So disappointed in this Diesel platform; wish there was a return policy.

[Rat2Desert]

My experience with diesel engines is more related to tractors, so forgive me if some of my questions appear stupid or novice - they may well be.
So these are turbo engines - and that generates heat, am I correct?
Am I also correct in that the tow ratings of these are based on several tests - including maintaining a certain speed up a certain grade with a certain load?
What is that speed in the test? 40? 50? 60? More?
Am correct so far or even close?
So if towing a load that is 80% of rating or more up a sustained grade - if you exceed their speed used in rating the truck you are running the engine full load, turbo in all the time and it's going to run hot?
If my truck is rated to tow 6,000 pounds and part of the test is a 5% grade at 50 mph and I try to maintain a speed of 65 up a similar grade - am I not exceeding their testing used to achieve the rating?
Am I so far off based even someone with an IQ of 180 can't figure out my questions or thinking?
How many are laughing so far?

For context, I have owned, and towed extensively with, 3 Grand Cherokees and now have a Rubicon Diesel waiting for shipment to my dealer.

I've been watching the forums for quite some time to see about heating issues with the diesel, as I've had heating issues in all the Cherokees when towing uphill, heavy and especially in the heat. I wrote it off to a relatively small radiator and the vehicle being a compromise. I had hoped that maybe the diesel might do better with the low end torque, and even if not I've gotten very tired of grinding up hills with a gas engine at 5K.

Anyway, I looked into the tow ratings further and what I've found is that the rating is for 100 degree ambient at max GCWR at 40 MPH. I hadn't seen the speed rating before, it makes sense now - there has to be a limit somewhere in the speed/weight/temp balance in a compromise like this vehicle.

I can live with 40 mph, that is actually pretty much my cooling limit with the Cherokee. But, as others have mentioned I really wish this was published somewhere, it is a crucial bit of data when facing the possibility of a severe power loss when towing. Quite unsafe if not prepared.

That said, I've learned to drive the temp gauges, limiting my speed to keep water below 220 (on the Cherokee), even opening windows with the heater full blast. As dumb and painful as that sounds, that procedure dumps heat incredibly fast and, for me, is worth enduring to gain some speed up a hill . . . at times. I wouldn't trade the Cherokee for a better tow vehicle, likely wouldn't consider trading the Gladiator either. I know they are compromises, I embrace the utility while accepting some limitations.

Looking forward to getting my Gladiator in the next few weeks and giving her a go . . . I'll be making some trips towing throughout the southwest in August, definitely will be seeing heat and hills !

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[dcmdon]

Power is a measure of force times speed. essentially torque x rpm = power.
Torque is a measure of force only.

To go up a hill at speed, you need power.
A diesel makes a lot of torque (and power) low in the rev range.
A normally aspirated gas engine makes less torque, but can spin faster. So it can make similar power by turning faster and using gear reduction to increase the torque.

Power is power.

100 ft-lbs of torque at 1000 rpm = 50 ft-lbs of torque at 2000 rpm (= 19hp)

They will both pull a trailer up a hill at the same speed because they are both the exact same hp. Its just that the higher RPM, lower torque engine will need 2x the gear reduction.

They will also generate the same excess heat. (diesels can be more thermodynamically efficient than gas engines. So they make less waste heat per hp. But auto engines aren't really designed to maximize that)

So regardeless of the engine. Making power requires dumping heat.

One other thing to remember. Wind resistance increases as a square function. Resistance is a measure of force. Remember that power is force times speed.

So the POWER necessary to overcome wind resistance increases as a CUBED function of speed.

That means that going 60 mph requires 3.375 (!!!!) times the power as it takes to go 40 mph!!
Let that sink in for a moment.
(60/40 = 1.5, 1.5^3 = 3.375)

At highway speeds the majority of the drag is aerodynamic, not a result of rolling resistance. (Which increases linearly, so the power required increases as a square function)

The bottom line is that driving a vehicle at 60 mph requires the vehicle to dispose of about 3 times as much heat as driving at 40 mph. Its a pretty steep curve.

One last thing. At various times in my life I've roadraced and autocrossed cars.

For a car to survive on a race track it has to shed a lot of heat. The motor makes near maximum power a lot of the time. Then all that energy is dumped into the brakes. Engine oil gets hot, coolant gets hot. So radiators need to be big. Brakes get hot, so they need to be big. Differentials . . you get my point.

In autocrossing its an entirely different situation. An autocross run takes about a minute. So heat is an absolutely non-issue. Radiators can be small. Transmission oil coolers are nonexistent. Brakes can be small and light since they will barely be warm at the end of a run.

Its all about heat.

OK. I've beaten this horse till its hamburger. I hope this was helpful to some.

Don

 

[jsalbre]

They will also generate the same excess heat. (diesels can be more thermodynamically efficient than gas engines. So they make less waste heat per hp. But auto engines aren't really designed to maximize that)

The issue is largely the turbo. Tons of excess heat and intercooler even further reducing airflow through the radiator.

 

[Jonny A]

Some folks claim the Mojave hood is designed so, so it will be able to cool the 392 when released at some date. Why not have diesel versions have a Mojave hood and a working hood scoop.

 

[Jonny A]

The diesel will tow circles aroubd the minivan motor

After reading this.... obviously not.

 

[Mr._Bill]

Some folks claim the Mojave hood is designed so, so it will be able to cool the 392 when released at some date. Why not have diesel versions have a Mojave hood and a working hood scoop.

If that would work, the Jeep engineers would have already done it.

 

[am1978]

Some folks claim the Mojave hood is designed so, so it will be able to cool the 392 when released at some date. Why not have diesel versions have a Mojave hood and a working hood scoop.

Better Rubi scoops. https://www.sbfilters.com/jeep-scoops/as-1015

 

[InvertedAerialX]

This may be the dumbest idea, but for some stupid reason I'm still going to mention it, how about removing the hood completely? Secondly, I read somewhere a LONG time ago, that whne towing, You shouldn't tow over the mileage of the vehicle ie (1,000Mi + 1,000lbs, 2,000Mi + 2,000lbs) Is there any truth to that?

 

[dcmdon]

The issue is largely the turbo. Tons of excess heat and intercooler even further reducing airflow through the radiator.

All modern diesels have turbos. Even the huge, slow turning engines in container ships that are ridiculously efficient.

The presence of the intercooler in front of the radiator reduces cooling efficiency. Yes. But not engine efficiency. (An engine that is 100% efficient would produce no heat).

 

[dcmdon]

I wouldn’t expect to see an improvement. They really wrung as much as they could out of it:

https://jalopnik.com/the-engineering-behind-the-jeep-gladiators-tow-rating-1833657453

This is a great article. But don't forget that these engineers are working within the constraints of a new production vehicle program. The aftermarket can produce larger radiators that cost too much for production. A stepped radiator made of aluminum. (thin around the edges to fit the stock mount but thick in the center) is one example.

There is always a way. There are also always constraints. Height, width, thickness, durability, cost.
If you flex on one or more, it can work. Cost is the obvious constraint that can be moved when we are talking about aftermarket products like the Aluminum Gladiator radiator I linked to in an earlier post.

Jeep could also get creative. Like by using an air to water charge cooler. Or a top mount intercooler with a hood scoop. There is always a way. What matters is how much time and money you want to throw at it.

I suspect that since the diesel is already a $4000 option, they were reluctant to bump the option price even more by using anything expensive like an air to water charge cooler or an aluminum radiator.

 

[bring44]

The diesel will tow circles aroubd the minivan motor

Most unproductive and dumbest comment of this thread. Are you aware that the 3.6 is in many other vehicles other than a minivan?

 

[dcmdon]

Increases of mpg on engines in the last 20 years is more about the engine controls than breaking in. Things do loosen up a bit but it's broken in way before 2,000 miles. Things do keep loosening up but that's wear, not breaking in.

When Subaru came out with their 300 hp STi, a lot of hp in 2004, there were problems with oil consumption and ring blow-by. One thing they found was that many of the people with this problem immediately switched out the factory fill to something like Amsoil, Redline, Mobile1, or Royal Purple synthetic.

Subaru determined that the synthetic oil was lubricating too well and the rings weren't seating. So they eventually recommended against using synthetic until 3000 miles or so.

This isn't really break in. In fact Subaru allowed full throttle use because it seated the rings faster. Just not for sustained periods.

 

[CreepyJeepy]

Power is a measure of force times speed. essentially torque x rpm = power.
Torque is a measure of force only.

To go up a hill at speed, you need power.
A diesel makes a lot of torque (and power) low in the rev range.
A normally aspirated gas engine makes less torque, but can spin faster. So it can make similar power by turning faster and depending on gear reduction to increase the torque.

Power is power.

100 ft-lbs of torque at 1000 rpm = 50 ft-lbs of torque at 2000 rpm.

They will both pull a trailer up a hill at the same speed.

They will also generate the same excess heat. (diesels can be more thermodynamically efficient than gas engines. So they make less waste heat per hp. But auto engines aren't really designed to maximize that)

So regardeless of the engine. Making power requires dumping heat.

One other thing to remember. Wind resistance increases as a square function. Resistance is a measure of force. Remember that power is force times speed.

So the POWER necessary to overcome wind resistance increases as a CUBED function of speed.

That means that going 60 mph requires 3.375 (!!!!) times the power as it takes to go 40 mph!!
Let that sink in for a moment.
(60/40 = 1.5, 1.5^3 = 3.375)

At highway speeds the majority of the drag is aerodynamic, not a result of rolling resistance. (Which increases linearly, so the power required increases as a square function)

The bottom line is that driving a vehicle at 60 mph requires the vehicle to dispose of about 3 times as much heat as driving at 40 mph. Its a pretty steep curve.

One last thing. At various times in my life I've roadraced and autocrossed cars.

For a car to survive on a race track it has to shed a lot of heat. The motor makes near maximum power a lot of the time. Then all that energy is dumped into the brakes. Engine oil gets hot, coolant gets hot. So radiators need to be big. Brakes get hot, so they need to be big. Differentials . . you get my point.

In autocrossing its an entirely different situation. An autocross run takes about a minute. So heat is an absolutely non-issue. Radiators can be small. Transmission oil coolers are nonexistent. Brakes can be small and light since they will barely be warm at the end of a run.

Its all about heat.

OK. I've beaten this horse till its hamburger. I hope this was helpful to some.

Don

This was an awesome post.

 

[dcmdon]

Some folks claim the Mojave hood is designed so, so it will be able to cool the 392 when released at some date. Why not have diesel versions have a Mojave hood and a working hood scoop.

The Mojave hood scoop is not functional.

If that would work, the Jeep engineers would have already done it.

The 392 hood looks the same but the scoop is functional. The news stories on the 392 talked about how heavy it was and how complex the runner system on the bottom of the hood was. Unlike a car hood scoop, this one needs to separate air from water, so it has a system of channels that remove the water from the intake air.

Most unproductive and dumbest comment of this thread. Are you aware that the 3.6 is in many other vehicles other than a minivan?

Aren't there versions of it in the Ram?? So its a Ram pickup motor.

 

[Mac]

When Subaru came out with their 300 hp STi, a lot of hp in 2004, there were problems with oil consumption and ring blow-by. One thing they found was that many of the people with this problem immediately switched out the factory fill to something like Amsoil, Redline, Mobile1, or Royal Purple synthetic.

Subaru determined that the synthetic oil was lubricating too well and the rings weren't seating. So they eventually recommended against using synthetic until 3000 miles or so.

This isn't really break in. In fact Subaru allowed full throttle use because it seated the rings faster. Just not for sustained periods.

Same issue with current Yamaha outboards, people don't run them hard enough and the rings do not seat and you end up with fuel diluted oil, very hard to convince people to take a brand new motor and run it hard at wot when it is brand new.

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