Expansion Tank Level

[Jenson]

I’m have not got an ounce of engineering knowledge but am an experienced rider. I have a new Tiger 900 and in checking it over saw that from the factory the coolant level was at the min mark.

My question is - As it is at the min line, does that mean the cooling would be less effective than if it were to be at the max line? As in less coolant in the system to transfer the heat. I’m not entirely sure how an expansion tank functions.

Thanks for any clarity.

 

[92saturnsl2]

No, you will not lose any cooling performance regardless of where the level is in the expansion tank, so long as it's not empty.

That tank is there to hold excess coolant and give room for expansion, hence the name. It's common for them to read "min" when the engine is cold, but it will reach closer to "max" once the engine is at operating temperature. A lot of expansion tanks have hot/cold markings instead of min/max to lessen the confusion.

 

[Bonz]

No, you will not lose any cooling performance regardless of where the level is in the expansion tank, so long as it's not empty.

That tank is there to hold excess coolant and give room for expansion, hence the name. It's common for them to read "min" when the engine is cold, but it will reach closer to "max" once the engine is at operating temperature. A lot of expansion tanks have hot/cold markings instead of min/max to lessen the confusion.

Respectfully, I would disagree. It is normal over the course of time for fluid to evaporate off over heating/cooling cycles. Even in a properly operating system, it happens. We are talking long amounts of time however it happens.

Max is the desired cold fill line which gives the range between the two lines to account for that fluid loss, as many folks don't check that as they should. None of us would let that happen but that's the reality.

If somewhere in the middle/at/below minimum when cold add appropriate amount of antifreeze/distilled water mixture to bring it up to the max line. If it's in between minimum and max, it's technically okay but not the way it should be. The space above the max line is there to handle fluid coming from the cooling system if it gets overly hot. There is an overflow line out the back of the reservoir if it gets so hot it expands and starts puking fluid. Then you should be figuring out why that happened.

Like the oil sight glass if you have one, there's a maximum and a minimum line. Anywhere in between is fine, but the full/max line is best and how it should be.

 

[ZeeOSix]

^^^ My Owner's Manual for the Busa and XSR900 say that the cold coolant level in the reservoir tank is fine if it's between the MIN and MAX lines. But also say if it gets to the MIN line or below when cold to fill the tank to the MAX line when cold. I typically do fill the tank to the MAX line when cold initially, but will let it drop to ~1/2 way down when cold before topping it off again.

 

[Jenson]

Respectfully, I would disagree. It is normal over the course of time for fluid to evaporate off over heating/cooling cycles. Even in a properly operating system, it happens. We are talking long amounts of time however it happens.

Max is the desired cold fill line which gives the range between the two lines to account for that fluid loss, as many folks don't check that as they should. None of us would let that happen but that's the reality.

If somewhere in the middle/at/below minimum when cold add appropriate amount of antifreeze/distilled water mixture to bring it up to the max line. If it's in between minimum and max, it's technically okay but not the way it should be. The space above the max line is there to handle fluid coming from the cooling system if it gets overly hot. There is an overflow line out the back of the reservoir if it gets so hot it expands and starts puking fluid. Then you should be figuring out why that happened.

Like the oil sight glass if you have one, there's a maximum and a minimum line. Anywhere in between is fine, but the full/max line is best and how it should be.

But if the coolant is at the min level does that impact the ability to cool the engine? As in less coolant in the system?

 

[92saturnsl2]

But if the coolant is at the min level does that impact the ability to cool the engine? As in less coolant in the system?

If that tank is an overflow, it holds excess coolant that is not circulating through the system, and simply gives a place to hold coolant that expands. The only time it would matter is in the case of a pressurized reservoir which IS part of the cooling system, and even then that small amount of coolant would have a negligible difference. If there's a cap that holds pressure you have the latter type-- if it's a simple screw on / click on cap you have the former.

 

[ZeeOSix]

But if the coolant is at the min level does that impact the ability to cool the engine? As in less coolant in the system?

No it will not impact the ability to cool the engine.

Just make sure the level never gets so low that the cooling system will start sucking air back into it as it cools off. In other words, never let the coolant level in the expansion tank get below the MIN line when cold, which gives you plenty of headroom before the system could suck air.

If it was my bike, I would add coolant to bring the level to the MAX line when cold. Reference your Owner's Manual and it will probably say the same basic thing as the two bike's OMs snip-its I posted in Post #4.

 

[Bonz]

Like has been shared, sorry if it was requiring to read between the lines... No, a lower level in the overflow tank will do nothing to hinder the cooling system. Only, as has been said, if it gets empty and the radiator starts sucking in air, will it then affect engine cooling negatively because the radiator is not filled to its optimum capacity with coolant mixture.

 

[SZR48207]

Next time you park at home after a long hot ride, check the level again and you'll see how it works. My Tiger 800 always settles at the MIN line and burps the rest of the fluid out the drain hose that exits near the swingarm pivot.

The other aspect to know is that the coolant in that tank does not directly flow into the radiator. The radiator cap has a spring plunger that only "rises up" at a certain PSI, and only once it has risen up is when the flow between the coolant tank and the radiator itself is free. So in a few years if you DIY the coolant change, then it's imperative that you fill the system with new coolant from the radiator cap opening first. Once you have topped off the radiator capacity then you can add some extra into the tank at the min level and monitor it for a few rides until things level out.

 

[Bonz]

Next time you park at home after a long hot ride, check the level again and you'll see how it works. My Tiger 800 always settles at the MIN line and burps the rest of the fluid out the drain hose that exits near the swingarm pivot.

The other aspect to know is that the coolant in that tank does not directly flow into the radiator. The radiator cap has a spring plunger that only "rises up" at a certain PSI, and only once it has risen up is when the flow between the coolant tank and the radiator itself is free. So in a few years if you DIY the coolant change, then it's imperative that you fill the system with new coolant from the radiator cap opening first. Once you have topped off the radiator capacity then you can add some extra into the tank at the min level and monitor it for a few rides until things level out.

With respect, here is a screenshot of a portion of the 2012 Tiger 800 coolant fill procedure. ...cold engine, if level is low, fill to max line. It should not burp out coolant when filled to the max line unless it's getting too hot and doing what it's supposed to or there's something with the system that is causing that fluid to come out prematurely.

Not trying to be a buzz kill, I have never seen a reference for filling to the minimum line. Unless it's a workaround like you're describing because yours burps out fluid when filled to the max line.

The print is a little messed up however it's clearly stating to fill it to the max line.

 

[92saturnsl2]

With respect, here is a screenshot of a portion of the 2012 Tiger 800 coolant fill procedure. ...cold engine, if level is low, fill to max line. It should not burp out coolant when filled to the max line unless it's getting too hot and doing what it's supposed to or there's something with the system that is causing that fluid to come out prematurely.

Not trying to be a buzz kill, I have never seen a reference for filling to the minimum line. Unless it's a workaround like you're describing because yours burps out fluid when filled to the max line.

The print is a little messed up however it's clearly stating to fill it to the max line.

Pretty much every vehicle I've ever owned will burp coolant out the overflow when filled to the max line cold. I don't see a bike being much different, same principle. In the case of my Pacifica it's guaranteed, you simply can't put coolant above the min line or it will leak out after a long drive until you're back to a cold MIN level again. The owners manual says to fill between the lines, doesn't matter, you end up with that same MIN cold level when you're done.

My other vehicles may not go all the way to MIN, but if you fill to MAX when the fluid is cold, it will never stay that way, at least some will leak out.

 

[Bonz]

Pretty much every vehicle I've ever owned will burp coolant out the overflow when filled to the max line cold. I don't see a bike being much different, same principle. In the case of my Pacifica it's guaranteed, you simply can't put coolant above the min line or it will leak out after a long drive until you're back to a cold MIN level again. The owners manual says to fill between the lines, doesn't matter, you end up with that same MIN cold level when you're done.

My other vehicles may not go all the way to MIN, but if you fill to MAX when the fluid is cold, it will never stay that way, at least some will leak out.

For sure can’t argue with your experience, but 99.999% of vehicles don’t have that issue filled to the max line nor do manufactures say fill to the min line as the cold fill level.

Kawasaki ZRX1200, max line no burp. 2004 Honda ST1300, no burps. 2003 Suzuki V-Strom 1000, no burps. 1982 Yamaha Vison 550, no burps. 1980 Honda CX500, no burps. 1994 and 2000 Grand Cherokee, no burps. 2006 Honda Civic, no burps. 2010 Acura TL SH AWD, no burps. 2012 Nissan Juke, no burps.

It is what it is, and works for you so good deal.

 

[ZeeOSix]

My other vehicles may not go all the way to MIN, but if you fill to MAX when the fluid is cold, it will never stay that way, at least some will leak out.

I've never had any vehicle puke coolant out the overflow tube if the tank was filled to the MAX line when cold.

 

[02SE]

I've never had any vehicle puke coolant out the overflow tube if the tank was filled to the MAX line when cold.

Same here.

 

[DGXR]

The reservoir is not actively involved in the cooling of your engine. The reservoir provides a place for the coolant to go when it expands due to heat and comes out of the radiator cap. It also provides a supply of coolant for the engine to pull back in (and refill itself) when it cools down. This is all part of the system design. You always want to have some minimum quantity of coolant in the reservoir.

 

[Bonz]

Fill it to where are you want, however it’s designed to be filled to the max level, haven’t seen a vehicle that suggested filling to the minimum line when cold. Never had a vehicle puke fluid unless there was an actual overheating condition. Then I would want it at the max line in order to see the fluid coming out.

 

[BigCahuna]

This is how I view it. When filled to the min level when cold, that is how much actual fluid the motor needs. When it gets up to operating temp, the fluid expands and will move up to the max level mark. Some will ask, then why is there room over the max mark?. The simple answer is ,we don't all ride in 72 degree f temperature, so in hotter climates the motor will run hotter and the fluid will expand more, but not go out the overflow. Then when it sits and cools off, like a few hours or over night, the fluid level will be back at the min level. Over time the fluid may evaporate, or exit the overflow hose if the bike sits in traffic, or is run very hard. A dirt bike may have the radiator plugged with dirt or mud, and it will get hot quick.,,

 

[ZeeOSix]

No vehicle I've ever owned makes the coolant level go from the 'min' level when cold to the 'max' level when hot. If the level was at the min level when cold, no matter how hard the vehicle was driven the level would maybe go to half way between 'min' and 'max' lines when fully hot.

 

[ragtoplvr]

This tank has to allow for expansion of the fluid. Antifreeze is slick, you do not want to spill any. As long as the hose inlet in the bottom of the tank is covered in all conditions, you have all the cooling available. If you should happen to boil a little, then there is room to catch all the expelled fluid so it can return to the colling system when it returns to a normal temperature. Adding fluid to the max line does nothing to but make a sill more likely. Modern motorcycles are very finely engineered, to be a light as possible, there is no extra tank volume like on most cars and trucks.

If you happen to get caught in traffic on a hot day you are likely to reach or even exceed the max level . No fluid should spill unless you are so hot that you are venting steam. In that case you should pull over.

 

[Bonz]

I guess my ZRX 1200 isn't a new finely engineered motorcycle, being it was made 20 years ago. The only time it overflowed was when synchronizing the carburetors and I did not realize the fuse was blown on the fan. It got so hot it did bubble over, temp gauge was well past halfway on its way to red. Fan comes on at the halfway point on the temp gauge on the hottest of days at high elevation here in Colorado or when the outside air temperature is pushing 100° in stop and go traffic.

I get it, you don't want it coming out and dumping where the rear tire can slide on it, that makes some good sense. However if the manual shows filling it to the max line when cold, and it will only allow a person to fill to the min line when when cold in operation, that tells me the manual is wrong or the bike is getting hot too easy.