The tiger is overheating and I can't work out why

I’ve a 2011 Tiger 800 and a few weeks ago the temperature gauge flashed red and complained it was overheating so I pulled over and stopped the engine, and found the fan wasn’t running.

I put a switched live to the fan to keep me going and carried on riding, but the bike kept overheating. So I took the thermostat out and found it wasn’t opening as early as it should, so I removed the middle bit and replaced it, effectively leaving the thermostat always open.

The bike’s still been overheating quicker and quicker though. I’ve just stopped six or seven times in 40 miles, each time it takes about as long sat with the engine off to cool to halfway down the gauge as it does to then get back up to the top once I get going again.

I can’t think what would be causing this - it’s like running nine the engine stops the cooling system working.

I’ve replaced the coolant with fresh water to check there’s no blockage, and it seems to be moving fine - the level in the expansion tank is roughly constant.

Any ideas what I’ve done, and how I might fix it?

Should it be water, or hybrid oat coolant?

Porridge? It’s from the Midlands, not Scotland!

I mean this:$(KGrHqNHJDEE9ow5+j9qBPn-Lh13s!~~60_35.JPG

Wants the oil level like? Is the water pump working? Is the oil pump working?

if you run the bike with the rad cap off, can you see the water in the hole sloshing around?

Yeah, I don’t recall having checked the water actually moves across the radiator, thinking about it, though it does get convincingly hot. I got a puncture in the end so I’ve recovered it back for a more proper look tomorrow now :slight_smile:

It not being full of ‘proper’ coolant shouldn’t stop it cooling, it just means I’ll crack the engine if I leave it out to freeze, and it’ll get a little furry.

Sorry just realised the problem


Possible faulty temp gauge sender unit ,wiring etc …If the fans not kicking in, the temp in reality might not be as high as the gauge suggests…

Try earthing the temp sender body if the housing isnt directly part of the engine as it may be not earthing and giving a false reading .

I’d start by fitting a working thermostat. The thermostat needs to open and close. You’ve prevented the thermostat from closing and therefore the coolant isn’t being held in the radiator long enough for the radiator to have any cooling effect its bound to get hotter and hotter.

Cooling systems are fairly simple, other things to check

Coolant level
System pressure cap
System blockage, remove thermostat and flush through with a garden hose
Radiator blockage, flush through with a garden hose, check for even heat distribution all over the radiator
Temperature sender unit is working, swap it out or test it - multimeter and a Youtube video will show you how

and that is pretty much all there is to it

Hmm the theory behind a thermostat is that it retains the heated water in the engine to maintain a constant temperature
Cold water leaves the rad from the lower pipe into the water pump through the engine where it heated then through the thermostat if the required temperature is reached … generally 87-94c if this isnt reached there are small bypass sections in the coolant systems to allow internal circulation to relieve the pressure … once the water reaches its correct temperature the thermostat opens allowing the hot water to escape into the radiator and into the cooling fins to redo this cycle again and again… if it is removed or stuck open this makes the system run cooler not hotter as it is constantly flowing through the cooling radiator not get hotter if there is a airflow through it ie moving vehicle or rad fan working
… … if thermostat is stuck shut this will cause the temperature to rise quickly as the water cannot flow through the radiator to cool with the airflow .
Triumphs are bitches to bleed the air out of the system a airlock could cause the overheat but considering thermostat was shot it may have fecked the pump . Or vice versa … knackered pump means no flow thermostat stuck in hot hot water it gives up and shuts its mouth

Yes and no. The coolant needs to be held in the cylinder block to reach normal running temperature and held in the radiator to allow cooling and to prevent overheating. On the motorway at a constant cruising speed its likely the engine will run cooler. However, sitting bumper to bumper in city traffic and its likely the engine will overheat. The job of the thermostat is to balance out these two extremes.

Oh dear missing from my list the water pump. Probably the hardest working part of the system and the least likely to fail but fail they can and do.