First off thanks for all the speedy replies
Second, I'm far from a first time tractor owner, but thanks for pointing that fact out. The only first about this mitsubishi is it's the first tractor I have owned that has a multiple speed PTO.
Third- since when have diesel engines been designed to operate best at high RPMs? That's poppycock. You ever looked at a diesel tach VS at gasoline tach? My diesel truck redlines around 3200 RPM and runs down the road about 1500 where my gas truck's redline is nearly double that and runs down the road about 2300. Those are trucks obviously- but just for sake of proving a point. Of course the motor likely generates the most horsepower near the rated RPM, otherwise the rated RPM would not be there, because the place of the rated RPM is based on power specs.
The huge advantage of a 3 cyl diesel at 18 HP vs and 18HP single cylinder gas is torque- and torque is what keeps everything spinning. As far as HP goes, that 18 HP is probably up at 2400 RPM. The highest torque is probably made closer to 2000 RPM or lower. EVERY engine's peak torque is different(and almost always lower RPM) than HP- and that's fact. It is likely that this tractor makes MORE torque at 1800 than at 2400, so as far as rotational force is concerned, the 1800 RPM is likely easier for the tractor to turn than the 2400. Now obviously the strain is more when you go from the 540 speed PTO and increase that load by 1/3 to 720- so that's more work needed to be done.
I'm not stupid, so obviously if the tractor is not operating as well on the higher PTO speed and is barely chugging along at the lower RPM, lord help me I will go back to lower PTO and higher RPM. I wasn't concerned as much with saving fuel as much as saving wear on the engine. There are a reason big rigs chug down the road at 1500 RPMs- because they are aiming for 500,000 miles without a major overhaul. I haven't mowed with this new mower much yet, so I don't even know how it will act at will act in the situation at hand. I probably won't get to until next year either. I just purchased it when I sold my riding mower(which was gas and I always operated at full throttle because the book said to LOL)
I really do appreciate your input on the situation. It got me thinking about it a little more this morning. Obviously it's near impossible for you all to judge the situation via the internet- you're going 100% off of what I tell you.
All that being said- the main reason for this post was to know if I was correct on the PTO speeds on this tractor. All the selector says is :1 - 2 - 3. I was assuming on those pto speeds above. Thanks!