oil in water

[geoffl]

just took off water filler cap to check anti freeze & noticed oil in water. van is 02 transit & is running fine but dont know how oil is in there. any ideas

[big mk5]

normally if theres oil in the water it means head gasket has gone ....but sometimes the antifreeze in the coolant has alittle look of oil has it leaves a little rainbow on the top of the water .....is there any gunk or mayonnaise in the oil cap? to be sure id get the expansion tank checked for exhaust gasses with 1 of those chemical kits