As summer approaches (or is already here, depending on your whereabouts), keeping your RV or the vehicle that tows your RV road-ready means keeping an eye on the cooling system. With changes in technology and marketing, knowing what liquid to put in your cooling system can be a challenge for a professional technician and a downright nightmare for RV owners.
Green, pink, orange, red, even blue—the colors that coolant manufacturers put in their coolant are supposed to help us discern what goes where. Sorry, but if anything, this colorful mishmash does anything but help. We’ll try and (if you’ll pardon the expression) boil down the matter to something that may help you swim your way through the confusing world of automotive coolants.
“When I was a lad,” the saying goes, antifreeze, as it was generically called, was all green. Pour the right amount in the radiator, add water, and hey Prestone! Your rig was ready to roll. The underlying principles are still the same, so let’s review them.
In our RV world, pretty much all engines are water cooled to remove waste heat. Plain water tends to be corrosive, eating up metal parts, and it also freezes. Freezing water expands, and expanding water in the closed spaces of the engine breaks parts. On the other side of the scale, water heated up to an extreme turns to steam, and steam-filled areas of an engine overheat, leading to catastrophic failure.
Antifreeze, or coolant as it is termed today, has additives that reduce chances of corrosion, reduce the freeze point of the cooling system liquid, and likewise raise its boiling point. As well, automotive coolants contain additives that help lubricate seals and water pumps, and aid in the transfer of heat from engine surfaces to the coolant liquid.
The “green stuff” so common not long ago was primarily ethylene glycol. Everybody’s car and truck used the green stuff; the only options one had on purchasing was to buy the stuff in a concentrate or the “pour and go” pre-diluted mixture. Then things began to change as coolant manufacturers introduced extended life coolants. Some call this orange coolant, but different manufacturers may use a different colored dye. The extended life coolant is also known as OAT coolant, for “organic acid technology,” the basis of its construct.
The extended life coolant was said to be better for vehicles because while the old green coolant had to be changed out every two years, the new version could run for as long as five years. Now enter a third coolant, a hybrid OAT coolant called HOAT. So you’ve got HOAT, OAT, and the good old green stuff, and none of them like to mix. The old style green mixed with HOAT or OAT can precipitate a cooling system disaster.
Then it had to happen: Some wise guys in the back rooms of coolant manufacturing circles had the brilliant idea of a sort of Coolant United Nations. Is your cooling system a little down? Don’t know what kind of coolant you’re using? Buy the new universal coolant and you can top off any of them safely! The jury isn’t back in yet on just how safe or how effective universal coolant is.
Which Coolant for You?
The idea of reduced maintenance intervals has a sort of positive ring to many. After all, if the price isn’t outrageously different, who would prefer to climb under the rig every two years to change out coolant when they could put in an OAT or HOAT coolant and go five years? This time, there’s no question about who’s in the details: The devil is!
Owners of some older vehicles say they’ve found the devil in their cooling system. Having gone from the old green coolants to the extended life coolants of various varieties, they say various gaskets, seals, and engine components have suffered problems (read that “failures”). A class action lawsuit was settled some years back to satisfy litigants who said one of the newer OAT coolants ate up engine gaskets, leaving them with kaput engines.
What to do? Probably the safest thing is to simply use the type of coolant specifically recommended by your vehicle manufacturer, at least while the engine is under warranty. Once outside the warranty period, if you want to take your chances, then you could experiment with other types of coolant.
Should you choose to do this, be sure to completely clear your cooling system of all traces of the earlier coolant. This may mean multiple flushes of the system, but don’t run any risks of mixing types of coolant in your system.
For our part, we’re sticking with the old “green stuff” in our mid ‘90’s diesel engine tow vehicle. But diesel owners using the green should keep in mind that besides checking the coolant for its ability to protect against overheating and freezing, there’s yet another factor to be concerned about: cavitation.
Engines throw off excess heat from combustion by routing water along the cylinder walls that are typically lined with a cast iron sleeve. As the piston travels up and down, it brings with it a bit of side motion—causing the piston to strike the liner sleeve, “piston slap.” Think of this slap like the clap of the clapper against a bell: It produces a vibration. In the case of a bell, the vibration is in our hearing range, and it typically is pleasant.
But the vibration caused by a piston slap is an extremely high frequency, not what we hear with our ears, and the results can be anything but pleasant. As the piston slaps the liner, it moves out, and then quickly returns to its normal position. As it moves out, small bubbles are created in the coolant, and as the liner moves back in, the bubbles implode, creating in scale a huge shock wave. Left unchecked, these shock waves will repeat and repeat, hammering away at the cylinder liner until finally, tiny pits are formed. The pits eventually form holes in the liner, allowing the engine coolant and lubricating oil to meet. Disaster is not long in coming.
Enter SCAs. These coolant additives transform cylinder liner rust (iron oxide), which is soft, into a much harder form. This hardened material resists pitting, actually healing itself, provided a high enough level of SCA is maintained in the system. Since SCAs typically contain nitrites, overdosing the system can also lead to damage, as too much nitrite in the coolant will eat away at the solder that holds the radiator together. Hence, the need for using the right amount of SCA.
Figuring out the right amount is easy during a cooling system flush and recharge. By taking the known cooling system capacity, you simply read the chart provided by the SCA manufacturer and dump in the right amount. SCA will eventually need to be added to the system, and if say, a coolant hose comes loose, you’ll be adding “make up” coolant. Here the use of system test strips will help you determine how much SCA to add. The strips are easy enough to use: On a cold engine, pop the radiator cap, extract a small sample of coolant, dip a test strip, then following the instructions for the proper timing of the test, compare the test strip to a color chart.
It’s not a bad idea to carry extra coolant with you on the road. Add the correct proportional amount of SCA to the backup coolant in advance, and you won’t have to worry about diluting the system’s SCA when you add the makeup.
Our bottom line? Stick with the type of coolant recommended by your manufacturer. Be conscientious about testing the coolant to ensure it keeps its ability to protect against freezing, boiling and cavitation. When time or miles driven dictate, CHANGE the coolant. These steps will ensure you get the most mileage out of your cooling system.
Russ and Tiña De Maris are authors of RV Boondocking Basics—A Guide to Living Without Hookups, which covers a full range of dry camping topics, and of Camp Hosting USA—Your Guide to State Park Volunteering. Visit icanrv.com for more information.