Losing oil, but no drips and no smoke?

[nerdvana]

I've had an oil leak or two since I bought my car nine years ago. A few years back I got the one fixed that was coming from the front crank seal, but never tracked the other one down. Figured it might be the rear crank seal or something. Anyway, haven't driven it much in the last two years, but on my road trip this past week (900 miles) I noticed the oil leak had stopped. However right at the end of my trip I saw the oil pressure drop off and found out that I was at the low mark of the dipstick. I had filled it to the upper mark at the start of the trip. The exhaust does not have any signs of smoke, the area under the car is clean (no drips anywhere) but I lost almost 2 quarts of oil in 900 miles! Trying to figure out what is going on and what I should try next.

On my most recent oil change I switched to Mobile-1 20w40 high mileage, from previously using castrol syntec high mileage. I'm not sure if the oil leak stopped then, or more recently.

Another semi-strange symptom is that the oil pressure sender used to always bounce around 70+ psi when the engine was above 2k rpm, but now it often holds steady at 50 psi, with occasional vibrations into 70 as I shift.

Any ideas?

[David T]

Check your oil level when cold on level ground. Like first thing in the morning before you start the car. There is a big difference between checking it cold and after you just ran it. To lose 2 qts in 900 miles you are losing it fast or burning it fast. No way you wouldn't notice a leak or have blue smoke pouring out. Pull the plugs and see if any are black and oily. Check the oil pressure sending unit on the rear, left side. See if the air filter is oily and make sure it is clean. Do not overfill the oil. I keep mine 1/2 way between low and full.