How much does water expand per degree?

[Tom_Hughes]

Hi guy's,

Need to borrow some brains please. I took more shop than academic's. In attempting to solve the boil over problem I have, can one of you really bright fellows tell me how much water expands per degree?

Let's say I have a gallon of water at 90 degrees ambient temperature. If the same gallon of water gets to 195 degrees, how much water will I have? What if the same gallon at 90 degrees gets to 220 degrees? Just trying to figure out capacities. Any & all help is appreciated! I spose I could go ask my 14 year old daughter, she does does not share the same level of excitement in the car that I do...

 

Its been a long time since I was a boiler tender in the Navy, but here are my thoughts on the expansion of water in your closed cooling system. If all of the air is bled off the quantity of water as it heats up does not change. The pressure will increase. If your radiator cap is spring loaded it will releave the excess pressure by allowing the water to expand when the water escapes at a high enough pressure to open the spring loaded cap. This process also is the process that bleeds off the air out of the cooling system. In fact if your system is closed and there is no possability for any escape of pressure the pressure can build up to a point that the dencity of the water and steam becomes equal, around 2,050 psi I think, when you can not tell the difference between the two. Don't worry this won't happen in your car. Joe PS: Tom, check your thermostat, it may be bad.

 

[Dave Bilyk]

approx water density is 62.4 lb/ft3 just above freezing, at 90deg - 62lb/ft3, at 195deg - 60.25, at 220deg - 59.6
this suggests that a given volume of water will expand about 4.7% from cold to 220deg, the cooling system capacity will increase I think by about 0.5% for the same rise. So working on 4.2% you would need about a 1/3 of a pint per gallon in your cooling system. Antifreeze if you use it will change this but I dont have any figures. When you stop the engine, or if you have internal hot spots, local boiling might increase the expansion tank capacity required, so 1/2 pint per gallon might be better. I'm sure there will be a rule of thumb based on experience, but the above seems reasonable as a starting point.