Nearly 50 years of playing with these 235 and 261 motors and I have never run oil that thick. All of these motors leak a little. But proper oil flow is both a cushion between the journals and the bearings, valve tips, gears, other parts, but also acts as a coolant. So the idea is to have oil flow through the bearings. I run my 235 and 261 motors really hard. Harder than most. I just won the street tire drag class at the Trifive Nationals in Bowling Green Kentucky this past August in a trifive powered by a 261. First time an inline has run in the actual competition and first time ever for an inline to with a class. I zinged the 261 pretty good, up to 5800 rpm. I run 10W30 Penn Grade 1 (the former Brad Penn, which is itself the former Kendal 1 oil from back in the day). Before the oil formulations changed and eliminated the ZDDP I need for my cams, I rang Quaker State and Pennzoil, also 10W30. If I am working on an older motor, I might go 10W40 if I think the bearings are worn enough to need the slightly thicker oil.
Others run the heaver weight oils, straight weights, full synthetics, or the Rotella diesel oil and swear by the stuff. I have been racing and being hard on 235s and 261s for most of my life. And truth be told, I have not had any oil related issues so I tend to stick with what works.
But that is just me.
Last edited by Dragsix; 11/13/2025 12:19 AM.
