exactly what is the deal?

[coleslaw]

I have a couple of Yanmar marine diesels that seem to be a little more maintenance intensive than the Cummins I have in a different boat. The Yanmars (Toyota engine, light weight, high output, etc) specify 125 hour oil change and 250 hour or annual coolant change. Fine. . .but then I cruise cyber-space and find all this other stuff that either isn't in the manual, or isn't quite the way I read the manual. Whatever. I am good on changing the coolant every year, it's not that big of a deal. But why use long life yada yada instead of the readily available NAPA stuff that meets all the manufacturers specifications? If it is being changed every year, what is the downside?

 

[Ray H]

If the NAPA brew drains without cloudiness, scale, or an insoluble, semi-liquid, silicate glop after your owner manual's recommended coolant change interval, there's no downside to its use. Correct me if I'm wrong, but I suspect your Cummins engine specifies an extended coolant changeout predicated on the basis of using an SCA (supplemental coolant additive) periodically to replenish the anticorrosion properties and pH balance of the coolant to extend its working life. (ethylene glycol doesn't "wear" out, but the corrosion protection additives in antifreeze do) The same technique would very likely provide maintenance economy without compromising the reliability of the Toyota engine. But, there could be claim-deniability issues if that engine is still under warranty, though.