Oil Consumption - what is 'normal' ?
Found on the internet- this applies not only to 0-200 but to the C75 and C85 as well
First - "normal" oil consumption on an O-200 is about a liter every 15 hours or so, some a bit more, some a bit less.
Second - if you fill it to six quarts, "full" on the dipstick, the first hour or so will see half a quart (half a liter) go out the breather tube. You aren't burning it, it is now on the belly of the airplane. Generally, don't fill the oil tank on an O-200 to much past five quarts unless you are going for a six hour ride or more. Try setting the oil level to five quarts on the dipstick and recheck your hourly oil consumption then.
Third - O-200s leak oil, sometimes quite a bit. Check the valve covers (the edges will look like potato chips), check the oil sump gasket (there are two), check the front crank seal (oil appears on the back of the prop) AND check that the vacuum pump isn't bad - gaskets good and the correct gasket (vac pump replaced recently??), no leaks at the case-to-pump junction either. You'll very likely wind up straightening the edges of the valve covers, don't get Continental's valve cover gaskest, get a set of R.E.A.L. (trade name) silicone gaskets instead - about $20.
Oil pressure is OK if it is "in the green" - anywhere between 10 and 50 psi if the engine is above idle. On higher time engines, you may drop below the green at idle. I don't like seeing this, but it's there.
How many hours since MAJOR and how many hours since top overhaul? The bottom end is ready for an overhaul about every two tops - 3,500 hours and it is time for a bottom end overhaul ($$$$$$$$).
O-200s usually eat the center main bearing. You can buy +.010 bearings easily, you can get +.020 bearings under an STC but this gets expensive. Crank life is about 4,000 hours and then it is usually too worn to be reground.
Do you have oil on any/all of the spark plugs? If not, you aren't burning oil, it is leaking. If you have oil on ONE plug or both plugs in ONE jug, look there for your problem - cracked piston or broken rings, bad valve guide.
If a rod bearing is "going" it will sling oil on the cylinder bore and the oil ring won't be able to cope with it. You can change the con-rod bearings on an O-200 without splitting the case, and that's an easy palliative (not cure) for low oil presure.
You can check for a bad bearing by removing the cowl and using a long screwdriver as a stethoscope - be careful of the propeller!!! - listen around the center of the crankcase - a clunk-clunk-clunk sound at idle means it is overhaul time.
Best Regards,
Echo Mike