A couple of weeks ago we talked about proper cooling system maintenance. We briefly touched on the need for RVers who depend on diesel engines to properly check for supplemental coolant additive (SCA) in their engine coolant. Let’s give a little more attention to this area, as it’s one that’s frequently misunderstood.
First, why the need for SCA? This additive is a protection against a nasty happening called cavitation. Engines throw off excess heat from combustion by routing water along the cylinder walls–which 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 pleasant.
But the vibration caused by a piston slap is an extremely high frequency, not when we hear with our ears, and the results can be anything but pleasant. As the piston slaps the liner it moves out, 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 on doing 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. But SCA will eventually need to be added to the system, and if you say, have a coolant hose let 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. If you dilute your spare coolant to the correct level to simply “dump in” the system, by having already added the proportional amount of SCA to this backup coolant, you won’t be needing to worry about diluting the system’s SCA when you add the makeup.
photo: Comparing SCA test strip against color chart. R&T DeMaris photo
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