If you have a modified mini and understand that adding an expansion tank is among your next steps, but can't see a place to fit the OEM tank as fitted to MGs, Austin Americas, etc. This may interest you. It is a fine reproduction of the tank fitted to several Volvo models. It snaps into a bracket sometimes found on the firewall and sometimes spot welded to the fan shroud. It is well made and mounts in many places in mini engine bays. First, buy or make a blanking cap to fit atop the radiator, as this tank is fitted with the pressure cap. Find a place to mount the tank, run suitable hose, and then completely fill the radiator to the top of the neck, and fill this expansion tank to between 1/3 and 1/2 full.

Here is a blanking cap

//www.minimania.com/part/GRC126/Classic-Austin-Mini-Radiator-Cap-Non-Pressure-Blanking

Here is the Volvo tank

https://www.ipdusa.com/products/12141/125576-coolant-expansion-tank

Coolant to the top of the gills in radiator when cool/cold...the 'empty' upper tank is the expansion chamber.

Modern vehicles and industrial engines use expansion tanks, just like MGs, ADO16, and minis built in many offshore places. I fit expansion tanks to my minis and drive in the hottest temperatures without concern.

An 850, however, need only be NOT OVERFILLED and does not need an overflow tank or an expansion tank.

When you have 14 bhp at the wheels, it makes sense to not add stuff you don't need.

A very loose statement.

A quick look under the bonnet of any current model car will how this is not the preferred solution of the modern car companies...

Cheers, Ian

the over flow rad tanks for the mokes from OZ are the best .but NOT cheap these days..

I like it.  Very clever.

bicycle bottle holder + bottle. Bottle cap already set up for a tube.  Bottle holder makes easypeasy mount inside the fender well.

My car came with a plastic 1-liter Mt. Dew bottle as an overflow reservoir that worked, I suppose, but it looked pretty tacky.  I think this looks much more professional and it works great.

since i have the nice shiney alloy radiator as well i have an aluninum cylinder from jegs.   works well and i like the looks of it   sorry   dont know how to post pictures here but i could email them to you, maybe i figured it out

I use a small Polaris snowmobile engine coolant reservoir that works fine and mounts easily with one bolt/nut. Bought it on eBay for $12.

All you need is the correct radiator cap, a few feet of fish tank hose and a suitable container.... an empty (a 500ml/1 pint) brake fluid container works perfectly....

Doug got it in one...

Cheers, Ian

One of the Polaris 4 wheeler overflow tanks work well they are shaped similar to the bracing on the bulkhead behind the radiator.
Never fill the radiator up completely fill it to about 1.5 inches from the top.

dido.. what rosebud just said.  I use same 2 core alloy rad. but use the six blade tropical fan blade. and just dril holes in the thermostat to get more flow.. btw. do NOT use a 16 PSI cap.. 15 PSI is the max on 1275 cc and 13 PSI on 998cc. I have found works best   later bc

Almost any reservoir will return fluid to the radiator IF the radiator and cap were designed for that purpose.  All that is necessary is that the tube filling the reservoir goes to the bottom of the "tank" and doesn't stop "at the top".  It is the vacuum created in the cooling radiator that sucks the overflow back.

I have 2-core aluminum radiator w/ a 15 lbs. cap and have never lost a drop of coolant, even with sustained 220°F water temps [link]. So, unless you're losing coolant, I'm not sure you need an overflow container. Unless of course you just want some extra bling under the bonnet.

Greetings everyone.  I am looking to install some sort of coolant resovoir to my 74 mini850.  Car currently has an aftermarket aluminum radiator.  Hoping for more than just a catch can; I'm hoping more of an overflow type that will return coolant to the radiator upon cool down.

What do you all use?

Where did you get it?

Where is it mounted?

pictures and suggestions welcome!  Thanks in advance!!!