5W-30 on an older car in Dallas, TX?

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Hello board, brand new here and i do believe this is my first post. A family member told me about this site and i decided i would take a looksee. I have a basic question about motor oil for my car.

I have a Ford Mustang 5.0 its a fox-body or "fastback" as they call it (badge says GT not LX, has the hatch not the trunk) and its got a decent amount of miles on it, no performance mods it is a stock 5.0 convertible. I have run a few different oils through it, from 10W-40 to 5W-30 and a few different brands. People like to tell me that the thin oil will lubricate the engine better, and will be better for the engine in the long run. They also like to say that 10W-30 is obsolete even though it says to use that in my owners book. My question s that when it gets to be a steamy 100-degree plus and im driving around, will a 5W-30 be thick enough?

I do believe i used 10W-40 last summer it was Quaker State if remember. This summer, i am tempted to switch to either a bargain-budget oil from walmart called Supertech or even another brand of cheap oil, or perhaps spend the extra $6 on a better quality older vehicle engine oil. I am asking if i can use 5W-30 in my engine, someone suggested 5W-20 to me but coming from 10W-40, that is my question, do i use the 10W-40 or can i use 5W-30 without fear?

This is the DFW area.

(I am a second owner, car stays outside, unknown history, oil drains out black most of the time, gets a pretty fair distribution of use and my goal is longevity of the car and whatever is best for the engine. Also, if using 87 grade gas is ok or if i step up to plus, i have heard that the more octane is better in high heat and humidity conditions, so of course the AC will run as well, i have a 1989 mustang.)
 
I'd personally use the 10W-30. more specifically, I'd use a 10W-30 HDEO, like Rotella 10W-30.

You don't 'need' the 5W 'ability' of a 5W-30 oil. Above, say, 40 degrees, there will be no difference in start-up flow between a 10W-30 and a 5W-30.

both are 30-weight at operating temps, BUT, with a 10-30, you get a slightly thicker oil that will shear less, and have les volatility. I'd say those are benefits I'd want in a summer-driven car in Texas.
 
Welcome to the boards.
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If I may make a suggestion, I would say go with a 10W-30 synthetic blend. A 10W-30 will be more shear stable than a 5W-30, and if the climate doesn't get cold enough to warrant a 5W-30, then there's no reason not to use 10W-30.

As far as brand is concerned, there's no problem using whatever is on sale. Although I would suggest Motorcraft, as it is an well priced quality lubricant. Hope this helps.
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Originally Posted By: addyguy

You don't 'need' the 5W 'ability' of a 5W-30 oil. Above, say, 40 degrees, there will be no difference in start-up flow between a 10W-30 and a 5W-30.

Beg to differ.
Using PU as an example; their 5W-30 is 11% lighter at 20C and 16% lighter at 5C vs their 10W-30.
And compared to a typical 10W-30 dino, the PU 5W-30 is 27% lighter at 20C and a whopping 36% at 5C.

My advise to the OP is to stick with the 5W-30 grade and if you want shear stability go with a good syn like PP or PU.
 
The DFW area can get down to the teens in the winter - I'd run 5W 30 at least for my winter fill .
 
You can always do 10W30 during the short Tx winter,and 10W40 the rest of the year. Get a good dino oil like Valvoline or Pennzoil.
 
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