Dump the oil and go get some diesel engine oil with as close to the visc. rating as you can find, dump the oild and filter, fill it up with diesel engine oil and go for a drive to your nearest radiator place, and ask them to check the gass content of your coolant.

Reasons - if its blown a head, that is the quickest way to find out. Also, diesel engine oil has a massive amount of detergents in it, to help deal with the sodium and particulates that accumulates in the sump, making it a perfect "running in" oil for petrol engines.