I've got a mid sized Rival deep fryer I've used for many years.  It's black with a lid that snaps down and uses about a quart of oil.  As I mentioned I've used it for well over 10 years without issue.

Tonight I tossed a handful of fries in, stirred them with the  paddle that came with the unit and closed the lid as I always do.  A minute or two later I looked and oil was boiling over and running all over the counter top.  I have no idea why this would happen.  The unit has high and minimum oil markings on the liner, I was at the "low" mark, added the same or less fries than usual.  Only variable I can think of was I used Kroger brand fries, a brand I've never used before.  Any ideas what might have caused the problem?

Using a cover during the heating of the oil or during any part of the deep frying operation is extremely dangerous and you should never turn you back on the fryer until you have established that the operation is going smoothly. Using a new brand of fries would demand extra initial vigilance. Is the lid that you closed a perforated splatter shield?  Even that kept you from seeing what was beginning to happen and probably exacerbated the boiling of the water causing the foaming of the oil, much like covering boiling pasta will do with the pot of starchy water. I'm sorry for what happened to you. Too many disasters can happen when you are dealing with oil at high temperature.  It was probably the ice crystals that caused your mess, as was suggested above, which I am sure was lovely to clean up. I am glad that you were not burned. I wish you better results in the future.

Can you imagine the events that led Pyrex Flameware to carry the warning to never use it for deep frying? The stuff was barely stable at boiling temperatures.

Well it's the type of fryer with dual filters and meant to be closed when in use.  After I tossed the fries in I always agitate them to separate them and give it a quick look, then close the lid.  In 10 + years of use only time it happened.  I believe it was the Kroger brand that might have had an unusual amount of ice on the fries, but that did not stick out in my mind.  It was fresh bag I just bought so it shouldn't have been an issue.

I'll make some more tonight and keep a better watch on it.  Instructions say to close lid.  No harm done, just a big mess to clean up.

This style:

I tried again tonight.  Checked the temp, set at 375, unit cycled off, temp was 348, so a bit low.  Tossed the fries in again and same bubble up, but watched this time with lid open, came almost up to top with "foam".  Got to be the fries.  Odds are Kroger coats them in something as most people bake them and want them crispy. Bag does have deep fry instructions too.  Weird.

Interesting.  I use this very infrequently, oil might be 6 months old used 2 or3 times in that period.   Just basic corn oil, avoid the blends.  I'd consider lard, but to be honest it's too much work for an occasional batch of fries with a burger.  Getting the fryer out is much simpler than heating the oven , baking the fries and heating up the kitchen in the summer.

Eddie, those sound great!  Will try sometime.  Only issue is it kind of defeats the "quick meal" I that I usually go for when doing hamburgers.

I often wondered how much extra calories I get by deep frying.  As  the fryer has 2 lines for min and max, I watch the level before and after and the difference is imperceivable.  Tonight I'm going to try another method and weigh the fryer before and after and see how much change there is.

They do look good!  Will try soon!

BTW, looks like a handful of fries absorbed about 20g of oil.  Google says that is about 180 calories, but a portion of that was in the paper towel I drained them on.  So I'd guess maybe 90-110 calories...