In my case I had a partial engine overhaul. Nothing major, just oil burning on continuous high speeds and I've had enough of oil topping up between changes (just once, tho). It's an import from Germany and over there they hammer cars really hard on their autobahns. +120 mph for extended periods of time is common over there. You know the impact of that on an old design small engine like of a 1992 3L.
I've only had one car that burned oil and I've owned more than my share of cars in my lifetime. One that had rod knock. Another that had bad lifters. The oil burner had bad valve seals.
How many cars have you owned and what brand/model were they?
Current is my trusty 99 Mustang. I hurt it a couple years ago with an oil incident so it either partially slipped a bearing, the lashers need replacing, or a piston is pushing oil through. I have terrible luck so I'm just waiting for the rod knock assuming the worst.
Some cars burn oil but you don't notice or know it if you don't run it under certain conditions.
When it burned oil it happened on highways only (I work next city) but when I took a long vacation once, the oil level didn't go near as low as it does on highways. It took +1000km to get there. Under the same change interval, of course.
The warning light comes up at -1.5L and I used to top up at ~3000km between the 5000km changes. Oh yeah, this old car has an engine oil level warning, engine oil pressure gauge, front brake pads wear warning and some other easily implemented feature that I wonder why other newer cars like the Crown Victoria 2009 don't have. But that's another subject.
The cars I had for personal use (not necessarily owned) were Mercedes 200E 1986, Crown Victoria 2001, Crown Victoria 2009 and finally the one I'm talking about Mercedes 300E 1992 (last two I actually owned). Believe it or not, these old MB's are cheap to maintain here. It's like owning a Camry in USA.
It does smoke at times. I have seen it blow blow blue smoke in the summer and then the same day it not smoke at all. I sit sometimes with the a/c on and engine idling. And nothing else seems to happen but sometimes i smell a weird exhaust smell while i do that sitting and running the a/c or heater. Notice it most as i take off after sitting with the engine idling. I add about 1 pint to one quart every few days of antifreeze along around the same times. Antifreeze is more than the oil for the same period. This all started when i had the thermostat stuck in the closed position. Thats why i think it is a seeping head gasket. Just to weak to take the heads off and replace the gaskets. My nephew has friends here that work on engines and am working on getting one of them to help. No More than what it leaks or burns, I never see it leak, I am not worried about it. Maybe this year. Right now its the only vehicle we have running. Baby it along till Robert gets his car on the road. Then i can work on getting things fixed.
I'm lucky my car still runs. Sitting in line to get my kids behind their school a fresh oil filter decided to pop the gasket and dump all 6qts of fresh oil all over the concrete. House was only 2 blocks over so I drove it back and it shut itself off 2 driveways before mine. Pretty sure doing that instead of pushing it screwed something up, just waiting for it to show itself.