[Vwdiesel] '81 Rabbit overheating

[Roger Brown]

Rolf Pechukas wrote:
>> I thought I would wait to see if someone else would comment, but  
>> water boils at 212 F (100 C) at sea level. It boils at a lower  
>> temperature as altitude increases & air pressure decreases. As  
>> pressure increases, the boiling temperature increases. This is why  
>> modern cars use pressure radiator caps to increase normal operating  
>> temperature. This is why modern cars often use 14 pound pressure  
>> caps. Then the operating temperature can run much higher. This is  
>> why some temperature gages go up to 265 degrees F. There is a  
>> formula to figure how much the boiling point rises or lowers with a  
>> change in pressure, but I forget what it is.
> 
> yeah, but my system for whatever reason is not pressurizing
> hence my concern about approaching 200+°f
> 
> Rolf in MA

No pressure in the system is a good thing, as far a negative sign of a leaking head 
gasket.  Coolant must exceed the boiling point to cause a pressure rise (due to the vapor 
pressure).  With a mix of glycol and water, the BP is probably up in the 230-240F range, 
depending on the mix you are running (plain water is 212F at sea level, but add antifreeze 
and that rises a fair amount).

-- 

   Roger