Here's why:
* API Service Classification: The 1985 6.9L diesel is an older engine, and you'll likely want to use an oil meeting the API CF classification. This is an older specification for diesel oil, and the 15W-40 weight is common for this engine.
* Viscosity: The 15W-40 viscosity is a good all-around choice for this engine. The "W" stands for winter, and the 15 means it flows well in cold temperatures. The 40 is the viscosity at higher temperatures.
* Type: You will need to use conventional diesel engine oil, not synthetic. Synthetic oils were not commonly used for older diesels.
Important Note: Always consult your owner's manual for specific recommendations for your vehicle. The information above is a general guideline and may vary depending on your specific engine conditions and the climate you live in.
Here are some additional points to consider:
* Oil changes: Be sure to change your oil regularly, as per your owner's manual or the recommendations of your mechanic.
* Oil filters: Always use a high-quality oil filter.
* Check for leaks: Inspect your engine for leaks after each oil change.
By using the right oil and following proper maintenance practices, you can help extend the life of your 1985 Ford F250's 6.9L diesel engine.
