So went for a ride on the weekend and the bike's overheating like mad.

Started investigating the problem and reckon the thermostat needs changing, but noticed the lower radiator was looking quite mucky. Whilst attempting to clean it up, it appears the fins are mostly crumbling away - which leads to my question...

Will a lack of fins cause a big problem (the rad still holds water without any leaks)?

Yes,The fins need to be straight and in good order so that air can pass through,
If the air cannot pass through it will not cool the water in the rad.

barneyho wrote:So went for a ride on the weekend and the bike's overheating like mad.

Please be more specific.

Is this when stopped in trafic or when riding?

What is overheating like mad? Is coolant comingout the pressure vent into the expansion bottle? (bubbling over?) Is the temp needle in the red?

The fins flaking off aren't the end of the world. What really hurts is when the rad gets blocked up with road crap as the air cannot pass through it. I'd take the bottom rad off and give it a really good clean. Get rid off all the crap stuck between the remaining fins and get rid of any fins that are starting to flake off. Also, test the fan to make sure it is working. At one point in the life of my bike, the bottom rad had vast amounts of missing fins, but as long as it was clean and the remaining ones were straight, the cooling was fine.

Generally, the stats seem to fail in the open position, rather than closed, but there will always be an exception to the rule. Clean the bottom rad and see how the bike responds to that first.

@ Neosophist - it was when I was riding. The temperature gauge was reading very close to the red marker and coolant has made it way through into the expansion tank.

I've since removed the lower radiator and the thing was a mess. Blocked/bent fins that crumble at the touch. Tested the fan (grounded the fan switch wire) and it works but didn't notice it coming on when the bike was over heating the other weekend. Could this be because the earth connection on the lower radiator is badly corroded or simply a sign the fan switch needs replacing?

Managed to find a reconditioned replacement which I'll fit this weekend and see if it still over heats. If it does, i'll change the thermostat.

p.s. thank you Hunter and Speedy for your replies too.

Right, changed the lower radiator for the reconditioned one and it appears to have made an improvement. Checked the thermostat and fan - both working fine, but the bike still seems to run quite hot. The temperature gauge needle sits around half way when on the motorway and as soon as I come off onto rural roads it creeps up to the 3/4 mark.

Shouldn't the temperature gauge sit at the 90 marker? or is this quite normal for nc30's?

I'm sure this is a silly question but... can you use a stronger mixture of antifreeze to keep the overall temperature at a lower level.