5L of Oil instead of 7L

I have a 1997 Nissan Terrano II 2.7 TD, which is my first car. I didn't know much about how much oil it needed, so my mechanic changed the oil two months ago, but only used 5 liters. I haven't had any problems with it so far, even though I've only driven it about 300 kilometers in those two months. Today I figured out it needed 7L not 5L.

Also, the fuel pump in my car was broken and was pumping too much diesel, which made the car use a lot more fuel than it should. Last week, the pump completely broke down, and I lost the acceleration pedeal. Now, I'm waiting for a new turbo and fuel pump to be installed.

But I'm really worried that when everything is fixed, there might be more problems. I think the broken fuel pump might have been helping to cool the engine because it was pumping so much fuel. So, when it stopped working, something bad might have happened to the engine.

What do you think?