Some designs keep operating temperatures at a quite moderate level too.
Sorry to bump, but I think it’s warranted.
I’ve recently acquired an OBD-Link MX+ and was able to glean some insight into the car’s coolant temps, which stubbornly resist rising above 175F, with 172F being the steady state indicated temp on the hwy.
Keep in mind, that’s with a “wet exhaust manifold” design that would put much more exhaust heat into the coolant
I also recently came across a technical promotion video Honda did for the 2018 Accord with this engine, and it specifically highlight how they had paid attention to effective engine cooling.
Anecdotally, the engine runs cool. I come home from work and the lack of heat radiating off the car is pretty remarkable. With the insight of the actual OBD data, I now have evidence to back up the anecdote.
Finally, the teardown video circulating from “I do Cars” showing the incredibly clean inside of the 94k mile example of the engine also suggests that the engine runs cool enough to prevent major deposit issues, although we do not know what oil was used in that torn down engine, it seems unlikely it was HPL or VRP.
All that said, I think that a 5w40 would be unwarranted here because of the lower operating temps. I hope to get an oil pressure and temp gauge setup at some point. But oil temps generally run about 30F hotter than coolant temps, so if I’m sitting at 200F-210F oil temps, then stepping up to 30 grade no VII HPL seems like it would be sufficient a HTHS increase.
It also has me thinking that a thicker 20 grade at temp in this engine is likely more real world viscosity than a lighter 30 grade might be in another engine.
So, to cap this thread’s OP question: the lower temps suggest a 40 grade is unwarranted for daily use (thought potentially still acceptable). A good quality 30 grade should be quite sufficient.