Carl,
Personally, I'm with MR, I would be concerned about an external level sensor getting hung up on something and getting ripped out.
Since even systems as simple as hydraulic elevators spring leaks, so it isn't that surprising that a moving hydraulic system in a harsh environment (a PT) leaks.
Granted more of the piping could be metal, and more of it could be armored, but there will always be flexible hoses in some locations. Ultimately, any pipe, any hose, any joint can leak.
I think the bigger issue is when do you want to know, and what do you want to do?
Obviously, a low pressure shutdown would help prevent significant damage, but with the PT, it would leave us with a nice ornament somewhere until we repaired it there.
Knowing sooner, like when the leak first occurs would be nice, but that would require something like matching flow sensors on each circuit, and it wouldn't catch slow, but significant leaks.
As Ken points out, a level sensor is problematic given the uneven ground on which these vehicles function, although a centered float valve would be relatively immune. For my money, it is probably the best solution. It would require cutting up the top plate, but as Ken has shown, it gives you the chance to add magnets, temperature sensor(s), and the desired float gauge: go for it! While I have concerns that a float gauge is going to be problematic, you could try a vertical float indicator, something like the attached image (item 3610K41, from McMaster-Carr)
I probably lean toward KISS methods when it comes to harsh environments, as more complex solutions tend to require a great deal of protection and redundancy to achieve the desired goals.
When I below a seal on my motor, the thing that saved the tractor was my noticing the dripping oil. I am not sure that I would be looking at a level gauge every 20-30seconds. Any buzzer would have to be pretty loud to get through the hearing protection.
All the best,
Peter
As this is the only fully hydraulic tractor i have ever owned, how do other tractors warn you of low oil? Or does that happen that often (hoses breaking / leaking or something else). Seems to be a popular occurance on the PT but I am not taking that assessment in context with other tractor owners.
