Just a Bronco driver for over 50 yrs!
- Jul 31, 2001
If I only need 4% reservoir capacity of my appr 384 oz system then I'd only need a pint capacity reservoir. That's what I had for decades but with the 460 stroker it would always burp about another pint or more on to the ground.It actually might change things. The liquid only expands at the same rate for a given temperature I'm guessing, but having more volume to start with would naturally increase the total fluid expansion. Necessitating a larger catch tank as well.
Good stuff but another item-Well, that' a pretty horrid theory. The increase in volume of water in relation to temperature is not a theory. It is also not a fact. Water reaches it's maximum density at about 4 degrees C. So if you go from 4C to 3C...it actually gets larger. Also, if you go from 3 degrees to 4 degrees...it gets smaller.
So it doesn't always increase volume with an increase in temperature. These aren't theories. They are simply observations from reactions to physical laws. Generally, water from 20C to 99C will increase about 4% by volume. This is the result of empirical testing, and observation. So if someone proposed a hypothesis that having more volume would increase the total expansion... that just becomes a confirmation thru observation. It doesn't describe the why, or the how.
So yes, 2 gallons of water will increase in volume by about 10 ounces, and 4 gallons of water will increase by 20 ounces. (from ambient to about boiling) If you are foolish enough to fill your radiator above it's capacity...that expansion will result in overflow. The capacity of a down flow radiator is usually reduced by 4 percent to allow for expansion. Some even have sunken fill necks in the top tank to prevent over filling. There is no decrease in cooling capacity in a down flow radiator if you reduce the fill level. A cross flow radiator will exhibit a reduction in cooling capacity if the upper fins are not wet. In this case, the radiator must be de-rated to allow for under-filling. If you need the full capacity of the radiator, then a surge tank may be installed to enable complete filling. You will find one on every V8 Bronco from 66-68. If you design your radiator such that over-filling (or complete filling) is not necessary...you can leave room for expansion in the radiator. Every V8 Bronco from 70-72 is designed this way. Once you decide to maximize the cooling capacity of the radiator, and ensure tube coverage, then a recovery reservoir is appropriate. The capacity of that reservoir should not be less than 4 percent of the coolant volume. Add a reasonable safety factor and you get to @nvrstuk and his 32 ounce solution. (maybe fill to 25% full, operating from 25% to 75%, leaving some headroom.)
Cooling systems designed for full coverage have coolant recovery bottles. Cooling systems designed for expansion in the radiator have overflow bottles. Properly designed cooling systems that have excess cooling capacity and appropriate fill levels have hoses that run to the ground.
I was going to put a puke can on my Bronco. But you let me convince myself that I don't need it. So you just saved me about $60.00. Thanks!
The fill neck on a Bronco V8 can be below the highest row of tubes. This allows room for expansion in the radiator. The fill line should be about an inch or two below the fill neck.
My theory based not on my ability to explain the physics behind it because I don't need to in this case (and most of you know I'm a numbers/engineer geek) but because I have a different situation than most Broncos that I tried to explain earlier.
When my HP numbers grew from a stock 289 to now 3+ times what the stock 289 ever generated the huge boiler fired heater I run now - called a 460stroker- generates a HUGE amount of btu's extremly quickly thereby (explained to me by an engineer at Griffin I think that's where it was) creating what he said was a much bigger rush/push/bubble/amount (for lack of a physics accepted term) of superheated water out thru the tstat and into the radiator. This "superheated" water as he put it created a large surge and expansion that would need to be expended out the overflow into the tank. Take an engine making 1/3rd the HP and the tank could be MUCH smaller he said. Hence the reason I needed to go to a full quart instead of 12+ oz or so which worked well for so long.
Back when I had my 289 or 351 with the tube running down to the ground the only time I dumped any fluid would be when the radiator was still accidently covered with cardboard from winter time. Pull that out and the water would sit a 1/2-1" below the neck pulling boat trailers, tent trailer, boat on top of the Bronco, over 12,000ft gravel mountain passes in 100deg heat with kids/6 weeks worth of gear- never mattered. It DOES matter with stooopid HP WHEN it is being generated tho.