Altitude and Cooling

[Phred]

In my A, I run a 195* thermostat, 50/50 antifreeze, in an unpressurized cooling system.
Here at home (elevation 800') the car will warm up to 205* on my AutoMeter temp gauge ans stay at that temperature regardless of of the summertime ambient temperature or how hard the car is being driven. Unpressurized 50/50 antifreeze boils at 227*F at sea level, so I feel I am in a safe place.

While driving last week in the Rocky Mountains (7000' - 12,000') coolant would run out from the radiator cap and the temp gauge would bounce from about 210/215* - 180*. Over the course of a few hours I was able to add about 1/2 - 3/4 gallon of coolant to the radiator to bring it back to its "normal" flat land level.

50/50 antifreeze boils at 212* (9000' altitude).

What was happening to cause the radiator cap leakage? I have three ideas.

1) the less dense air at altitude make the radiator less efficient.

2) if the coolant is not boiling but approaching the boiling point, will the coolant "expand" and be forced out the overflow and cap just as an overfilled radiator in lower altitudes would act? Or will the coolant not "expand" until it boils?

3) the coolant did reach the boiling point and the increased pressure forced the coolant past the radiator cap seal.

What is most likely happening?

A combination of all three ideas or just ideas 1 and 3?

Here's another question for you scientists. As the 50/50 coolant boils, does just the water of the mixture escape as steam, leaving a stronger concentration of glycol?

Thanks for your help

[tbirdtbird]

"Here at home (elevation 800') the car will warm up to 205* on my AutoMeter temp gauge ans stay at that temperature regardless of of the summertime ambient temperature or how hard the car is being driven."

Your baseline running temp of 205 is too high, leaving you no 'cushion'

Your cooling system needs attention. Water jacket/rad tubes are at least partially clogged with rust and scale.

Here in Texas in the summer and we do have summer, with a re-cored rad, block thoroughly cleaned with lye and section of bowden cable on a drill to break up the caked rust esp at cyls 3&4, plastic fan, stock pump, no thermostat, elevation about what you are, I run at 180 all the time; 25° cooler than you

[Tom Wesenberg]

I would install a 180 stat for starters. What was the outside air temp when it boiled?
As Tbird said, how is your cooling system for being clean?

[Phred]

I have intentionally installed a 195* stat, 50/50 coolant, and Mobil 1 oil to allow more heat and better thermal efficiency inside the engine.

Around home the temp gauge never reads higher than 205 even on the hottest/humid days of 90+*. With a sea level boiling point of 227*, I am convinced that in my "normal" driving altitude (500' - 1500') I have sufficient headroom/cushion.

Driving 1000 miles from IL to CO last week across the "fruited plain" and back at highway speeds in temps of 90*+, the gauge stayed at a steady 205*, however I suspect as I entered Colorado the temperature head room was shrinking as altitude approached 4000-5000'.

In my original post I am curious as what was happening at altitude. I am sure that the less dense air makes the radiator less efficient, and a lower temp thermostat would have reduced/eliminated my overflow/boil over.

My question remains: As the coolant approaches its boiling point does its volume increase significantly, or will the volume remain relatively constant until it reaches its boiling point and then expand greatly?

Peace, Phred

[Tom Wesenberg]

I would think the coolant remains about the same volume until it boils. I agree that the thinner air will be less efficient at transferring the heat to the air, but I'd have thought at those higher altitudes the temp would have been cooler to offset it.

I'm also wondering if the water only boils off, or if the antifreeze also boils away.
I guess a guy could make a weak mix of water and antifreeze and boil it on the stove to see if the mixture gets stronger as it boils.

I'll bet Mike K. knows the answer.

[wmws]

Sponsored Links (Register now to hide all advertisements)

I'm no scientist but I would say as water heats up it does expand quite a bit. And when it boils it seems to get air bubbles in it and that takes up more room. I have noticed on long trips in the summer that bugs accumulating on the radiator will block quite a bit of air. That may have added to your overheating.

[tbirdtbird]

"I have intentionally installed a 195* stat, 50/50 coolant, and Mobil 1 oil to allow more heat and better thermal efficiency inside the engine."

good luck with that. to do what you are trying to accomplish correctly, you would need a pressurized system. And even then you are risking running cyls 3&4 way too hot. It would have been interesting to shoot your cyl walls with an IR temp gun when all this happened; they would have shown at least 240 at 3 & 4. You are gonna end up with collapsed rings if you haven't already

"As the 50/50 coolant boils, does just the water of the mixture escape as steam, leaving a stronger concentration of glycol? "

what diff does it make your baseline is still too hot, as your mountain trip has proven

[BILL WILLIAMSON]

In MOST areas, a 160 thermostat works well. Why PUSH your "LUCK"?
Bill W.

[larrys40]

Phred,

I was out there last week as well with my '30 tudor... I had no problems with my stock cooling system with NO thermostat. I run a motometer but carry a infared if needed. Didn't even touch it and didn't add any coolant the entire time I was there with over 500 miles logged in the mountains alone once there last week.

I really think as tbird and tom said I would look at your cooling system, radiator, block , etc but mostly radiator as I feel that that's where the probable majority of your problem lies. Of course proper timing, mixture, ,etc are also factors. It may be you are not getting good heat dissipation from the radiator and/or full flow to all the tubes.
You might try an infared on it once hot and see what the temperature variances are. Cooling it should be hotter top and cooler toward the lower tank... about the same left to right. If you find cool spots significantly you know you have some flow issues.

Another fellow and his wife and us ran a full day of touring wednesday down 7/72/119 and peak to peak road down to 70 and over to 40 and back up Berth hold pass and up the back side of trail ridge road at over 12,000 elevation and never had a heat issue.. even on berth hold which is a very long grade with switchbacks.

I run a stock original '30/31 radiator. 50/50 mix is good and will increase your boiling point a little but with a good cooling system shouldn't be an issue. I agree with Tbird your running too close to the hot threshold... something else it up.
Hopefully you can resolve.

Larry Shepard

[Phred]

Larry/TBird,

I agree, next time I would run a 160* stat or no stat. I bet there would be no problems.

Did the same run on Thurs as you did on Wed after lunch in Estes Park. Very nice ride.

Peace, Phred

[Bruce]

Larry,
You were lucky to miss "FORD HILL." It was very steep -- low gear for a mile. There were lots of stripes of antifreeze splashed on the asphalt at the top. Most of 'em were left by guys with Motometers and no temp gauges. ... Bliss.
I, too, poured lots of 50-50 through the radiator while below the tree line. The altitude seemed to empty the radiator so that I could pour a quart or two in without seeing it above the baffle. (Brassworks). I really wanted a sight tube so I could see if the core was covered.
Above the treeline it was cool enough for the engine to perform and stay between 1608, where the stat opened, to about 190*.
I did ask my PHD Chemist friend the question Phred asked about the water evaporating before the antifreeze, thus changing the concentration if more 50-50 was added. He agreed that the water would evaporate faster than the ethylene glycol. Keep adding 50-50 and the mixture would become too concentrated.
In any case, I learned that mountain driving in a Model A sure is fun in a Roadster, 2nd/OD is the gear of choice, and 12,000 feet above sea level is "no sweat!" for a Model A.

[dansluck]

I put 12,000 miles on my Model A in the last two years driving at 5000 to 10,000 ft. I do not use a thermostat and use a 50/50 mix. Long grades of 6 to 10% can cause overheating of our little engines. Watch the T-gauge and Give her a rest break. Have Fun Dan