Question on boiling point and overflow

[robertwilbanks]

If the boiling point for water under pressure is around 240 then why does my radiator boil around 220. Also, when goes into the overflow tank doesn't it supposed to draw from the tank also?
It is an 86 and the radiator has 1989 stamped on it.
I have replaced the cap(GM), hoses, water pump, and thermostat(160).
I have cleaned the area in front of the radiator.
I added a oil cooler and mounted it so it did not block the radiator at all.
I have removed the rubber seals in the engine bay for more air flow.
The only leak I had was from the water pump but fixed that. No water loss that I can tell except boiling out.
Around town it is great. When I drive home up the mountain it hits 220+ and then starts to overflow. Turning the heater on drops the temp 10+ most times.
Once I hit the top of the mountain and start across it drops back down below 200 so over all, the system seems to work good. I just thought it should not boil at 220.

 

[dman]

water boils @ 212 @ sea level.. 0n a systm under ..psi you bring the boiling point up 1 deg for every 3 pound..of psi,,, 18 pound cap brings boil point to 218 deg...if turing on heat drops 10 degs of temp ,, sounds like rad prob...

 

[geekinavette]

Antifreeze will also raise the boiling point.

It's possible that it's not really "boiling", rather just building up too much cooling system pressure. My '84 had this problem when I bought it due to a cracked head. At about 210-220 deg the crack would open up and allow combustion pressure into the cooling system and overpressurize the system, which of course the cap released into the overflow tank.

Bill

 

[robertwilbanks]

la..la..la..I can't hear you...I don't want to hear words like "cracked head". lol. You may be right. I haven't seen any water in the oil or oil in the water but if it is like your then I probably wouldn't.
Thanks

 

[jmccloud]

Boiling

Had a Buick with your symptoms and it was a crack in the (new) radiator neck where the overflow tube attaches. When the cap opened up to let water 'escape' into the overflow tank, coolant ran out instead of into the overflow. When the car cooled off, air was sucked in reducing the cooling capacity. So the problem got worse each day.
Used 'J-B Weld' on the cracked tube (where it attaches, really hard to see) and all was well.
I'd kept the old radiator in the shipping box. Went back to inspect the box and found the styrofoam damaged where the overflow neck was supposed to have been protected. Should have looked closer upon first opening.
Hope yours is this easy to fix.

PS Be sure to use antifreeze, it raises the boiling point significantly per the above post. The pressure cap and 50% antifreeze should raise the boiling point to 260F at sea level but will be lower above sea level.

 

[robertwilbanks]

Update:
About 2 hours after a drive I had the hood open. With the garage door closed and no other sound I heard this sucking sound. This time it wasn't money being sucked out of my wallet (not much anyway). It was coming from the coolent level sensor. A closer look showed that the previous owner had a problem with it and instaed of replacing it used a sealant on it. It would not leak water out that I could tell, but is keeping the pressurized system from working correctly. I have ordered the new part and will post the results.