Here’s a good post from a few months ago. I like what the poster says about his temp gauge readings:
[ATTACH=full]1716087589[/ATTACH]
The Original Partstitute
One more thing I rarely see mentioned: The thermostat itself. This is a factory air-cleaner decal from a '70s CB300:
It was made by Robertshaw for Chrysler. The design of the stat was so important ("WILL" rather than "MAY" CAUSE OVERHEATING) they included a drawing of what it should look like. It's no longer available new anywhere; NOS is the only option. Sounds terrible, but several other vendors sold the Robertshaw unit under their own names and part numbers (Purolator, Atlas, even CarQeest at one point) so they're still out there. Cross-references are only good if the stat looks like the diagram above.
Does it make a difference? With dramatically increased flow, it certainly should. My '69 Valiant has a 10.x:1 340 w/painted headers, a shroudless thermal 5-blade clutch fan and a cheap 22" Chinesium/aluminum radiator. The VDO mechanical gauge stays at 180° like the needle's welded in place with ambient temps above well over 90°. The factory dash gauge is similarly steady (both gauges work simultaneously) and I've verified with an IR heat gun. I can't swear it's the 'stat, but when the ambient air is 98°, the car's motionless and running, and the needle stays planted like that, I'm not trying something else.
