Honda VFR 800 FI Y overheating (not the Thermo)

Well my 12 year old stead decided to dump its coolant out of the expansion tank after hitting 114 before the fan kicked in.

I thought it was the thermo switch and thought to stick it into Chiswick Honda and get it done and checked over before the season.

The guys have now told me they have changed the switch and its still not working correctly.

They should have drained the rads as I topped up the coolant with a different brand to see how much it took and to burp it. To me they should have found a blockage pretty quickly.

I doubt its the pump as I think it runs off the engine and is not a motorised unit?

So now I am wondering what else it could be? Its worked perfectly up to this point, the fan would normally kick in about 105 and come back down.

any ideas?

Also does anyone know how Honda charge for labour? I dont want to be charged for every hour they cannot find the problem. Although I suspect you cant expect them to work for free!


I had a similar problem on my NTV, in fairness all I did was remove the switch and wire it up so the fan was just always on, soon stopped the problem, you could place a switch inline so it’s not on all the time, if I remember correctly, all yuo have to do is pull the wire off the switch and ground it (touch it to frame) and the fan should come on, if it does then the fan is ok and the switch / sensor is knackered, hope this helps.

In the end after a few months, I did plug the switch back in and it was magically working but during that time, I had removed the fairing from the bike…

well they have changed the switch and it has not fixed the issue. I have asked them what else it could be as the pump has an impeller so shouldnt be that.

Guys said it could be a blocked radiator which is £250 + VAT EACH!

The bike is 12 years old and its a great bike but I am loathed to lay that money down. I reckon this must be something I can do myself. The crap thing about living in the bike smoke is I no longer have a garage so could crack on at my own pace.

So bikeless so far:(

Errr, I would test a blocked rad by removing all pipes from it, putting the hose in at the top point of it and see if the water comes out the bottom, leave it running for a bit as it may flush out some ****, if it doesn’t come out then it’s blocked, it will probably come out brown water at first but leave it going until it’s clear and then that should get all the gunk out of it. I’m not a mechanic by any stretches of the imagination but this is what I would try and it would confirm whether it’s blocked or not, you should after a few seconds, see water coming out at the same rate as it’s going in and at least it would clean it out as well.

Also is your temperature gauge rising? Does the bike cut out at any point or does it just keep going and just lets coolant boil out? Also if you check your oil, is there any like what mayo looking substance near the cap at all?

check that the thermostat is actually opening. the fan switch is just that, a switch. it will usuall work, or it wont. if its mounted in the radiator (which i believe it is) it will only operate if the water in the radiator gets hot enough to trigger it. your temperature sender, reads coolant temperature from the motor, not the radiator. if your thermostat isnt opening properly, then hot water from the engine, dosnt make it to the radiator, dosnt set off the fan early enough, and dosnt let cooler water from the radiators reach the engine

sounds like you need to visit the OMC :wink:

Lost the head with Honda last week. This was something they had not looked at yet. They ordered a new one on Friday so should be fitted today tomorrow.

I appreciate my bike is old but this is nearly 10 days in the shop.:doze:


Christ, still on going.

So its not the thermo switch, its not the thermo itself (both replaced) they are now telling me they think its the impeller?! Now correct me if im wrong, but the impeller is a single cast piece of metal so how would it go faulty?

The blades can wear over time with the friction of the water the bearing can also go which is what happened on my dads toyota previa (people carrier) which also uses an impeller pump

Thats true I guess considering its coolant.

Bike only done 25k ish though.

It is 12 years old though.

Pah more waiting.



Some cost cutting c##t of an accountant decided it would be a good idea to change impellers from metal to being made of plastic (affects cars too)

So the impeller fins can somehow degrade and wear out over time. Another good reason to flush out the cooling system with a hose when doing coolant changes, try and get any particles in the system flushed out.

Good point, I assumed it was a metal alloy, if its plastic and considering the size of it, there must be some forces acting against it.