there was statement made that diesel engines "run cool".
There is some truth to that.
'however', I'll elaborate. They do in fact run cooler than a gas counterpart, until they're loaded. Diesel engines are often under full load at rated engine rpm. At those conditions, they run a bit hotter than a gas burner does with the same horsepower. Load makes heat.
When you get into "they should have designed it better", they did design the systems to work in most applications. In the case of the 5740, you can't physically fit a larger radiator into where it needs to be so that issue is a non-issue. In almost all "overheat' situations, there is usually more to the story. A lot of times people neglect their cooling system servicing. In other words, the condenser, hyd oil cooler or intercooler in front of the radiator might get dirty and we'll warsh it out, but won't get deep enough to clear the radiator itself. Yamaha Rhino is a great example--oil cooler in front, can't get to that part of the radiator and the cooler MUST be removed in order to get the radiator clean enough. Overheating is gonna happen in that case. L5740, if it has a cab, it'll have an oil cooler and a a/c condenser in front of the radiator, both of which block access to the radiator itself. The condenser can be removed, at least partially, to get better access. Maintenance does not end at that point. Remember coolant does wear out and people never (or should I say, very rarely) actually flush/change the coolant on schedule, unless there is some kind of problem. In the case of RTV's, I've had to go in and actually manually remove the scale from the steam holes in the block on a lot of them because they get plugged up due to lack of cooling system maintenance. I'm doing one now actually. This one needs a radiator, head gasket, thermostat, water pump, and of course a good cleaning of the block & head....all of which would have been preventable if the system was serviced per the manual. $20 worth of coolant would have saved $1500, but people never think about that. Cooling system, brake system, and transmissions are the most neglected parts of a lot of equipment; IMO because on cars, we're "told" that it doesn't need to be serviced until 100,000 miles or more. But if you do it beforehand, the car will last a LOT longer (usually), much the same as tractors will last a lot longer with some maintenance. Tractors, mowers, and RTV's are not cars. They operate in DIRT and at completely different loads, as such they require totally different maintenance schedules. Tractors, mowers, and RTV's are also not big trucks although some of us seem to think our little D1105 is a big truck engine sometimes....
Then you get a few guys who say "don't wash out the radiator, blow it out". Fine, if you know you get all of it cleaned out. I use water, have for years. It works. Let it dry out, which doesn't take very long, before putting it back in the field. Water hose gets almost all the stuff out assuming access is clear.
Then the BX guys. BX radiator is mounted behind the engine mid ship. It's got a screen. The screen gets plugged and people pull the screen and clean it which is good. But often fail to clean out the radiator too. "Poor design" is what people say, in order to pass the blame elsewhere, often away from their own ignorance. G series mowers are similar design, seen lots and lots of BX's and G's with bad engines because of this. I have one that was a victim.