if it`s running hot then you obviously have an issue to sort

most minis (even 1500cc & 1600cc ones) don`t need any extra heater core or fandangled thing to help cool it

i`d expect you have issues with maybe thermostat stuck shut, or cracked head or blown/weeping head gasket, or too retarded ignition,,, or too lean mixture,,, or blocked radiator,,,, or water pump impeller corroded or not good enough,,, etc etc etc,,, Or any combination of all of the above

plenty of things can make them run hot,,, best to sort them all before attempting to "Cover up the symptoms" instead of "Curing the cause"

that`s what i say anyways,,, if it`s running hot then you have to sort the reason why it`s running hot
instead of trying to cover it up with a band-aid

simple as that !!!!!!!!!!

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

I agree. Had 6 Mini's and never had an overheating problem. 2 of them were seriously souped up....

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67 Deluxe
Dry suspension
1293cc, 11:1 comp, RE 282 camshaft, 45 Weber, extractors etc
4 synchro close ratio gbox
Cooper S brakes, no booster
Stealth box, as Doc says "goes harder and idles!"
RH tank cos I needed it crossing the Nullarbor etc..

Nice looking car . Whats the paint colour/code ? Original ?

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'78 1275 LS (Under Repair, Dependant #1's car)
'72 GT Powered Clubman (Mine)... Under (re) construction

IMO the stock factory Mini cooling with big motors (1275 and up) is marginal. Why else did the factory Cooper S drivers handbook suggest turning the heater on if the engine got too hot.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

What about the cleanliness of the inside of the block? Was it cleaned properly as part of the rebuild, or was it a crappy old one?

Mine ran fine until I gave it a run down the freeway.
It loosened all the old grid which the blocked the radiator and overheated.
Pulled it out and cleaned it and then ran a piece of stocking in the radiator inlet for a while as advised by a member on here. Changed it a few times to get the junk out.
Now runs fine.

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Find a job you love and you will never have to go to work !

hi 78 clubbie, not the original color. but its a original clubman GT 1972. if u lived in the south coast sydney area ill tell ya come for a drive with us. went sunday with the minis in the gong it was a great day out.