An engine comes off the hot-test stand, the coolant is drained, and by the time it reaches the shipping dock the water left in the jacket has evaporated and left a bloom of red rust on the passages. Nobody sees it until a customer pulls a freeze plug, or a warranty claim comes back with photographs. The same thing happens to a hydrotested pump housing, a pressure-washed casting, or a weldment that went through a rinse stage and sat overnight. Test water is the rust source that plants forget to count.
Three Cortec case histories from Indiana engine plants, spread across 25 years, show the fix is not more drying or more blowing out. It is putting the inhibitor in the water itself, at a concentration that is actually checked, so whatever stays behind in the jacket protects instead of corrodes.
1999: a 1,500-gallon flush station
Cortec Case History #125 (1999) describes a large engine plant in Lafayette, Indiana, that test-ran each new engine for several hours and then found rust on the blocks. The water running off the test turned red almost at once, and the plant traced it to poor corrosion control in the cooling-water system. It was also losing several thousand gallons of water a day, so a once-through fix was not an option.
The plant set up a 1,500-gallon station holding a 20 percent solution of VpCI-379 in water. After the test coolant was drained from the engine jacket, the VpCI-379 solution was flushed through the same passages. The film it left behind kept the blocks looking new, and engines arrived at their destinations with clean cooling systems. VpCI-379 went into the company’s specification, and the sister division in the next case was still using it two decades later.
2018: the same recipe, made freeze-proof
Cortec Case History #623 (2018) is a locomotive-engine division of the same equipment manufacturer, also in Indiana. Its cooling systems were rusting from test water during outdoor storage between build stages and again in shipping, and any residual water also had to survive an Indiana winter without freezing in the block.
Because the product had been in the corporate spec since 1999, the division adopted VpCI-379 directly and added the antifreeze to the flush: 20 percent VpCI-379, 20 percent glycol and 60 percent water, circulated through the cooling system, captured, tested for concentration and reused. The case makes the point that a water-based rust preventative can be run in freezing outdoor conditions if the glycol is in the recipe and the bath is tested rather than assumed.
2023 to 2026: 3 percent in the hot test, 5 percent in the cold-storage fill
Cortec Case History #831 (2023 to 2026) is the most recent and the most useful, because it starts with a plant that already had an inhibitor and was still getting rust. A large Indiana plant building engines for off-road equipment was seeing flash rust on internals after hot-test water evaporated, and rust from residual water in engines that had been given a glycol fill and flush for cold storage. The inhibitor it was using had been allowed to drift out of dilution while other problems took priority. Rust had become a warranty issue and the plant wanted six to twelve months of protection at a cost it could budget.
Full-scale testing began in May 2023 with a different Cortec chemistry, VpCI-649 BD, which carries a stronger vapor-phase component than the previous product. It goes into the cooling water at 3 percent during the one-hour hot test, and into the glycol fill-and-flush solution at 5 percent for engines headed to cold regions. After about eight months of storage the internals were in excellent condition. The plant told its sister plants in the United States and Asia, and the process has been adopted at several of them over the last three years. The low dose is what made it fit the budget.
| Case | Year | Product | Concentration | Where it goes |
|---|---|---|---|---|
| #125 | 1999 | VpCI-379 | 20 percent in water | Post-test flush of the cooling jacket from a 1,500-gallon station |
| #623 | 2018 | VpCI-379 | 20 percent, with 20 percent glycol | Circulated, captured, tested and reused; outdoor storage between build stages |
| #831 | 2023 to 2026 | VpCI-649 BD | 3 percent hot test; 5 percent glycol fill | In the test coolant itself and in the cold-storage fill |
Two things carry across all three. The inhibitor is in the water that touches the metal last, so nothing has to be dried perfectly. And the concentration is measured; #831 is a plant that had the right idea and still rusted engines because nobody was titrating the bath.
How to do this in your plant
- Find every place test or rinse water is the last thing on the metal: hot-test stands, hydrotest rigs, the final rinse of a Build-All or Magido parts washer, and pressure-wash bays. Each one needs its own inhibitor and its own concentration target.
- For cooling jackets and post-test flushes, charge a recirculating station with VpCI-379. The Indiana plants ran 20 percent; the VpCI-379 dilution table puts 1:1 to 1:5 at up to two years indoors, so a shorter in-process hold can run leaner. The dry film can be painted over, which matters if the block goes to the paint line next.
- If the water is a washer rinse or a dip after cleaning, VpCI-377 at 2 to 5 percent gives about a year indoors and leaves little visible residue; 5 to 10 percent gives up to two years. Our concentration testing guide shows how to build a refractometer chart for either product.
- For hydrotest water on pumps, valves, vessels and pipe, dissolve VpCI-609 at 4 to 8 percent, hold at pressure for at least an hour, drain and close the vessel without purging. Keep it away from copper and brass. If you blast before test, VpCI-609 can also go into the media so the steel is inhibited as it leaves the blast room.
- For a winter flush, add glycol to the VpCI-379 solution as in #623 and check the freeze point along with the concentration.
- Put the titration or refractometer reading on the daily checklist. That single line is the difference between #125 and the first half of #831.
Which Cortec products
- VpCI-379, 5-gallon pail: the cooling-jacket flush in both Indiana engine cases; paintable dry film; makes 10 to 100 gallons of solution.
- VpCI-379, 55-gallon drum: for a 1,500-gallon station or a recirculating flush loop.
- VpCI-377: washer rinse and dip-tank rust preventative when the part is not headed for paint; a winterized grade is available.
- VpCI-609: water-soluble powder for hydrotest water, standing water and blasting media on ferrous metal; up to 24 months sealed.
- VpCI-649 BD: the closed-loop and cooling-system inhibitor from #831; not a stock item at SRS, but we can quote it against a plant trial.
We stock VpCI-379, VpCI-377 and VpCI-609 in Elmhurst, Illinois, along with the titration kits to control them. If your engines, castings or vessels are rusting from the water you test them with, contact us for a sample pail and a concentration chart, or ask us to run the flush on a few units before you change the spec.
Sources: Cortec Case History #125 (1999), Cortec Case History #623 (2018), Cortec Case History #831 (2023 to 2026); Cortec product data sheets for VpCI-379, VpCI-377, VpCI-609 and VpCI-649 BD.