I recently replaced the plastic expansion tank to an aluminum one with a new cap. I have noticed however that coolant is leaking out somehow and in a couple of months at least a full tank has leaked out. I have looked at the usual leak points (thermostat, water pump, hoses) but all are clean. The only indication of coolant leaking is the task where traces of coolant is present. I am thinking maybe there is a problem on the expansion/contraction of aluminum vs the cap which is plastic? Any experiences from others who have used aluminum tank would be appreciated.

 

The caps themselves can become faulty. Usually people replace the black cap with a metal one when doing aluminum tanks. It's not necessary but if your cap is shot - the metal ones aren't that much more than stock one

 

I did not realize there is a metal cap applicable to the mini. Could you share the type and where to buy?

 

Also, don't over-fill the expansion tank: even a functioning cap acts as a pressure release valve. When there's too much coolant in the tank, the coolant pukes out under pressure.

 

I don't know what aluminum tank you got -- so I can't really help there. The guys who have the Canton tank almost always go with a metal pressure release cap.

The question you need to answer is -- is it the cap or is your system somehow over-pressurizing.

You say you leaked out a tankful of coolant, the tank should never be full -- about halfway up is where you fill it to. Did you properly bleed the system, is your oil a normal color, is there white smoke coming out of the exhaust, is your thermostat housing leaking? All things I would check.

Also - is it an OEM cap you are using or is it cheap eBay stuff??

 

Good point but should not go empty as well

 

I am not sure if mine is OEM. The aluminum tank is out of eBay and had to buy cap somewhere else.

Thermostat housing is OK as far as I can see. No leaks there.

 

Probably not. I thought from your OP that you meant that a total of one tank of coolant had leaked out as you were periodically topping it off.

 

Saw a canton racing cap at JEGS. Below is the part number and psi. Is this correct for mini?

JEGS Part Number: 074-81-016
Expansion Tank Pressure Cap
16 psi

 

^Dunno^ I've never installed one of those...

 

I'd give them a call and see what they say, but a cap would be a good place to start. I know M7 sells aluminum tanks with billet caps. Might be able to also give them a shout and see if they have a cap that'll fit the tank you purchased.

 

thank you or the responses. After some reading and some information from Canton, it appears that there are 2 types of aluminum tanks being sold out there. One is a direct replacement, meaning it takes the original cap. the other is one that has a billet radiator style neck. this is what canton sells and it takes the real pressure cap (billet type). using the billet style tank seems to make more sense to me because it takes the billet type pressure cap that most cars uses. this could solve the disappearing coolant issue.

One other question that I have is, - what is the spec of the cooling system of a mini as far as pressure is concerned? the Canton pressure cap is rated 30 PSI. Is this correct?

 

You're welcome. I believe the OE cap is rated at 16 PSI. There is some info about the Canton tank in this NAM thread here. Definitely read through page 2 about the cap PSI's. I'm not sure about the rate for the Canton, but I think 30 PSI is right, as stated in that thread.

 

did you check the connection of the bottom hose???????

start simple people . . . .

nothing difficult here .....

with a cold engine you can safely reach under

if the tank is empty and the engine cold ... fill it up and spread a bunch of paper towels UNDER the tank . . . .