Burning oil?

My wife has a 2003 Legacy L (2.5) she has had since it was new. It currently has 86000 miles. She got a new job this year and has been driving about 620 miles / week since September. I have noticed that the car is low about a quart of oil after about a month following an oil change. It has a very minor leak, so I know that that much oil isn't dripping out. How do I know if it's burning oil or is this normal when putting that many miles on the car? Also, would it be a good idea to use a full synthetic oil or even a blend?

 

Thanks!

mine did this, try changing the oil sending unit

mine did this, try changing the oil sending unit

 

Did your oil light come on? Her oil light hasn't ever come on, but the oil level is definitely low.

nope

That is normal because you could have a bad head gasket or a clogged pcv valve or multiple other things. If your exhaust is blue after you start your car, that means your burning oil inside the combustion chamber. Using full synthetic is definitely a good idea. It will rejuvenation your gaskets which can stop some leaks, but I wouldn't reccomend mixing oil, it's best to stick with one kind, but if it's synth oil with synth oil or non-synth with non-synth you'll be okay.

So 620 miles a week is 1800 or so miles a month. Burning a quart in 1800 miles really isn't terrible. Check, and top up the oil weekly and it'll be fine.

Check for leaks, look all around where the heads meet the block for head gasket leaks. Pull the spark plug boots to see if oil is leaking through the plug seals, check if the valve cover gaskets are leaking, and check around the timing covers to see if the cam/crank seals are leaking.

 

Switching to a synthetic can increase oil leaks/burning on higher mileage engines. but you don't have a whole lot on that one. You may want to switch to a good synthetic just to increase your oil change interval to around 5k miles so you're not changing it all the time with all that driving.