Dipstick oil pan heater

[yuke]

I was wondering if a dipstick oil pan heater would work in my 85 (300 SD).
I already have a lower radiator hose heater but does not heat the block like I would like it to and was thinking maybe a dipstick heater of the oil would be better but when I pulled my dipstick out to measure it which was 22" and tried to put a rod that was about 1/4" diam. in to see how far till it would bottom out I could not get the rod in more then about 3" and it stopped.

I was puzzled because it looks like the dipstick tube is about 1/2"diam. down to the pan do not know why the 1/4" rod would not go down might check with a thinner wire later.
I ask this because the sites where they sell the dipstick heater say you need a 1/2" opening to get them in. Is anyone using a dipstick heater on a Benz if so how do they work?