For a number of years, General Motors has been using its brand of extended-life anti-freeze, Dex-Cool. (Other car manufactures have adopted similar concoctions.) Some people have criticized these extended-life coolants, blaming them for an increased number of leaks in heater cores, etc.

GM now recommends measuring the DC voltage between the coolant and battery ground. If it measures higher than 300mV, then the cooling system should be flushed and new coolant installed.

You measure the voltage by removing the radiator cap and dipping one DMM probe into the coolant (being careful that the probe doesn't touch the metal neck or internals of the radiator). The other probe goes to ground.

Evidently, Dex-Cool passivates the various metal surfaces of the cooling system, and thus inhibits galvanic current between dissimilar materials (for example, between an aluminum heater core and ferrous engine parts.) When the inhibitors are depleted, the current increases, which increases the voltage through the coolant.

I have two GM vehicles. One vehicle, for which the cooling system has never been flushed, measures about 180mV with the engine running and various accessories switched ON. (With the engine and accessories switched OFF, I measure about 165mV.)

My other GM vehicle's cooling system has just recently been flushed, and its voltage measures about 1.0 mV.

Here is the GM (AC/Delco) technical bulletin: http://acdelcotechconnect.com/pdf/tsb/tsb_04D-J-051.pdf

I would imagine that this voltage test would be appropriate for testing conventional anti-freeze, not just extended-life versions.
Doug

:For a number of years, General Motors has been using its brand of extended-life anti-freeze, Dex-Cool. (Other car manufactures have adopted similar concoctions.) Some people have criticized these extended-life coolants, blaming them for an increased number of leaks in heater cores, etc.
:
:GM now recommends measuring the DC voltage between the coolant and battery ground. If it measures higher than 300mV, then the cooling system should be flushed and new coolant installed.
:
:You measure the voltage by removing the radiator cap and dipping one DMM probe into the coolant (being careful that the probe doesn't touch the metal neck or internals of the radiator). The other probe goes to ground.
:
:Evidently, Dex-Cool passivates the various metal surfaces of the cooling system, and thus inhibits galvanic current between dissimilar materials (for example, between an aluminum heater core and ferrous engine parts.) When the inhibitors are depleted, the current increases, which increases the voltage through the coolant.
:
:I have two GM vehicles. One vehicle, for which the cooling system has never been flushed, measures about 180mV with the engine running and various accessories switched ON. (With the engine and accessories switched OFF, I measure about 165mV.)
:
:My other GM vehicle's cooling system has just recently been flushed, and its voltage measures about 1.0 mV.
:
:Here is the GM (AC/Delco) technical bulletin: http://acdelcotechconnect.com/pdf/tsb/tsb_04D-J-051.pdf
:
:I would imagine that this voltage test would be appropriate for testing conventional anti-freeze, not just extended-life versions.
:Doug

:Sorry for the previous error. You can always get a scientific test on the coolant condition by using a specific gravity(or density) instrument (sure it is more expensive than a voltmeter). Even that squeeze bulb with the tube and five floating balls is good enough. However,I bet GM assumes that a)you have a 50/50 mixture which is never the case: dealers put 100% antifreeze(someone else pays for it...) and after you flush the system you can never get 50/50, b)you have a battery in good state and clean conductive electrical connections. We know that this is not the case in 99% of the cars.What about the testing temperature? I always used 35/65 to 25/75 coolant/water because it dissipates more heat that 50/50,but you must be careful: replace it every year for top performance and be aware of the water pump's need for lubrication that the ethylene glycol offers. Frankly,I am skeptical of any GM advice. Getting so detailed in checking the antifreeze also introduces factors to be considered beyond your ability.

The hydrometer test you describe only gives you the percent glycol and/or freezing temperature protection. It tells you nothing about the depletion of corrosion inhibitors. You can have satisfactory freeze-protection but depleted inhibitors.
Doug

::Sorry for the previous error. You can always get a scientific test on the coolant condition by using a specific gravity(or density) instrument (sure it is more expensive than a voltmeter). Even that squeeze bulb with the tube and five floating balls is good enough. However,I bet GM assumes that a)you have a 50/50 mixture which is never the case: dealers put 100% antifreeze(someone else pays for it...) and after you flush the system you can never get 50/50, b)you have a battery in good state and clean conductive electrical connections. We know that this is not the case in 99% of the cars.What about the testing temperature? I always used 35/65 to 25/75 coolant/water because it dissipates more heat that 50/50,but you must be careful: replace it every year for top performance and be aware of the water pump's need for lubrication that the ethylene glycol offers. Frankly,I am skeptical of any GM advice. Getting so detailed in checking the antifreeze also introduces factors to be considered beyond your ability.

For measuring the anti-freeze's anti-freeze qualities, a specific gravity bulb is ideal. However, what you are measuring for with a voltmeter is the diminishing of the rust inhibitor that is usually put into anti-freeze. Anti-freeze will, actually, last practically forever. Its anti-freeze qualities don't go away since the material that makes it not freeze has nowhere to go. However, when you put water or any water-containing fluid into your engine, the various metals in the engine behave like a battery, and the oxygen in the water (or water-containing substance) also oxidizes the metal. That is what produces the voltage. If you use pure water in your engine, you are supposed to add a rust inhibitor to it to prevent the battery action. I use water in the summer because my engine was designed for it, and it cools better. Most modern engines do well with ethylene glycol all year 'round. Ethylene glycol that is produced by reputable companies contains a rust inhibitor.

When you start getting battery action in the cooling system of your engine, passages clog with rust, and the worst part is that the steel bands around the asbestos head gasket, or, if the gasket is solid steel or aluminum, start to eat away. Once they eat through, you have a leaky head gasket. If you have a water-heated intake manifold (my engine uses an exhaust heat riser system), the gaskets in your intake manifold can be eaten away, too, if they are at all metallic. Some are asbestos only, or some asbestos-like material, but others have either metal inserts, are made fully of metal.

T.

Thomas: Back in the very old, old days, in the summer I did what you mention: run with pure water plus a corrosion inhibitor. 'course that was when all the materials in the cooling system were a bit more resistant to galvanic corrosion - e.g., no aluminum, etc.

Also, many moons ago, it was common to use methanol anti-freeze in the winter. Cheap, so just drain it in the spring. But methanol has a lower boiling point than glycol mixtures, so it's no good after engines began using higher temperature thermostats.
Doug

:For measuring the anti-freeze's anti-freeze qualities, a specific gravity bulb is ideal. However, what you are measuring for with a voltmeter is the diminishing of the rust inhibitor that is usually put into anti-freeze. Anti-freeze will, actually, last practically forever. Its anti-freeze qualities don't go away since the material that makes it not freeze has nowhere to go. However, when you put water or any water-containing fluid into your engine, the various metals in the engine behave like a battery, and the oxygen in the water (or water-containing substance) also oxidizes the metal. That is what produces the voltage. If you use pure water in your engine, you are supposed to add a rust inhibitor to it to prevent the battery action. I use water in the summer because my engine was designed for it, and it cools better. Most modern engines do well with ethylene glycol all year 'round. Ethylene glycol that is produced by reputable companies contains a rust inhibitor.
:
:When you start getting battery action in the cooling system of your engine, passages clog with rust, and the worst part is that the steel bands around the asbestos head gasket, or, if the gasket is solid steel or aluminum, start to eat away. Once they eat through, you have a leaky head gasket. If you have a water-heated intake manifold (my engine uses an exhaust heat riser system), the gaskets in your intake manifold can be eaten away, too, if they are at all metallic. Some are asbestos only, or some asbestos-like material, but others have either metal inserts, are made fully of metal.
:
:T.

By the way, using a hydrometer to check coolant freeze protection is "old technology," even though many mechanics still use it with satisfactory results. The modern way is to use a refractometer, which is more accurate, simpler, and isn't as dependent upon the temperature of the coolant under test.

Here's info: http://www.recycool.net/testers.htm
Doug

Just imagine if that methanol ignited. My manual also lists glycerine as an antifreeze. Sounds like a good, neutral, harmless ideal. Never tried it, though.

T.

I have a classic muscle car with big engine that absolutely doesn't like idling at a stop sign in the Houston summer heat. The temp gauge won't max out, but gets close. As others have stated a 50/50 ethylene glycol/water mixture doesn't have the heat transfer capacity that plain water does, but does give boil over protection. Red Line "Water Wetter" added to the colling system works great by improving heat transfer. See: http://www.racerpartswholesale.com/redtech3.htm for more info. It's used a lot in race car engines. Adding it, plus using a slightly lower thermostat cured my heat problem. PEP Boys carries it.
Steve

Consider, too, your idle mixture, your heat riser (if the engine has one), and the condition of the valves. Muscle cars often have long duration cams, which ruin the idle. Thankfully car manufacturers have now come out with variable valve timing (I had the idea years ago....too bad I didn't do anything with it...I could have been a millionaire.....it always puzzled me why noone else ever thought of it before). Besides a wide cam, though, valves (solid lifters) adjusted too tightly can ruin the idle and cause the engine to overheat. My Chevrolet, for instance (1951, 216.5 cu.in OHV 6), has a clearance of .008 for the intake and .015 for the exhaust. Sacrificing even a little (book says you can go .002" smaller) to quiet the engine will cause burned valves, misfiring (rough idle, too), overheating, and dieseling when the engine is shut off. I know from experience. I tried everyone's suggestion, and got bad results. A lot of people think that you should tighten up the valves for more intake and power. Follow manufacturer instructions STRICTLY. The manufacturer has already run many tests, and knows what will give good economy and longevity, unless, of course, power is your only goal, and you do not mind the side effects of poorly adjusted valves (including having to replace valves often).

A heat riser that isn't shutting off the heat in a timely manner will overheat the intake manifold. That will super-expand the incoming mixture, making it too lean for proper function, and will cause the engine to overheat. It may also cause sticking valves and a reduction in power. All-in-all it's not a good thing. In Texas your heat riser should be completely off at all times (once the engine has reached operating temperature...it should be on when the engine is cold to speed manifold heating, so that raw gas entry is reduced). The intake manifold should be warm enough to prevent hesitation, and to provide complete atomization (for good economy), but not so hot as to cause the above problems. If your manifold is heated with water, it may be hot all around, but if it uses an exhaust heat riser, all that needs to be hot is the bottom of the boiling chamber (where liquid gas is allowed to collect), which you can't feel with your hand, since it's down inside of the manifold. If the rest of the manifold isn't as hot (especially in colder weather), that's alright. In hot weather, too, you should consider using a bakelite or asbestos insulator between the carburetor and the manifold, to prevent excessive vapors in the carburetor (if your car uses a carburetor). A hot carburetor will force gas vapor through the equalizing tube and into the venturri, causing an overly rich condition. One other cure is to drill a 1/4 inch hole in the highest point of the bowl cover, to vent the vapors to the atmosphere, though I don't recommend it. The hole can throw the carburetor out of balance, especially with a dirty air cleaner. Also, upon sharp turns, gasoline can spill from the hole. The hole was recommended for Rochester model B carburetors made in 1950. It's a rather poor fix, in my opinion, for summer vapor troubles. Thank goodness for fuel injection. My car always smells like gasoline on a hot summer day....all of the gas vaporizing from the carburetor (and I didn't drill the correction hole).

....We probably should discontinue this thread soon since it is straying away from radios (though it started with volt meters). However, hopefully this helps. Again, if you have a wide cam, your engine might idle poorly no matter what you do. Wide cams can also cause overheating, since the valves don't close properly (which can also lean out the cylinders). The only time valves cool is when they are seated. Otherwise the stem carries away heat poorly, and a hot stem will also char the oil that lubricates it, causing it to gum and stick. Be sure, of course, to clean your block and radiator, though it sounds like you've already tried a lot of things before finally finding a solution.

T.

In my case, everything is on spec, except I have the timing slightly advanced for performance reasons. Thanks for your comments. Now back to radio!
Steve

One thing that might improve your idle is to put the timing to stock settings. Then, if you wish to have it advance more while driving, use slightly weaker springs on the centrifugal and vacuum advances...more on the centrifugal, as the vacuum advance protects against pinging when the mixture gets richer, or when the engine is under a lot of load (more pressure is built up during that moment). However, if you run your engine a lot at high rpms, you still won't get that extra advance once the weights stop on the governor. In that case, you might have to adjust the weight stop a slight amount.

Engines do idle much better when the timing isn't advanced as much. Everytime I advance my octane selector to get a bit more power, the idle gets kind of rough. Lately, though, I have found that having the selector set to zero (5 degrees BTC static setting) does the trick. Winter gas seems to be a bit more volatile than summer, and I get a nice light ping on hard acceleration without extra advance (the book recommends adjusting the octane selector until a slight ping is heard under hard acceleration (cast iron pistons can handle pinging a bit more than aluminum, and the engine is low compression)). In the summer, with the less volatile mixture, I find that it pings less.

.....Also, on one last note, if you are using a carburetor, and it is jetted for pre-ethanol gas, you might consider going up a jet size or two (one or two thousandths of an inch diameter increase). My engine runs rather lean on to-day's gas (it was already jetted lean from the factory). To get proper spark plug color and performance, I have to increase the jets just a bit, and increase the float level by about 3 or 4/32" (ethanol is heavier than gasoline, and will drive the floats up a bit more, making them shut off fuel sooner, which makes the fuel level lower, which makes the engine leaner, and makes it more difficult for the carb circuitry to draw fuel--makes for a rough idle). I found that I could not get the idle to go rich no matter what I did. If you are turning your idle screws out 3 or more turns, and still can't get the engine to go too rich, you need richer mains (depending on the circuitry). There are some really good sites to read from that explain a lot. In some carburetors you work on the idle and main circuits separately. They all tend to affect eachother, though. In my particular carburetor, increasing the jet size tends to correct everything evenly. If I find that it is going too rich on the mains when I get the idle working properly, then I need to cut down on the idle bleeds instead of increasing the mains, to richen the idle and off-idle ports. This does not happen, though, so I know that everything in my particular carburetor, as stated by the factory, is all compensated at the same time simply by changing the main jet.

Once I re-jetted my carburetor, my engine ran a lot smoother and cooler in all weather. When I first bought the car in 1998, it ran great because they didn't put as much ethanol in the gas. After a few years I noticed that I could not get the engine to go rich at idle no matter what I did to the carburetor (I now have 5 carburetors, since I kept thinking that maybe I'd come across a better one), and no matter what I did to the engine. Performance suffered, and the engine was rough all around. Re-jetting made a big difference, and decreased the engine temperature. My brother had a 1966 Impala that was the same way--was lean no matter how far the idle screw was turned out. Once adjusted properly, the car got 20 mpg on the freeway, and had tons of power.