Expansion tank options

Eastep

True Classic
As my understanding of an expansion tank is to serve as a reservoir for small quantities of coolant and provide a small amount of extra space for said coolant to expand as it is heated and pressure is generated and increased; a smaller expansion chamber should not effect the cars overall cooling system, other then not storing as much reserve coolant and a smaller amount of free expansion area.
Correct? Are there any other issues or concerns I should know about?
 
For whatever reason, the X1/9 needs a larger tank. A "standard" size tank doesn't allow for the amount of expansion / level change that occurs with the Fiat motor, in my experience. The stock tank is probably triple the capacity.
 
I would expect that the X requires a large expansion tank due to the amount of coolant contained in the system. The long pipes traversing the length of the car add a fair bit of capacity. As long as you can contain the expansion I do not see any reason for additional space.

Brian
 
Easy enough to test, check level cold and hot in the tank.
That's kinda what I'm asking about. The tank holds 1 gallon hot and 3/4 empty. At least mine did. But is there a "need" to have that much on reserve? As long as the system is full and there is enough say 500ml of expansion tank, there shouldn't need extra coolant stored? I wonder if there so much reserve for when the heater is used, and it holds roughly that much? My heat doesn't work so I have no way to test.
 
I thought about this a little more and here goes. As the coolant expands it begins to fill the tank more and more. As the space is taken up the pressure increases. With a large space the pressure will be lower. With a small space the pressure will be higher. If the pressure is too high, the cap will open. I am not sure if this is a problem or not, as when the car cools off there will be a vacuum and the next heat cycle the cap should not open.

Or maybe I'm totally wrong.

Brian
 
An antifreeze cooling system should not have any air space. That is why overflow tanks are used. I’m not sure if the X has an overflow but it should have. In an oxygen free system antifreeze is an anti-corrosive. If air is allowed into the system the anti-corrosive turns corrosive, very corrosive. A leaking heater core in other vehicles will corrode a floor pan much worse than water. Normally an expansion tank is used if the radiator is placed lower than the radiator. Air needs a higher level to escape. Volume of the tank in a closed system if a overflow tank is used shouldn’t need much volume. Even motorcycles use overflow tanks to keep air out of the cooling system. Theoretically the cap should never be opened.
 
An antifreeze cooling system should not have any air space. That is why overflow tanks are used. I’m not sure if the X has an overflow but it should have. In an oxygen free system antifreeze is an anti-corrosive. If air is allowed into the system the anti-corrosive turns corrosive, very corrosive. A leaking heater core in other vehicles will corrode a floor pan much worse than water. Normally an expansion tank is used if the radiator is placed lower than the radiator. Air needs a higher level to escape. Volume of the tank in a closed system if a overflow tank is used shouldn’t need much volume. Even motorcycles use overflow tanks to keep air out of the cooling system. Theoretically the cap should never be opened.

The tank on the X is an active part of the cooling system. Coolant is constantly cycled through the tank when the engine is running. Not sure where you get the corrosive/anti-corrosive idea from. Typical coolant systems like the X contain water/antifreeze mix, which mean oxygen is present in the system, and this is why the system needs to be pressurised. Air pockets can also develop as a result of hot spots in the motor/block under hard or spirited use. These events do not turn the antifreeze/water mix into a corrosive agent, any more than they were in the first place. If one uses a coolant use as Evans Waterless, the system can be left effectively open / un-pressurized, as it does not suffer the problem of water content turning to vapor around the cylinder liners, etc., as with standard coolant.

Expansion tanks have to be placed with the vent tube entry higher than the passages in the cylinder head, which is why the tank is located and integrated into the system as it is, so that air/coolant can escape to the lower pressure area.
 
As my understanding of an expansion tank is to serve as a reservoir for small quantities of coolant and provide a small amount of extra space for said coolant to expand as it is heated and pressure is generated and increased; a smaller expansion chamber should not effect the cars overall cooling system, other then not storing as much reserve coolant and a smaller amount of free expansion area.
Correct? Are there any other issues or concerns I should know about?
The top of the expansion tank must be above the highest point in the rest of the cooling system, and the outlet for the bottom hose from the tank must be below that point.

The volume of the reservoir, both above and below the waterline, must be large enough to take all the expansion of coolant as the engine warms without having to push any past the pressure cap. In practice, what you do is somewhat overfill the tank so that it does overflow a few times. When the tank is large enough it will stabilize after a few cycles with the water at or somewhat above the high point of the rest of the system, and will not lose any more coolant as the engine heats up.

A too-small tank will lose enough coolant when the engine is hot that once it's cool the level will be too low. If the cold level in the tank is below the high point of the rest of the system you will overheat - there's air in the head where there should be water.
 
The tank on the X is an active part of the cooling system. Coolant is constantly cycled through the tank when the engine is running. Not sure where you get the corrosive/anti-corrosive idea from. Typical coolant systems like the X contain water/antifreeze mix, which mean oxygen is present in the system, and this is why the system needs to be pressurised. Air pockets can also develop as a result of hot spots in the motor/block under hard or spirited use. These events do not turn the antifreeze/water mix into a corrosive agent, any more than they were in the first place. If one uses a coolant use as Evans Waterless, the system can be left effectively open / un-pressurized, as it does not suffer the problem of water content turning to vapor around the cylinder liners, etc., as with standard coolant.

Expansion tanks have to be placed with the vent tube entry higher than the passages in the cylinder head, which is why the tank is located and integrated into the system as it is, so that air/coolant can escape to the lower pressure area.

It’s no theory that a coolant system low on coolant for a long period of time will turn anti-freeze into a black muck and corrode the system it was meant to protect. I’ll use my Corvette as an example. It has a plastic expansion tank system. However as coolant expands the cap allows hot coolant to flow into a catch resivoir. Upon coolant contracting as it cools the cap allows coolant from the overflow resivoir to be drawn back in therefore no air is in the coolant system. By the way I prefer to use BMW’s blue anti-freeze in all my liquid cooled vehicles.
 
It’s no theory that a coolant system low on coolant for a long period of time will turn anti-freeze into a black muck and corrode the system it was meant to protect.

That's not really the same scenario as a running vehicle that's just a little low on coolant, which is what we are talking about here, no?.
 
That's not really the same scenario as a running vehicle that's just a little low on coolant, which is what we are talking about here, no

I was under the impression the tank holds a gallon, which seems excessive but the systems design using long transfer tubes to the radiator could present issues not found in other vehicles. Upon cooling the tank is drawing in two quarts of air? Heating up expansion pushes the air back out? I don’t like the idea of coolant expansion pushing anti-freeze on the ground. With a catch and return resivoir any overflow will be ruturned to the system. If the X is not set up that way, it’s not difficult to add one. All racing sanctions require a catch can.
 
Water doesn't compress so when it gets hot and expands the larger volume needs someplace to go. On old timey 'Merican cars the top of the radiator was higher than the top of the engine, so an air space (air can compress) in the top tank of the radiator could accommodate the expansion of the hot water.
In the X, and 124 Spider for that matter, the top of the radiator is lower than the top of the engine. So you need a different way to accommodate the expansion of the coolant. The X uses an expansion tank that holds enough air to allow expansion of the hot coolant without spewing it all out. On the 124 Spider there is no expansion tank, instead the expanding hot water is forced out of the pressurized system into a holding tank that is not pressurized. When the hot coolant cools down it contracts and sucks the coolant that is stored in the holding tank back into the pressurized side of the system.
You could do the same thing with an X, if you used the right type of radiator cap (two way valve). It would be easy to add this cap into the X system with a readily available radiator hose T fitting that holds a radiator cap. You would still need a holding tank that would accommodate the amount of coolant that the expanding coolant would push out of the pressurized system, but the holding tank wouldn't need to hold any pressure so could be much simpler than the expansion tank.
However, Fiat engineed the X system to use an expansion tank for a reason. I think it is intended to work like a water/air separator. It allows any air in the system to "bubble" out of the coolant. I don't know why the 124 Spider doesn't use an expansion tank. Cost?
 
Technically there shouldn't be an issue with overfilling the expansion tank as there is a bleed hose on the neck. One thing often overlooked that is worth checking, as I see a lot of photos where the cap is still the original, is to check the condition of that, a $10 part at most. My X is an 89, and whilst the cap looked good on the outside, an inspection of the seals showed they were completely stuffed. Maybe coincidence, but I had been having overheating issues, and whilst I replaced all the hoses, first port of call, I also replaced the cap, and voila, no more over heating issues.
 
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Technically there shouldn't be an issue with overfilling the expansion tank as their is a bleed hose on the neck.
That's right - if you overfill the excess just gets forced out, and indeed the easiest way of getting the level right is to deliberately overfill and then let the system spit out what it doesn't need.

You are also right about the cap. If it doesn't seal it won't hold pressure and the system will overheat.
 
You are also right about the cap. If it doesn't seal it won't hold pressure and the system will overheat.
And if you pull the cap to check the level, set the cap on the trunk lid, then drive off for a drive... the car will slowly overheat and will wonder why. When you get home and open the engine lid to see why it was running hot, you will be embarrassed and hope no one knows how dumb you can be. :oops: If you get lucky, the cap will be laying in the middle of your cul-de-sac and it wont have been run over by anyone. So that's a win I guess?o_O
 
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