As the title says, my coolant bottle is frothing...very very slowly. Last night when i turned my engine off i decided to check for froth or anything like that again, so slowly took my coolant cap off and as i was doing that, coolant seemed to have forced it self out the side of the coolant bottle. the stopped when pressure was relieved. I will ass that the other day i added a little bit of radweld as i had a small leak coming from the back of the engine somewhere. I am not loosing coolant anymore but i am getting some frothing. No mayo stuff on oil cap and dipstick looks good. Could anyone shed some light on the problem could it be air getting into the coolant bottle? from the small leak where it forced itself out? head gasket? I may possibly change the coolant bottle and see if that makes any changes.