Maybe John T or Lakota know the anser to this brain teaser...??
Have you tried **white Lithium spray lubricant? Or for extreme measures, marine based RED grease.
I've had that happen on manyyyyyyyyyy older RV heater fan motors and "sometimes" the squeal stops one they have ran a while. Ive also tried the usual sprays and White Lithium Grease and 3 in One Oil or even graphite based lubes which helps temporarily, but after they set another long period and she turns cold its squeal city all over again. Id use an air blow gun to clean out all the old dust and oil and as you say try some light (for easy penetrating flow) high temp lube but it, depending on the type of bearing and/or seal, may or may not actually get inside there where its needed. Since its a problem anyway and may need replaced, I figure there's no harm in trying different lubes of all sorts n sizes be they silicone or petroleum or graphite, but as noted, getting it to actually penetrate into and remain in place where its needed seems to be the problem....While a good somewhat heavier "grease" (as opposed to lighter sprays) may be best, its hard to get a thicker substance where its needed.... I usually lived with that problem but I was a used RV dealer and often fixed them by trading them off lol
The motors use bronze Oillite bearings. They get lubed by "cooking" them in oil at 400 degrees F. When they cool they are more-or-less dry. When they warm up - they slowly release trapped oil to lube the fan shaft. Sounds like your's have lost their factory "cooked in" lube and need to be recharged. Putting grease or oil on a cold bearing is not going to recharge it.
EXACTLY and that's when all mine squeaked WHEN IT WAS THE ABSOLUTE COLDEST TIMES LOL and while my lube attempts helped in the short run, they were never long lasting as getting any sort of lube where its actually needed is the problem. Oh well, maybe he will get lucky (which I doubt)
You can buy replacement DC motors for these RV furnaces with full ball-bearing support instead of Oillite bearings. They cost an extra $50 though. I yanked apart the motor in my Suburban NT16 furnace and recharged the Oillite bearings by "cooking" in 30W oil. A lot of work but I'm cheap. Worked fine ever since. "Cooking" is how those bearings get lubed at the factory when new.
Perhaps Grainger may be a source for a replacement motor, its been too long since I shopped for them. If I were going to keep an RV for a long time Id consider paying the extra bucks for ball bearings, those originals with age seem to eventually develop that horrible "squeal" and of course due to design, especially in the absolute coldest times when needed the most grrrrrrrrrrr............and while sprays or lubes or other such snake oil may help in the short run, you just cant get much correct real lube WHERE ITS MOST NEEDED like done originally in the factory..........My current 2001 hasn't yet developed the squeal but if its the original cheaper bearings (NOT roller) its likely just a matter of time. Seems like a great number of the older units I used or bought and sold eventually squealed
Let us know how it turns out.........
Here's one method for re lubrication found in Practical Machinist, no guarantee its the proper method for your particular unit:
"Re-oiling: following oil loss during storage, immerse in high quality mineral oil to ISO VG 60 or ISO VG 150 (SAE30 or SAE40) at 80°C to 100°C for 10 to 15 minutes and then cool in cold oil."
Hey I'm sure your stove can achieve those temperatures!!!!!
For more discussion regarding re lubrication:
More fun historic information on those bearings can be found at:
The articles above discuss several different lubricants and methods, surely one will work for you or is right for your particular bearing and its application.
I don't know if yours are similar to those discussed above or are the same kind that Mr Demarrais re lubricated, its a question of what type and grade of oil and the bearing and the temperature that should be used, but hey if its dry and needs oil and isn't good as it is, I see no harm in trying, nothing ventured nothing gained, and if it fails you can always simply replace them or upgrade to ball bearings.
Give it a try on the wife's kitchen range lol Keep us posted. It cant be any worse then the all different lubes/sprays I tried which worked only for short periods but once it wasn't so darn cold it stopped squeaking anyway???
Years ago, I had this problem and went to a local repair shop. The owner heard me talking to his counter man and came out to look. He inspected my motor and then went out back to return with a new old, old stock motor cap, said he hadn't sold one for years and gave it to me for nothing! Guess where I went the next time I had a problem?
That's where Id shop the next time for sure. I wonder if what happens is that when that awful SQUEAL sounds most people just take it to a shop rather then tackle it themselves when the shop is more then happy to install a whole new motor OR EVEN A NEW FURNACE!!! at a higher profit versus take it apart and re lube the bearing.
The fix that Mr Demarrais suggested may be beyond the skill or ambition of many RV owners so they may try temp fixes like spray lubes or buy a new motor or fan and be done with it. Like him, I fix the majority of my own problems but I sort of enjoy doing that plus I save some bucks.
NOTE (Never say never and Never say always) the Practical Machinist web site fixes I posted MAY OR MAY NOT be for the same bearings or use the same temperature or use the same oil or cook for the same time that he used to fix his bearings so DO NOT necessarily rely on them (Practical Machinist) as they may NOT be correct for the posters particular furnace bearings!!! Still, the time and temperature and oil and cooking time he uses may well work for the posters furnace (and a whole variety of other applications as well, as many have similar Suburban or Atwood furnaces) just as well NO HARM IN TRYING any methods I figure (Practical machinist or others) as its no good as it is GO FOR IT
Very fun chat (for us RV nuts at least lol)
Hope he lets us know how his re lube efforts worked out but the answer may not be known for sure until the passage of time and cold temps have been present?? Hopefully it will last longer then temporary spray lube regardless of his method??