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2005 GMC Sierra 2500HD 4WD Questions & Answers
Auxiliary battery use
The extra battery is there because of the glow plugs and intake heater of the duramax. During cold weather both of these systems draw high amperage from the batteries. A single battery will function, but not as well as a pair.
I have a 2005 GMC 2500 Duramax, The problem I have
the maximum pay load is 3534 lbs (3.5 tons ) and the maximum towing capacity is 18000 lbs or 9 tons
from your description of 2 thermostats I take it is a v8 hopefully a 6.6 ltr v8 turbo diesel
it should have come with a 6 speed allison auto transmission.
with a 35ft, 5th wheeler behind it the combined gross max mass would be getting close to max allowed
add any speed on the highway and the transmission will be running at high oil temperatures and that heat is transferred to the radiator by the transmission oil cooler in a tank of the radiator
the high oil temps could be slippage in bands and clutch packs in the transmission( not noticeable under normal driving conditions) so an check and adjustment would not go astray
next if the adjustments are set properly, it may become necessary for you to consider an air to air transmission cooler so that the heat from the transmission is transferred to passing air flow and not accumulated and added to engine coolant temperature
those kits are available from most accredited transmission specialist shops and will reduce the transmission oil temp by at least 40%
taking that the coolant temp is 95 -98 c the transmission oil will be running a lot lower, saves the oil and the transmission and will help prevent boiling of the coolant
it may be necessary for you to lock up the fan clutch as well
Blower not working on truck
check for power/ground at the blower motor if you have this replace the motor. if not you will have to check the wiring back from the motor to the switch.
Why transmission won't work in reverse
That transmission is a 4L80E a pretty hefty transmission.The reverse band is probably slipping or broken,or you may have some broken hard parts either way the transmission needs to come apart comepletly.
P0300 code
sounds like you have checked a lot of things if it was mine I would do new intake gaskets, I had a 2002 Sonoma I did a lot of what you did and every time I gave it back to owner a few days later lite was on and p0300 I did intake gaskets and its been good 2 yrs now,not sure what gaskets you got but gm use plastic ones I got new gm ones and they were aluminum type call gm dealer parts good luck
Duramax won't start!
just had this problem it was the PDM ended up replacing the glow plugsbest price and life time warranty for both was at Auto Zone recommend if you buy the PDM get the extension cable and move the PDM to a cooler location
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