We cut the fan blades back on my r33 using a little alloy template we made. Not dodgy if you do it right. What is dodgy is when the fan continues to hit the piping regularly and fractures the fan blades! Thats what happened to mine, had to buy a complete fan unit to replace it, not cheap!
Does the thermo have anything to do with the air con? Normally on cars thay have a fan that runs for the a/c as well as an engine cool fan?