24 replies to this topic

[NLinPEN]

I am not sure whether my question is specific to the SPI model, or applies to all (newer) versions of the Mini. The car had a coolant overflow tank (a.k.a. expansion tank) mounted in the left front wheel arch. However, this was a bit of a botch job by a previous owner: the tank was dangling by a piece of metal wire from the fresh air hose that goes to the vent in the dashboard. This held up until it didn't: the air hose came loose under the weight of the tank, the tank came down and got stuck between the wheel and suspension. I am not sure whether this tank is original to the SPI model, or some aftermarket model.

Obviously I want to mount this tank properly. But I can not find a clear drawing or photo on where it is supposed to be mounted, and how it is to be mounted. What is the correct location? What kind of brackets do I need? How is this tank mounted to the car's body?

 

If anyone has a drawing, or some photos of how it is mounted I would appreciate it.

[MikeRotherham]

The tank is original to Spi and later carburettor models.

 

Here is a link to one on Ebay with a number of images of what the tank should look like and how it sits under the wing:

 

https://www.ebay.co....tm/256974127982

 

The threaded bolt is secured through the bulk head by a nut.

 

To use this tank you also need the correct radiator cap which allows coolant to enter and leave the expansion tank.

Edited by MikeRotherham, 18 February 2026 - 05:06 PM.

[Quinlan minor]

As above.

Edited by Quinlan minor, 18 February 2026 - 09:39 AM.

[Ethel]

Here's a piccy of one snuggled in

 

 

Note the hose is at the bottom so coolant can be sucked back when it cools. It has a fill level for the same reason.

 

The radiator cap, mentioned above, has 2  rubber seals: 1 between the cap itself & the filler neck as well as the spring loaded one.

[NLinPEN]

The tank is original to Spi and later carburettor models.

 

Here is a link to one on Ebay with a number of images of what the tank should look like and how it sits under the wing:

 

https://www.ebay.co....tm/256974127982

 

The threaded bolt is secured through the bulk head by a nut.

 

To use this tank you also need the correct radiator cap which allows coolant to enter and leave the expansion tank.

Thank you for this: it is very useful. The photos confirm that I do have the original expansion tank (PCF10097) on my car. Which makes me wonder why the previous owner(s) did not mount it in its intended position. Those photos on eBay show that it sits on a bracket and is located next to a black canister (isn't this emissions-related?). That black canister is present in my car.

Due to the tank getting stuck between the wheel and the suspension did it get mangled. But I am not sure if this has made it unusable. There is a crack near the top of the tank, see photo #1. Photo #2 shows more mangled-ness, but no other cracks. I don't know whether this expansion tank operates under pressure, or that it is at atmospheric pressure (e.g. an overflow bottle). Having to make this airtight would be a bigger job then just slapping some duct tape on it.

Attached Files

•  1.jpeg   36.01K   3 downloads
•  2.jpeg   31.35K   2 downloads

[NLinPEN]

Here's a piccy of one snuggled in

 

 

Note the hose is at the bottom so coolant can be sucked back when it cools. It has a fill level for the same reason.

 

The radiator cap, mentioned above, has 2  rubber seals: 1 between the cap itself & the filler neck as well as the spring loaded one.

Thanks for your comments related to the radiator cap. I will check whether mine is the correct one.

[Ethel]

That has been in the wars 

 

I'd guess the black buttony shaped bit, on the top by the bracket is a pressure relief valve of sorts. It looks pretty basic so may only be intended to avoid the tank going bang as a last resort. You could try and rig up a test rig with a foot pump to if tank is battered but functional. Anything a few psi over the radiator cap will likely do

[MikeRotherham]

I was never sure if the expansion tank was pressurised or not.

 

If it is the pressure must be very low.

 

The black 'bung' with a centre doesn't can't hold much pressure.

[NLinPEN]

 

Here's a piccy of one snuggled in

 

 

Note the hose is at the bottom so coolant can be sucked back when it cools. It has a fill level for the same reason.

 

The radiator cap, mentioned above, has 2  rubber seals: 1 between the cap itself & the filler neck as well as the spring loaded one.

Thanks for your comments related to the radiator cap. I will check whether mine is the correct one.

 

The radiator cap has indeed two seals, and both look in good condition. They are not torn or damaged. The cap is rated for 88 kPa.

Attached Files

•  3.jpeg   41.64K   1 downloads

[NLinPEN]

I was never sure if the expansion tank was pressurised or not.

 

If it is the pressure must be very low.

 

The black 'bung' with a centre doesn't can't hold much pressure.

For now I'll assume that the cooling system will work with the tank being an overflow tank, at atmospheric pressure. Just like you I have my doubts about that black "overpressure valve". It looks rather flimsy to me.

[Ethel]

It all depends on the relative water levels in the radiator & tank. I expect Rover had to fit it because of environmental regulations against squirting antifreeze out. It will do that, even if it can't recover lost coolant when it cools down. If the radiator as lost some of its contents it ought to get below atmospheric pressure when it has cooled, but the rubber hoses won't allow much. Vented steam would condense inside the bottle, which would drop the pressure a lot if it wasn't vented - I just can't see coolant making back from the tank to the radiator under gravity alone, the water level must be a fair bit lower.

 

0.9 bar is 13 psi the original cap was 15psi, but it'd only allow it to boil over at 118 C instead of 120 to 121 C. There are masses of similar looking radiator caps, so it could be worth some research to check it's for the correct filler neck height - if you have cooling problems. 

[coopertaz]

The tank is original to Spi and later carburettor models.

 

Here is a link to one on Ebay with a number of images of what the tank should look like and how it sits under the wing:

 

https://www.ebay.co....tm/256974127982

 

The threaded bolt is secured through the bulk head by a nut.

 

To use this tank you also need the correct radiator cap which allows coolant to enter and leave the expansion tank.

presume for jap. spec, my 1995 spi and 1992 carb model had standard rad and both were low mileage original models when we got them. both did have the charcoal canister under the wing though

[NLinPEN]

 if you have cooling problems. 

To avoid that this thread is going into a different tangent: no, my car does not have cooling problems. I have tried my best to make it work hard and demonstrate any cooling problems in the hot Malaysian climate, but there simply aren't any.

[bangermadness08]

What is the correct cap for a 1995 spi?

[Ethel]

Minispares say 15psi (yes, the stamping on the cap is more accurate)