VFR 800 2002 Strange Heat problem

Hi,

since a long time I have had a strange heat problem with my VFR 800 20002.

When driving, the engine warms normally up to about 105°C and*:

1. Sometimes the fan starts and the temperature goes down (normal)
2. Sometimes the fan starts and the temperature keeps rising (problem).
3. Sometimes the fan doesn't start and the temperature keeps rising (problem).
4. When the fan does start, it often only has a weak effect to lower the temperature (problem).

If the engine keeps heating, it goes up until about 118°C and then the cooling liquid flows out of the overflow flask an on the street.
Then I have to stop and full up on liquid which I have started to take with me everywhere I go.

The problems eventually led to a dead thermostat, which I replaced, but the problems persisted.

What I have noticed:

If I do have problems and look at the radiator reserve flask when I have stopped, the liquid is very high in the flask.

The problem is caused by frequent rewing of the engine.
For example in slow trafic, frequent breaking and accelerating causes the problem to appear.
The cooling system works normally if I'm driving at constant speed on the highway

I suspect that air is forming inside the cooling system causing either the thermosensor to not be submerged and/or disrupting the normal flow of cooling liquid.

I have three theories about the cause*:

1. There is a badly tightened hose clamp somewhere on one of the cooling liquid hoses.
2. I am using the wrong cooling liquid (is that even possible?)
3. The radiator cap is tired and untight and is letting in air.

Any other ideas*?

 

Get a new cap easiest and fastest first remedy. Cooling systems must maintain pressure to raise boiling point of coolant mixture. Air is not getting in but coolant is boiling off. No harm in checking all hose & clamps for leaks or cracks.

 

I was going to suggest the cap too.

 

I know your bike is only 14 years old, but I've seen water pump impellers go bad at that age.

If your water pump impeller is badly corroded it can cause cavitation. By design the normal flow of coolant through the water pump is orderly and uniform, but with a corroded impeller it becomes turbulent. This would introduce the air bubbles that you suspect are causing the odd, intermittent, RPM-sensitive cooling problems.

So there's a moment (a set of parameters) where the impeller cavitation occurs and this introduces a stream of tiny bubbles into the coolant. These tiny bubbles expand when they pass through the hot engine passages, increasing the overall volume of the coolant, causing venting into the overflow bottle.

Repeatedly passing through the parameters at which this phenomena occurs will have the effect of turning your coolant into a foamy mess instead of a uniform liquid. A foamy mess doesn't have the cooling properties/ability of a uniform liquid.

It would also explain the expansion of the coolant volume you're experiencing, which is what is forcing coolant out of your radiator and into the overflow bottle.

 

Or...

It could be something completely different (but similar in result): It could be that there's a tiny air leak into your cooling system. This tiny air leak only occurs when you hit the gas and rev the engine up. When you do this the water pump impeller suddenly accelerates and pulls hard on the coolant coming in through its inbound line. It may be that there's a little spot underneath one of your coolant system clamps that isn't up to the task of keeping your system sealed when the water pump pulls extra hard on the coolant during engine accelerations.

 

Might also need to burp air from the system . Air in the system can cause havioc. As mentioned, start with a new cap and checking hose connections. If fan is intermitent, might be the relay switch. I have a manual switch also for in town riding.

 

It is not uncommon for the the overflow bottle to have an elevated level after it has been in a high temp situation. It is also not uncommon for the temp to continue rising once the fan starts operating., certain conditions, like those you mentioned, sometimes overwhelm the fans capability to cool the radiator. If everything is functioning properly, as the engine cools back down, it will siphon the fluid back into the radiator, however, it isn't common to have the catch bottle overflow. I would check the cap, check that the rad fan switch is fucntioing properly and that a good ground is created when the switch engages.

Don't overthink it, start with the basics and know that you are dealing with a machine that doesn't do well in warm weather combined with traffic. Stop and go traffic is not something these bikes like a whole lot.

 

Hi,

thank for all the answers everyone, there are a lot of useful tips here.

Bofore I order a new radiator cap I would like to add two observations to the list of things I have noticed.

5) In cases where the fan doesn't start and the engine keeps heating. If I turn the ignition key to off, so the engine stops, then back to "on", the fan starts immediately.

6) Even when the fan does start and the engien is at ~105°C, the left-side radiator is cold to the touch. I can put a finger through the grill and touch the radiator and it is cold to the touch.


Any comments would be most appreciated.