One of the more common questions that we get asked is, "What's up with my 5.0 motor? Man, the thing eats oil like crazy!" It seems as though none of our Cougars have ever NOT used oil. The norm seems to be around 1-2 quarts between oil changes. So why does this happen, you may ask?
The problem seems to be the slightly undersized piston rings from the factory. Especially with the 1986-88 5.0L engines, the flat-top aluminum pistons were purposely made a tad smaller than a comparable forged piston, so that when the engine reached normal operating temperature the pistons would expand correctly. Since cast iron (block) and aluminum (pistons) expand at different rates, this makes sense...on paper. In reality, until normal operating temperature is reached, oil has the potential to get sucked into the combustion chamber if the piston rings are worn enough (see the section on Pinging/Knocking Noise From Engine for more information). If you kick the car into passing gear and see a small cloud of smoke behind you in the mirror, that's the bit of oil you just burned. While not a major problem it's semi-annoying, and it does cost you money to buy extra oil between changes. Again, the only way to solve the problem now is to replace the piston rings. But if you've got knocking as well, you can kill two birds with one rock and have them both changed, eliminating your knocking and oil-eating problems permanently. Make sure you check for external oil leaks around the oil pan, filter, and valve covers first.