I share this because many GL1800 bikes/trikes have experienced increased temperatures.
I bought my trike in 2005. Put a belly pan on it in 2006 before a cross country ride.
I have had to put up with increased temperatures ever since 2006. I NEVER thought it could be from the belly pan.
In 2008 my mechanic (hubby) flushed the system twice. Took everything possible apart and checked for what people have said to check for - nothing.
Before going into reversing the fans I had the louvered belly pan installed.
While the "high heat" problem has not been totally resolved it has been improved to the point that I can ride at high speeds, even going up hill, without the gauge heading to the red line.
So - for MY trike the original belly pan CAUSED the excessive heat problem. The louvered belly pan has resolved the excessive heat problem.
Will I have my hubby reverse the fans? Probably. This machine should not run any hotter than his 2-wheels.