Honda vfr750f 1996 4th gen overheating

Engine keeps overheating when idling, temperature goes higher than 230. I’ve changed the thermal switch which now kicks at 190 ( used to be at 210) i’m using engine ice coolant. When im riding the temperature at 190+- but when i stop at the traffic light it can go up to 220 and higher. Do i need an extra fan or it could be the blown head gasket? not sure if the thermostat is working normally either. Any advices please ?


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could be a bad radiator cap that wont hold pressure, first thing to try, replace it, and keep colant level up.

 

A simple thermostat check is to start the cold bike and keep a hand on the radiator. A working thermostat keeps the coolant circulating in the engine until you reach about 172F, then the thermostat opens and allows the coolant to head to the radiator. So a radiator that stays cold for a few minutes and then quickly gets hot shows the thermostat is OK. On the other hand if the radiator slowly and steadily heats up, you have a stuck thermostat that needs to be replaced.

Squirrelman's suggestion about the radiator cap is sound but would also have a symptom of coughing coolant out of the reservoir when hot. If the cap can't hold pressure then the coolant will boil into steam at a lower than desirable temperature and the steam will burp coolant out of the reservoir.

When you have the cap off it would pay to run the engine and verify that you can see some flow happening in there too.

Are your radiator fins full of dead flies and not allowing air to pass through?

I have faith in Honda's designs and a correctly functioning VFR should not need any help with cooling beyond the standard parts. Your cooling system is designed to start to cycle the fan on/off around 212F. When idling do you hear the fan start/stop?

One last question...AFAIK the 4th gen has an analog temperature gauge; how do you know the temperatures are what you have reported?

 

My 1995 VFR, that has had the complete cooling system gone thru, is the coolest running VFR I have ever ridden. So much so I took it apart again cuz I thought the thermostat might be sticking partially open. Nope. I replaced it anyway. Exactly the same.

 

You say "the", not "a".

Is your head gasket blown?

 

what have you done exactly when you said complete system redone ? water pump, thermostat, cleaning radiator ?


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yeah, could be the thermostat, cause the radiator is getting warm pretty quickly. Radiator is clean, i’ve done a full coolant change, new oem radiator cap. About the last question, last owner put a koso universal speedometer and it shows me the temperature, not sure if he put any other sensors in there


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also i noticed when im filling radiator and after starting it coolant rises really quickly. There no boiling, no white smoke when the exhaust and my oil is clean too. Could be some air there after coolant change


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Water pump removed, verified clean, not leaking. All cooling system o-rings on engine replaced. Hoses verified good and all spigots cleaned / restored. Thermostat verified good. And then subsequently replaced anyway. Radiator flushed, all fins straightened. Light coat of matte engine paint. Fan / (original) thermoswitch verified operational. Valvoline Green Coolant. New 1.1 Honda rad cap.

 

As I'm filling, I will squeeze the two radiator hoses a bit. The system bubbles and the level drops. I repeat until it no longer does it. Temp cycle the system up to the fan kicking on and off. Cool down, check / add rad level. Final fill to lower line on coolant res tank.

 

Exactly my process, minus the bitchin looking fins on the Radiator

 

oh wow, you did a great job. Thank you for your help, i’ll try to do that too myself, i appreciate it


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yeah i’ve done that already


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