I tried another cooking on warm experiment last night with a pork roast about double the size of the chuck roast I cooked the other day 6#. I cooked it on high until internal temp went to about 140 and then turned it to low until internal temp went to 155. I should have just stopped right there as it was delicious but I was trying for a pulled pork recipe with the meat not so well done. At 155 I tuned it on to warm where it stayed all night, I checked the temp in the morning and it was 180 degrees??? The roast I cooked a couple of days earlier stayed right at 140 degrees and it was 1/2 the weight. I am going to buy a sous vide anyway but I would like to figure out what would cause this unless it was simply a malfunction? The pork roast did produce a lot more liquid with all the onions and celery I put in and that is my first suspicion. The roast was 3/4 immersed as opposed to the beef roast being less than 1/4 immersed. Any suggestions??
Was the lower liquid level the other time causing the heat to cut out more often?
I think (like you basically already said) it might just be not the right tool for the job.
Low is at around 190 degrees. So even though you turned it to warm (which I think is around 160), there’s still a lot of heat in the crock pot and the liquid that continuing to dump into the roast.
The higher water level increased the heat transfer to the food, while the lower water level for the beef meant that lost of that heat got transferred to the air and out the top, never making it to the meat.
This is my thinking also, my lid leaks quite a bit and I think with low water levels it dissipates a lot of heat in the surrounding air.