Coolant Temp/Syn Oil

[yoscirocco at hotmail.com (daniel savatteri)]

So I started using Moble 1 15w50 in my 16v.  My highway cruising coolant 
temp has risen to above the led on the gauge (needle just clears the LED). 
Goes back to normal when sitting still. The strangest thing was that when I 
put the A/C on the coolant temp drops to normal (needle directly on the LED) 
when cruising. This is the same viscosity oil I use in the Castrol GTX which 
I've never had a problem with for years.  I know synthetic oil is slightly 
thinner than reg oil but that shouldn't be the culprit. Coolant level is 
correct and is relatively new, I do need a new battery and am suffering long 
cold starts because of the battery.  I'm stuck, need advice from the 
almighty list. Please Help!

Dan Savatteri
Black MK2 16v

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