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Old 01-30-2012, 08:24 PM   #1
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245 degree transmission oil on long steep grades

I have a 2009 Yukon XL Denalli and have had heating concerns out west on some of the long steep hills in Utah, Colorado, Wyoming, Montana. Pulling a 5000# ac trailer temps would reach 245 degrees using Tow Haul mode or shifting manually to control down shifting.
Now have a larger 28 footer that could weigh 8000+ lbs loaded. Brochure says 7900lbs maximum towing capacity.
Question is have you experienced a similar problem or heard of anyone who has...thinking about changing the rear end to a 3.73 or getting a bigger oil cooler if not both in hoping to solve capacity and tranny oil heat issues. Or buy a 3/4 ton Yukon XL. I drove one and the 6.0 engine seems week compared to the 6.2. Hate to do that if not necessary.
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Old 01-30-2012, 08:44 PM   #2
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That's a little high, IMO. You'll definitely need a 3.73 and an additional cooler. Even then you're still overloaded. The 3/4 ton is probably the way to go....with a 3.73.
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Old 01-30-2012, 09:47 PM   #3
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Hi ashe, there is some great info that should help you out in the link below.

Actual transmission oil temperatures can vary, depending on where the temp sensor is installed in your particular application. Your owners manual may have an maximum transmission oil temperature for extreme Towing conditions, as you have mentioned.

A must read; Automatic Transmission Cooling | OldIHC

Good luck, and I hope this helps.
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Old 01-30-2012, 09:56 PM   #4
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I had a 2008 Tahoe with the 5.3 vortec and a 3.73 and 8000lb tow rating and it would run hot towing a 6000lb SOB on long climbs. You will be better with a 3/4 ton.
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Old 01-30-2012, 10:29 PM   #5
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Quote:
Originally Posted by ashe
I have a 2009 Yukon XL Denalli and have had heating concerns out west on some of the long steep hills in Utah, Colorado, Wyoming, Montana. Pulling a 5000# ac trailer temps would reach 245 degrees using Tow Haul mode or shifting manually to control down shifting.
Now have a larger 28 footer that could weigh 8000+ lbs loaded. Brochure says 7900lbs maximum towing capacity.
Question is have you experienced a similar problem or heard of anyone who has...thinking about changing the rear end to a 3.73 or getting a bigger oil cooler if not both in hoping to solve capacity and tranny oil heat issues. Or buy a 3/4 ton Yukon XL. I drove one and the 6.0 engine seems week compared to the 6.2. Hate to do that if not necessary.
Do you have the tow package with the external transmission cooler?
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Old 01-30-2012, 10:35 PM   #6
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Your transmission will not last long at 240F; wear accelerates very quickly past 220F. I fitted a large cooler to replace the small one on our diesel; this has made our transmission temps rarely exceed 200F, even dealing with 10% grades that are miles long. If my roadspeed drops to 25 mph or below due to off road conditions, we're down in 4low w/ the front hubs unlocked to let the transmission get into 3rd where it will lock.

Make sure to use a cooler w/ a thermostatic bypass so that transmission will warm up in winter time.

I'd also get a bigger tow vehicle if you're already past the max weight...

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Old 01-31-2012, 12:42 AM   #7
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I think this is an example of the sort of thing you can run into towing heavy trailers with a 1/2 ton. I'm not sure it's entirely a cooling problem, the 4L60e just isn't designed for that kind of sustained load.

There are some choices if you want to add more cooling. Aftermarket transmission coolers are one. You might also pick up some cooling from a Mag-Hytec aluminum pan, which would also add some oil capacity that might help a little.
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Old 01-31-2012, 01:14 AM   #8
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GM recommends that the maximum transmission-fluid temperature (measured in the sump) for short durations shall be no greater than 285 degrees F. At 300 degrees F, research shows, metal parts inside the transmission begin to warp and distort, seals begin to melt, and fluid life is extremely short because of heavy oxidation.
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Old 01-31-2012, 02:28 AM   #9
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I would strongly recommend using synthetic lubricants, engine, transmission, on and on! They protect much better in normal and extreme conditions, even when not towing!!
Automatic transmission fluid - Wikipedia, the free encyclopedia
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Old 01-31-2012, 03:26 AM   #10
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I am pretty sure the 1/2 & 3/4 ton Suburbans with 6.0 or 6.2 Litre motors use the same transmission so you have nothing to gain from a 3/4 except a slightly larger factory cooler. Because you have a 6 speed transmission you have little to gain with a 3.73:1 axle ratio.

I am sure you have an external cooler but do confirm it is there to be sure. You could also have a inacurate gauge. What RPM and speed are you climbing at? It may just be a matter of dropping a gear and easing up on the speed a little.

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Old 01-31-2012, 07:25 AM   #11
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Wow, I just want to say how much I appreciate the input and experienced shared on my question so far. Very helpful and keep em coming.
Nick
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Old 01-31-2012, 07:33 AM   #12
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Wow, I just want to say how much I appreciate the input and experienced shared on my question so far. Very helpful and keep em coming.
Nick

POI....The PCM will go into "limp mode" if the trans temp exceeds the 280 degree threshold.
Working at a Chevy store I never pulled that fault code when scanning.

Bob
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Old 01-31-2012, 07:54 AM   #13
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Thank goodness for my Allison that never rises more than about 10 degrees from where it is apparently thermostatically controlled, regardless of outside temperature or grade. Most of the time, the temperature never varies.
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Old 01-31-2012, 08:09 AM   #14
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I am pretty sure the 1/2 & 3/4 ton Suburbans with 6.0 or 6.2 Litre motors use the same transmission so you have nothing to gain from a 3/4 except a slightly larger factory cooler. Because you have a 6 speed transmission you have little to gain with a 3.73:1 axle ratio.

I am sure you have an external cooler but do confirm it is there to be sure. You could also have a inacurate gauge. What RPM and speed are you climbing at? It may just be a matter of dropping a gear and easing up on the speed a little.

Andrew T
IIRC, no 6 speed in '09. While the 6.2 and 6.0 use the same trans DESIGNATION, the 6.0 may have internal differences, because it is designed for higher loads. All GM vehicles with a 6.2 ALUMINUM block will have lower tow and load ratings than the CAST IRON 6.0. Since the tow and load ratings are lower on the 6.2, I suspect the trans coolers/radiator, etc. are not as high capacity as the 6.0. EVEN THOUGH the 6.2 is capable of higher HP and higher torque, the torque load capability is not as great with the 6.2 as with the 6.0, and could cause accellerated wear over time. 6.2 was designed as a "luxury" V8, not a work horse, like the 6.0.

The reason there are no 6.2's in 3/4 ton and up, is due to the fact that an aluminum block will "twist" at very high torque loads. thus, the lower ratings and PROBABLY not the same ancillary equipment.
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