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Cooling system woes

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Pukka
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Location : Woking, Surrey

Cooling system woes Empty Cooling system woes

Post by Pukka on Wed 20 Feb 2019, 2:00 pm

Having an issue with cooling. Bikes running hotter than usual and repeatedly checking the system the coolant level is always about 20mm below filler neck no matter what has been done.

First problem was I noticed on a ride home that the temperature gauge was reading higher than usual. Once home checked the overflow reservoir while low still had enough visible coolant in it. Once cooled however the level did drop enough to not be able to see it looking though the top of it reservoir but needed less than 50ml to actually be able to see it again. Obviously wanted to bleed the system after this. Opening the radiator cap sure enough the level was low (about 20mm below the filler neck). Bleed the system and just had a general check of everything else at the time. Took the bike out to check if this was the only cause but unlucky it wasn't and was still running hotter than usual. The level in the overflow was returned to the max mark and didn't drop any after this test. Opening the radiator cap again the level was low by the same amount.

Cooling system woes Guage

Blue line indicates where it usually sits just below the white line of cold. Even if it was allowed to rise, which would take a while too beforehand, it very quickly (easily under a minute of riding above 30ish mph) returns to this.

Green line indicates where it now sits when up to temperature.

If left to idle (or slow riding under 30 and not as quickly) within a minute it reaches the red line. It does still rise above this but at a slower rate than to this point. However Checking all the hoses with an inferred thermometer shows that the temperatures are rising steadily. The fan does work (after fixing items below) but seems to completely run at random to what the gauge is showing/ what the temperature is measured on the fan switch side of the radiator. I imagine the air getting in is causing hot spots and not allowing the sensors to work as intended. I should also mention this was checked a few times in mostly cold conditions but one of those times the outside temperature was -1oC! Still made no difference to the outcome of above. Once it rises it now takes over 10 minutes of 40mph+ to lower it back to the green line.

I have no visible leaks and no real indicators that a head gasket leak is a possibility- No bubbles showing in funnel after bleeding, no over pressured coolant hoses, no smoke out of exhaust, no mixing of oil/coolant.

I have done the following since the problem started. In no particular order and majority tested between them but making no difference and still resulting in the dropped coolant level:


  • Noticed radiator hoses were soft to touch even when up to temp and could hear a faint hiss of air from cap when squeezed. Replacing cap solved both these problems. However its still running hotter and level is low below cap
  • Pressure tested the coolant system. No visible leaks. Didn't loose any pressure at all after 40 minutes at 1.1bar. Would have also performed a compression test but cant find my tester.
  • The majority of the hose/unions had visible coolant residue (but no obvious current leaks) so I removed all hoses and removed all the residue. Also checked and replaced any hose clamps that needed to.
  • Tested thermostat -Opened at 83oC and was open 9mm wide at 95oC. New O-rings for stat and the housing assembly.
  • Tested fan switch – Switch failed to close even in coolant measured at 106oC. (Replaced and checked new switch which closed at 99oC just to get the satisfaction that my testing procedure was correct)
  • New radiator earth point as old one had broken off. Checked fan by earthing to ground which worked.
  • Flushed radiator multiple times. Wasn't particularly dirty externally or internally and had good flow rate through out. Also straightened out some of the fins.
  • Spark plugs didn't indicate any fouling or mixture problems
  • Checked condition of carb heater hoses. Hoses where in good condition but one of the clips had failed and didn't need much effort to pull said hose off (with clip still attached). Replaced all hoses and clips anyway. Also cleaned and synced carbs and adjusted the mixture screws.
  • Overflow reservoir isn't leaking anywhere and hose isn't blocked (can blow into hose and get visible bubbles and can also suck fluid through with a syringe.)


Not really sure where to go from here really as anything i do really doesn't seem to make any difference  Neutral . Any ideas would be appreciated!
teamster1975
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Post by teamster1975 on Thu 21 Feb 2019, 1:20 pm

I think the only thing left is water pump or head gasket, there must be air in the system if the fan is triggering at random. Maybe do a sniff test on the coolant?
Good to see someone else from Woking on here, I live up near Wickes Smile
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Pukka
Crotch Rocketuer
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Location : Woking, Surrey

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Post by Pukka on Thu 21 Feb 2019, 3:41 pm

I decided this morning actually that a coolant sniff test would be a good thing to do. Just put it off really because of none of the typical symptoms were showing and the fact when the system was pressure tested it didn't loose any pressure.

I determined the water pump was at least working enough due to the flow seen just underneath the cap, but may have to be a thing i check in the future just to rule it out.

What a small world! I'm only a 5-10 minute walk from the Wickes. Shocked
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Pukka
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Post by Pukka on Sun 24 Feb 2019, 5:50 pm

Thought i'd update what Ive done today. Did a coolant sniff test which came back negative. Will test it again sometime in the week though as i ran out of fuel.

https://www.ebay.co.uk/itm/BT-3-BLOCK-COMBUSTION-LEAK-TESTER-KIT-CO2-BLOCK-HEAD-GASKET-TEST-FLUID-35bb/273245490361?epid=527979883&hash=item3f9eb34cb9:g:MuUAAOSwLEtYi8Gi:rk:1🇵🇫1

Used the kit above which seems adequate enough. Under-filled the system a little to be able to push air into it by squeezing the hoses, normally these things are attached with a rubber bulb to draw air out through the tester.

Left it on at a fast idle for 5 minutes while up to temperature and occasionally burping the hoses, the fluid didn't change. The kit instructions did suggest a more accurate test would be to test air taken the top of the radiator (while running) into a 20ml+ syringe. Did this 5 times but again no change. Just to confirm the fluid wasn't a dud i blew into the tester and it almost instantly changed to yellow.

I will try this again a few times just to get an accurate reading but still scratching my head at the issue really.
Jameshambleton
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Post by Jameshambleton on Sun 24 Feb 2019, 6:21 pm

Check the cable going to the thermosensor, it works on a ground based resistance for the clock gauge reading, any form of grounding will cause the needle to read extra high.
jchesshyre
jchesshyre
the 900
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Post by jchesshyre on Sat 04 May 2019, 6:40 am

I had exactly this issue and started to think it might be the head gasket. I replaced almost every part of the cooling system and in the end I sorted it when I replaced the coolant hoses going to the carbs. What can happen is that there can be a leak that for some reason doesn't leak fluid but allows air bubbles to be sucked in slightly while the system is in a state of negative pressure during cool-down, meaning you then always have a bit of air in the system.

Here's the thread about it http://www.cb500club.net/t2839-another-puzzling-cooling-issue.

Also have a read through this thread http://www.cb500club.net/t3451-another-minor-heating-issue.
OldRocker
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Location : West Sussex. UK

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Post by OldRocker on Sun 05 May 2019, 1:04 pm

Is the thermostat opening when engine reaches temperature? if not change it for a new one, alternatively is the water pump operating correctly and the filters clear. Maybe worth a check to see.
motofan
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Post by motofan on Tue 07 May 2019, 1:12 pm

Fit a new radiator cap.
jchesshyre
jchesshyre
the 900
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Post by jchesshyre on Tue 07 May 2019, 2:02 pm

@motofan wrote:Fit a new radiator cap.

He's already done that.
motofan
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Post by motofan on Tue 07 May 2019, 2:27 pm

Oops, didn't see!
Good luck with it.
motofan
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Post by motofan on Tue 07 May 2019, 2:38 pm

So if the cap was faulty, as I just re-read, apologies, and it had been drawing air in for a while could that have made corrosion deposits in the motor, not the radiator and would flushing the motor be an idea?

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