So after a sudden momentary loss of oil pressure, I discovered I have water in my oil 91 5.7L and I'm loosing oil someway other than leaking on the driveway. I added a quart to get home, and when I got home to change the oil I only got out a little more than 3 qts from pan and filter. (that includes the 1 quart I put in :shocked My theory is the engine oil cooler in the radiator has failed and is leaking allowing oil into the cooling system. (will drain tonight to look). I've been thinking hard about this all day and want to share my thoughts for others input. If you have water in your oil, here are the ways it could've gotten there (in my thinking). 1) Condensation - theoretically if you leave your vehicle sit for long periods during between season changes, you can get small amounts of condensation in the oil. Symptoms - no loss of oil, very small amounts of water. 2) Failed Engine Oil Cooler in Radiator - if you have an engine oil cooler built into your radiator the cooler can leak allowing oil into the coolant and coolant into the oil. Symptoms: You will loose oil into the cooling system while driving since oil pressure is higher than cooling system pressure. You will also loose coolant into the oil immediately after shutting down the engine since the cooling system will still be pressurized and the engine oil will not be pressurized. 3) Intake Manifold Gasket Leak - Since coolant flows through the intake manifold, if the gasket leaks, coolant will leak down into the lifter valley and down into the oil pan. Symptoms: loss of coolant, but NOT loss of oil. Oil does not flow through intake so you should not lose oil into the cooling system. 4) Head Gasket Leak - it is possible that you have a head gasket failure leak between an oil galley and a cooling passage or between a cooling passage and the lifter valley. Symptom: water in oil and oil in coolant for same reasons listed in 2. 5) Cracked Block - it is possible you have a crack in your engine block allowing coolant to seep into the oil pan. Symptom - coolant in oil, but not loss of oil. I've just made these up from thinking about stuff, but I've never taken apart a small block before so I don't know if these are accurate, for example, are there oil passages and coolant passages near each other in the head gasket? Etc. Any thoughts feedback?