It never helps to spray WD-40 on something like this. WD-40 is one of the worst things you can use. Never think of it as a lubricant again.
It is extremely unlikely that there are oiling ports on the motor. Modern motors are sealed. You could check for small holes labeled “oil”, but don’t expect to see them. Randomly oiling the axle or such isn’t going to work.
I’ll agree that most residential motors are sealed, but I have motors that I’ve bought in the last few years for commercial applications that aren’t. I just thought I would put it out there before he sprayed down the motor with WD-40 and it over heated.
I’d imagine that dust would be a problem if it wasn’t sealed.
We replaced a motor on a big roof fan and it did this same thing from new. Drove us nuts. It turned out that the air intake vents on the new motor were too close to the existing rain cover and when it was hot up there, the thermal overlimit switch blew. New motor must have been a slightly different shape. We moved the vent away from the motor by 1" and all was fine.
Moral: Something has gotten sucked onto or is blocking the air vent on the end of the motor. Dust, dead mouse, paper, spiders, etc. If the motor housing is too hot to put your hand on when it trips, you’ve found it.
Haven’t read all of this but: if testing a tempermental fan of this size DO NOT PUT YOUR FINGERS IN IT!!!
This is what pencils are for - the rubber tip works almost as well as your finger, and is a lot easier to replace.
What voltage is the thermostat and where is it?
If it’s upstairs, running a bit of wire (anything will work - phone cord, speaker wire, whatever) to someplace convenient and hook up a bulb or a recording clock, something that indicates that it has broken the contact.
Or: put a jumper across the terminals on the t’stat - it is now always on. If it still cuts out, it is the fan. If it keeps running, it is the t’stat. A wire with small alligator clips on it is ideal for this - but a paper clip with one end screwed down on one terminal and the other on the other terminal will work just fine for a test of a few hours.
So here’s the weird thing.
I went off to Home Depot and got another motor, and installed it. And after connecting the wires I turned it on just to test the connections, and lo and behold it did the exact same thing - went on for a second and immediately off.
Turns out that that particular aspect at least had nothing to do with either the motor or the thermostat - it seems to be the switch. The switch is not fully locking in the ON position, and if you casually flick it on it can bounce back just a tiny bit- just enought to turn it off. If you hold it firmly down it stays on.
Question now is whether that was the entire issue all along - and somehow or other the heat would push the switch a bit off the ON position and it would resettle at ON when it cooled down - or whether this is an unrelated issue. I don’t see any reason for that to be heat related, but I don’t know a whole lot about these things, so that’s not especially meaningfull.
As a practical matter, connecting and disconnecting these motors is not the most pleasant way to spend the hour or so that it takes - it’s hard to maneuver the motor in and out of the space (especially since the original installers cut a hole which is partially blocked by a roof beam) and it’s extremely hot up there. So I’m not doing it all over again for a chance that I might save $56 (if the old one is faulty, I would have to reinstall the new one all over again).
So I left the new one up there - we’ll see how it goes.
I have to say, from over here, that’s a little bit funny. But I have a switch at work that does that too. Oddly enough it’s in a really hot attic also, but I’m sure that’s just a coincidence. Luckily this one just controls some lights and you can feel it bounce back if you have your finger still on it.
After a while you get in the habit of just making sure to push it into the on position with some force so it stays on.
BTW, for $60, I’d leave the new motor in too and just install a new switch.
It could be the heat is causing the contacts in the switch to expand and they lose connection. If the switch is just barely making contact, it might not take much for the contact plates to move apart.
The switch could be acting like a thermostat. Hotplates, irons, thermostats, etc work like that. There are two copper plates that expand when hot. At a certain temperature, the plates have expanded enough to move apart. When they cool down, they come back together again. You should probably replace the switch since you want firm connection between the contacts.
A third vote to replace the switch.
Well it depends on what happens. If it keeps turning off in midday, then I put in a new switch and hang on to the old motor. If it stops happening, then I leave the switch and ditch the old motor (though I would wait until the next heatwave, to be sure).
if the switch is a wall type light switch then those can fail easily, the springs inside which hold the switch open or closed can get weak or contacts can get corroded. loosing contact immediately after turning on and only going/staying on by holding is an indication of this type of failure.
I’d replace the switch anyway. If it is messed up, it will mess up the rest of the way and break for good. It may be putting a resistive load in series with the motor, and it may be a source of sparking.
If I replace the switch too soon, I won’t know whether the old motor is worth keeping. (Apparently - based on reviews at Home Depots website - these motors wear out pretty quickly. I know I’ve replaced mine at least once, or maybe even twice, in the 17 years since the fan was originally installed).
Of course, what I could do is wait till I’ve confirmed the status of the motor and then replace the switch. But it’s possible that by that time I will have mentally shifted away from dealing with that fan, and moved on to other things. That’s how things go, sometimes.