I'm getting ready to take my 65 up into the mountains of Colorado to go to the Vettes in the Rockies event this weekend.( Great event) Being the prudent person that I am I went for a test drive. The event will be held near Breckenridge Colorado which is aprosimatly 9000 ft. in elevation. I have been driving my car around at my home elevation in Boulder of 5600 ft. It runs nice and cool, about 170 degrees in most conditions . It gets up to about 190 under sustained idle on a hot day. When I drove up to a town at an elevation of approximatly 8600 Ft. it ran nice and cool , BUT, when I shut the car off to go in and have some lunch the radiator spit out about 2 pints of coolant. Being the engineer I thought about this throughout lunch and then on into supper. The level in the expansion tank had normalized at my home elevation and I had a 13 pound cap on so it should not have boiled over, but it clearly did? I think what happened is that the radiator cap is just a spring and the atomosheric pressure affects it's ability to hold in the liquid.You have to add the spring and the atomosheric pressure together to get "holding pressure" I've pretty well convinced myself of this, so my question is...for an elevation of 9000 ft. What expansion tank pressure cap should I have. I think there is about a little over a one pound atomospheric pressure difference so should I have a 14 or 15 pound cap to prevent future coolant loss on my Rocky Mountain high excersions? Any thoughts or expirience from the group? Jerry
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Re: C2 elevation/ expansion tank cap
Jerry-----
I think that you've got it sized up about right. However, I wouldn't worry about it. The 13 lb cap will do you just fine at the higher altitudes, albeit that you'll likely lose a bit more coolant via the overflow. Coolant loss is noraml on all pre-1973 Corvettes without coolant RECOVERY tanks (an external SUPPLY tank is NOT the same as a coolant RECOVERY tank). A little more or less at higher altitude is no big deal.
For additional info, though, GM discontinued the 13 lb caps years ago and replaced them with 15 lb caps. I recommend using a 15 lb AC RC-26 cap for you application at low, medium, and high altitudes. Re-install the original only for judging puposes.In Appreciation of John Hinckley -
Re: C2 elevation/ expansion tank cap
I basically agree with Joe, but recommend the 15 psi cap to give extra boilover protection.
The boiling point of the coolant is a function of absolute pressure, which is the sum of cap pressure plus atmospheric pressure, so the boiling point is reduced at altitude, but it should not be enough to cause coolant loss.
Suggest you check the holding pressure of your 13 psi cap. It might be a little low, but, if original, keep it, and install a new RC-26.
Also, coolant loss can be caused by overfilling the system. The tank should be about half full at OPERATING TEMP, so it will be below half at room temp.
The only time I ever experienced coolant loss was following engine shutdown after some real hard running. Residual heat caused some boiling inside the engine resulting in slight coolant loss out the overflow. After hard running some "cool-off" time in the form of a mile or two low speed driving or a few minutes of idling will remove excess heat and prevent boil-over after shutdown.
DukeComment
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Thanks guys 15# it is. *NM*
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Re: C2 elevation/ expansion tank cap
Jerry,
You've already been given the answer you need, but your issue reminded me of a related experience I had going to the Regional meet held at Breckenridge a couple months ago.
Our family stopped here in Kansas and bought some groceries on the way out. As we approached Breckenridge over one of those honk'in tall mountians, we heard a muffled explosion from the sack.
The foil package containing potato chips had bloated to point of exceding it's elastic limit....yup, we had chips all over the place.
The family got a good laugh out of the deal, and it provided a good educational moments on atmospheric pressure at altitude for the girls...
tcComment
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Re: C2 elevation/ expansion tank cap
Would you use a 15lb. cap on a c-1 with an original radiator for every day driving as well and use the 13lb. cap for show only?Comment
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Re: C2 elevation/ expansion tank cap
A 15 psi cap provides better boilover protection. C1 caps were about 7 psi in the fifties. IIRC. The weak links in the system are the radiator and heater core, but if yours are in good condition they should hold. I believe radiator shops use about 30 psi when testing the intregrity of radiators and heater cores.
DukeComment
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Re: C2 elevation/ expansion tank cap
If you go far enough back they were 4-pound caps and running these systems with a modern 15-pound cap could result in breaking seams!!!Comment
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