engine roar while towing

[mshicks]

hello everyone, ive had my '05 duramax for quite a while and love it, but now im towing a 12000lb horse trailer and im getting a very loud engine roar. the rpm's arent changing, nothing on the dash seems out of whack either. i tow with o/d off and tow/haul on. love the truck but kinda anoying because it seems to come and go about every 5-10 minutes. the sound makes you think the engine is going to blow! just wandering if anybody has encountered this same problem. appreciate any replies
thanks mh

[StrangeEngine]

hello everyone, ive had my '05 duramax for quite a while and love it, but now im towing a 12000lb horse trailer and im getting a very loud engine roar. the rpm's arent changing, nothing on the dash seems out of whack either. i tow with o/d off and tow/haul on. love the truck but kinda anoying because it seems to come and go about every 5-10 minutes. the sound makes you think the engine is going to blow! just wandering if anybody has encountered this same problem. appreciate any replies
thanks mh

That's the engine cooling fan coming on. Nothing to worry about. Completely normal.

- Mark

[Buck]

Some fans tend to be more active than others.... The fan can pull something like 10000 cfm of air, so that is what causes the "roar". I would be glad that it is working, some have had fans that don't run enough. It seems your truck is running on the warm side. The fan generally kicks on around 205-208 degrees. What is the coolant level in the clear tank on the pass side. It should be where the middle seam is when the engine is cold.

What were the speeds? You can tow the Allison in OD, it is fine. It is a heavy duty unit built for towing. That will likely limit your fan roar. When I tow I only use the tow/haul, not the OD lockout, let the Allison do it's thing :)

[mshicks]

thanks for the replys' im usually cruising in the 65-70 mph range in the mountains of east tenn. so that makes sense that the trans is working warmer than usual. ill check that fluid level though.
thanks mh