07 Sprint St 1050 Overheating

Hello,

The title explains the basic problem.

I'm hoping for some suggestions on what to try next - should I give it another go with radiator/cooling system flushing compound?

This is the tale so far.

My 2007 Sprint ST 1050 started overheating at motorway speeds - or shortly after coming off the motorway. I drained the coolant (removing both the RHS radiator bleed bolt and the cylinder jacket drain bolt), took the thermostat out, back flushed and forward flushed the cooling system (including flushing out the header tank). I tested the thermostat in the kitchen - it was okay.

Then I put the thermostat back, refilled with tap water and Wynn's radiator flush fluid, ran the engine up to temperature and for another 10 minutes. While that was going on, the fan cut in, cooled the system, cut out, cut in again, cooled the system, cut out, etc. So the fan was working. I got some splutters out of the header tank vent/overflow pipe - I assumed that was due to the rad flush reacting with limescale or similar.

Drained the water/rad flush out (flakes of limescale came out), removed the thermostat, back flushed and forward flushed the cooling system, flushed out the header tank again, put the thermostat back in. Following the Haynes manual's advice, I refilled with water (deionised, just to be on the safe side), ran the engine up to temperature, then ran it for another ten minutes. The fan cut in as before, did its job as before. Everything seemed fine.

So I drained the cooling system (more flakes of limescale came out), syphoned out whatever was in the header tank, refitted the hose to the water pump and the cylinder cooling jacket drain bolt, then refilled with the Triumph OAT coolant including the header tank. After a bit of shaking the bike around and running the engine, I stopped getting bubbles out of the filler cap (I put the radiator bleed bolt back in at some point). I then ran the engine and it got to up temperature, then hot enough for the fan to cut in. The temperature dropped, the fan cut out. Everything seemed fine.

But now I've got the bodywork back on, the bike overheats at high speed - although not quite as readily as before, and when stationary, the fan can't cool the system down far enough to cut out although it does stop the system overheating. The bike's fine going round town at 20mph, 30mph, 40mph - and 70mph on the motorway - but it shouldn't be overheating at all.

(what was that, officer? The motorway speed limit is 70 mph and I certainly wouldn't ever exceed that by 20mph, not even late at night with light traffic and street lighting)

I suspect another go with rad flush might be worthwhile, since I saw limescale come out when draining after the deionised water run, which I did after the rad flush run.

Is that a good idea, or do I have a more serious problem? I'm feeling decidedly baffled.

I'd appreciate any suggestions or words of wisdom or suchlike.

Thanks (he said, hopefully)

 

Thanks to both of you. I did have a look at the radiator externally and it seemed fine. There was a lot of strange muck which came out when I drained the coolant - chatting to the bloke who did my MOT, it seems likely the initial overheating problem was caused by mixing OAT coolant with "normal" coolant and the draining/backflushing/rad cleaner/ etc should have sorted it.

The good news is I think I've solved the problem. Elsewhere, I got a suggestion to run the engine with the radiator bleed screw loosened (I removed it) until only coolant ran out.

I unscrewed the bleed bolt with the bike on the sidestand so any air would be directed up towards the bleed hole, put it on the centre stand, and started the engine. Coolant ran out almost immediately so I wasn't sure the process had had any effect. Anyway, I put the bleed bolt back in while the engine was still pushing coolant out, checked the coolant header tank, and took it out for a fast ride. That seemed fine, so I put the fairing lowers (etc) back on.

I've done a fast ride since (about 25 miles on the motorway, getting the engine hot first, then some different roads with speed changes and traffic lights) and not been able to get the bike to overheat. Fingers crossed and touch wood and all that, but everything /seems/ back to normal, so that's good.

I'd previously followed the Haynes manual's instructions on getting the air out of the cooling system - it seems it took one more little step.

Thanks for your thoughts.

 

Thanks - I wrote up what solved my problem precisely in the hope that it might help others. I was surprised the simple suggestion worked because I'd already followed the Haynes manual's instructions and everything seemed fine. But there's always something new to learn, isn't there?