This article pertains to the Vanagon water-boxer engine platform.
I have had an oil temperature gauge in every Vanagon I've owned, and I have always noticed that the water-boxer engine design runs at surprisingly high oil temperatures—higher than you would expect for a water-cooled engine. I have seen oil temperatures as high as 285°F. So, what’s the deal? The reason has to do with the combustion chamber design employed in the water-boxer.
About 95% of the heat generated by an engine comes from the combustion process—the rest comes from friction. The oil in a water-boxer gets most of its heat directly from the bottom of the piston and lower half of the cylinder. The combustion chamber design in a water-boxer is mostly in the crown of the piston, not the cylinder head. This has been the trend in the internal combustion engine technology for the last 30 years or so. I don’t know all of the reasons for this, but one obvious result is higher oil temperatures. A lot of the heat from the combustion chamber ends up being absorbed by the oil—much more than would be the case in a flat-top piston. This is because there is much more surface area on the crown of the piston through which heat can be transmitted.
All GoWesty rebuilt water-boxer engines are fitted with Porsche piston-cooling oil jets, commonly referred to as “piston squirters." Porsche introduced this idea way back in the early '60s with the very first Porsche 911 oil-cooled engines. They are designed to keep the piston cooler by transferring some of the heat from the piston to the oil. Piston squirters are commonly used today on turbo-charged engines. Since our engines have these, too, and are larger displacement and run higher compression ratios, you would expect our engines to run way higher oil temperatures. But the thing is—even the original, standard displacement engines run very high oil temperatures.
To get oil temperatures up in the 260°F+ range, one has to push the engine quite hard. Even when I was running a stock engine in my first Vanagon, I had an oil temperature gauge in it (because, well, I am a geek about these things). It was common to see oil temperatures in the 260°F+ range. Over the years, as we developed our engine program, I switched to a 2.4, then to a 2.5, then a 2.6, and am now running a 2.7 liter water-boxer. I get similar numbers under similar conditions, not way higher like one might imagine.
I use the oil temperature as a true measure of how stressed the engine is, and I have backed off when I was far from home—just to play it safe. It is typically on the way back from a long trip, or anytime I am within 100 miles from home. that I really push it to see if I can break the engine—because, well, I'm a geek about mechanical stuff, and I want to see broken parts. The good news is that I have tried really hard to break every water-boxer I've ever had, and so far—no matter how hot the oil has gotten—I have not been successful. Dammit, I always make it home!
So, should you run out and get an oil temperature gauge? Probably not. You don't have much control over your engine oil temperature, and it will probably just worry your passenger. But should you use the absolute best, full synthetic engine oil you can buy? You bet—you can skimp on the seat covers, but not on the oil!
S. Lucas Valdes
President/CEO, GoWesty Camper Products