2009 Silverado 3500 HD Duramax LMM overheating

On that year Duramax, it's normal to get up to 230 degrees water temp, fan kicks on then cools down and starts over again. As others have noted, kick the tranny in manual mode to be around 2,500 RPMs up the hill and it will run cooler. If it's truly overheating, you'll get a fuel filter error message. I had that once when I didn't shift down early enough on a long 35 mph pull.

To reduce temps, get a cold sir intake. I had an S&B and it ran cooler after getting it. You can also get bigger exhaust to get the air out quicker.

busterja21 wrote:
i had an 08 dmax pulling about 13k up eisenhower and other CO passes. What i found works best is to put the tranny in manual shift,and keep the rpms around 2500 or slightly higher. engine temp sometimes climbs to 3/4 mark, but fan should kick in and bring it back down. seems counter-intuitive to the diesel to run at higher rpm, but it worked for me.

One the keys to keeping heat under control on the Duramax is to prevent lugging under load. This is actually true about all diesels. This usually means running in manual mode and keeping rpm in the sweet spot of the torque curve. Typically somewhere between 2100 and 2500 rpm depending on the model year.

if you run in "drive" the Allison is a bit slow to kick down under load -thus the need to run manual mode.

Also, if you don't hear that jet engine sound of the fan coming on as you near 200ish on the coolant temp - the fluid clutch on the fan has failed. Be aware that GM programs the coolant temp read out to be very static. It is a well documented item in the Duramax enthusiast world.

IIRC, there was a short lived Duramax heating problem that had to do with the fan shroud not sealing or something like that...but I'm not a diesel person and just remembered coming across that (read most anything related to thermal dynamics)

Interesting thread....
So you make an annual trip west but don’t hit the mountains, but now since you’re going back to (different) mountains you think it may overheat again?

107000 miles on our 05 duramax and no heating problems on ours and it was an Oct 04 build. You are correct many have. looks like our 05 has been better for us than your ford from the repairs you mentioned. Miles will bring on issues as you have said. Towing days will end when we ever get home again. Might just keep this truck to enjoy it in the garage. Happy towing everyonne. Chevman

Travel glampers wrote:
Thanks for the info you all,

I'll be heading back to CO in June (San Juan Mts.).

Do you know what changes GM made?

GM's overheat issues was with 05 models only. You should be good.

Most of the overheating problems were solved by 2009. Have you checked the stack for debris? This is one of the things that often affect the temp on an older truck.

Thanks for the info you all,

I'll be heading back to CO in June (San Juan Mts.).

Do you know what changes GM made?

i had an 08 dmax pulling about 13k up eisenhower and other CO passes. What i found works best is to put the tranny in manual shift,and keep the rpms around 2500 or slightly higher. engine temp sometimes climbs to 3/4 mark, but fan should kick in and bring it back down. seems counter-intuitive to the diesel to run at higher rpm, but it worked for me.

That was a common (and real) issue back then but yes, there are mods to make it better, although it may not totally solve the problem.
GM made changes a year or two later that took care of it.