For a 1990 Mustang GT 5.0, 10W-30 was generally recommended, especially if you live in a moderate climate. Using a conventional (not synthetic) 10W-30 oil that meets the SF, SG, or SH API rating would be appropriate for a well-maintained engine. You'll find this information on the oil bottle.
Here's a breakdown of considerations:
* Climate: If you live in a very hot climate, you might consider a 20W-50 for better high-temperature protection, but 10W-30 is usually sufficient. In extremely cold climates, a 5W-30 might be a better choice for easier starting. However, sticking with 10W-30 is generally a safe bet.
* Engine Condition: If your engine has high mileage or is showing signs of wear, a higher viscosity oil (like 20W-50) *might* offer better protection, but this depends on the specific issues. It's generally best to consult a mechanic.
* Synthetic vs. Conventional: While synthetic oils offer some advantages like better protection at high and low temperatures and longer drain intervals, a conventional 10W-30 oil meeting the specified API rating will be perfectly suitable for a 1990 Mustang GT 5.0. Synthetic blends represent a middle ground offering some benefits of synthetic at a more affordable price point.
* API Rating: The API rating (e.g., SF, SG, SH) indicates the oil's performance level and quality. Always look for an oil meeting at least the minimum rating specified for your car's year. Older cars often don't require the latest specifications.
In short: Start with a conventional 10W-30 oil with an API rating of at least SG. If you have concerns, check your owner's manual (if you have it) and/or consult a mechanic specializing in classic Mustangs. They can advise on the best choice for your specific vehicle's needs. Don't forget to use the correct oil filter as well!
