I was stuck in traffic on a fairly warm day recently and my mini got very hot. It then started missing and coughing and spluttering like crazy. I found a spot to get out of the jam but when the radiator had cooled a little I took the top off for a look. Instead of nice green coolant which I expected to see I had brown froth... The engine is not much over 5000ks since a rebuild and this is the first time it has gotten that hot.
I thought it may have been fuel evaporation causing it to run rough but it still ran rough after it had cooled for 20 mins with the fuel pump running for around 5 mins. A few good revs and sinking the boot in cleared it up. I've had this when idling at lights too long before.

So the questions. What is the brown froth? Have I done some damage? What is causing it to run rough, miss, cough and backfire when it gets hot? How can I fix these issues. Oh and how to stop it getting hot when stuck in traffic???

got a mini friendly mechanic? sounds like a good tune would be a good idea, but might've done a head gasket

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did I tell you that I won a trophy?

Yeah, what Simon said.
Get a rolling road tune, then see if the froth returns before doing head repairs.

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Dean Hutton's first car was a Mini.

1st do a compression test
2nd a cooling system pressure test

Exhaust gasses pressurizing the cooling system or the water galleries in the block havn't been cleaned out and it didnt have the coolant circulating as it should and took the easiest/weakest route to release the pressure. Similar principle to electricity.

didnt you have a similar trouble with the purple one about 18ish months ago or am i thinking of the wrong person??
If you are the right person, the new owner is now very happy with his rebuilt engine as there was quite a substantial amount of damage to 2 of the pistons (from memory No.1 and no.2) crowns..........

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http://www.youtube.com/watch?v=nDMkVq1jRGU