thermostat doing its own thing
 

hello. i recently bought a 99 passat 1.6 petrol for my wife, the thermostat gauge in the cockpit seems to dip when motoring ..ie.. it comes down from 90 degrees to near cold reading when on the open road, however it does not overheat when idling or in traffic, i have noticed a few oil splaters in the expantion bottle. and a lil cream on the oil cap. instantly i thought head gasket, but after a lil digging i found there is an oil cooler ,water cooled..corroded pipes perhaps? has anyone had this issue?? im hoping it aint head gasket, is the head gasket an expencive fix? presuming i get the head skimmed and new bolts and gasket myself..whats the average time for a head gasket repair (assuming the head aint warped) any feedback much appreciated:confused::):confused: