CB500 twin - Overheating

[Fire99]

Hi gang,

Bit of a random one to throw out there. I've a 90's CB500 which by and large is normally as reliable as a very reliable watch but recently it's started overheating particularly the faster you ride.

I've checked the thermostat in a saucepan and that seems to open without too much fuss, and I've flushed and refilled the coolant.

Levels seem ok, coolant is still.....coolant colour and there is no emulsion on the oil dipstick.

Bike's done 39k but is 20 years old but I would have been surprised if the headgasket was causing problems on one of these.

Any thoughts?

Cheers much.

[Djtemeka]

could be a bubble in the coolant pipes? try "burping" the pipes. Is the water pump working?

[tr7v8]

Feel the rad, is it evenly warm, could be a clogged rad.

[DuraAce]

Water pump ?

[podman]

tr7v8 said:

Feel the rad, is it evenly warm, could be a clogged rad.

Agreed, doenst sound like you've ever changed the coolant?

Flush the rad/change the coolant , tighten all the clips as you go...if it isnt fixed after that, id be inspecting the header tank on a frequent basis..

Sorry, just re-read your original post...id say its more likley to be the head gasket than the water pump TBH, does it bubble/use any coolant at all?

Edited by podman on Saturday 4th April 19:08

[Rubin215]

When you say overheating, what are your symptoms?

If you're thrashing it, you will expect the temp gauge to go up a bit; this is nothing to worry about as long as it drops back to normal.
If you keep filling the overflow tank up to maximum it will drop water a small amount of liquid out as the engine warms up; this is nothing to worry about as long as it doesn't drop below minimum.
If the temp gauge is going right up into the red and the overflow tank is bubbling over when you ride then dropping to below minimum when the engine cools down, then the engine is properly overheating; you have a problem.

[Fire99]

Hi Guys,

It's had a coolant flush. Level remains pretty constant and doesn't use any or drop in level.

Normally it runs very cool on the temp gauge (a normal habit of this engine apparently) but recently the temp has been climbing even when cruising at say 70mph. The faster you cruise, the higher it climbs up the temperature gauge so there is definitely a problem.

I'm surprised since this engine is allegedly pretty bomb proof at 40k..

[bass gt3]

Fire99 said:

Hi Guys,

It's had a coolant flush. Level remains pretty constant and doesn't use any or drop in level.

Normally it runs very cool on the temp gauge (a normal habit of this engine apparently) but recently the temp has been climbing even when cruising at say 70mph. The faster you cruise, the higher it climbs up the temperature gauge so there is definitely a problem.

I'm surprised since this engine is allegedly pretty bomb proof at 40k..

Is the radiator hot all across it's surface or are there hot/cold spots when the temp gauge is reading hot? If it's not loosing water than the cooling system efficiency is falling.
Either there's a blockage in some of the rad cores or the water pump is failing

[evo8]

I would double check for a kinked pipe and as others have said, check radiator or could be pump failing.

Could you disconnect the rad and shove a garden hose in one side, turn the water on and see what comes out of the other side?

[Rubin215]

Fire99 said:

Hi Guys,

It's had a coolant flush. Level remains pretty constant and doesn't use any or drop in level.

Normally it runs very cool on the temp gauge (a normal habit of this engine apparently) but recently the temp has been climbing even when cruising at say 70mph. The faster you cruise, the higher it climbs up the temperature gauge so there is definitely a problem.

I'm surprised since this engine is allegedly pretty bomb proof at 40k..

But is it actually overheating?

Does the needle end up in the red?

[Fire99]

Rubin215 said:

But is it actually overheating?

Does the needle end up in the red?

To be honest I back right off just before the needle hits the red (to protect the engine) but you can feel it is starting to run a bit rough by then so I'm pretty certain it is running very hot and this is just cruising down as low as 60.

Definitely a million miles higher than its normal operating temperature at those speeds (and higher).

[Benni]

Do you have a chance of changing the temp sensor and the temp gauge ?

Could be that your engine is fine but wrong temp levels are displayed ?

Maybe check temps with a cheap IR gun ?

[Fire99]

Thanks for the input guys.. Well gave the bike a bit of a run to get some heat into it. Got home and with the engine still running and the gauge showing fairly hot, the bottom of the radiator you could rest your finger on and the top of the radiator was lukewarm.

I squeezed the top rad hose and the temperature on the gauge rocketed..

Dead waterpump perhaps?