Ford Repair: Oil Viscosity, low oil pressure, oil viscosity

Question
I have a 96 Sable SW with the Duratec DOHC 6 engine with 65,000 miles on it.

After sitting for 5 days (unusual) I started the car and got a flashing CK ENG light. After a few more starts the light stayed on. I pulled the codes and the only code was P0301 which was #1 misfire. I cleared the codes and ran the car at high speed for 100 miles. No more codes as yet.

My theory is, due to the unusual delay in use ( 5 days)  oil got past the valve stem oil seal and fouled the #1 plug.

Q # 1 Do you agree?
Q # 2 Should I cahnge to 10 30 oil rather than the 5 30 oil I've been using?

I'm concerned that the DOHC engine still neds 5 30 oil even though it has 65,000 miles on it.

Thank you in advance.

olins@yahoo.com

Answer
A common problem for a misfire code on this engine with this mileage is a bad Spark Plug and/or Spark Plug Wire.  I don't think that oil seeping past your valve seal is the problem.  You can remove and inspect the plug.  Replace the plug and wet-test the wire with a spray bottle (watch and listen for arcing).  The misfire code only returns after the processor has seen the cylinder misfire three times. It could take a thousand miles of driving if the plug is just starting to fail.

I don't think you should stop using 5W30 oil unless the engine is burning excessive amounts (1 quart per 1,000 miles) or you have low oil pressure due to engine wear.

I hope this helps,
Dave