also keep in mind it had the oem thermostat which is something like 195*F. If the coolant temp rises a mere 15*F that would probably move the gauge in the cluster some. And a 15*F rise in coolant temperature is an acceptable expected number for a redtop being abused on the highway with an OEM radiator especially.
now, on to the real issue. A 3600-3900rpm cruise is a BAD THING for many engines. That could eat up the rod bearings over time. I am sorry if you disagree but this is a matter of opinion. No I have no personally run a redtop at 3900rpm for 150k miles and proven this; I could be wrong. But why take the chance? I am conservative when it comes to these engines. I want them to last forever. To make sure that happens, I would only run mine at 3000rpm maybe 3200rpm tops. I baby it because I want it to last. I wouldn't even spin it past 5500rpm. If you care about something, don't abuse it, amirite?
That engine was tight and clean. the oil came out looking like it went in. it stayed like that because I took care of it.
