When I am doing a block flush, I disconnect the lower radiator hose from the radiator end and drain whatever comes out.  Then I remove the thermostat housing and thermostat.  Then I duct tape a garden hose inside the lower hose and turn it on full blast.  That flows fresh water under pressure through the entire engine.  Then remove the garden hose and stick it in the thermostat hose and repeat the procedure.  That will backflush the block.  Flush in this manner until you get only clear water out the bottom hose.  When flushing from bottom-up, you may want to position a rag over the thermostat hole as water and crud is going to be coming out there...in a hurry.

That procedure does not touch the radiator.  Stick the hose in the fill neck and turn it on and let it flush for a while.  If that doesn't clean out the old stuff, you have bigger problems than a flush is going to cure.

You can also duct tape the garden hose to the lower hose of the radiator and let it backflush the radiator, letting it flow out the top.  Not sure if that really is going to push anything back out the top, but can't hurt anything.

Be sure to use an original style thermostat housing and not one of those crappy chrome jobs that leak like crazy.

As far as price...  There are different types of t-stats.  Some are fail safe... they fail in the open rather than closed position.  The higher flow type t-stats are supposed to let more coolant flow through them at higher RPM.  Those are what I use, but I have no data to support whether they work any better than a stock one.

Pablo wrote:

One thing you should look for on the new thermostat - either a very small hole drilled in the flange around the valve, or a very small notch in the edge of the valve.  When installed, the hole/notch should be in the up position.  You may need to hold the t-stat up to a light to see the hole/notch.  If you don't see one, ask for another brand of t-stat.  That hole/notch allows air in the block and heads to escape when you put water in the radiator.  Without the hole, you can get a "cavitation".  Hot air will not open the t-stat, and you will experience a geyser out of your radiator.
Good Luck

 Pablo, I always thought the 5/8" bypass hose going to the thermostat from the water pump was so the water pump could suck some water and have it circulating a bit even though the thermostat is closed.  While that hole-in-the-stat thing is useful in alot of applications, I do not see how it will improve the original design.  There is already water (and air, if present) passing right by the side of the thermostat.  Kind of like a 1/2" hole rather than a 1/8".  Have I missed something on this?

It is still possible to have air trapped in the heads and intake manifold that is above the level of the bypass hose.  When you first start after filling, the t-stat is not in the coolant and won't open when it should and temps in the engine will skyrocket and the cap will ultimately release with dramatic results.  The small bleed hole in the t-stat allows the air in the manifold to escape when filling to lessen the chances of air entrapment.  That is fine as long as the top of the radiator is above the manifold.  The solution then is to bleed air while filling.  I remove the temp sender and/or fan switch and fill till coolant just bubbles up.  Having experienced air entrapment at least once, I always bleed air through the biggest hole I can find.  If you have coolant on the outlet side of the t-stat it doesn't help because it is not circulating back into the engine so it actually hurts - it keeps the t-stat cool and even less likely to open.

Filling a cooling system has always been a concern of mine. Here's my method.
After filling and letting all bubbles surface, start engine, run at idle for one to two
minutes, shut off and slowly loosen cap to safety position, pause and remove cap
refill with water. (I add antifreeze after check hot for leaks) Continue this same
procedure until water has circulated. The reason for warming up this way is to minimize
hot spots where air pockets  are present. I don't know how hot head/block gets but in the combustion area it must be hundreds of degrees. Which can't be good?
Howard  
 

Last edited by hmartin025 (8/07/2013 9:05 AM)

I agree with MS on this one.