So, today we had bright blue sky and sunshine, so I changed the engine oil and filter. I used the method of firstly draining the sump, then changing the filter half filled with fresh oil and then filling the sump and ...immediately got oil pressure. Pew. Was thinking of: Why not drain the sump and then fill the sump with fresh oil and then change the filter with half fresh oil. This allow you to start the engine right after fitting the filter. What do you think? Crossing my fingers that the Gulf 20W50 works ok, I normally use Valvoline VR1 20/50 Racing for the Mog and our AH 3000.