Puzzling issue with overheating and weak battery on 4th gen

Several days ago, while stuck in stop and go traffic in 90+ deg heat, my '96 VFR started overheating. I don't believe the radiator fan kicked on, but I couldn't be sure because there was a lot of traffic noise that would've masked the sound of the fan. Anyway, when the needle finally got to the red zone, I pulled over and stopped the engine. After about 20 minutes I tried starting it but the battery was flat. Got a jump and got to where I was going. Three hours later, the engine started without any problems from the battery. It fired instantly. So anyway, the next day I tested the fan by short-circuiting the fan thermostatic switch lead to ground. The fan worked. Next I removed the switch, immersed it to its threads in a container of coolant which I slowly heated to about 202 deg F, while having it connected to an ohmmeter to test for continuity. The switch didn't close. Maybe I didn't heat up the coolant enough, but at this point, I'm thinking I've got a bad switch. So I bypass it with a toggle switch that'll allow me to turn on the fan manually if I needed to.

Yesterday I was taking the MSF ERC course, and anyone who is familiar with it knows that the bike spends a lot of time idling and running at low speeds. That plus it was close to 100 deg yesterday. This was the perfect situation to replicate the conditions the bike was in when it overheated. Well, the thermostatic switch was working! And I never needed the toggle switch. The battery did go flat again, though.

I don't believe the overheating issue and the dead battery are related as my experience yesterday demonstrated. I think the dead battery was caused by prolonged low speed riding when the charging system wasn't keeping the battery charged. I'm pretty certain when the bike overheated that the fan didn't kick on, and my test of the thermostatic switch seems to suggest that the switch was the culprit. But, yesterday it worked. I'm now left wondering what the root cause of my problem was. Anyone have any suggestions?

 

this may or may not be the thing to do. but on all 3 of my 1st gens i put in a 180deg thermastat and wired the fans to stay on all the time to help keep things cool. i can ride all 3 in 90deg+ heat all day with out overheating and they warm up just fine when its cold.

 

how old is the battery it may just be weak

 

The battery is 18 mths old, and stays on a Battery Tender whenever I'm not riding. Yesterday after I got home and took the seat off to check the battery it felt incredibly hot to the touch. I'm thinking that with the battery being located directly behind the rear cylinder heads and in combination with prolonged low speed running in high ambient temperatures it could've caused the battery to go flat. Or, as you said, it just could be a bad battery to begin with.


Still puzzling over the overheating issue, though.

 

Your R/R is overcharging the battery, causing it to die a quick death. I would check the symptoms listed on countless threads on VFRW regarding this pesky unit.

The starter might also be getting heat soaked and requiring more energy to turn over that when it is cool. Hence, the bike will start when cool when it would not earlier when hot.

If I were you, I'd replace the thermo switch, and investigate a new R/R, and probably a new battery, too.

 

Have you put a voltmeter across the battery and checked the output at idle? If it's a little low it may be pulling the battery down if idling a long time.

IIRC, mine is around 13.2v at idle and goes to 14.5 or so at 3000 rpm.

I don't see a lot of real hot weather here, but I have been stuck in traffic and it will climb to 5/8 or 3/4 scale. The fans runs but really doesn't come down until you get moving, I don't think the water pump is all that efficient at idle.