Heat Pumps and Electric Heating - Outside Compressor Fan Not Spinning

So, Saturday I noticed my outdoor fan motor was not spinning. The compressor was humming along and the fan inside was running. It was a mild day so not a lot of heat was needed.

Touched the top of the fan and it was warm, so I know it was trying to run.

Turned everything off, took apart the unit, noticed there is an oil fill plug. Added some oil I had around (WD-40 and a very lite oil). Ran fine till today.

When it comes on the fan energizes and just sits there. Previously I could spin it and the fan blade would start up, with a bad whining noise till it really got going. Now it energizes but I can't get it spinning enough to start. Today is much colder than Saturday. I'm thinking I used to lite an oil and it either burned up or congealed.

Is it just the fan that's bad? Or is the capacitor going out and not supplying enough power?

What kind of oil should I use?

I'll get a new fan soon, but I'd like to postpone for a month.

WD40 is bad to lubricate motors with. It will evaporate and usually will wash any of the original oil. I use 20w ND oil and mine lasted a long time. If you could spin it at first and runs then the cap is bad. You may have inroduced a new problem using the WD40 which usually will loosen up a shaft but will not last long. How easy does the shaft spin? Also check end play. Too much can cause a bind as when the motor is energized it pulls to one end or the other. There are thrust washers to set the spacing and will wear out over the years.

When the motor energizes it does seems to stick to one side rather than spin smoothly. I think the unit itself was slightly lopsided when I was checking it, so maybe that contributed to the thrust washers wearing out. Actually when I think about it, it seems to catch on the low side of the lopsided rotation.

I'm guessing that I need to replace the motor as replacing the thrust washers/bearings etc will be to costly and difficult compared to a new unit. Is that correct?

Replacing would be the safest bet. Mounting is usually vertical or horizontal for most motors. Some large motors require horizontal because of the armature weight but I have seen many mounted vertically. You have to follow the manufactures instruction. Yours is mostly likely using sleeve bearings and can be mounted in any position. When vertical the thrust washers on one end or the other has to catch the more wear than the other. Some motors armature will center in the field but when not running it by weight settles on the lower thrust washers. These type need periodic oiling as I haven't seen too many with sealed bearings. Simply more costly to build and install in home HP's. Most hi speed fan motors are sleeve bearings type. Make sure you match the rpm and hp, no less and is a sealed one for outside use. Also it should come with a new capacitor and if not get one. But if it is part of the compressor capacitor, check the end and if bulged it needs replacing anyway. A fresh one will help it to start better. I have seen aux start kits put on unnescearly when the original cap was actually going bad. Once more WD40 is not a long term lubricant especialy in hi speed applications. It will wash out what is there. Use 20w ND oil and a syringe to be sure it gets to the wick. The brass sleeve is poruss that let the oil get to the shaft. They can stop up and and something like WD40 can clean and open them but proper oil must be applied before running too long at high speed.