Hi,the other day i filled my radiator up to full,a couple of hot days later,the coolent level was down below the coils or fin things inside the radiator,is this normal,i cant remember what it was like last summer thanks

Get an expansion tank, and put a non pressure cap on the radiator and a pressure cap on the tank, this is good so when the coolant gets hot and expands it doesn't shot out the radiator, insteed it shoots into the tank and then draws itself back through. Mokes had them but the best ones I've seen are on Rover SD1s and Range Rovers. They are brass (painted black) but with a bit of stripper and some polish look fantastic.

BTW to answer your question, losing coolant from the radaitor is normal, but if not topped up will lead to terrible overheating!

<edit> The expansion tank will require a shorter necked pressure cap than standard mini one, which is available from most speed shops and mini specialist will know what I'
m talking about.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

Expansion of the coolant will push some out of the radiator if you fill it all the way. I generally fill mine to about 10mm below the cap level but sometimes o really hot days it will push out more. So long as the level stays constant and doesn't drop it's probably ok.

I've found the addition of an expansion tank as used in modern cars and Mokes etc is better as then there is no air in the radiator and the volume of water circulating is slightly more.

Daniel
PS - I must have been typing same time as slinkey, oh well

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Videos - Turbocharged A-Series on Dyno & at Wakefield
Mafs waz not my strong subgeckt at skkol

Later models 1977-78 here had a `water level' mark inside, 1/2 way down the tank.
Yes it's normal to lose 1/2 a tank as it expands...
But- tomorrow when it warms up, the 1/2 tank of air will get expelled, and the tank is then actually full when motor is hot.
That's the theory, anyhow.

<edit> you can easily add a plastic expansion tank off a modern Jap car, just find a rad cap which is `recovery' type (has a rubber seal around the outer lip).
Only antiques like Jags, Mokes and M1100s had a pressurized metal expansion tank.

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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.

so if its normal to lose coolant, is my mini misbehaving? (hasnt lost any coolant in about 2 months and has driven on a few hot days. no expansion tank)

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78 Leyland Mini - Prince

It's not normal to lose coolant continuosly, the point is that after you fill up the level may drop due to coolant being pushed out as it's heated. It expands at higher temp and has to go somewhere.

If there is an air space at the top of the radiator tank then the excess water fills this area and compresses the air to the rating on the cap, normally 13psi. If you have an expansion tank then the radiator is always full with coolant, not air.

Daniel

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Videos - Turbocharged A-Series on Dyno & at Wakefield
Mafs waz not my strong subgeckt at skkol