radiator question

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pineneedle

Member
I am planning to start my rebuilt 304 for the first time in the next several weeks. If (?) I get it running, should I leave the cap off the radiator until the air is purged out of the system? Is there danger of doing any damage by either a. Leaving it capped and unpurged, or, b. Leaving the cap off in order to purge the air? Thanks in advance. Pineneedle
 
A proper radiator cap will purge the air out as the coolant heats & expands, then admits more coolant after engine shutdown as the engine & coolant cools.

When starting a rebuilt engine, I always fill with a 60% coolant & 40% distilled water mixture, fill to full, a new radiator cap of the correct pressure and the overflow/recovery tank attached.

Never had a problem with this method.

You can certainly keep the cap off initially, add coolant mix as needed as the air is expelled, then put the cap on as the system becomes full (most air is expelled).
 
Be careful about keeping an eye on the temp. Sometimes air gets trapped up against the thermostat and it wont open. If you have the heater hose fitting on the side of the housing, loosen it up and the air can escape.
 
I have found just opening the heater valve seems to work. Without doing that they do seem to trap air. If it does, just let her warm up good and shut it down. The thermostat will eventually heat soak and open to let the air out.
 
Thanks for the replies. Jeff, I've looked over the thermostat housing on my 304, and the only thing I can find is a threaded hold with a pipe plug in it. It is on the drivers side of the housing. Is that the vent to which you refer, or am I missing it? Pineneedle
 
No, the hole he is talking about is down inside the housing. It is very small in diameter and can become plugged with shmootz if your cooling system was not properly maintained over the eons.
 
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