Just for grins, take the fan off and make a highway-speed cruise for a few miles. You don't need a fan above 30 MPH, and I'll wager the engine won't sound half as stressed once the fan noise is out of the picture. Any engine speed below 2500-3000 RPM isn't going to hurt a good-condition 235, even if it is a little noisy.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!