Some thoughts on engine cooling

A fellow who moved to a hotter climate with his Syncro was considering my deluxe auxiliary oil cooler kit because he was concerned about the overall cooling capability of his van.  Here are some thoughts I shared with him:


The Vanagon water cooling system has plenty of excess capacity and if it’s in decent trim it can handle any temp or load condition you could ever subject the engine to. That capacity depends on the heat-shedding component, the radiator. All these vans are at least 27 years old now, but a car radiator has about a 20year service life, it doesn’t matter what car you’re talking about and it’s as dependent on time as it is on mileage (corrosion is occuring whether the engine is running or not, but is accelerated by heat).


So the best advice I can give to a new van owner is if the van has its original radiator, then it’s years overdue for a new one. Or if you simply don’t know, at under $200 for the part it’s fairly cheap insurance to just replace it. Coolant on any water-cooled car should be changed every 3-4 years so swapping it out while the system is drained doesn’t add much to the service cost and then you know you have full capacity and a lot of service life in that critical component.


Oil temp is an almost separate question, though, as oil is heated by engine rpms more than load, so you can have a tip-top water cooling system and still see overly high oil temps during extended high-rpm operation. With the unusually low gearing Vanagons have, high rpms is just a fact of life, but smallish four-cylinder engines are designed to be operated at higher rpms than engines of larger displacement, so running the engine at high rpms for hours isn’t detrimental to the engine, except for the fact that the oil will run at an undesirably high temp. 


Many engines have the same arrangement the 2.1 wbx does, a small oil-to-water heat exchanger (OWHX) that gets called an oil cooler, but cooling the oil isn’t what it’s for. Many manufacturers started to add such things in the late 80’s as US emissions standards became more stringent. Coolant comes to full temp more than twice as fast as oil, and the OWHX is there to pass heat from the fast-warming coolant into the slow-warming oil to get the entire engine warmed up as quickly as possible because that lowers the average emissions profile (engines run deliberately rich and are markedly less fuel efficient at less than full temp). Also, in an engine’s life, most of the actual wear occurs during warmup, so getting to full running temp quicker does extend engine life as well. 


So the OWHX is primarily an emissions control device, with only a marginal ability to limit upper oil temp because the temp differential between hot coolant and hot oil is small, and so is the OWHX, so there isn’t a lot of heat exchange area. So it will allow oil temp to climb quite a bit higher than coolant temp, and the result is lowering oil pressure. This is the main cause of nuisance oil pressure warnings. Just as importantly, though, oil service life is also shortened if it’s run chronically at temps over about 230ºF because the additive package breaks down more quickly (the oil itself never wears out, but 20% of engine oil is chemical additives that fulfill a number of critical functions).


So, to put a lid on peak oil temp, some additional applied cooling is a good idea, and by keeping oil temp under control you can also get the maximum service life from the lubricant, which saves money, time, and precious resources. 

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