High temp light coming on, but only after riding over an hour during highway speeds or around town.

[1983lux]

Hey all,

I've been having some trouble with a 2003 RSV I bought recently.  80,000 km's on it. The symptom is the red light coming on saying it's overheating, it will often come on and off for a few minutes at a time.  It never happens on a short ride, say less than 30 minutes.  It only comes on when going highway speed for a long time, 120-130 kmph, often when going uphill.  It sometimes goes off after I get over the hill and let off the throttle a bit, or if I stop for a minute or two.  If I pull off to a side road and go slower (90-100 kmph), it generally goes off and never comes on at that speed.  If I get into town in a start-stop situation, it will come on and off periodically.   Both rad and coolant reservoir are full, and I took my time filling them and burping it periodically/refilling over the course of 48 hours or so. 

So far I have changed the oil and filter (15w-40 rotella T4), rear diff fluid, and did a coolant flush with new blue coolant (for honda, assuming these engines like silicate free and aluminium friendly like my old wing).  however, I didn't drain the waterpump or cylinder plugs, just drained the rad, ran the flush idling for 20 minutes with rad cleaner and water, then refilled. It was doing the same thing with the old coolant it came with, which was green and looking pretty old.  My next step was to change the thermostat, although i'm not sure the symptoms fit.

At this point, I'm thinking it's either that my temp sensor is overly sensitive, and comes on in situations where the bike is apt to heat up a little (like pushing a lot of wind resistance at high speed, or puttering around town), or the cooling system is not working as well as it should, and the bike goes slighly over temp when on highway or idling in town, but quickly can cool off below the critical temp if I slow down (on highway) or get moving (in town).

 

What do you all think?  Thanks!

[1983lux]

Also, forgot to note that the fan works, when bike is hot, it’ll be running if I shut bike off with key still on.

[M61A1MECH]

The bike does have a temp sensor,  that turns the fan on and turns the light on. There is a fairly easy test that can be done with each one, see the tech section for a copy of the repair manual that tells how to test it. I have attached a PDF of the pages from the manual that should help.

Troubleshooting temp sensor.pdf

[1983lux]

Thanks!! Although I think I’ve sorted it.  Took thermostat out and it will not open in boiling water.  I though a stuck closed thermostat would’ve made it overheat faster, but maybe since the engines so exposed to air it takes quite a while