I just read an interesting article in the caravanners forum (dedicated owners discussion group) Posted Dec 13 about the possible reason why Jeep Grand Cherokee v6 diesel engines fail. The upshot of a lot of Research and investigation by GDL Automotive Services Warriewood NSW is that most of the failures are in vehicles that are driven conservatively and tend to lug in the higher gears, where as the ones that are driven hard don't fail. The failure rate is higher in the 8 speed than the 5 speed. Worth a read.
John
MY08 D3 - The Antichrist - "Permagrimace". Turn the key and play the "will it get me home again" lottery.
The Hyundai instructions for driving the CRD 2.2 with the 6 sp and 8sp auto are quite explicit about this and emphasise the need to avoid "lugging" especially when towing...."to avoid damage to the engine and transmission". The "Jeep" article clarifies the issue. V. helpful.
MY99 RR P38 HSE 4.6 (Thor) gone (to Tasmania)
2020 Subaru Impreza S ('SWMBO's Express' )
2023 Ineos Grenadier Trialmaster (diesel)
I wonder what percentage of failed 3.0 RRS and D4 are the high output with 8 speed auto.
I still maintain the design of the V /crank in these engines is obviously substandard... But if owners could help negate some of this with gear selection, or indeed a trans remap, that would be a fantastic relief for many.
It's not open for debate, the only way to make more power at lower revs is to put more fuel in per fire, and the only way to do that cleanly is to increase aircharge, and also advance timing to allow fuel burn to finish in time, this is a KILLER for cylinder pressure, so even just thinking about this, logically it does make sense.
The increase in cylinder pressure to make 450nm at 1900rpm vs 450nm at 2800 would be considerable.
I could do the math, but this sort of math is not fun!
This really is something for owners to think long and hard about, it's not hard to knock back a gear....
Mines only the 2.7L D3, but with the van on the back at 100kph on the flat I see a significant difference in temperature and fuel consumption between 5th and 6th. 5th runs quite a bit cooler.
I generally just aim for a cruise at ~2000RPM and select gear to suit. I'm comfortable down to 1500RPM at very low loads, but it feels better spinning a bit quicker.
Last edited by BradC; 26th January 2023 at 03:09 PM.
MY08 D3 - The Antichrist - "Permagrimace". Turn the key and play the "will it get me home again" lottery.
BradC,
I've changed the terminology I used that you quoted, of course what I said was incorrect, it's much easier to make 150kw at 2800 than 1900... Torque on the other hand..!
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