My '65 Valiant sat for years and the water jacket is clogged. I could not get the cleanout plug loose (it's stripped) but I knocked out the freeze plugs (2) and flushed that side as best as I can.
I was thinking of reinstalling the cleanout plugs and running the car with radiator flush for a while to try to loosen up the crud. How long can I keep the flush chemicals in the car without harming the engine? I already have the thermostat out; should I connect the radiator "in" and "out" hoses together (bypassing the radiator entirely) and run the engine for a few minutes to really get it circulating?

You'd do a number on the water pump if you really have that much crud stuck in there. I'd bypass the heater core as well.

Cut 4 sides on the plug with a dremel and get a pipe wrench, vicegrips, square socket, etc. in tight on it. Make sure your soaking the plugs with some sort of penetrating oil, PB Blaster if you can get it.

Getting the radiator out of the picture wouldn't be a bad idea either. You don't have to connect the hoses together. You can disconnect the top hose and divert it to just dump out somewhere, then connect the bottom hose to a basin of water.

You can buy flushing kits too at your auto parts store that let you flush your system via the water pressure coming out your garden hose, with the engine off. You would have to leave your heater core hooked up though when doing this because those fittings are intended to tee in your garden hose to one of the heater core hoses.

I had to heat my plug with a torch before it would come out. But I got it out.

Mitch

That I have always done with these is Tee's is basically pull the hoses off the heater core and and put the Tee inline where the heater core would normally be.

Also you might get a new gasket for your water pump, so you can pull it. this does 2 things, you can see what kind of shape it's in and help clean out passage ways.

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Mike C
http://cuda.iclownz.com
67 - Barracuda Coupe - 225 - Automatic

I have this prestone stuff in my system right now that says to leave it in for 3-6 hours of driving.

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I have this prestone stuff in my system right now that says to leave it in for 3-6 hours of driving.

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Some real points to consider are the facts that your car has sat for awhile and the system is clogged. Running flush thru the system will help clean it but if you tie the radiator hoses together you won't be cleaning the radiator, whats the point in not flushing that? Even with it tied together, any large chuncks of rust that are in the block will get to the radiator and either get wedged into or sit on top of the cooling tubes and not allow the system to do it job of cooling. Best bet is flush the snot outta the whole system and then pull the radiator and check for chunks of rust in that, and see how clean it really is. Maybe CYA and take it to a Rad. shop and have it boiled out, then you know its clean. You said that you removed 2 freeze plugs, CYA and replace the others if the ones you did yank looked like they were rusted thin and weak. Thats all you need is to blow a freeze plug because they were rusted to the point of being useless.