What kind of MPG's to you see when towing your camper in the Summer Dave ???
Towing Heavy Transmission Temps
- Thread starter Foggy
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8-9 mpg
OK... When I can keep it in 5th I get about 9-10... In 4th gear it's 7-9 mph
But way better than when I was supercharged.. that was 4.5-5.5 mpg
Wow...no wonder you went back to NA.
I would wager that a switch to 3.73 would keep you in 5th more. And 4.10's, fuhgeddaboudit - you'd hardly ever see 4th. The Suburban 3500HD is interesting to have alongside the other two to compare. The 6.0/6L90 spends 95+% of its time in 5th pulling the same camper.
strutaeng
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...I was gonna ask if everyone here is talking about the 6LXX transmissions? Seems like it?
mikez71
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There is a dedicated channel that is PE active or inactive that should show up...
I always thought the PE was like an accelerator pump, but watching one of these youtube tuning videos, apparently it is for cylinder cooling when you are heavy on throtte/load.
Or the HOT table for PE, which seems to be set at 87% throttle from factory. Perhaps you're over 87% in 5th, but under in 4th.
I hope so! (they are going into 5th gear...)
Yes, 6L80 for the XL Denali's.
strutaeng
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Gotcha @Geotrash & @mikez71
@Foggy I think the transmission is running a bit warmer on 4th gear simply because it's running at higher RPMs. Higher RPMs I'm pretty sure simply means more friction (= more heat). Probably not a linear relationship because you have higher ATF flow, and different clutchpacks engaged/holding and other factors. Maybe we can look at the range reference chart...
Also, the engine IS making more power at the higher RPM as well, so the more power, the higher the heat generated.
But TBH, those transmission temperatures don't seem concerning to me at all.
I'm not too familiar with the 6LXX, and not sure what the temperature difference between the 6L80 vs 6L90 would make. I'm thinking the 90 would run slightly lower temperature since it has the larger output planetary gearset, if both were pulling the same exact gross combined weight, same speed, same power, etc.? But usually on the heavier trucks there's also differences in driveline losses due to larger axles, etc.
Also, maybe @NickTransmissions can offer some insights from an geartrain perspective?
@Foggy I think the transmission is running a bit warmer on 4th gear simply because it's running at higher RPMs. Higher RPMs I'm pretty sure simply means more friction (= more heat). Probably not a linear relationship because you have higher ATF flow, and different clutchpacks engaged/holding and other factors. Maybe we can look at the range reference chart...
Also, the engine IS making more power at the higher RPM as well, so the more power, the higher the heat generated.
But TBH, those transmission temperatures don't seem concerning to me at all.
I'm not too familiar with the 6LXX, and not sure what the temperature difference between the 6L80 vs 6L90 would make. I'm thinking the 90 would run slightly lower temperature since it has the larger output planetary gearset, if both were pulling the same exact gross combined weight, same speed, same power, etc.? But usually on the heavier trucks there's also differences in driveline losses due to larger axles, etc.
Also, maybe @NickTransmissions can offer some insights from an geartrain perspective?
All good thinking. Some observations to add that seem relevant: There is only around 1K difference in weight between our campers. Mine is also 32' long and they likely have a similar 'sail' areas, which generates most of the drag that the driveline needs to overcome.
I have no data for this, but I would estimate that the additional power needed to tow our respective campers on an average highway drive would be less than 5% and probably much less. And if I'm understanding Tom's notes right, his transmission temperatures are averaging 5-10% higher than mine. Not a linear relationship of course, but for an otherwise nearly identical drivetrain and cooling setup, both spending most of the time in 4th, I still suspect something else is going on.
I say nearly because I have a new Denso factory radiator and he's running a larger Mishimoto. Yet he's still seeing coolant temperatures slightly higher than mine as well. I was running a Cold Case 2-row radiator for 3 years before it started leaking, and mine ran even cooler still. The coolant temps rarely came off the 210 mark, and only during sustained climbs. With the new factory radiator, I see temperature rises earlier in the climb on hot days.
Long story short, I suspect it's his engine that's actually generating the additional heat that's finding its way into the transmission fluid as well. But, it's just a theory. It could very well be both.
donjetman
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Just some thoughts I had:
I've owned a few 40K to 50K # motorhomes with 11L & 12.7L diesel engines and Allison 6 speed autos. The rule to keep them from getting hot is "keep the rpm up. Don't lug em." I don't know if the same applies to gasoline engines.
For many yrs I've been doing used ATF analysis with some of my vehicles. My ATF samples I send to JG Lubricant Services because a President/owner, x GM fluid engineer Tom Johnson, is at ph 877-971-7799 ext#2 to answer question(s). I've talked to him several times. Give him a call. Nice man.
IIRC, Tom says your Dexron6 atf temps aren't hurting a thing. Prolonged temp greater than 235 and the fluid starts to degrade.
If your worried about Dexron6 viscosity thinning out, you might consider running an Allison approved TES668 atf. They have a higher viscosity. Some Corvette folks that "track" their car do it.
You might consider ordering some kits too so you can see what is what.
https://www.jglubricantservices.com/docs/Technical Information Sheet.pdf
https://www.allisontransmission.com/parts-service/approved-fluids/on-highway-fluids
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