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Old 01-14-2015, 04:03 PM   #1
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Allison Transmission running colder than normal

2006 Apex with 400hp cummins and Allison 3000 transmission and Silverleaf. In three days of driving south for winter the transmission would warm up to the 180-185 degree range which is the normal running temp for my rig. That temp held for the first 250 miles of travel or so and then fell back to 140-150 degree range for the last 100 miles or so. Same thing happened the second day of travel. On the third day of travel the temp never went above 145 degrees during a 300 mile trip. All of these temps are being read off Silverleaf readings. Nothing in topography, outside temps, or wind speed/direction to account for transmission temperature change. Rolling MPG also drops from the 8.5-9.0 mpg range to 5.0-5.5 mpg range. No noticeable change in transmission performance or sound when temp drops.

Ideas? Do I have an Allison problem? Silverleaf problem? Is there a thermostat that controls transmission temp and if it failed would it cause tranny to run colder instead of overheating? Any help would be appreciated.
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Old 01-14-2015, 04:20 PM   #2
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Maybe Silverleaf problem, I can't think of anything that would cause that drastic a change in mileage and drop transmission temps except maybe a stuck open thermostat on the engine. Is engine temp low also? Is the mileage change computed on paper at the fuel pump or just silverleaf readout?
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Old 01-14-2015, 04:24 PM   #3
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not sure if it helps
but our return from south texas last week, outside temps 38 -40F
the tranny never went over 160.
in fact the engine temp only peaked 190 once, then rest was in the 180 range

the temps stayed so cold i started watching them waaay to much
thought something was wrong
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Old 01-14-2015, 04:27 PM   #4
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Do you have an engine driven cooling fan? The clutch could be locked up, that would account for the MPG drop and the trans being cold. The trans doesn't typically have a thermostat (Some foreign trucks do, so it's possible) to regulate temp, so if the cooling fan is drawing too much air across the cooler that could explain it.
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Old 01-14-2015, 10:13 PM   #5
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You could start easy by rebooting the Silverleaf and Vansco system and check temps again.
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Old 01-15-2015, 03:02 PM   #6
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Sknight had the answer. The transmission running cold is a by product of a bad cooling fan drive controller. After verifying that the temps being reported via Silverleaf matched actual transmission temps via hook up to a diagnostics machine, noticed that cooling fan was on full bore. That would also account for the deterioration of rolling mpg what with the hydraulic pump running full time. Have a new Sauer-Danfoss unit ordered with a delivery by the end of the month. Thanks for pointing me in the right direction.
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Old 01-15-2015, 10:39 PM   #7
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Happy to help!

Kind of amazing isn't it? That fan can kill three MPG all by itself? It takes an amazing amount of power to run those things when they're at 100% lockup.
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