The radiator looks full. When I am in gear, the gauge is normal, below middle. When I idle or coast, the gauge goes up to 3/4. It never did this before. My fan now keeps running after I shut ignition. I didn’t really think about this until I had to replace a battery. One more symptom. When I put the heat on, it takes a few minutes to warm up.
Is it a stuck/broken thermostat? Do I need a flush?
Is the fan running when the engine is idling and the gauge is reading 3/4?
If so, it could be a thermostat that’s not fully opening, or maybe a partially blocked-up radiator.
“My fan now keeps running after I shut ignition. I didn’t really think about this until I had to replace a battery.”
Probably a bad fan control module.
I thought about this. But my car, like others, apparently allows the electric fans to continue running even if the engine is shutdown if the temperature is too high.
My '88 Accord did this too, but the OP implied the fans ran until the battery was run down and ruined.
Does the fan have one or two speeds? If the latter, does it run at high and low speed?