@Gordon Nichols posted:
Jeff, Somewhere on here in the distant archives, I had been running 20w-50 oil and did a quick run to Fall River from Tiverton, RI. Blasted back into the driveway and checked the oil temp with a dipstick thermometer.
Then I did a quick oil and filter change but used 10W-40 and re-traced my route and speeds (mixed highway and back roads, all at sea level or close to it, same ambient temp both runs).
That was back around 2006 or 7 so it’s getting foggy (I’m sure the posts are still buried on here somewhere) but IIRC, it ran 5°-10° cooler just with the lighter oil. I have no oil pressure gauge but it had a Melling 30mm oil pump back then so I never worried about it.
Been running 10W-40 year round ever since.
There’s a good explanation of this in the Samba mega oil thread. The thicker oil doesn’t travel though the engine as fast as the thinner oil does and, being more dense, doesn’t transfer heat In the (OEM) oil cooler as well. Or something like that. I bought it
But if you’re running an external oil cooler with a proper thermostat it shouldn’t much matter. I’d assume those temps you noted were oil coming out of the engine? (Stock sender location?)
This is one reason I decided to stick to VWs recommendation from BITD and run straight 40W in the summer.