I am a single mom and own a house built in 50s. Every fall when it starts to get cold my downstairs toilet stops flushing or clogs and I hear gurgling in the sink, toliet and tub when ever any of the other is used.
The first year I had a plumber come out and he put a clean out in and told me it was roots from my old clay pipes. I rented an 75' auger myself and ran it clear to the street the next year. It did not seem to help. The problem resolves itself when the weather warms back up. I did research and think it might be my vent. I had put a heater in my basement where the old iron pipes come down and out the house. That seemed to be the only thing that even remotely helped. I think I found the vent on my roof ...is it that little pipe sticking up off the roof? See pic
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I am not sure I can get to it. Someone said pour hot water down it. Any advice? I can't really afford a plumber.

In order for the vent to be the problem, it has to be frozen over with ice. The ice forms from condensation from inside the pipe. Is it a 3" diameter pipe ? Increasing the size of the vent reduces the chances it will freeze up. Can you access the pipe from the attic ? If so wrapping the pipe with insulation can also help.

Gurgling in the downstairs plumbing is almost ALWAYS a sewer stoppage problem and it depends on WHAT kind of 75' rod you used, some would be completely ineffective and the proper ones can be dangerous for a DIYer to use.

That is what I thought but there is no doubt that the tempature has some effect, the problem happens the same time every year, when it gets cold...but not necessarily freezing.
So if it is a sewer line block would the weather effect it?