Proper way to back flush cooling sys?

[Dave Kay]

Will be installing a new radiator this weekend on my '86 GMC SB and would like to back flush the block before installing new unit. My idea is that I don't want any rust or sediments to be pushed into the NEW radiator. Have the Prestone kit w/garden hose adaptor and the instructions make no mention about removing the thermostat before back flush... is this nesassary?

[TexasRed]

I'd remove the thermostat anyway and replace it. . . .unless it's like real new.

[VeeTwin60]

Is there any other thoughts on this?  I'm replacing my radiator and thermostat this weekend and I have the same flush kit as the guy above.  I've never done this before, so any pointers/tips/help would be appreciated.

[VileZambonie]

The way I do it is with a machine I have but since you don't have one I would suggest you run a good cleaner in the system first. Run it to operating and for at least 15 minutes after the T-stat opens. Drain the system when it's hotter (no pressure and be careful) Remove the engine block drain plugs (sometimes you need to stick a pocket screwdriver in the hole due to scale build up to allow it to drain. Flush out the heater core and passages with a garden hose. Once you refill the system add a conditioner. It helps prevent oxidation, scale and cavitation.

* fixed typo

[VeeTwin60]

Thanks.  Sounds like a lot of work, but I want to do it right.

[VeeTwin60]

That was easier than I thought.  Messy... but easy.  Thanks again.