I doubt the side shields are a factor unless they are built in some manner to direct atmospheric ambient air flow rather than air from around the engine. Some tractors have a similar design but that feature is often built into the hood. John Deere is an example.
Being this is a pre-owned tractor there is always a chance a previous owner has leaned the fuel for better economy and that can cause undue heating. Also be sure the engine is operating at full designed throttle, especially when under a load.