2003 Vfr800, Cooling Problem

Hello all,

For the past few months my vfr's cooling system has been acting a bit crazy, so I performed the following:

1. Radiators cleaned.

2. Cooling system flushed and cleaned.

3. Thermoswitch replaced.

Additional info - Engine is great, no valve adjustment needed (but checked), new plugs (the right ones of course), KN air filter is periodically cleaned, What can I say - mechanically the bike is just fine.

So whats the problem?

Well:

Previously: fan would switch on at 107© and off at 98 like clockwork.

Now: fan starts at 108-109 and off at:

1. when bike is at a minimal speed and up - fan goes off at 98.

2. when bike is almost static (traffic light, traffic jam etc) it simply goes down to about 102-100 and stays there - the fan continues to work and is unable to lower the temp.

Another problem is (I don't know if its related) - when I ride the bike in the morning, the idle revs are naturally high. When getting to work (15 KM, average speed of 100 KM/H), the engine has warmed up (of course). So why are the idle revs still high? - 2000/2500 (depends on the temp. 2000 is when the air temp is about 15©).

I don't remember this as the usual behavior of the cooling system - am I wrong? I recall some time ago that no matter what - the cooling system would reach 98© and the idle revs after a short ride would drop to 1300.

What could the problems be?

Yours truly,

Mr. frustrated.

Haven't done this work myself, but have read that the most common problem after a flush/change of coolant is residual air pocket. Look up maintenance threads on coolant flush and see if there are some tricks to getting out that last bit of air. Most seem to think they have no air, but end up finding that there was some remaining.

My thermoswitch is non-functional. Can you tell me, is the thread on it 16mm with 1.5mm threadpitch? The reason I ask is that a Honda switch is unavailable here, so I'd have to order one from overseas, or I can buy a non-Honda one as several are available in various on/off temperature points. I' don't want to have to take the old one out until I've bought a replacement.

HS has a thread as well as myself that shows how to install a manual fan switch that will get you by until you can get a new thermo switch. I think I have a good one in my parts box if you need it. Not sure what shipping would be but let me know if I can help.

Sent from my crazy hand held thingy using Tapatalk 2

If you have too much anti-freeze vs. water, the cooling capability goes down considerably. Anti-freeze is not a good coolant unto itself.

Suspect air in the system, as in NOT enough coolant. When bike is COLD ! Remove right fairing panel, place bike on side stand, remover radiator cap, check coolant level, should be right up to the top. If not, ignore for now. Start engine, DO NOT rev it, be aware that coolant may splash out of radiator cap. Look at the coolant through the cap hole, there should be very little flow, as the thermostat is recycling the coolant until bike warms up.

Leave bike to warm up slowly & watch for thermostat opening, signalled by coolant volume increasing out of the top hose above right rad. When this happens, stop bike & add coolant to bring it near the top of the top hose. Start bike, watch coolant for a minute, then stop again, what has happened to the level ? Keep stopping/toping up/starting until fluid level wants to overflow. Stop engine, top up to the brim, then replace rad cap.

Start bike & whilst waiting for it to reach full working temperature, rev the engine, intermittently but hard, as in up to 10K rpm. Watch temp on dash & check fan operates at the temp you expect, if not allow to cool.

Remember you can't remove the rad cap from a HOT/Warm engine, it will squirt BOILING coolant at you !

When cool remove rad cap carefully & check coolant level, top up & repeat steps above.

Filling on the sidestand is the only way to ensure there is coolant at the top of the left rad, otherwise there is a definate air gap pocket there which is where the fan switch is.

The VFR does NOT have a head hose in the cooling system & its possible when filling on the main stand for an air pocket to form in the cylinder head area. Rapid fluxtuations in coolant flow when on the sidestand will purge these.

That should cure your problem.

huntinggunns

HS has a thread as well as myself that shows how to install a manual fan switch that will get you by until you can get a new thermo switch. I think I have a good one in my parts box if you need it. Not sure what shipping would be but let me know if I can help.

Thanks for the help and your kind offer, but I've had a manual switch fitted for ages. There's just the odd time when I forget to use it, and end up with a very hot bike. A few times I've ended up with a puddle of coolant on the ground under the bike, which is weird because a very good bike mechanic serviced it 5 or 6 months ago. Some time afterwards when I was testing to see if the thermoswitch was working, the temp got up to around 110C, and I ended up with a very large amount of coolant spit onto the garage floor.

Since then I've also done the "topping up on the sidestand" thing, and last weekend topped it up again, and ran it for ages with the fan on, and even with lots of revving the temperature never got above the mid 80s.

So... I have no idea what condition the cooling system is in with respect to the pump, radiator cap, thermostat, etc. It's done 61,000 miles, and apart from a few coolant changes, I'ts had no work done on it. I'm thinking I'll fit a lower temperature thermoswitch (say 95-85 C) as most of my riding these days is commuting, where due to the entrained air column when sitting in a stream of cars, there's actually very little air movement through the radiators. Then if it behaves OK, I'll leave it alone. If I get any more coolant puking, I guess I need to look at a new radiator cap and pump overhaul?

I was actually going to buy all the parts on ServiceHonda, but they didn't have the pump parts under "water pump" in the catalog!

OK, thanx for the help :unsure: I ended up just diving in and taking things apart to see what was going on. To answer my own question, the thermo fan switch is 16mm with 1.5mm thread. It also doesn't have a long 'snout' into the radiator as appears on the parts diagram; it's very short (only about the length of the threaded bit) and there's only space for one about 15-20mm longer than that.

The waterpump seems fine, so instead of ordering a NZ$85 Honda fan switch (and waiting maybe a month or more for it), I'm going head out to the autoparts store armed with the numbers from four car ones and see what they've got and how much. (I'm also aiming for a 95C-85C model).

enzed_viffera

huntinggunns

Some time afterwards when I was testing to see if the thermoswitch was working, the temp got up to around 110C, and I ended up with a very large amount of coolant spit onto the garage floor.

If you are getting coolant out of the expansion tank, then the rad cap is faulty. The coolant tank should be filled to the MINIMUM mark when the bike is cold, when fully hot the level in the tank should NOT exceed the Maximum line. So buy a new rad cap, or clean the one you have carefully & ensure that the spring acts as it should & that the lips that hold it on are NOT bent outwards. Try seating the cap 180 degrees out of sync with how you normally put it on, I've seen this work before.

You know the pump works, as on the stand you should see the water come out of the top hose. Another thing to check is the expansion hose from the rad cap to the expansion bottle, this needs to be air/water tight, as the expelled fluid has to flow down it to the expansion bottle & then get sucked back up it when the bike cools down. If there is a leak anywhere in the system, then it will suck air in, which expands when heated & displaces coolant out of the system into the expansion tank.

For the fan swithc, I replaced mine with I think it was a Nissan Sunny one, kicks in at 90c & stops at 75c by design, in the real world, it comes on at an indicated 92c & off at 78c which is perfect. With my additional right side fan, it does not run for long & keeps the engine nice & cool.

After you install the cap check to see if u can move the cap. In other words take your fingers and try to move the cap up, dont turn it but see if the cap is lock in place, Mohawk right this a common problem with these size caps .

Oh just remembered, the only other thing that cuases fluid expulsion is a blown head gasket allowing combustion gases into the fluid circuit ! Highly unlikely but just so you know.

and you have a trail steam following you also. Its a crack head that pressurizes the cooling system,, I think .

Hi guys,

A little update. I noticed a leak in the radiators, causing of course a decrease in the coolant level.

Soon I will replace the old with new ones.

Will report back of course.

Just to add that your automatic choke (higher idle when cold) that later doesn't drop down to normal idle RPM is also related to having air in the system, as it is triggered by the coolant running through a device known as the "wax unit"... if there is an air pockt trapped in this area it will also malfunction.

OK. Its been a while but I have an update.

I've replaced the radiators and the cooling system works PERFECTLY!

Thanks for your help.