~ Scott,
~ I don't know how to bleed a cooling system. How do you
~ do it?
~ Don Mathis
TR6s may differ, though I doubt it from the time I recently
spent peering over the cooling system in Berry's.
Bleeding (sometimes called "burping" in this case) the cooling
system is a way of ensuring that no trapped air remains in the
passages. To bleed most systems, you need to run the car till
the thermostat opens -- which you can tell by feeling the upper
radiator hose. When it's hot to the touch, the thermostat has
opened and you can begin.
CAREFULLY remove the radiator cap -- if you do this immediately
after the thermostat has opened, you have no fear of high-
pressure gushers of hot Prestone. Let the car run for 15
minutes or so with the cap off and the hood up; you don't want
it to overheat, of course, but you want to cycle the coolant
through the system enough times that any remaining air will escape
through the cap.
You should notice that the coolant level gradually drops in the
radiator, at least if you needed to bleed the system; if it
doesn't drop, all the air is out. If it does, add more coolant
(again, a mix higher in water than in glycol will cool better
than a pure 50-50 mix) and let it cycle for a few more minutes.
This is most important in cars for which the thermostat isn't
the highest point on the system; most conventional LBCs are set
up so that the 'stat is pretty much the top of the cycle, but
it's still something that's easy to overlook if you've drained
the system and then only refilled the radiator. You need to
fill the radiator, the engine, and the heater before you have
enough coolant.
--Scott
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