What oil should I put into my 1988 5.0 ford mustang?

What oil should I put into my 1988 5.0 ford mustang?

If it isn't leaking anywhere syns. One little leak and it will make it worse.
I use 20w50 Castrol GTX high milage in my 85 Jeep with 200k. 40psi oil pressure @ idle. I'll get another 100k.

Look on the oil cap, SAE 5-30 oil.

Olive oil

Cannabis oil. It makes a dreamy drive!

Oil has changed a lot, old weight standards have little relevance to lubricating ability and resistance to burning off. I know it's disconcerting to see oil pressure drop with thinner oil, but volume will actually go up. Actually think about it, completely blocked flow will cause the most (back) pressure, and no lubrication.

An ACEA A5 or GF-5 5W-30 would be fine. You want oil to be thin at start up to allow the oil to flow easily to all parts. First try 5w-30, but if you experience excessive oil consumption you could try 5w-40.

Ford WSS-M2C913-D is the current post manufacture spec, but with nearly annual changes in oil specs requiring modifications of oil blends the oil makers have mostly quit trying to meet that old standard.

10W-30 or 5W-30 if you live a cold climate. Dino, blend or full synthetic, the choice is yours.

Using oil stated by owners handbook will result in no issues.