[stanger66]

OK,
Thicker oil will NOT make loose gas mileage. What it does is if you noises coming out of engine #1 it quiet them up and #2 plus have the thicker oil in your engine with hi mileage such as yours will make you engine work easier because worn parts make the engine rougher. Now with the thicker oil you only want to use it in the warmer months-spring,summer,half of autumn NOT in the winter months. The colder it is the harder the oil pump has to work when cold real thick oil.
Now the numbers represent weight of oil lower #'s the thinner it is and the higher the
thicker the oil. I would probably go with either 10w40 or 15w40 or 20w50(thickest).

Now with synthetic oils most newer cars use either synthetic blend or full synethic-the reason for them you dont have to change every 3k miles but you do it every 5k or so. It doesnt break down easy and when you use it you have to keep using it you cant switch back and forth between syn. and reg. oil. Your seals will eventually start leaking than usual. A lot of time people will do that and wonder why they have to replace gasket so quick. Synthetic oil goes for about $5-$10 a quart and oil $1-$4 a quart.

When you have more than 60k+ on a car you dont want to put synthetic oil in the car because you will develop leaks.

Their is only 1 advantage to synthetic oil is that is doesnt burn or smoke if your engine smokes prior in cars with excessive mileage.
You also probably want to use high mileage oil--ie penzoil.
You should be able to find it in any parts store.
I would also advise changing the oil about 2500 to 3000 miles especially if you drive it hard LIKE ME.
I change my oil in my t-bird and stang every 2000 to 2500 miles (I love the gas pedal to much especially sitting next to ricer when I'm in my t-bird) and blown them away.

ross