New thermostat needed?

My CB is my second CB and I've always thought it ran a little hot, considering how cool the first one ran and the reputation they have for doing so.

It's a slight thing but in this weather I notice it and sometimes it seems as if the cooling system is only just 'breaking even'. I have noticed that the water pipe feeding the top of the radiator is cooler to the touch than the one feeding the thermostat, which to me suggests that my thermostat is not opening fully.

I'm going to get a replacement as I have three second hand ones (including the one in the bike) which all don't quite open early enough when testing in a saucepan of water and I think I need to cut my losses and rule this out.

Has anyone tried one of these http://www.ebay.co.uk/itm/182618361769 ? I'm rather tempted because it's half the price of a Honda one, but if it's a load of crap and either doesn't work properly or breaks after six months then obviously it's not worth it.

I have used one of those aftermarket ones in my first CB and had no problems.
Is your fan cutting in as it should, maybe you have a dickie fan switch. I have wired mine so that I can turn it on when in standing traffic, to make sure I don't overheat, don't trust those fan switches.

Keep Smiling.

Yes fan is cutting in fine and doing its job OK. The needle doesn't go into the red, it's just in any given circumstance the needle is slightly higher than I think it should be based on my last bike, and stays higher slightly longer than I think it should. Although all this 'than I think it should' sounds a bit iffy, I put so many miles on my last bike (owned it from 24,000 to 145,000) that I just know it's not right!

Thanks, I'll try one of those then!

Just a thought, it has been quite hot lately and mine is running hotter than normal.

I know, but still I'm sure it's definitely not operating as it should. Off for a trip to South Wales today and I'm going to run it with the thermostat out - if it runs cooler then I'll know for sure that it's the culprit.

Are you still in South Wales or was that just a day visit?
If you're still here I have a thermostat you can have that worked correctly last time it was used.

jchesshyre wrote:(owned it from 24,000 to 145,000)

Nice one!!

Always good to see these kinds of mileages. ; - )


Okay - back on topic. Just wanted to mention that in passing.

Oh amazing, no I haven't left yet and am there tonight till Sunday lunchtime.

We're staying near Llanarth - any good?

Haha I appreciate the passing thumbs up trevor machine ; )

Current CB is on 69,000 and I bought it with 13,000 on. I also have a VTR1000 which I bought a year ago with 29,000 on and is now on 59,000 (yikes that's a lot of petroleum) but it's currently being repaired after I came off it on a big roundabout at 60mph six weeks ago - I only suffered a grazed leg but she needed new plastics all round, new RH rad, new silencers and headers, new clutch cover, and a few other bits : (((

Anyway yes back on topic...

jchesshyre wrote:We're staying near Llanarth - any good?

Oh - soz to drift off topic again, but I really love that part of Wales. Did you try the honey ice cream at Aberaeron yet? So ace. I also like New Quay very much - a lovely little harbour town, not a great deal to do there admittedly, but it has a peaceful atmosphere and good sea views. You've probably been there a few times now, if you've been staying close by. I also like calling in at that curious, tiny cove at Cwmtydu - but my favourite place is Llangrannog. I used to love swimming in the sea there - there's a second beach reachable only at low tide, or via a steep and somewhat lengthy cliff top walk. Diving off the rocks down in the cove is awesome.

jchesshyre wrote:Oh amazing, no I haven't left yet and am there tonight till Sunday lunchtime.

We're staying near Llanarth - any good?

That's a bit of a trek from me. I am at Gorseinon, on the edge of the Gower near Swansea. It's about 40 miles as the crow flies from you. I can meet up with you tomorrow between 8:15 am and 11:30 am if it's any good to you. I am about 1 mile off the M4 motorway junction 47. It's still on the bike, so I Don't know how long or hard it is to get off. I've just got back home, but if you want to come tonight before 10pm you can.

Ah, don't worry. We're only here for tomorrow and half of Sunday, and I have actually already ordered that pattern one on eBay. I really appreciate the offer though.

Taking the thermostat out has sorted the issue and the pipe going from the thermostat to the rad is now too hot to hold my hand on after a ride, rather than just bearable as it had been before (and is the same as the pipe feeding the thermostat) so fingers crossed the replacement one will sort it.

Oh and trevor machine - massive cheers for the recommendations - they sound brilliant and I will definitely check some or all of them out tomorrow :-D

No worries. Enjoy your stay. :-)

So, I've just got back from a lovely time in South Wales, and [what I think is] the problem with the cooling system is still there, without the thermostat.

Let me describe the symptoms as briefly as possible. When making progress along a fast A road on a hot-ish day like today, cruising at 60-80 with quite frequent slowings down to 50 for traffic and then fast overtaking, the temperature gauge was between 1/3 and 2/3 up the gauge. Then when changing onto a dual carriageway at a steady 80 it took about ten minutes to slowly move down to about a needle's width above the C block on the gauge.

If I'd never owned a CB500 before I'd call this reasonable behaviour (other than possibly the taking ten minutes to cool down once cruising at a steady speed) but I'm so sure my first CB was generally more eager to return to just above the C mark and really only went halfway up the gauge or more if I got stuck in town traffic, on a hot day.

Can anyone confirm whether the above is normal or not? My gut says it's not.

If it's not, then the thermostat clearly isn't to blame as all of the above was whilst running without it fitted.

I should add that there's no overflowing or anything like that occurring. However, when I opened the system on Friday to take the thermostat out, the coolant level was low. This may be because I didn't fully bleed the system when I changed the coolant a few months ago but then again the symptoms are still here after I topped it up and bled it on Friday, so perhaps there is a vacuum leak in the cap which means that as the bike cools, air gets sucked in instead of coolant from the expansion reservoir.
*edit* just opened the system to put the thermostat back in until the new one arrives, and the coolant's all the way up to the brim so there's no vacuum leak.

This was an issue I had way back but then I got a Firestorm and put this bike away for a while...but here's the thread where I wittered on about it and documented some of my troubleshooting :-D http://www.cb500club.net/t2839-another-puzzling-cooling-issue

I do have an aftermarket (eBay generic) radiator on the bike - perhaps this is the culprit after all, if perhaps it's made of an alloy with inferior thermodynamic properties than stock? I have a Delkevic one in the garage waiting for the next winter when this one springs a leak, but It's a bit of a faff swapping this just to experiment.

I wonder whether it could be the pattern rad is not as efficient as the stock or Delkevic? Might also be worth putting a flush through the cooling system in case there is some sludge in there.

I get worried when mine gets 1/3rd up the gauge. 
I was going to suggest the coolant level as mine did something similar when it was low but you've already ruled that one out so next suggestion is. 

Have you checked the waterpump is working?

Yes, the waterpump is fine.

I was going to wait a few days to post this so this doesn't get clogged up again with 'I think I've sorted it...oh wait I haven't'... but last night I took off the carb heater hoses which I'd replaced last time I was troubleshooting the cooling system, but I'd used nasty stiff generic fuel hose. It seems to have gone even tougher than when I fitted it, from the heat cycling presumably, and had even cracked a little round the ends of all three hoses, and (I'd forgotten this) because of its stiffness the clips weren't up to the ends of the pieces of tubing and so possibly weren't even doing their job properly. It had been a temporary fix to replace the knackered old ones on there (which I'd decided were at least part of the problem) and then I'd ordered nice soft proper ones and never got round to fitting them, partly because of buying a Firestorm. 

Well anyhow I fitted these last night and the problem appears to be sorted...but I will have to wait a few days of riding in various temperatures and situations to be sure. The thing is, the ones on there weren't leaking, but I remember once being told that it is possible to have hoses in a bad condition where they don't leak coolant under pressure but can leak air inwards when the slight vacuum develops in the system as the bike cools, which as we know should only enable the coolant to be sucked back from the overflow reservoir. I don't know enough about the physics of these things to know whether this is possible, and there are certainly no signs of leaking coolant around the carb heater hoses, but it does seem to have sorted it - when slowing for town traffic today after being on a dual carriageway the needle only slightly moved up and then very quickly returned to just resting above the 'C' block once I picked up speed again, (which is absolutely how I remember my last CB500 behaving) rather than sitting a bit higher all the time even at speed and taking ages to move back down after getting hot in town.

I hope all this does end up being helpful to someone if they encounter the same problem one day...

jchesshyre wrote: I remember once being told that it is possible to have hoses in a bad condition where they don't leak coolant under pressure but can leak air inwards when the slight vacuum develops in the system as the bike cools, which as we know should only enable the coolant to be sucked back from the overflow reservoir. I don't know enough about the physics of these things to know whether this is possible...

I don't really know whether this is true, but given how easily air can leak into low-pressure/vacuum systems I can well imagine that it is possible.  Also if you had a tiny crack in the hose you wouldn't notice the water leaking out (the water is hot and in the summer would evaporate almost immediately) and air would certainly get into any gap that water can get out of...

EDIT: Further thoughts - this only backs up what I was saying the other day: all CB500s are getting to a point where wholesale 'rubber parts' replacement is a good idea! This probably applies to other things than just the cooling hoses...

Yes indeed.

It really does seem that replacing these hoses has done the trick, but I'll report back in a week or two...

It's a reminder that the cooling system's proper functioning is a sum of its parts and their good condition. If there's an issue like mine where the system has not failed but is not working at optimum performance, then it can be misleading to look for a single culprit when there could be a number of minor shortcomings in parts of the system which together reduce its efficiency enough to be noticeable. In this case it may seem as if one part - the carb heating circuit - was to blame, but in fact this is the end of a process of sorting the cooling system which I began ages ago but which the acquisition of a Firestorm and associated laying-up of the CB put on hold.

So, to sum up, since I got this second CB500 of mine three years ago, it's had all new coolant hoses and o-rings, a new pressure cap, and a different (used) thermostat, and a total of three flushes and coolant replacements, and is now, finally, fingers crossed, cooling itself effectively.

Well, my cooling system is Officially Sorted. 

It's a hot day today and the gauge is now staying just resting above the 'C' block, regardless of whether I'm cruising at 30 or 80, as I thought I remembered it always used to do. When I pulled into a layby after sitting on a dual carriageway for five minutes and sat with it running for a minute it started rising slowly straight away, then when I got going again it went back to its resting place in literally thirty seconds, whereas before it would take more like ten minutes of riding at speed to settle back down after stopping with the engine running on a hot day. All good. 

It actually did spring a tiny leak in the radiator at the weekend - small enough to only leak just after startup then seal itself up as the system heated up. So I fitted the Delkevic rad I've had in the garage for two years. This can't have been helping, even though swapping the carb heater hoses the other day definitely also made a difference. 

I'm very happy now and glad I correctly remembered how these bikes' cooling systems should behave.