Engine failure due to cylinder liner cavitation corrosion is disturbingly common in the industry, yet it typically can be prevented through proper cooling system maintenance.
That's according to Mike Goodheart, director of sales at Penray, who has been heading up efforts by the American Trucking Associations' Technology & Maintenance Council to write a comprehensive Recommended Practice on coolant maintenance.
If a cooling system is not properly maintained, one of the most common and costly results can be the perforation of wet-sleeve cylinder liners, caused by cavitation corrosion. This is caused by repetitive pitting of the liner as a result of liner vibration.
As the fuel inside ignites, the liner vibrates within the block. The outside wall of the liner actually moves away from the coolant, causing a near-vacuum for an instant. This low pressure causes the surrounding coolant to boil, forming tiny bubbles. The liner then returns to its position with extremely high velocity, pressing against the bubbles with a violent force. The bubbles implode (collapse) against the liner wall surface at pressures up to 60,000 psi.
The collapse of these bubbles blasts small holes in the steel liner. This pitting process will repeat, digging tiny tunnels through the liner. Eventually, the liner wall will be perforated all the way through, allowing coolant to enter the combustion side of the cylinder.
If that happens, you're likely looking at an expensive in-frame overhaul. But because it's preventable, it's probably not going to be covered under your engine warranty.
The RP, several years in the making and currently in the process of being approved byTMC membership, got its start when the organizers of TMC's technician skills competition were looking for clarification on coolant issues, Goodheart says.
The proposed RP contains a glossary of terms, a list explaining the different coolant/antifreeze types, and the steps a technician should take to make sure coolant is still doing its job. The RP goes into much more detail, but here are the basic steps:
- Look at the color, which helps determine the type of coolant.
- Look at clarity and general physical appearance.
- Determine freeze point to make sure it's the proper water-to-coolant concentration and correct if needed.
- If it's conventional coolant, use a test strip to determine the amount of nitrite additive, which is what protects the wet sleeve liners, and adjust as needed.
- If it's an extended-life coolant and the color indicates it's been mixed with conventional coolant, coolant would either need to be flushed and replaced or converted to conventional coolant through a supplemental cool ant additive precharge.
- If it's an extended-life coolant that does not appear to be contaminated with non-ELC product, and has not reached the 300,000 mile mark, it's good to go. At the 300,000-mile mark a chemical extender is required, and at the 600,000-mile mark the coolant needs to be discarded.
Don't get sloppy
Many fleets, especially smaller ones, Goodheart says, will start out with a good cooling maintenance program, but as time goes by, they cut corners. Maybe they buy the wrong antifreeze because it's cheaper. Before you know it, there's an expensive overhaul not covered by warranty.
"Even the new trucks today will lose coolant," Goodheart explains. Over the course of a year, he says, an average fleet will use about half its capacity of antifreeze. So if you've got 100 trucks that each have a 12-gallon coolant capacity, you'll use about 600 gallons per year. "So there are constantly challenges to keep the coolant in good condition."
A mini-technical session will address the issue via a panel discussion at the TMC's fall meeting, Sept. 10- 13 in Pittsburgh, Pa.
Types of coolant/antifreeze
In recent years, cooling system maintenance has been complicated somewhat by the different types of coolant available. A new TMC Recommended Practice identifies five major types:
- Conventional/automotive (must be treated with separate supplemental coolant additives, or SCAs)
- Fully formulated conventional (includes additives)
- Nitrited organic acid (extended-life) coolant
- Straight organic acid (ELC) without nitrites
- "Universal antifreeze," primarily automotive, is basically a combination of all of them.
The RP did not address "waterless" coolant or recycled coolant, in order to keep the scope narrow enough to be able to complete the work.
Evans Waterless Coolant is a relatively new type of coolant. There's no water; it's all a blend of glycols and the necessary additives to protect the cooling system. Because it boils at a higher point than coolants with water, Evans contends, the coolant allows the engine to run a bit hotter. That, in turn, allows you to adjust the fan-on time, and that translates into fuel savings - and fewer problems with cavitation, the company says.
"There are various types of coolants out there, and they all can work if you are diligent to treat them properly," says Mike Good-heart, director of sales at Penray, who has been heading up the TMC efforts to write the new RP.
"There's no maintenance-free coolant, no coolant you can set and forget."