7.3 IDI Engine Oil Change Information

6.9 & 7.3 IDI Oil Change Intervals

The factory recommended oil change intervals for the 6.9 and 7.3 IDI engines is 5,000 miles or 6 months under normal driving conditions and 2,500 miles or 3 months under severe driving conditions. Maintenance is to be performed by either the mileage or time interval, whichever may come first. Due to the age and potentially high mileage of these engines that remain in service, we highly recommend that IDI owners adhere to the 2,500 mile or 3 month oil change interval, whichever comes first. This more stringent service regiment will help combat oil consumption, fuel dilution, and soot contamination in these aging engines.

Oil Contamination and Consumption in 7.3 IDI Diesels

Diesel engines require an engine oil that is specifically developed to combat wear under rigorous conditions. Motor oil is subject to three categories of breakdown - thermal, chemical, and mechanical. Each mode of breakdown contributes to the degradation of the oil on a molecular level, thus necessitating the need to change the lubricant and filter routinely.

Thermal breakdown refers to the oil's exposure to high temperatures. A primary factor in the thermal breakdown of engine oil is the fact that the oxidation rate is proportional to temperature; the higher the temperature, the more rapid the oil oxidizes. The 6.9 and 7.3 IDI, like most diesel engines, employs an oil cooler that uses the lube oil supply as a means of removing heat from the engine. While the sump temperature may remain at a relatively constant operating temperature, oil is subjected to extreme thermal shock as it is used to lubricate and cool.

Chemical breakdown covers both the oxidation of engine oil and the infiltration of chemical contaminants. Oxidation occurs anytime the oil is exposed to oxygen, thus it attacks engine oil even when the engine is not running. This is why oil change intervals are specified in both time and mileage. Contamination is the result of blowby constituents, mainly fuel and exhaust gases, entering the crankcase and mixing with the lube oil supply. Soot and diesel fuel are particularly problematic contaminants that alter lubricant properties.

Mechanical breakdown is the physical alteration of the molecular structure resulting from extreme pressures. Every critical component in an engine is protected by a thin layer of engine oil separating two or more moving parts. The movement of these parts literally grinds and crushes engine oil.

Possible Causes of Excessive Fuel Dilution

Fuel dilution in diesel engines is the natural phenomena by which diesel fuel compressed in a cylinder infiltrates the crankcase by leaking past the piston rings. While there is an opportunity for fuel vapors to be scavenged through the closed crankcase system and returned to the intake air charge, much of the gases ultimately settle into the lube oil supply. In extreme cases, fuel dilution is referred to as "making oil", because the engine oil level increases in time as it collects diesel fuel.

Fuel dilution rates are typically reported in an engine oil analysis and are otherwise unmeasurable unless there is a serious problem resulting in a noticeable increase in the oil level. Diesel fuel breaks down engine oil and lowers its viscosity, reducing its lubricating properties. It is generally accepted that fuel dilution of 5% or less by volume is a normal, acceptable rate with no cause for concern. When fuel dilution exceeds 5% by volume, it is most often considered excessive and the risk of accelerated wear and/or equipment damage is high.

There is also an opportunity for fuel dilution rates to be high without causing a significant increase in engine oil level due to oil consumption. Such instances are generally the result of one or more compromised ring seals creating a condition where oil is being consumed and fuel is being introduced into the crankcase in high amounts. This would also be accompanied by high soot levels in the engine oil. It only takes a single bad cylinder to cause excessive fuel dilution, soot contamination, and oil consumption over the period of an oil change.

Excessive fuel dilution can be caused by one of or any combination of the following conditions:

• Extended periods of idling, especially in cold ambient temperatures. Combustion temperatures are considerably lower at engine idle, resulting in a high propensity for diesel fuel to stick to the cylinder wall and get washed into the oil supply.
• Frequent and/or heavy towing.
• Lugging the engine (high load, low engine speed).
• Frequent driving in stop-and-go traffic conditions. Fuel dilution may be more prevalent while the engine is being worked hard, thus driving at constant speed should yield lower fuel dilution rates than frequently stopping and accelerating. Additionally, stop-and-go conditions typically result in longer idle times.
• Taking short trips that result in the engine being shutdown before reaching normal operating temperature.
• Leaking and/or dirty fuel injector(s) resulting in poor atomization and/or allowing fuel to leak into the cylinder when the engine is off.
• Compromised piston ring(s) resulting in a poor seal against the cylinder wall (low compression in any cylinder will indicate a poor seal)

Possible Causes of Excessive Oil Consumption

A highly common source of oil consumption in an IDI diesel is through the crankcase depression valve (CDR valve). The CDR is a simple spring loaded diaphragm valve that is responsible for recycling crankcase fumes (comprised of oil/fuel vapors and exhaust gases) by evacuating them from the crankcase and introducing them into the intake manifold. The CDR valve is highly susceptible to sludge buildup and can allow excessive engine oil to be consumed through its flow path if it becomes stuck in position. A severely clogged air filter can also cause excessive engine oil to be consumed through the CDR valve flow path.

A compromised ring seal in one or more cylinders can be a serious contributor to excessive oil consumption. However, as these engines age they develop more means for engine oil to sneak into the combustion chamber and there is no reason to jump to the conclusion that an engine is toast because it's using a bit of engine oil. Worn valve stem seals, for example, can allow engine oil to seep down into the cylinder.

At what point oil consumption becomes "excessive" is quite disputable and oil consumption is the product of many variables. In our opinion, a reasonably healthy IDI diesel should not consume more than a quart of oil per 1,000 miles of driving. For reference, the distance between the "add" and "full" markings on the oil dipstick represents 2 quarts of engine oil. If you find yourself frequently adding engine oil to your IDI, consider inspecting the CDR valve and performing a compression test.

7.3 IDI Oil Change Parts List

[1] - Larger FL1995A oil filter from a 7.3L Power Stroke can be used but oil capacity will be increased and must be adjusted accordingly.
[2] - Acceptable to reuse this part if it is not damaged. Oil pan drain plug is becoming obsolete; part number linked to a suitable USA made alternative to the now defunct OEM part.
[3] - Crush washer type drain plug gaskets are considered one time use and ideally replaced at every oil change. OEM drain plug featured a plastic sealing washer, which are widely unreliable and prone to leaks; highly recommend updated DP-110203 copper sealing washer.

FL784 vs FL1995 Oil Filters for IDI Engines

A common upgrade for IDI diesel owners is to use a larger FL1995 oil filter from a 7.3 Power Stroke. The Power Stroke oil filter holds roughly 2 quarts while the IDI filter holds 1 quart. This therefore increases the engine oil capacity from 10 quarts to a total of 11 quarts. While adding an extra quart of oil may not seem all that beneficial, it helps fight fuel dilution and other forms of oil contamination. This is objectively the only benefit to using the larger oil filter; if fuel dilution reaches 5% between oil changes on a 10 quart system capacity, then adding the additional quart of oil would technically bring the fuel dilution rate below 5% (all things equal).

It is a common misconception that the 7.3 Power Stroke oil filter is in some way, shape, or form superior because the more modern turbodiesel has higher filtration needs. The FL1995 has a greater filter media surface area, but the filter medias are made of the same material. Figure 1 below compares the filter material as removed from a FL784 (left) and FL1995 (right) oil filter. In actuality, the size and capacity of each filter is relative to the engine platform's sump capacity. The 6.9 and 7.3 IDI have a sump capacity of 9 quarts and an oil filter capacity of 1 quart. The 7.3 Power Stroke has a 13 quart sump capacity and an oil filter that holds 2 quarts of oil.

Note that the FL784 and FL1995 oil filters have been superseded by FL784A and FL1995A part numbers. The later "A" filters employ a synthetic filter media, but again there is no discernible difference between the IDI and Power Stroke versions save for their respective size. A comparison between the new and old style filters can be seen at FL1995 vs FL1995A oil filters. As a generality, we recommend using the Power Stroke's FL1995A oil filter on IDI engines; while the benefit is not necessarily substantial, there are no notable disadvantages.

Viscosity Charts & Oil Requirements

The API category requirements for the 6.9 and 7.3 IDI have long been superseded several times over. Any diesel engine oil meeting modern API standards is sufficient for the IDI engines. Synthetic engine oils are preferred for their superior properties, including greater wear protection and resilience against thermal, mechanical, and chemical breakdown. Amsoil synthetic motor oils are at the forefront of the industry and we highly recommend their products for maximum engine protection.

The 6.9 and 7.3 IDI oil viscosity charts are similar, although the 6.9 IDI chart (figure 2 above) references several less common oil viscosities. SAE 15W-40 engine oil, which is suitable in ambient temperatures greater than 0 °F, is by far the most commonly selected viscosity grade for the IDI engines. In warmer climates, an SAE 30 engine oil is indicated as preferred for the 7.3 IDI engine. SAE 10W-30 engine oil is indicated as the cold weather viscosity for both applications, but has a much greater temperature range for the 7.3 IDI than for the 6.9 liter. Anticipated ambient temperature is the single determining factor in selecting an oil viscosity. Failure to use an appropriate viscosity for the ambient conditions can result in accelerated wear and/or engine damage due to poor flow conditions.

Engine Oil Recommendations

Diesel Hub recommends the following products for vehicles equipped with the 6.9 or 7.3 IDI:

Amsoil Signature Series Max Duty 15W-40 diesel oil - Superior diesel oil for maximum engine protection

Amsoil Heavy Duty 15W-40 diesel oil - Premium diesel oil for next-level engine protection at an economical price

Amsoil Signature Series 10W-30 diesel oil - Superior flow and cold start protection in cold weather, recommended within temperature range

Amsoil synthetic engine oils offer:

• Superior protection against fuel dilution and oil consumption

• Superior resilience against thermal, mechanical, and chemical breakdown of engine oil

• Improved oil flow and engine protection in sub-zero temperatures and during cold starts

Amsoil is a leading manufacturer of synthetic oils and lubricants, including a line of motor oils engineered to meet the demands specific to diesel engines, old, aging, or new.

How to Change the Engine Oil in a 7.3 IDI Diesel

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• Ensure that the vehicle is in park/ gear, the parking brake is set, and the engine is not hot; do not attempt to change the oil on a hot or recently ran engine, always allow it to cool off first.
• Place a suitable container with a minimum 10 quarts capacity beneath the engine oil pan.

• Remove the oil pan drain plug with a 3/4 inch socket or wrench and adjust the drain container position as needed to minimize splash-back.

• Locate the oil filter on the driver side of the engine and position the drain container so that oil dripping off the bottom of the filter will be collected. Fluid drain pans are generally large enough that they can be positioned beneath both the filter and oil pan drain.
• Loosen the oil filter by rotating counter-clockwise until oil begins to drain down the sides. Allow the oil to drain for several minutes, then remove the oil filter completely.

• Thoroughly clean the oil filter base and inspect to ensure that there are no remnants of the previous filter gasket stuck to it (this is quite common).

• Clean and inspect the oil pan drain plug. If it is the factory magnetic type, inspect the magnet for metal filings and then thoroughly clean it.
• Discard the old drain plug gasket. Drain plug gaskets are designed to be used a single time; once they are torqued to spec and the washer is crushed, they should not be reused. We highly recommend copper or aluminum type gaskets as plastic and nylon gaskets (shown at left) have a higher propensity to deform and leak.
• Install the oil drain plug with a new gasket. Torque to 28 lb-ft to ensure a proper seal.

• Use clean engine oil to thoroughly lubricate the gasket on the replacement oil filter.
• If desired, prefill the new engine oil filter with clean engine oil.

• Install the oil filter until the gasket contacts the mount (indicated by an increase in resistance), then tighten it an additional 3/4 to 1 full turn.

• Locate and remove the oil fill cap at the front of the engine. There are several styles of fill caps and filler necks, but on all model years it drains into the injection pump gear housing cover.

• Use a funnel to add 10 quarts (minus what was added to the oil filter if it is prefilled) of new engine oil to the crankcase. If using a FL1995A oil filter from a 7.3 Power Stroke, add an additional quart of oil.
• Reinstall the oil fill cap once complete.

• Verify that the engine oil level is correct using the dipstick. Note that the oil level may appear slightly high at this time if the oil filter was installed empty. Under no circumstances should the oil level be low.
• Verify that the oil pan drain plug is not leaking.
• Start the engine and verify that there are no leaks around the oil filter or drain plug.
• Turn engine off, allow vehicle to sit for a minimum 5 minutes, then verify proper oil level once more.