Oil is the life blood of any engine and choosing the right oil is important for proper lubrication to minimize friction and wear, provide cooling to internal engine components, and to help clean and carry away contaminants to be removed by the oil filter. Using the correct oil for your engine and changing it as required is critical for durability and longevity of the engine. In an engine such as the 7.3L PSD which utilizes an oil driven HEUI injection system quality oil is even more important for the proper function of the engine.
Ford’s Recommendation
Motorcraft Super Duty Diesel Motor oil is the recommended brand by Ford. The acceptable SAE Oil Viscosity for the 7.3L PSD depends on operating temperatures. Ford’s standard recommendation is SAE 15W-40 oil which is suitable for climates with ambient temperatures above 30℉. If you are in a colder environment where the ambient temperature never gets above 90℉ but stays above -10℉ Ford recommends SAE 10W-30 oil. In the very cold climates where the ambient temperature remains under 30℉ Ford recommends SAE 5W-30 oil, and in extreme frozen conditions where the ambient temperature is below 0℉ the recommendation is for SAE 0W-30 oil.
Following the temperature recommendations means that it may be necessary to switch oil viscosity seasonally (think summer vs winter) in some climates with a wide temperature range between seasons. Many climates can run 15w-40 all year round without issue but for others you may need to switch to a the proper recommended colder climate viscosity to run during the fall and or winter until things warm up. Ford recommends using the block heater any time the temperature is below 30℉ for easier starting. Due to the nature of cast iron, the glow plug system is not enough to heat the cylinders and the head when the temperature of the engine is also 30℉ or below.
Motorcraft Super Duty Diesel Oil is a high quality motor oil available in 15w-40 and 10w-40 viscosity and designed for use in all Ford Power Strokes. It meets the requirements of Ford’s WSS-M2C171-F1, Cummins CES 20086, Detroit Diesel 93K222, Volvo VDS-4.5, Mack EOS-4.5 and API Service CK-4. Motorcraft also has a Full Synthetic 5w-40 Diesel Motor oil for colder climates that meets Ford’s WSS-M2C171-F1, API Service CK-4, and also meets older API Categories: CD, CF-4, CG-4, CH-4, CI-4, CI-4 plus and CJ-4.
Choosing the Right Viscosity
Viscosity is the measure of an oils resistance to flow, some may refer to it as the thickness of the oil. An oil with lower viscosity flows faster than higher viscosity oil. Generally a low viscosity oil can reach vital engine parts quicker and circulates faster through the oil system, while a higher viscosity oil tends to adhere more to engine parts to provide better lubrication. The correct viscosity for an engine is dependent on the engines design tolerances as well as ambient temperatures covered above. Modern engine designs have very tight tolerances that require low viscosity oil such as 0 and 5 weight while many older engines designs have looser tolerances that need a “thicker” oil. Modern oil options are multi viscosity and contain thickening agents meaning the oil viscosity changes with temperature. To understand your oils viscosity you will notice that SAE standard rating has two numbers in the format: “##W – ##” The first number is followed by a “W” which stands for Winter or the viscosity of the oil when a cold temperature and then a second number is the operating or hot viscosity of the oil. All OEM oil viscosity recommendations are for an operating viscosity of 40 for warm ambient temperatures and 30 for cold ambient temperatures. Also, depending on how cold, a lower rated W viscosity is also recommended. This lower cold viscosity will help the engine properly lubricate on startup when cold but once operating temperature is reached the oil reaches is operating viscosity.
You may choose a different path than Ford’s recommendations based on modern oil options. Many synthetic diesel oil options have a viscosity of 5w-40 and are chosen over the OEM recommended 15w-40 all the time. Lower viscosity will flow better and is definitely a must in cold climates but a quality synthetic will offer as good as protection as conventional 15w-40 in warmer climates too. Synthetic oils are engineered to withstand extreme conditions both hot and cold. Many have run 5W-40 all year round even in hot climates without issue.
When making the decision on what viscosity note that lower viscosity is a must when the ambient temperatures are cold, the lower the ambient temperature the lower the viscosity recommendation. At freezing 5w pours while 15w will flow slow like honey. One thing for sure is that you should choose a high quality Diesel rated oil no matter what Brand or viscosity and that viscosity is more important for cold than warm, with the exception of conventional vs synthetic for hot conditions. If choosing conventional or a synthetic blend then 15w-40 will break down less and provide better protection in the heat than a lower viscosity weighted oil of the same type. Synthetic oils are designed to resist break down with additives to withstand both extreme cold and extreme heat conditions so they are of less concern.
Should I Switch to Full Synthetic
Conventional, Synthetic Blend, or Full Synthetic are all personal choices. Many prefer to run OEM recommended Motorcraft fluids and filters while others choose their brands based on availability, price, and oil specification. There has been a lot of great improvements for oil since the 7.3L PSD engine was engineered and manufactured. Synthetic engine oil lasts longer than conventional oil because they are more chemically stable compounds than conventional oil, synthetics are also formulated and tailored with additives that provide additional benefits over conventional oil to combat sludge and deposit buildup, help reduce wear, prevent oil breakdown, and even have added high temperature protection. How much longer synthetics last may depend on the design of the oil. For example, Amsoil Heavy Duty Diesel Oil recommends following the factory service interval but their Signature Series Max Duty Diesel Oil claimed service life for turbocharged pick-up trucks is 2 times your OEM spec, 25,000 miles, or 1 year (whichever comes first). That’s a lot of miles they clam you can safely go on one oil change. Another benefit of synthetic oils is they are stable at lower temperatures meaning the colder it is the better synthetic out flows the equivalent conventional oil.
There are a multitude of top quality Diesel oil brands that many choose to run instead of OEM Ford / Motorcraft oil such as Shell Rotella T, Chevron Delo, Amsoil, Mobil Delvac, etc. Many of the Diesel rated synthetic oil options are SAE 5w-40, however, some now offer full synthetic 15w-40 such as Rotella T6 which offers both a 5w-40 and 15w-40 viscosity.
Many big box stores offer specific brands of Synthetic oils at hard to beat prices even though Synthetic is often more expensive than conventional and synthetic blended oil. Many users of full synthetic oil in their 7.3L PSD report that their internal engine noise runs quieter especially with 5w-40 full synthetic, others report their HEUI injectors seem to run better on the “thinner” synthetic oil. There are reports of higher oil consumption for some using 5w in warmer climates. At the end of the day conventional oil will oxidize and acidify more easily than Synthetic which is bad for your engine and the only way to prevent it is through following the recommended routine oil change maintenance.
Oil Change Service Intervals
The factory oil change interval is 5,000 miles or less. The HEUI injection system depends on good clean and functioning oil to operate efficiently making service intervals important for your engine. Oil controls soot, prevents wear of internal components, and helps prevent deposit but all oil eventually breaks down as protective additives deplete, and oxidation causes acidic byproducts to form which over time means the oil becomes harmful to the engine and can lead to corrosion, sludge, and failure to lubricate. Regular oil changes are the best way to prevent this not only within the engine and its core parts but also the injectors. Buildup caused by dirty oil in the injectors is often referred to as stiction a condition that begins to cause problems and eventually can cause an injector to fail. Good clean oil is an important factor in the longevity of your 7.3L PSD.
Oil Analysis
Many modern synthetic oils have drastically higher mileage ratings than the OEM recommendation oil change interval. If you choose to run your oil longer no matter what brand or viscosity we recommend you get it analyzed. Analyzing your oil helps you find out exactly what is happening with your engine and how much life your oil has left. Sending in a sample for analysis as often as every oil change also isn’t so much it breaks the bank.
Blackstone Laboratories performs oil analysis so you can know what is going on in your engine. This helps warn of any problems developing, shows how well your oil choice is working, and identifies the life of your oil and whether you are changing it too frequently or not frequent enough. Depending on your driving conditions even conventional oil may be able to last longer than the OEM service interval, but the only way to know this is through testing. Testing is the only way to know how much life your oil has left at a certain point and it gives you the information you need to confidently make the decision to run your oil longer than the OEM service interval. Analysis also gives you peace of mind that everything is good inside your 7.3L PSD or it can identify potential problems forming. There are many oil analysis providers to choose from.