to remember is that it takes xxx hp to do xxx work at a certain speed and HP=Heat. R&P gearing wont do anything except get you off the line harder unless you are stuck between transmission gears which is pretty hard to do with modern 8 and 10 speed autos.

4.88’s and 35’s is a 15% change to the RPM at 70mph. I’ll go from 1750 to just over 2000. And in the mud which I’m in from time to time it will help the motor not fall flat on its face when shifting gears.

 

[CrazyCooter]

4.88’s and 35’s is a 15% change to the RPM at 70mph. I’ll go from 1750 to just over 2000.

I know how to do the math........I've been in the drivetrain business for 28 years. 33" to 35" is 6% and 3.73 to 4.88 is 23.6%.....more like a 17.6% change.

You will also be towing in your weakest transmission gears that generate the most heat. With 37's and 3.73's you would be towing in 6th (Direct) in the rolling hills and 7th when it's totally flat and light winds.

Your money, your truck........I would never advise a client to put 4.88's in an Eco JT/JL.

 

[just_another_guy]

Something to remember is that it takes xxx hp to do xxx work at a certain speed and HP=Heat.

That pretty much sums it up. You can't change how much HP you need to haul something, so there needs to be a way to get rid of the heat that comes along with it.

 

[Wapiti Jeep]

I know how to do the math........I've been in the drivetrain business for 28 years. 33" to 35" is 6% and 3.73 to 4.88 is 23.6%.....more like a 17.6% change.

You will also be towing in your weakest transmission gears that generate the most heat. With 37's and 3.73's you would be towing in 6th (Direct) in the rolling hills and 7th when it's totally flat and light winds.

Your money, your truck........I would never advise a client to put 4.88's in an Eco JT/JL.

Not saying you don't know how to do the math. I feel like the truck could use more power especially when pulling. I am not a fan of programers, and IMO regearing seems to be a logical solution. But I do get what you are saying.

So how do you fix it falling on its face in the mud? I use the truck often to show land. Been stuck because when it shifted it fell flat. Tried going manual and needed second gear to get the tires to clean and it fell flat again. I know, off topic, but we all want the most out of our trucks.

 

[Hondo1]

After going with 4:56’s with my 37’s I would never look back at 3:73’s. I gained fuel mileage while towing and while empty, I have better off idle torque when off road.
I see absolutely zero down side here.

 

[ShadowsPapa]

That pretty much sums it up. You can't change how much HP you need to haul something, so there needs to be a way to get rid of the heat that comes along with it.

HP equation includes time.
You can change the HP needed to do something by doing it more slowly.
Running 50 mph instead of 60 mph with the same load takes less HP.
I understand that there's a practical limit to how slowly you tow the load - but I'm just pointing out that if you reduce speed from 65 to 55 mph, you indeed reduce the HP needed to pull the exact same weight.

1 HP is the power necessary to lift a total mass of 33,000 pounds one foot in one minute.
Extend that to 2 minutes and it would take less HP.

 

[2kXJ]

I wonder how much cooler it would run without all the emissions bs?

 

[just_another_guy]

HP equation includes time.
You can change the HP needed to do something by doing it more slowly.
Running 50 mph instead of 60 mph with the same load takes less HP.
I understand that there's a practical limit to how slowly you tow the load - but I'm just pointing out that if you reduce speed from 65 to 55 mph, you indeed reduce the HP needed to pull the exact same weight.

1 HP is the power necessary to lift a total mass of 33,000 pounds one foot in one minute.
Extend that to 2 minutes and it would take less HP.

Ok? You could also change the force variable by lowering the weight, but that also wouldn't be much of a comparison, would it? I think it's pretty observable that it takes less power to go slower, or haul a lighter load.

 

[CrazyCooter]

We've already proven that the JT ecodiesel will pull its rated towing weight all day up the steepest grade at 10mph without overheating........what is the point of lower gears?

What we need to do is focus on a solution to shed the heat required to travel at safe speeds while towing. Gears won't change heat load because as Shadow's equation points out above, it takes hp to do work at high speed!

A tuner is that last thing on my mind! More hp is just more heat we can't get rid of!

 

[CrazyCooter]

After going with 4:56’s with my 37’s I would never look back at 3:73’s. I gained fuel mileage while towing and while empty, I have better off idle torque when off road.
I see absolutely zero down side here.

I could agree because your final is now what is was originally in 7th. This transmissions 1st is so low that you could launch in 2nd. Without the need of a lower first, why not just stay 3.73 and tow in 6th and 7th leaving a nice double OD for when you are unloaded?

Why are people obsessed with towing and climbing hills in 8th gear?

 

[ShadowsPapa]

Ok? You could also change the force variable by lowering the weight, but that also wouldn't be much of a comparison, would it? I think it's pretty observable that it takes less power to go slower, or haul a lighter load.

The solution? Better cooling LOL....... be it oil, coolant, or both. You can't expect people to go only 45, you can't expect people who buy to tow to haul only 1,000 pounds.
The equation is pretty simple really - either lighten load, lower the speed - but there are practical minimums to each.

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