I think it might be getting clogged up a little over the years with rust from the block. Tracks now require you to run only water in the cooling system and I've noticed the car heats up a little faster than it used to.
I'm not disagreeing, I am just asking a question. Vinegar certainly is an acid. Acetic acid diluted to 5% to be exact. But I wonder if it would really destroy an aluminum radiator if it was used for a flush. When I flush a radiator, I run it with the flushing stuff (Blue Devil Radiator flush is good, and the bottle says safe for Aluminum Radiators) in it for about 10 minutes and then drain the cooling system, flush with water and then fill up with 50/50 anti-freeze and water mixture. I don't see how some vinegar can destroy the radiator if it is only in the cooling system for a few minutes and then flushed with water.
Just use thermocure, it's really amazing. It says to drive with it in and use for several days.
I watched the video on Thermocure before I bought it. They also showed how you could drain the radiator into a bucket and reuse that water mixed with thermocure in another engine as well, or use the drain water to clean parts.
Thermocure is designed for cleaning engines, largely through driving the car for several hours to allow the heat of the coolant to react with the coolant to remove the rust. I'm sure people try all sorts of things but you're better off using a product that is designed for shower heads & toilets. Repeated exposure to that hot solution is what does it. By the way, if you have really hard water and the toilets have been there for quite awhile you may need to replace them. Our water here is really hard and all our toilets started not flushing well. I replaced one toilet and when I turned it upside down found the minerals had reduced the diameter of the poop tube to just a fraction of new. Had to replace all our toilets to resolve. No quick "pour through" fix would have helped.
