Hopefully i can help..
Its certainly not uncommon for these to cause an issue like that with oil geting into the coolant system as oppossed to the water in the oil..and the reason for that is that oil pressure in the engine is alot higher than the coolant system pressure so any small crack within the oil cooler itself internally being part of the both systems oil/coolant- the oil will always leak into the coolant tank..the oil cooler is part of your oil filter housing - if you locate the top cap for the oil filter element you see the cooler further down and you see the coolant hoses leading to it...There isnt anything else really that would cause that fault..and the cooler if refitted to the second hand block would be the next place to have replaced..ideally with new seals etc..obviously after its been fitted that whole coolant system will need to be properly flushed out..aswell as new oil and filter and replacement coolant once the whole coolant system has been cleaned out..But if as you say you spotted a trail of oil under the van..then maybe have look under there or have somebody check up to see where that leaks coming from..If there is no oil registering then it wouldnt be advisable to drive the van or run the engine or risk more damage due to lack of oil..ideally it would need to be recovered to the garage concerned im afraid. if its lost that much oil in a space of 7miles..I do hope this helps
one quick question how would you flush the coolant system
Hi..there..sorry for the delay..
Its does take a bit time to actually flush the system out - you need the whole coolant system cleared out "thoroughly" including radiator & matrix too either with a powerwasher/hose with detergent can help.there are such brand out there inc additives /cleaners such as "Forté Bio Degreaser" or even household dishwasher tabs into the system - you will need a few of them to flush the system.firstly remove thermostat itself and reinstall the housing - while flushing system let the engine circulate the water/detergent around the system - never allowing the engine to overheat and just keep draining off when the engines cool and refilling inc additive/detergent each time,repeat the process until is cleared out,although you will never get rid of it all,there will be still small traces..bear in mind oil can effect the rubber hoses over period of time and they will eventually deteriote and cause problems - thats why It is recommended to if at any point the cooler itself does go and contaminates the coolant system you do have to replace every rubber hose,then as above the heater matrix/radiator and the engine coolant passage ways/expansion tank etc till clear re flushed till clean as best you can get it..But like i say it a very time consuming job clearing all that out..I do hope this helps