Just bought car.. which motor oil should i use?

91stang50GT

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Nov 1, 2005
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i just bought my 91 gt about a week ago and i want to change the oil before i put it on the road but i dont know wether to use synthetic or not and what type because i have no idea what has been used in it in the past or what is in it right now due to only having 4k miles put on it since 2001 by previous owners. Needless to say the last owner does not know if synthetic has been ran in it or not. The car has 82,000 miles on original motor. Synthetic or no? and what weight/brand? I heard if you change to synthetic from non-synthetic, it could worsen oil leaks. Is this true?
 
I did use and found I liked the valvoline high milage 10-30 on cars with over 80,000..consumption seemed to either decrease significantly, or stop altogether. I would be most concearned with the quality of the filter more over the brand of the oil as long as it's kept clean. Search around here and you'll see the filters and oil that are most popular.
 
I vote Mobil 1 and K&N filter.

I also agree with Dman though about the oil filter. Some are a little sketchy, like Fram.

Most oils on the market now are of very high quality.
 
Every motor is different... Some folks can get away with running a synthetic grade oil and some can not. You will have to experiment a little to know for sure.

When you select the weight of oil, you will want to run the thinnest weight that will give you good oil pressure on a warm idle. (Ford recommends 30PSI warm at 2,000 PRM for the stock 5.0L engine) In my case my car loves 10w30 in the winter and then 10w40 in the summer.

For the filter, use the Motorcraft brand or one of the expensive ones. Skip over the fram filters.
 
5W 30 is what ford recommends even though the oil filler cap says 10w 30(they changed their minds) I use 5w 30 synthetic blend motorcraft and a motorcraft filter. I mean, hey they designed the darn thing so they should know what belongs in it.
 
I would run a cheaper dino initially and do a short change since the car has not been driven much of late. I would also consider AutoRx for it.

FL1A is as good a bang for the buck as there is.

Good luck.
 
91stang50GT said:
i just bought my 91 gt about a week ago and i want to change the oil before i put it on the road but i dont know wether to use synthetic or not and what type because i have no idea what has been used in it in the past or what is in it right now due to only having 4k miles put on it since 2001 by previous owners. Needless to say the last owner does not know if synthetic has been ran in it or not. The car has 82,000 miles on original motor. Synthetic or no? and what weight/brand? I heard if you change to synthetic from non-synthetic, it could worsen oil leaks. Is this true?
I run only synthetic Mobil One and never have any problems with leaks.
 
Aaron'S'tang said:
I run only synthetic Mobil One and never have any problems with leaks.
Then you are one of the guys who doesnt have leaks. Some do and some dont.
It is a possibility on any car which has seen prolonged dino oil, so we warn that it *could* leak.
 
between the 3 cars that i work on now and the four previous cars plus my truck ROYAL PURPLE can not be beat. in my three vehicles i have it in the trany, rear end, motor, and the additive in the radiators! love that stuff!

Dyno proven