Thunderbird 900 Spitting Out Its Coolant

Hi all,
My 1997 Thunderbird 900 keeps spitting out its coolant. It seems ok on longer runs but it hates the stop start of a commute, especially if I am in the mood for spirited riding.

The loss of coolant seems to be from the filler cap (the twist on one). No other leaks are apparent. The spray pattern from the residue suggests it is getting hot and then being forced out of the cap.

I have tried bending inwards the cap flanges to make it seat more snuggly. The inner spring seems to function ok. No obvious perishing of the rubber mount ring.

It did this a bit when i first bought the bike a few years ago. I drained it all down, removed various pipes and flushed it. If memory serves I could not actually get the water pump off but the ol girl behaved herself after a good flushing.

Because it has been losing coolant I have been too cheap to mix in 50% coolant. I'm wondering if water only is less effective at managing the heat. My next step is to flush her out again and do a proper 50/50 water and coolant fluid mix.

Any other suggestions? Thank you.

 

As ever, some really helpful suggestions.
I do not think the head gasket is blown. No leaks or smoke.
I don't suspect the thermo switch either as it seems to switch on and off at the appropriate time.

Ill check the drain hose from the expansion tank but I think it's ok.

The rad could be gunged up. The bike was refurbed by the previous owner very well but who knows what it was like before that. There was rust staining in the overflow bowl when I bought the bike. I

've tried draining the system by undoing the water drain bolt on the pump, the bleed bolt on the side of the engine and pumping water through with a garden hose. It ran clear and strong. But i am guessing it could still do that even if the finer heat exchanger parts were gunged..?

I will buy a new cap but something is making the bike get hot, hot enough to overcome the pressure seal on the cap.

I might look at the kettle descaler trick, and back flushing the rad seems like a very good idea too.

Thanks all.

S

 

Yes. Fan kicking in.

 

Rode to work and back today. V hot out there. Bike not spewed its fluid out. 50/50 mix of water and collent, plus a drain down and wash through seems to have helped.

I still want to take the rad off to rinse through while invertef though.

 

Ok so she is still losing coolent. It is quite annoying and cannot be doing the engine any good. It is not a leak. I don't think its the filler cap. I took rad off and back flushed. No debris and it looked pretty clean. Drained the system again. Took the down pipe off that leads to the water pump. Didn't seem blocked. Refilled with 50/50 water and antifreeze. Once she was all back together again I let it idle for about 10 mins. Water widdled out around the centre stand, obviously via the expansion tank overflow hose. Maybe I over filled it? 2L of fluid, plus a little in the expansion tank. I think that is as per the manual. The fan did come on, but it seemed to take a while before it kicked in. I refilled it and rode to work the next day. About half an hour of fast commuter traffic. The "hot" dash light came on towards the end. It was ok on the way home, and I was not nursing it, giving it some beans. When I took the tank off there was water in the expansion tank. I topped up via the filler cap and she took just under a litre. Its all a bit odd.

The sensor on the left side of the bike is a bit manky. The wire is still connected but maybe the signal is weak, making the fan come on later than it should?

I have not been able to remove and inspect the water pump. But everything seems to run clear.

Recently, one cylinder was a bit reluctant to fire on start up. It would kick in after 20 seconds. So I have changed the plugs. Right one was quite oily and looked different to the other two. Probably not an issue related to the coolent problem.

Oil looks fine. I don't think it is a blown gasket.

Any ideas?

Thanks

 

No I have not. But I did wonder whether it would be worth getting a new one. Will look into it. Thanks.

 

The t bird does have a bleed screw. Filling up slowly leads to some gurgling and it seems to sort out any bubbles. 2L goes in which is he correct volume I believe. I fill the reserve tank to the line. A bit of expelled water would be ok but every couple of rides she throws at least half of it out.

Maybe the temp sensor / thermostat is kicking the fan in too late.