L3902 fuel stop selenoid

[whitetiger]

I was under the impression that as the coolant in the radiator contracts, it draws coolant from the expansion tank back into the radiator to avoid creating a vacuum.

That is how it is intended to function, but introduce a coolant leak, and the radiator does not create the vacuum necessary to pull coolant back into the radiator as it cools.
If the coolant is leaking out and there is no vacuum to replenish the radiator, the engine will run hot, and your gauge will not show it, as there is no coolant touching the temperature probe.
SNAP-CRACKEL-POP!!

 

[TheOldHokie]

That is how it is intended to function, but introduce a coolant leak, and the radiator does not create the vacuum necessary to pull coolant back into the radiator as it cools.
If the coolant is leaking out and there is no vacuum to replenish the radiator, the engine will run hot, and your gauge will not show it, as there is no coolant touching the temperature probe.
SNAP-CRACKEL-POP!!

And presumably the temperature gauge never moves off the peg?

 

[whitetiger]

And presumably the temperature gauge never moves off the peg?

Actually, the fact that the temperature gauge is still on the COLD mark while running for several minutes should set off a mental alarm.
WARNING WARNING WARNING

 

[TheOldHokie]

Actually, the fact that the temperature gauge is still on the COLD mark while running for several minutes should set off a mental alarm.
WARNING WARNING WARNING

That was my point.

 

[McMXi]

That is how it is intended to function, but introduce a coolant leak, and the radiator does not create the vacuum necessary to pull coolant back into the radiator as it cools.
If the coolant is leaking out and there is no vacuum to replenish the radiator, the engine will run hot, and your gauge will not show it, as there is no coolant touching the temperature probe.
SNAP-CRACKEL-POP!!

OK .. that's what I thought. So we should all be removing the radiator cap on a regular basis and checking the coolant level, and watching the temperature gauge to make sure that it's moving into the normal hot range. As I said, this is a great thread for many of us because we might avoid an expensive problem, but unfortunately not for the OP. I feel bad for @ripleyb and know how much it stings to make a mistake, particularly an expensive one.

I've yet to make a big and expensive mistake with a tractor, but a few years ago I did something really stupid with a boat motor and still haven't got around to resolving it. It's on my to do list and I need to put some money in so that I can sell the motor and get more money back. In all fairness, it wasn't entirely my fault but it's entirely my engine so it's my problem to fix.