Thermostat advice/help please
Discussion
Hi all
Currently carrying out a minor recommissioning of a an old Honda Hornet 600 FY that's been languishing in a friends garage for the last 4 years.
Have been working through it and got it to the point of it passing its MOT Saturday morning (yay)
I had had it running in the garage prior to MOT and the rad fan had cut in, but on my way back the engine temp gauge went right up to the red and the fan didn't cut in. Always part of the plan to change all the fluids anyway as the bike had been laid up for so long, so I've been draining and flushing all the old coolant out today and have ordered some new coolant and a crush washer for the drain bolt from Honda that I'm picking up tomorrow, so thought it best to have a quick check of anything related to the coolant system would be a good idea.
I've bridged the wiring across to ground and the fan switches on ok, so i know the fan itself is good.
So, to the thermostat - I have removed it and put it in a pan of boiling water. Initially it didn't open, but after about 90 seconds it did start to open, and then closed back ok.
The temp printed on the stat is 82 degrees C. As water boils at 100 degrees C i was surprised it took so long to open. The mighty internet videos I've watched show most people getting there's to open after 15 or so seconds. So the question is, is it faulty?
If its taken over a minute at sustained temps of 100 degrees does this mean that it would take a lot longer to open if installed therefore causing the engine to get hotter than it should?
Cheers for any help offered. Would rather fit a new one in advance of putting the new coolant in, but wanted to confirm my thinking was correct if its not working as it should be?
Si
Currently carrying out a minor recommissioning of a an old Honda Hornet 600 FY that's been languishing in a friends garage for the last 4 years.
Have been working through it and got it to the point of it passing its MOT Saturday morning (yay)
I had had it running in the garage prior to MOT and the rad fan had cut in, but on my way back the engine temp gauge went right up to the red and the fan didn't cut in. Always part of the plan to change all the fluids anyway as the bike had been laid up for so long, so I've been draining and flushing all the old coolant out today and have ordered some new coolant and a crush washer for the drain bolt from Honda that I'm picking up tomorrow, so thought it best to have a quick check of anything related to the coolant system would be a good idea.
I've bridged the wiring across to ground and the fan switches on ok, so i know the fan itself is good.
So, to the thermostat - I have removed it and put it in a pan of boiling water. Initially it didn't open, but after about 90 seconds it did start to open, and then closed back ok.
The temp printed on the stat is 82 degrees C. As water boils at 100 degrees C i was surprised it took so long to open. The mighty internet videos I've watched show most people getting there's to open after 15 or so seconds. So the question is, is it faulty?
If its taken over a minute at sustained temps of 100 degrees does this mean that it would take a lot longer to open if installed therefore causing the engine to get hotter than it should?
Cheers for any help offered. Would rather fit a new one in advance of putting the new coolant in, but wanted to confirm my thinking was correct if its not working as it should be?
Si
Edited by stepaway on Monday 9th October 17:09
Hi all - bit of an update on progress!
Fitted a new OEM thermostat along with OEM Honda coolant - at idle I now have a steady temp showing on the gauge and the fan kicks in regularly to keep the temp down at the level shown in the pic below. I haven't been able to ride the bike yet as i'm not insured/taxed on it, but assume that it should run cooler when actually riding due to the wind passing over the rad/engine block cooling it down, so any overheating problems at idle will be worst case scenario?
I ran the coolant up post replacement as per the shop manual very slowly and carefully and squeezed the pipes to remove any air bubbles. Flushed the system twice and was coming out clear with no residue visible.
However the rad cap started to leak coolant whilst idling, and I lost about a half inch of level below full in the rad when the cap is off
I let it cool down again and ran it up to temp again and with the small loss of coolant lower in the rad had no further coolant leak other than a little whisp of vapour out of the cap once it was up to temp.
Obviously i want the rad to run full of coolant, so this has started me thinking as to if it is the cap itself that is faulty and not functioning as it should. Does it release coolant into the expansion tank when it is too hot or over pressurized? As i understand it the cap has a dual job. Seal and pressurize the whole system, and then the spring lifts inside to open a valve that then lets the coolant into the expansion tank when the coolant is too hot or too high a pressure?
The expansion tank has coolant up to the upper line, and the pipe to the radiator is clear with no blockages
If the system is working properly, does warm coolant then flow into the expansion tank through the syphon hose? I regularly felt the expansion tank and hose while the bike was up to operating temp and leaking, but neither were warm. Should they be? If they are not, could it be that the rad cap is not letting fluid through hence it venting it out of the cap and on to the floor, is that how it works?
Or do I potentially have a bigger problem (Head gasket?) There is no visible water/creamy residue etc in the oil and the bike starts and runs ok.
While the bike was empty of coolant I whipped the water pump cover off and the impellors are fine and it spun when i cranked the bike so pretty sure water is being pushed round the system ok.
I know you'll say order a new rad cap anyway, but they're £60 and it would be helpful to know if my thinking is correct before ordering one up. Happy to do so if someone can give me some logic as i'll freely admit i'm a tad confused on what's supposed to do what where the rad cap/expansion tank etc is concerned.
Here's a Youtube vid link to the cap leak on initial start up when the rad was full to the top of coolant - it had been idling for about 7 or 8 minutes at this point.
https://youtube.com/shorts/SpKCNbR3XmM?si=J1mSV8c-...
And a pic of the inside of the cap
And a pic of the system as per the Honda workshop manual for reference...
Fitted a new OEM thermostat along with OEM Honda coolant - at idle I now have a steady temp showing on the gauge and the fan kicks in regularly to keep the temp down at the level shown in the pic below. I haven't been able to ride the bike yet as i'm not insured/taxed on it, but assume that it should run cooler when actually riding due to the wind passing over the rad/engine block cooling it down, so any overheating problems at idle will be worst case scenario?
I ran the coolant up post replacement as per the shop manual very slowly and carefully and squeezed the pipes to remove any air bubbles. Flushed the system twice and was coming out clear with no residue visible.
However the rad cap started to leak coolant whilst idling, and I lost about a half inch of level below full in the rad when the cap is off
I let it cool down again and ran it up to temp again and with the small loss of coolant lower in the rad had no further coolant leak other than a little whisp of vapour out of the cap once it was up to temp.
Obviously i want the rad to run full of coolant, so this has started me thinking as to if it is the cap itself that is faulty and not functioning as it should. Does it release coolant into the expansion tank when it is too hot or over pressurized? As i understand it the cap has a dual job. Seal and pressurize the whole system, and then the spring lifts inside to open a valve that then lets the coolant into the expansion tank when the coolant is too hot or too high a pressure?
The expansion tank has coolant up to the upper line, and the pipe to the radiator is clear with no blockages
If the system is working properly, does warm coolant then flow into the expansion tank through the syphon hose? I regularly felt the expansion tank and hose while the bike was up to operating temp and leaking, but neither were warm. Should they be? If they are not, could it be that the rad cap is not letting fluid through hence it venting it out of the cap and on to the floor, is that how it works?
Or do I potentially have a bigger problem (Head gasket?) There is no visible water/creamy residue etc in the oil and the bike starts and runs ok.
While the bike was empty of coolant I whipped the water pump cover off and the impellors are fine and it spun when i cranked the bike so pretty sure water is being pushed round the system ok.
I know you'll say order a new rad cap anyway, but they're £60 and it would be helpful to know if my thinking is correct before ordering one up. Happy to do so if someone can give me some logic as i'll freely admit i'm a tad confused on what's supposed to do what where the rad cap/expansion tank etc is concerned.
Here's a Youtube vid link to the cap leak on initial start up when the rad was full to the top of coolant - it had been idling for about 7 or 8 minutes at this point.
https://youtube.com/shorts/SpKCNbR3XmM?si=J1mSV8c-...
And a pic of the inside of the cap
And a pic of the system as per the Honda workshop manual for reference...
Edited by stepaway on Friday 13th October 11:36
I certainly wouldn't say head gasket.
Expansion tank shouldn't be hot while running, there shouldn't be any coolant flow unless the radiator's too full/empty. The leak in the video would suggest that the flow up to the expansion tank isn't working correctly. If the lines is definitely clear then I'd replace the cap.
Expansion tank shouldn't be hot while running, there shouldn't be any coolant flow unless the radiator's too full/empty. The leak in the video would suggest that the flow up to the expansion tank isn't working correctly. If the lines is definitely clear then I'd replace the cap.
In the interests of closure (as I hate it when threads don’t get resolved when a solution is found), the new rad cap arrived from David Silver spares today, so fitted it and ran the bike up to temp and all appears well with no more coolant leaking 
Haven’t ridden the bike yet, but I’m confident all is now well.
Only fly in the ointment was s
tting it that something had truly gone wrong when the bike started stalling after 5 minutes of running at idle, only to realise that the fuel tap needed flicking across to reserve as the thimble sized main tank had run out. Going to need to get used to no fuel gauge or gear indicator!
Haven’t ridden the bike yet, but I’m confident all is now well.
Only fly in the ointment was s
tting it that something had truly gone wrong when the bike started stalling after 5 minutes of running at idle, only to realise that the fuel tap needed flicking across to reserve as the thimble sized main tank had run out. Going to need to get used to no fuel gauge or gear indicator! In the interests of closure (as I hate it when threads don’t get resolved when a solution is found), the new rad cap arrived from David Silver spares today, so fitted it and ran the bike up to temp and all appears well with no more coolant leaking
Haven’t ridden the bike yet, but I’m confident all is now well.
Only fly in the ointment was stting it that something had truly gone wrong when the bike started stalling after 5 minutes of running at idle, only to realise that the fuel tap needed flicking across to reserve as the thimble sized main tank had run out. Going to need to get used to no fuel gauge or gear indicator!
Thanks for all the help all
Haven’t ridden the bike yet, but I’m confident all is now well.
Only fly in the ointment was s
tting it that something had truly gone wrong when the bike started stalling after 5 minutes of running at idle, only to realise that the fuel tap needed flicking across to reserve as the thimble sized main tank had run out. Going to need to get used to no fuel gauge or gear indicator! Thanks for all the help all
Glad it seems ot be fixed - only other thing to mention is that rads are made of aluminium and the necks are quite thing and fragile. I got my bike back from my local bike shop and it had clearly been knocked (they had taken the rad off to remove and weld up some cracks in the exhaust headers) and the top of the neck was slightly warped, so the cap didn't seal quite tight. After removing the cap it only took a light tap or two to knock the high spot down, and it's been perfect since. Just something to watch out for.
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