Commander overheating

[Ian]

Chaps, I have a problem with my Commander that puzzles me. I've had it since 1995 and although it has always been ready to run hot I have never had this problem before.I had a water pump fail when the Oldham coupling at the pump shaft end broke. Graham rebuilt the pump for me and supplied the new parts.Fitted the pump and found that it boiled over after some 60 miles. I only managed about 500 miles on it and took the pump off again, to find the Oldham coupling split in two. Graham kindly supplied a new coupling again.Refitted it and now I find that for the first five miles the gauge sits at its usual 85 degrees, then goes up to 105 and as soon as I slow down it boils over.I took off the outer cover of the water pump and found that the impeller will move left and right about 10 degrees easily by hand. When I fitted it there was no slack. It is still connected to the eccentric shaft and spins up fine.I also suspected the thermostat, so I removed it. It is the original, made by Wahle in W Germany, and is marked 82 degrees. I put it in a saucepan, boiled the water and it opened up just fine.So, what else can I look at to find the cause of the overheating? The pump will still be pumping something, the thermostat works, the bike itself is in rude health. I'm running out of ideas, so I'm wondering if there's anything blindingly obvious that I'm missing.Any suggestions extremely welcome!Thanks in advance,Ian W.

[Dell Boy]

My bikes run at 82 degrees. I put this down to running the impeller with virtually nil clearance.If yours is wobbleing about [which it shouldn`t be] it is probably wearing on the pump housing resulting in excessive clearance & reduced pumping effect.I got over 20,000 miles out of my last pump which is good going.Usually fail between 6 to 16 thousand miles.Are there any engineers out there who can come up with a sealed drive train to the impeller that wont collapse due to corrosion as the current design does but will still utilise the existing housing?I will nominate you for a kniighthood if you can. I have replaced about 15 pumps over the years & am sick of doing this chore plus the expense incurred each time.Derek.

[johnbirchjar]

Hi guys, did'nt Richard replace his pump with one from a car?(admitedly it required a fair old bit of modification!)but if one intends to keep ones bike for a number of years it must be worth the effort (seeing as water pumps seem to be one of the few "achilies heels" with water cooled rotaries) J.B.

[Ian]

Couldn't agree more about the coupling. I'm far from an expert but it looks like a classic case of cheapo bodgery to me! The only time this bike has ever let me down on the road has been that coupling's fault!A Blue Peter badge to the man who can fix it.I've replaced six pumps over the years and never had this overheating problem before. I'm going to try it at the weekend without the thermostat but this too is a bit of bodgery.There isn't really a rad cap but you refill through the header tank so it's hard to tell if it's really full. There could be an airlock. Anybody know the coolant capacity and I'll measure it as I fill?Water definitely circulates. When the engine is warm but before boiling the header tank is hot to the touch.The original failure was the pump coupling. This overheating problem has only occurred since refitting the repaired one.Yours, frustrated,Ian

[wust588]

How old is your radiator?Maybe a good time to have the rad overhauled?Is the fan working ok, and spinning in the right direction? Obvious I know, but it should suck, not blow.Is the impeller sitting close to the pump casting, and are the casting vanes in good nick?Perhaps you have an air lock somewhere.The commander cooling is borderline at the best of times, but it shouldn't boil over.Maybe there is a blockage somewhere actually preventing the impeller from turning?ATB.John.

[Richard Negus]

Water can only fill the upper half of the radiator if the bleed pipe allows air to escape into the header tank. I've seen at least one example where a gobbet of loose RTV has found its way along that pipe until it comes to a restriction where it enters the tank. Result is that the rad is only half-full of water and cooling capacity significantly reduced. Is the rad core equally hot all over? Touch the front face with the palm of your hand to check.Is there a piddle of coolant into the header tank when you rev the motor? Hot engine, take the cap off carefully, and look inside as you blip the throttle. If the water level is too high, you should see a disturbance on the water surface.

[Gerald Pleace]

Had the same problem on my Commander recently. It went from running at the normal hot of 90-95 to very hot 110-115.I noticed the top of the radiator was incredibly hot and no return to the header tank. I tried the wire in the hole at the top to no avail. Today I thought I would try a bit harder and removed the pipe at the top and poked through the wire, finding that it was clear once the too high coolant level had settled over the garage floor.I took bike outside and removed the bottom connector for the pipe which drained the header tank completely leaving a thin layer of grey sludge in the bottom.I took my long piece of thin wire and fed it through the copper pipe that runs along the top of the radiator meeting some resistance on the way and wiggled it a bit before removing it and refitting both ends of the pipe.On refilling with a mix of anti freeze and water and starting up, (much banging of the stand to get the solenoid to work, another job to do!) water levels stayed the same with no more rapid rises. Thermosatat opened about 90 and water returning strongly to the header tank from the supply pipe.Test riding brought the temperature to its normal slightly too hot level but no further and restored my faith in the grey beast.Best bike Ive ever had again!Hope this cures your problem too.RegardsGerald