Lionel Legacy smoke unit shuts down

If it’s truly the elements I’d check resistance across the element. Should be 8 ohms. Also check that it hasn’t magically shorted to frame ground. 

I found sometimes, it is just the motor is gummed up, and the motor doesn't have enough force to start the fan spinning.  Did you try some cleaner on the motor shaft.  I use JT's Megasteam Eliminator.  Just a thought before you start ripping into it and replacing things.  

Two blinks is the smoke resistor, so the advice to check it's resistance and any shorts to the frame are good.  As soon as the resistor fault is detected, the smoke fan will stop, so I don't think this is a motor issue.

I "fixed" it using the mess around with it until somehow--who knows why really--it works.

The resistor was OK--read 8 ohms. I did clean the smoke unit some more. Perhaps I had put in too much smoke fluid and that had caused an excess load on the fan motor. Also, I noticed a few wires routed under the fan motor that seemed to be pressing against the leads to the fan motor. I couldn't really see--the wires are fine and my eyes are not--if the normal heat in the fan motor leads might possibly have melted just enough insulation to short a motor lead against one of the three other wires. Just to be safe, I moved the wires apart.

Anyhow, not sure why, but we're smoking again. Thank you, Zachariah, Sean, and John, for pointing me in some useful directions.

Check that...not really fixed.

Ran the engine a bit more today to confirm that things were definitely OK. Yes, it did smoke normally—but only for a few minutes; then the dreaded two blinks began again. Each time I reset, the interval between smoke and two blinks was shorter.

I’m at a loss. How can it smoke great—both volume and height—then need to shut off? Is it possible there’s not enough smoke fluid and the resistor is getting too hot because it doesn’t have enough fluid to draw off it’s heat? The area of the hood by the smoke unit does feel very warm. Could the smoke unit need more fluid even when the unit is producing good smoke?

How much fluid should actually be in the bowl? Should all the fluid be in the batting, or should there be some fluid sitting under the batting? When I put the smoke unit back together, I arranged the batting so that the resister pressed against it, but was not surrounded by it. Was that the right way to do it?

Other ideas?

Perhaps the spacing of the thermistor and smoke resistor is off?  I found that basically perpendicular to the PCB for each works pretty well.  Both the thermistor and the resistor should be in firm contact with the wick, but not totally buried.

The resistor and the thermistor seem to be in the proper position. Still, the smoke unit will run—and smoke—for, at most, a few minutes before shutting off with the cab light flashing two blinks. Could the thermistor be at fault? How would I test it? FWIW, here are some photos: