best coolant fluid for engine life?

[tyssniffen]

I run a 40 gal old water tank, open (not sealed/pressurized), not insulated, for my cooling tank, and as I have the whole thing apart right now, I see that within the block, where the water flows, is pretty rusted up.

sorry if this is a dumb-obviously-not-an-engine-guy question, but what fluid should I use to keep this whole system nice an happy?

I was just about to go buy maybe 2 gals of antifreeze, thinking it must have some additives to help with rust, etc, but then started thinking maybe I should just add the additive to some water.  I don't have freezing problems here in Northern California.

and, since I know there's often been a lot of talk about it, my thermosyphon process has always worked great.

throw some oil in there? vinegar? "corrosion inhibitors"?  http://en.wikipedia.org/wiki/Corrosion_inhibitor  ?

Tys

[Tom]

Machinest's soluble oil will give inexpensive rust protection. Just mix it with water.

[mike90045]

I'm running about 25 gallons of 50/50 antifreeze.  No rust so far, and in the open top tank, it seems to be OK after 3 years.  I do plan to install the old radiator from wifes car, to reduce the coolant load to about 4 gallons, much less antifreeze to buy for it.   We are at 1400' and do get frost/ice so plain cutting oil won't do for me. (Just dumped a 4 gallon ice cube out of a 5 gallon bucket last week)

I do use DeIonized (pure water as make-up water) because i use about 1 gallon per 5 hours of run time, and boiling and concentrating water could build up some strange deposits.

I can look into the coolant, and see the thermosiphon action swirling out of the upper hose as it enters the tank.

[AdeV]

I would say the best fluid to use would be a water-antifreeze mix to the summer concentration (for California), or the winter concentration everywhere else. The antifreeze does indeed contain rust inhibitors, and I don't know if they're available OTC. Don't forget to completely change the coolant every couple of years (as the inhibitors will "wear out"), I guess with open tank you'd want to top up with pre-mixed water/antifreeze. Antifreeze alters the boiling point of water so you might find your engine runs a couple of degrees hotter.

PS - Tom, I think unless you're using the engine regularly, you'd have to buy the relatively expensive synthetic soluble cutting oil; the normal stuff becomes, essentially, a gigantic petri dish - much loved by bacteria and other heebie jeebies; "sump life" is a big thing for machinists... A friend of mine put regular soluble in his mill, and had endless trouble with it going off. I got some super-expensive stuff and - touch wood - no problems with excess wildlife 3 years later.

[dieselgman]

In closed systems the science of diesel engine antifreeze maintenance is well developed. The SCA additive packages can be supplemented when needed (off the shelf), and usual life expectancy for a coolant charge is 3 to 5 years with routine testing and adjustment. We use a simple litmus-type test strip to determine pH and also SCA concentrations. In an open system like the Lister cooling system, the evaporation of water and exposure to oxygen is an issue. I would think you could use the same technology, with an increased service interval and do just fine. Once an antifreeze solution decays far enough, it can gel and cause hot spots or circulation blockages. It can also become acidic and damaging to metals and if excess SCA silicates build up in the system, they can deposit internally on water jacket surfaces and thermal transfer can be impeded. Routine maintenance is the key to good performance.

dieselgman

[buickanddeere]

dieselgman pretty much as it covered. A sealed system to limit O2 and CO2 contact with the coolant is required for long life. The question is how good is good enough? My Petteroid ran for a couple of decades twice daily to milk cows just boiling livestock water trough "liquid" for coolant. Then again the coolant passages in the head were 95% closed tight with mineral deposits. The engine probably would have seized or failed if it had operated that way for 8hrs straight instead of two 1/2 an hour cycles per day.