So I just recently bought my 07. I had an inspection done at mazda before buying it and the coolant light came on on the way there. They did a full inspection and only recommended a flush. I did that but the light comes on, only at highway speeds (80mph). Keep in mind I'm in az so its 100+ out but I've checked the coolant level and it seems ok. Any ideas why the light is coming on? It goes off pretty quick if I toss it in neutral but comes back on after putting it back in gear.

 

"Some vehicles may experience the coolant level warning light comes on even though the correct amount of coolant is in the coolant reserve tank and radiator. The coolant level sensor float in the coolant reserve tank is deteriorated and absorbs coolant. The float gets heavy, and sinks, causing the the coolant level warning light comes on. As a mass-production change, the design of the float has been modified."

1. For VINs JM1FE****** 157838 to 403405
(built on or after July 1, 2005 through JM1 FE**** ** 403405 (built before May 19, 2009), replace the tank only.
http://parts.arlingtonmazda.com/prod...52d351%29.html

2. For VINs JM1FE****** 100000 to 157837
(built before July 1, 2005), replace the tank with sensor.
http://parts.arlingtonmazda.com/prod...2d351G%29.html

 

That makes sense but what about why it only goes on at highway speeds in hot weather?

 

Because it sucks more coolant out of the bottle at times, especially under heavy load situations.
See here........... https://www.rx8club.com/series-i-trouble-shooting-95/coolant-bottle-greatest-secrets-revealed-182793/ but you already got the quick answer from NY.
Please do ome searches next time instead of generating yet another thread that's been made about a billion times. There is a ton of info on this site if one takes the time.