I just bought used 2009, 5.3, flex fuel, with 18,000 miles and oil pressure was always at 40psi, regardless. I did first oil, oil filter, air filter change with 5w30 full synthetic and one qt Lucas full synthetic. Now pressure is always at 60psi. It's a little difficult to read the dipstick. Possibly too much oil? Is 60psi okay? Thanks

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the catalytic converter could be clogged

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Nope, it's not a problem. The numbers relate to the viscosity or slippery'ness (if thats a word) of the oil. The first number (5 or 10) is the viscosity of the oil when you first start the car. 5 is more slippery than 10. The second number (30) is the operating viscosity of the oil after your car has warmed up.
Simply put, in the winter your oil thickens when it cools down so you need smoother oil (5w30) when you start the car.
Winter = 5w30
Summer = 10w30
Hope this helps.

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synthetic oil has smaller molecules which is why it is good for new cars - it gets into more places. it sounds like your car has been taken good car of but it still has some miles on it. what is happening is the synthetic is getting past the oil ring on your pistons (dont worry) and a small amount is getting burned off (not enough to fail emissions or notice in the exhaust) this happens just because of old age (being anything over 60000)i would try switching to a conventional oil at least for one oil change and that will solve your problem because the bigger molecules in the conventional oil will have a much harder time getting past the oil rings on the pistons.

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I use 5W30 Mobile 1 synthetic-5 quarts.

The air filter change is a real pain.
Remove driver side tire.
Remove driver side wheel well.
You will see the filter canister in the front of the wheel well.

I had a mechanic do it for me and it took him 1.5 hours. If you plan to do it yourself, be sure you have plenty of time and alot of patience.

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5w30