3Rd Gen Overheating ?

[Guest sleeping@65]

I have a 1991 VFR with close to 100K on it, and it has been a great bike. With that said, lately it has been overheating on 80 degree F. + days in traffic. It usually happens after 20 minutes of riding at 55-60mph. Once I start hitting lights at the end of my commute, the needle goes very high almost to the red and the bike seems hot (feels hot and starts shifting poorly).

* I have checked the thermostatic switch located in the radiator and it seems to be working properly. The fan cycles just like it should.

* Cooling system is extremely clean so I don't think there's a clog anywhere. This bike has been maintained well.

* I have changed the thermostat as I suspected it was stuck. New thermostat didn't change anything.

* I have triple checked the radiator cap and yes... it is fully tightened.

The odd part is that I can see a temperature drop as I give it some throttle. The lower the RPM, the hotter she gets. So, my next thought is an internally damaged water pump? Another VFR enthusiast thought it may be electrical, but everything electrical seems to be as it should.

The only other far fetched idea I have is that the bike is going too lean while I'm riding it. (I know the carb boots are old and hard and need replaced), but I just couldn't decide if this could be a possible cause. I'm tired of chasing my tail and I want my baby back Any ideas?

[taglicious]

valve chatter at all? it's hard to determine sound but possibly by these points...hesitation, sometimes hard to keep idling, possibly when it gets warmer(the engine) it runs funny? I'm 20 miles from hitting 200k on my O.G. '90 and as she's never needed an adjustment, I may be actually doing one... finally. ;)

[gll429]

aaaaaaaannnnd you have a normal vfr750.. welcome to the club.

do this and be done..

[Headrush]

It's a mechanical driven pump so it can't go weak unless the internals start falling to pieces. It runs in series with the oil pump which may run faster (not sure without checking) with higher engine revs giving more pressure. If this is the case it would explain better cooling at higher revs, so I'm thinking you may have some resistance somewhere, blocked radiator maybe?

I'm a plumber btw, so just my fuzzy logic :)

[Guest]

aaaaaaaannnnd you have a normal vfr750.. welcome to the club.

do this and be done..

I could do this, but it just seems odd to me that I have ridden this bike so many miles and it just started doing it after about 90K or so. There's got to be a reason behind it. And yes, a blockage would surely do it, but my entire cooling system looks pristine inside. No signs of calcification or scale buildup or anything anywhere. And my fan comes on just fine, but she still gets hot. So for those of you who add this switch, do you just keep the fan engaged longer than what the radiator fan switch would on it's own?

[gll429]

hhmm you said you replaced the thermostat? as in the one with the spring and plunger? or just the electrical switch?

[Switchblade]

Radiator clogged or Water Pump .

[Guest]

hhmm you said you replaced the thermostat? as in the one with the spring and plunger? or just the electrical switch?

Yes, I replaced the thermostat (spring and plunger). No change

[gll429]

in that case..

drain the coolant and remove your pump.

its rare... but possible that the shaft broke one way or another and is not turning the pump.

[Switchblade]

I thought one of the vanes on the water pump mite have snap off .

[V4 Rosso]

Have you checked the charging system?

[Guest]

in that case..

drain the coolant and remove your pump.

its rare... but possible that the shaft broke one way or another and is not turning the pump.

That will be my next move. I will let you all know how it goes. I probably won't get around to it for at least a week as I am busy with school and such, but I hope you're right so I can have an answer to this. It's driving me nuts! Thanks.

[taglicious]

Looking fir an update... you still sleeping? ;-)

[Guest]

Well, I haven't updated simply because I am confused. After I replaced the thermostat it overheated once or twice, then it seems to have disappeared. I'm not sure if it's gone just because the outside temp has been mild (below 85 F) or if I just had an air bubble in the system somewhere. I'm glad it's no longer overheating, but I guess I'll have to wait until next summer to put it to the ultimate test once again. For now... my VFR and I are all good !!!

- John

[erbilabuc]

overheating was confirmed by temp gauge or by coolant overflow?

[Guest]

temp gauge was almost pegged, transmission became clunky and she actually died on me one time and I had to let it cool down for 20 min.

[erbilabuc]

if there was nothing going to overflow then your coolant was probably low. The overflow is supposed to have coolant in it so when the system gets hot and expels/expands it creates a vacuum in the cooling system and then is able to pull what is in the reservoir back. I think you had an air bubble from low coolant for some time and eventually it built up. I lived in the Mojave desert for almost 9 years so I got to get a lot of experience with the cooling system of vehicles every year.