Coolant Expansion

[lorenzo]

After scooting around the track the other day on my K7 GSXR 600 I found it was getting quite warm quite easily and that it lost a bit of coolant at one point after coming in from a session then having a steady (brisk walking pace) ride down to the suspension dude. It had no fan on there, which I've now rectified, and after having a pretty thorough check over it, it seems that it's simply the coolant getting past the radiator cap and into the expansion bottle. This raised 2 questions in my head: Firstly, the cap on the radiator, is it too soft? The bottle starts filling at 104C on the dash, which coincidentally is the temp that the radiator fans comes on. Surely the radiator fan is supposed to come on before it starts boiling over into the bottle, isn't it? Do I have a soft spring on the cap? It says 1.1Bar, but I've no idea how to test the pressure on a spring. I'd have thought that the fan should come on first, 4 or 5degC before the cap gives way, so that it gives the system to cool what's in there down before burping a bit of it out?

Secondly, should the cap allow coolant to get slurped back up into the system? This is what mine's doing, which again, leads me to believe that the cap is duff. It fills the bottle up, from about an inch deep, right to the top, maybe 150ml or so of coolant, then about a minute later, with a noise like the bathplug being pulled out, it goes back down.

Answers on a postcard marked "It's fucked mate, I'll give you a tenner for it" to the usual address. Thanks.

Incidentally, the bike'd been sat for a fair while when I got it, there was a good bit of silt in the system, just pale brown water with some smaller dust sized bits in there, no flakes as such, mild corrosion, I've flushed it out a couple of times, ran a bottle of rad flush through it plus taken off various hoses and flushed them out down the various orifices, the whole thing's running more or less clear now, but I'm still running plain water to get things sussed out before I go and put coolant in there. It did occur to me that it could simply be that I've put a touch too much water back in there, I know my NC30 likes the level to be about 20mm below the cap, I did this more or less to the top, perhaps 6 or 7mm off, but the way the cap started sucking stuff back up had me a bit worried.

[Gobert]

Yes it should refill the radiator from the expansion bottle as the coolant cools down.

Rad cap replacement is the first thing I'd do.

As I've said in the other thread, bleed, bleed and bleed again as these bikes are prone to air pockets which can cause all sorts of trouble.(loads of good bleeding tips on gixxer.com)

[lorenzo]

Cheers Gobert, after posting on here I had a shufty around on gixer.com, I could see lots of threads, each explaining how tricky it is to bleed the system. I think my initial issue was caused by a number of things; that it'd got air left in the system from me flushing it out, that it was purely using water, and of course, any issues I have with the cap.

KP, I've used a bottle of wynns rad flush, it says one bottle per 10 litres, so I used it in two batches; first I drained the system, refilled with water & flush, ran the bike up and let it cool, then drained it down and washed out with plain water, then refilled a second time with water & flush, then finally ran it through with plain water with all sorts of hoses off until everything was clear. I didn't take the stat out, I wasn't sure if there's a gasket in the housing and didn't want to create any issues only a day or two before it goes on the dyno, but I'm fairly certain that the innards are 95% as clean as they will ever get. I may give it a second flush at some point over the winter, I'll see how it goes.

The end result so far, now running about 35% coolant and half a bottle of water wetter that's been pretty thoroughly bled, is that it takes a good bit longer to get up to the higher numbers, 95deg upwards isn't coming zooming up on the dash like it was. The fan comes on at 104, but the bubbles aren't really coming out of the overflow pipe like they were, every now and again I see one, but not much. The bottle (it's not the stock expansion tank, it's a generic bottle which holds 250ml) started with 180ml in there, went right up to the top, and maybe lost 10ml or so, then dropped back down to about 140ml, so it's obviously taken some back in with it. Once it'd cooled a little, I opened the cap and managed to put perhaps another 50ml in there to take it right back to the top.

Once the fan comes on it drops relatively steadily down to 99 before the fan stops, then slowly builds up again. I'm not unduly worried by anything right now, it seems to be able to control its own temperature fairly well since the flush, which is a bit of a relief, it just seems like it was suffering from a little neglect. I've a dyno session on wednesday morning, we'll see if the flush was successful or if it wets its pants again!

[Mark/Foggy]

Hoi matey, shuffle over to the expansion bottle level thread, there's some advice there that might be useful.