I've been running a "window screen" on my truck for 27,000 miles. Several thousand have been towing. Always have a few degrees variation empty or towing. Never over 200 and mostly aroung 190. Temperature variation is most noticeable during altitude changes. And don't start worrying until the gauge is climbing past 240.
It's much easier to shake those BUGgers lose from the "window screen" than it is to try and pry them out of the fins.
It's much easier to shake those BUGgers lose from the "window screen" than it is to try and pry them out of the fins.