Location: Scottsdale, Aridzona
(68.2.104.9) | (This is Yahoo FMC MSG #11300. I was OFF +4° on how much 50/50 ethylene glycol/ water mix raises the Boiling Point. It raise it 11°F, not 15°F. I have corrected it in the "repeat" below. LC)
FMC Radiator Coolant Boiling Point.
I use only the GREEN STUFF (straight ethylene-glycol), and mix my own with distilled water (that I get at the Grocery Store).
50/50 mix of ethylene-glycol and water boils at 223°F. The stuff is in there to lower the FREEZING POINT, but it also raises the boiling point 11°F (212+11=223).
The pressure cap is what saves car/truck engines. The original idea for pressurizing the coolant system was to get the vehicle over MOUNTAINS !
Rule of thumb is that there is 1/2 psi ambient pressure drop per 1000 ft. of altitude above (or below) sea level. Standard Sea Level Pressure is 14.7 PSI. (Yes it goes up and down . . . you figure it out)
At 10,000 ft. Wolf Creek Pass, CO, ambient pressure has dropped 5 psi (1/2X10+5). Ambient Pressure there is 14.7 PSI - 5 PSI = 9.7 PSI. No wonder your FMC, or you, hasn't got a lot of power.
BUT . . . Each PSI of pressure above (or below) 14.7 PSI on 50/50 glycol/water raises (or lowers) the Boiling Point a little more than 3°F.
If you start with 50/50 mix (223°BP) and have a 7 psi radiator cap, that 7 PSI raises the BP 21°F (7X3=21°F).
Then at sea level you have 212°+11°(Anti-Freeze)+21°(Pressure Cap)= 244°F Boiling Point.
The 10,000 ft altitude lowered the coolant Boiling Point 15°F (5X3=15), which used up all the "cushion" the 50/50 glycol gave you, and BP is back to 208°F (223-15=208).
But if you had a 7 lb. pressure cap (7X3=+21º in BP), it puts it back up to 229ºF (208+21=229) Boiling Point at 10,000 Ft going over Wolf Creek Pass.
Newer radiators (AND HEATER CORES !) use 15-16 psi caps that increase BP (15 X 3 = 45°F) to 223°+45°=268°F and HIGHER.
Race cars (sprinters/Nascar) use 25 psi, even 30 psi caps with straight water !
A stock FMC at Sea Level, with 50/50 and 7 psi cap has a 223° + 21° = 248° F Boiling Point.
A stock FMC at Sea Level, with 50/50 and a Stant #31349 cap (10 psi recovery type) has a 223° + 30° = 253° F Boiling Point.
A stock FMC at Sea Level, with 50/50 and 13 psi cap has a 223° + 39° = 262° F Boiling Point.
That is the MAXIMUM RADIATOR COOLANT TEMP on the inside, before it pops the radiator Pressue cap seal . . .and you and you FMC BOIL OVER.
What is the temperature of the air on the OUTSIDE that is carrying, by conduction and convection of the fins/tubes, that coolant heat away ?
Is there any conduction, convection, RADIATION, of that air, that is smart enough to follow the arrows into the side grill doors, and up from the bottom, as it makes its way to those fins/tubes ?
The FMC Parts Manual and Service Manual and Service Bulletins in Sections 13 call for a 13 PSI CAP on a STOCK FMC 440.
What relief pressure is the radiator cap on your FMC ? Ever tested it ?
How accurate is you Coolant Temp Gauge ? Ever tested it ?
Remember, you foot (wearing a flip-flop ?) on the gas pedal is RIGHT NEXT TO THE HEATER CORE SUPPLY HOSE with 200°F+ coolant passing thru it.
Wonder if the stock FMC radiator and heater core and sink water heat exchanger and all the 45 year old hoses and fittings could take 13 psi ? Probably NOT. 15 PS ? 10 PSI ? 7 PSI ?
Boil ON ! Cool ON ! PICK ONE ! Lou #120
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Coolant Boiling Point (Radiator)
