Two questions

[Danr55]

If I recall my physics, more viscous fluids are harder to heat up initially, but will retain more heat, longer than less viscous fluids.

[Car Nut]

Any difference in temperature between 5-20 and 5-30 should be miniscule. If you really have a difference of 20 degrees, then you have a different issue than the difference in viscosity.

It ain't the oil.

[vettestr]

Skully,
Now that you have about 6K miles under your belt with her, now is a good time for a general check up. A thorough shake down would include checking bolts for proper torque, check all fluid levels and a good performance tune. If injected with ECM control then you are limited on what or how you can make changes. The clutch cable is already dealt with.

I like a 180* T-stat but something as simple as a bad radiator cap could cause her to run a bit hotter. A performance tune would find optimum ignition timing, verify timing tab/pointer and check or set air fuel ratios and more. Some of these issues can make engine run a little hot although I doubt oil viscosity would add 20 plus * to average run temp. Jeff C