Ok, about a year ago I picked up another 65GS (see this posting:
http://65gs.com/board/index.php?topic=1651.msg9411#msg9411) and it tends to run hot (210+) at idle speed and would get down to around 195F - 200F cruising. The motor is a 66 nailhead and according to the previous owner was bored 0.060" over (yea, I know) in 1972. I am running 91 with some percentage of ethanol (that is all I have available). So far I have done the following with temp being monitored with a heat gun and new temp gauge:
1) - Reset timing from 12 advance to stock timing and confirmed that advance time is functioning (along with new plugs and wires) - No Change, although I think the plug wire change made the motor run smoother.
2) - Removed heat riser valve in the pass side exhaust manifold - No Change
3) - Installed a recored 4-core rad, flushed the motor, replaced existing 180F Tsat with a new 180F Tstat, and refilled with 50/50 - No Change
4) - Removed what appeared to be an original 3 blade impeller water pump and installed a new 5 blade (only broke off one bolt), topped with 50/50 - No Change (to my amazement)
5) - Installed a fan shroud and replaced 16" 6-blade flex fan with a new 18" 7-blade Flex-i-Light - Noticeable increase in air flow with rate of temp increase at idle seeming to be slower but still makes it to 210F
6) - Drained some 50/50 and topped with water (I am guessing about 20/80 now) - No Change
7) - Added a bottle of Water Wetter - Rate of temp increase at idle seems to be slower but still makes it to 210F
8) - Advanced initial timing back to 12 and other set points (currently at ~8) and adjusted idle screws (were running lean) - No Change
9) - Took out the Tstat - Significantly slowed the rate of increase (after reaching 180F) but sill reaches 210F. Runs about 165F on the highway in 60F ambient temps.
At this point I can live with the idle condition and want to see what happens when summer in Wyoming finally gets here. If the cruising temp can stay around 170F or higher I will ok for the summer. If not, I will try a high flow Tstat. Based on all the above it seems clear to me that I have an air flow problem at idle and that I probably would not have the problem if the motor was not overbored to 0.060". I am considering converting to electric fans over next winter. Any thoughts or are there other things I need to try? BTW - I have actually enjoyed working through this problem although I have used it as an excuse for not making progress on my restoration.
Dwaine