Could using the wrong oil (non C rated) have ruined my 240 engine?

[ROLLGUY]

I loaned my 240 to a friend a couple months ago. He returned it after logging about 3,000 miles on it. It has been sitting for a month or so because I could not get the engine started. I tried several things again today, and still no start. I had the block and lower rad hose heaters plugged in for about 6 hours, and the battery charging. I also put a blow drier on high connected to the air intake hose. It sounds like it wants to start, and even smells like partially burnt fuel. I changed all the glow plugs the other day as well. I found a half used quart of 10W-40 oil in the trunk. It was regular gasoline (S rated) oil. I knew the car did burn oil, so my friend had to have added some during the 3,000+ mile trip. Could using the wrong oil cause damage to the engine? The other possibility is that he could have ran it out of oil. I don't know for sure. I guess I need to do a compression check next......Rich