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Old 23-07-18, 07:31 AM   #11
SV650rules
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Default Re: Cooling fan

The thermostat keeps the water out of the radiator and shortens the cooling loop to just water pump and cylinders to allow it to warm up faster, when water reaches a certain temp the stat opens and allows water into radiator, if water gets too hot the fan will kick in. Venting hot water to atmosphere is not done (unless you remove radiator cap when engine is hot, which releases pressure and lowers boiling point (just like kettle boils at lower temp up a mountain) one of the things coolant additives do is raise the boiling point to something like 120degC or more, because last thing you want is water boiling in a cooling system. Any expanding coolant from cooling system is routed under rad cap relief valve into expansion tank, when system cools the coolant is sucked back into main system. Cars and bikes work the same in this respect.

Venting hot coolant to atmosphere on a bike could easily result in a severely scalded right knee, but no modern system vents to atmosphere anyway, the cap seals on rad, the spring loaded valve only allows coolant access to expansion tank.
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Last edited by SV650rules; 23-07-18 at 07:36 AM.
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Old 23-07-18, 07:57 AM   #12
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Default Re: Cooling fan

sorry beg to differ on cars and bikes being the same. My modern car has a completely pressurised system (unlike my bike) where the rad only has a plug not a pressure cap which is instead located on the remote expansion tank. This tank is, importantly, only half full so as the system heats up the coolant expands to occupy more space in it and consequently increase system pressure. The pressure cap remains closed at all times unless there is overheating and the system pressure rises too much when excess coolant is dumped to atmosphere via a hose......
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Old 23-07-18, 08:19 AM   #13
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Default Re: Cooling fan

Quote:
Originally Posted by glang View Post
sorry beg to differ on cars and bikes being the same. My modern car has a completely pressurised system (unlike my bike) where the rad only has a plug not a pressure cap which is instead located on the remote expansion tank. This tank is, importantly, only half full so as the system heats up the coolant expands to occupy more space in it and consequently increase system pressure. The pressure cap remains closed at all times unless there is overheating and the system pressure rises too much when excess coolant is dumped to atmosphere via a hose......
+10.

I've had this argument for years.Motorcycle cooling systems are totally different from car fully pressurized systems.

There are lot of diagrams on the Net that should be ignored showing the incorrect idea that coolant flows out and back to the Rad on Motorcycles from the,"Emergency Overflow" bottle.

If the cooling system is nominal the Rad cap will never lift and if it does there's a fault with the machine that needs to be addressed and the bike should not be ridden.

No one should ever use the level in the Overflow bottle as a gauge on how much coolant is actually in the system on a Motorcycle.

I you own a car pop the Bonnet/Hood and look at the system.The,"Expansion" bottle has a,"Do Not Open When Engine running/Hot" warning sign as it's a,"Pressurized" system.

The Bottle is at the same height as the top of the Radiator to aid flow whereas on most motorcycles it's either in line with the Bottom of the Rad or at least well below the Top and open to Atmospheric pressure.

Also on an Car there are two tubes going in and out to the Radiator to the Expansion Bottle,not the single escape tube on a Motorcycle.
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Old 23-07-18, 08:44 AM   #14
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Default Re: Cooling fan

errr well actually on motorcycles (and my 50 yr old classic car) the coolant does flow back and forth to the expansion bottle. The rad is filled to the top so that as the temperature increases the volume of the coolant expands (a little) and would burst the rad if the cap didnt lift and allow the excess to go to the bottle. Then on cooling the volume reduces and coolant is sucked back to the rad via a small spring loaded valve in the cap (the caps for the two designs are quite different).
I think bikes use this older, poorer system because it avoids having a beefy expansion bottle with pressure cap and, on overheating, dumps boiling liquid to the expansion bottle not directly to atmosphere.
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Old 23-07-18, 08:58 AM   #15
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Default Re: Cooling fan

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errr well actually on motorcycles (and my 50 yr old classic car) the coolant does flow back and forth to the expansion bottle. The rad is filled to the top so that as the temperature increases the volume of the coolant expands (a little) and would burst the rad if the cap didnt lift and allow the excess to go to the bottle. Then on cooling the volume reduces and coolant is sucked back to the rad via a small spring loaded valve in the cap (the caps for the two designs are quite different).
I think bikes use this older, poorer system because it avoids having a beefy expansion bottle with pressure cap and, on overheating, dumps boiling liquid to the expansion bottle not directly to atmosphere.


I never fill my SVs rad to the top.I fill it to just below the neck.Always have done on all my liquid cooled Motorcycles and never had a problem.

Also you must have seen the coolant level drop when you have,"Burped" the system when changing coolant when the Thermostat opens so on a properly running Liquid cooled Motorcycle the coolant isn't actually near the top/Rad-Cap when the engine is running?

This is why the manuals state not to top-up the coolant when the engines are warm as it will be a false level and over-filled?
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Old 23-07-18, 10:39 AM   #16
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Default Re: Cooling fan

Modern car and bike systems are identical pressurised systems with expansion bottle, they are doing the same job with the same coolant so why would they be different ? I know my car has a pipe from radiator filler cap neck to the expansion bottle and the rad cap seals on top of the neck, so only way for fluid to get in and out is to and from expansion bottle via the pressure valve in the cap, exactly the same as my AL7, and unless the rad is filled right to the top neither system will work as designed because any air in the system will expand much more than the coolant when it gets hot and blow air into expansion bottle, when the system cools it will suck coolant back on (the coolant entry / exit to expansion bottle is the lowest point in the bottle so it is always covered by coolant, so system is designed to stop air being sucked back into rad.

The expansion bottle on any car i have ever had has not been a 'pressure vessel' just a plastic bottle with a cap and a tube long enough to reach bottom of bottle, it does not care if cap is screwed on or not as there is a small air hole in the cap to stop pressure build up or vacuum in the bottle. Nothing should ever get dumped to atmosphere unless there is a catastrophic failure (or if you read the warning by the cap 'never remove cap when engine is hot' because the rad will be under pressure and removing that pressure suddenly by removing the cap can cause boiling and spray you with hot coolant) - but the expansion tank is not pressurised.

ideally the pipe from rad to expansion tank should be full of coolant with no air in the pipe, this means that the only thing to be sucked back into rad would be coolant not air, but every time you take rad cap off the coolant drains back into expansion tank because it is lower than neck of radiator, but then again if expansion bottle was higher than neck of rad the bottle would empty itself every time you took rad cap off.
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Last edited by SV650rules; 23-07-18 at 10:59 AM.
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Old 23-07-18, 11:43 AM   #17
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Default Re: Cooling fan

oh dear I didnt know this was going to be so complicated. Riff Raff although you dont fill your rad completely or it burps I bet that every time you remove the rad cap after having used the bike a few times its full of coolant. This is because as the liquid expands on heating it pushes the air out to the expansion bottle where its lost then on cooling coolant is sucked back into the rad to replace all the space available.
Also you shouldnt top up the expansion bottle while hot because its level isnt stable but goes up and down depending on the engine temperature. Once cool the level can be correctly assessed although even then it varies a little with ambient temperature........
Next one: cars have both types of system and if you fill (not just top up) your cooling system through the expansion bottle its the later one (not SV). Heres an example on ebay of this type of expansion tank with pressure cap:

https://www.ebay.co.uk/itm/VAUXHALL-...UAAOSwJo5bFfJL

In both designs if overheating occurs (for example due to fan failure) the pressure in the system will go up and has to be released by a pressure cap either on the rad or on the expansion tank depending on which type you have. The SV type will discharge the excess pressure from the rad to the expansion bottle where it should cool and not produce much steam. The other type however discharges from the bottle usually by a hose down under the vehicle and can produce steam.

Last edited by glang; 23-07-18 at 11:46 AM.
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Old 23-07-18, 11:48 AM   #18
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Default Re: Cooling fan

I still disagree.I've just checked my coolant level in the Rad and it was low so no coolant has been drawn back in.

Car cooling systems have two radiators and are sealed from the atmosphere including the Expansion bottle.

My 1999 curvy and previous Hondas use the same,"Open to the Atmosphere" expansion bottles.

I've also checked the Partfiche for the 2017 SVs and the expansion bottle is also open to Atmospheric pressure TTBOMK.

There's plenty of images for how a Car cooling system works differently from Motorcycles,

https://www.google.co.uk/search?q=ca...w=1440&bih=763

I'm not going to argue the point any more just agree to disagree but I would urge anyone reading this to check the coolant level in the Radiator on their machine with the Engine cold and don't trust the Expansion bottle level.Only takes a minute.Just remember the little screw that locks the cap( there's one on my Curvy).
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Old 23-07-18, 12:03 PM   #19
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Default Re: Cooling fan

Quote:
Originally Posted by R1ffR4ff View Post
I still disagree.I've just checked my coolant level in the Rad and it was low so no coolant has been drawn back in.

Car cooling systems have two radiators and are sealed from the atmosphere including the Expansion bottle.
Maybe because you have an air gap in the rad it is acting as a mini-expansion vessel, and unless your bike gets really hot (which it shouldn't in UK anyway) the rad is not using the expansion expansion bottle the way it is designed to. I have never had a car with a pressurised expansion tank, they are just a regular moulded polyethelyne bottle with a flimsy screw on cap with an air hole in it. I have never had a car with with two engine cooling radiators either (one of mine is for aircon) - although I did have DRZ400SM with the engine cooling radiator split into two, one each side of engine.

The pressurised bottles on cars are normally level with top of rad and are called header tanks rather than expansion bottle and they don't have a pressure cap on the rad the pressure cap is on the header tank, where the coolant gets topped up, and any boil over coolant will get shunted through a pipe down under the car. IMHO this is a bad design anyway, I drive Honda cars and the expansion bottle and cooling system is the same as my AL7, with an 'open to air' expansion tank and the pressure cap on the radiator, but coolant is topped up via rad cap (although I have never had to top any of my Honda cars up).
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Last edited by SV650rules; 23-07-18 at 12:14 PM.
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Old 23-07-18, 12:05 PM   #20
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Default Re: Cooling fan

now Im confused! Cars have two radiators? Do you mean the interior heater heat exchanger or the maybe the aircon heat exchanger....
Anyway I think we're talking about the same thing: SVs HAVE OPEN TO ATMOSPHERE EXPANSION BOTTLES WHILE **SOME** CARS DONT.
You have a problem with your cooling system if coolant isnt being drawn back in as otherwise theres no point having a liquid level in the expansion tank. Its possible that your rad cap isnt sealing properly (the top seal not the inner one) or the hose from the rad to expansion has a small leak which doesnt let out coolant as theres no pressure but lets air in during cooling down when a vacuum is produced. Just for this reason I have a clear pipe fitted to my old car with this type of system so that I can see its always full of coolant
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