class a motorhome with chevy 8.1 vortex 36 ft southwind

Its the fan clutch. When engine temps rise, the fan kicks in. That process really brings temperatures down quickly and it will disengage again.
Now....at the speed you indicated, there really shouldn't be any reason for it to kick in. That normally kicks in on steep grades or long grades.
You might consider having the radiator inspected and flushed and the finned area power washed. Make sure that the power wash doesn't flatten any of the fins.
The following responses will tell you not to power wash...your choice.

thanks hershey.

At 50 mph. Your still probably in 4th gear yet.
Not knowing what chassis and trans you have.

But my old WH W20 with Allison 1000 and the Chevy Vortec 8.1. Never got into 5th below 55 mph.

are the fan clutches on an 03 southwind liquid or mechanical.

rvten wrote:
... my old WH W20 with Allison 1000 and the Chevy Vortec 8.1. Never got into 5th below 55 mph.

I think that should read, "Never got INTO 5th unless it was ABOVE 59 mph."

Once shifted into 5th, or "OD" ... I'm not to certain what speed (with minimal throttle to maintain speed) on flat ground forces it back out of OD. The computer will easily hold 5th (or OD) at 55 mph and very light/no throttle pressure.

My RV is on the Ford chassis, but still a Southwind and YES it does get loud in the cockpit when that fan clutch engages.
I have been able to minimize the noise by installing heat and noise supressing mats under the dog house, around the firewall and on top of the dog house when I replaced the carpet. The radiant heat has also greatly reduced. I'm going to buy another batch from Thermo-Tec (Cool-it) and plaster another layer or two on the firewall plywood. an effective, easy and cheap fix.
And the above posts are correct. that giant beast-fan kicks-in at about halfway on my engine temp (the V8 usually runs "Normal" at 1/3 point) gauge and really cools things off in just 30 seconds or so depending on the situation (long up-grade, towing etc.) Our Ford uses 4th gear as its overdrive so the RPMs really ROARRRRRRRRR in 3rd...

X2 what sprig said. My 8.1 and Allison doesn't shift in to 5th until that speed quoted around 59-60, before that sounds like its at max roar but them shifts smoothly. and rolls on quiet. As long as you feel no slippage in the trans. you'll get use to it.50 to 60 sound like an odd range. Allisons Trans takes a little getting use to.

If your fan clutch is cutting in you also so hear a Definite roar but a lot louder roar. but temp should be up a little more than your normal range.

Been some time that I drove the W20.
Thought the MPH was hire than 55.

To the OP. Reason we mention this. Engine is working harder in 4th than in 5th.
Trans also.. Many coach builders did not allow for good engine air flow also.

thank u mustangGT alot of good tips.

I'am getting about 5 mph towing, thought the engine roar was part of the problem any suggestions.