6.5 Diesel Engine Oil Change Information

6.5 Diesel Oil Change Intervals

The 6.2 and 6.5 Detroit diesels require an engine oil change every 5,000 miles or 12 months under normal driving conditions. Under severe service conditions, an engine oil change is required every 2,500 miles or 3 months. Service is required at the prescribed mileage or time interval, whichever should come first. "Normal" driving conditions can be largely interpreted as "ideal" conditions; long trips at constant speed without any payload or ambient temperature extremes. It will be rare for a 6.5 diesel to meet these ideal conditions, and special consideration should be taken to account for the age and mileage of the vehicle.

"Severe" service conditions, sometimes also described as "heavy duty" or even "short trip" conditions, can be defined as driving that meets one of or a combination of the following criteria:

• Routinely using the vehicle for short trips (< 10 miles)
• Conditions that result in frequent engine shutdown and starting (delivery services, for example)
• Extensive periods of idling (generally accepted as more than 10 minutes of idling in a 60 minute period)
• Frequently driving in stop-and-go traffic conditions (idling time under such conditions should also be taken into consideration)
• Frequently towing a trailer or hauling heavy payload (unfitted vehicles, i.e. heavy flatbeds, boom trucks, etc, should take equipment weight into payload considerations)
• Driving off-road
• Driving in extremely cold or extremely hot conditions (where motor oil will have a tendency to breakdown more rapidly)

The verbiage used to describe severe service conditions varies with model year, application, and even the publication source (i.e. owners manual vs workshop manual). However, they generally describe the same driving types and scenarios and are universally applicable across models, years, and even engine platforms. The majority of 6.5 engines operating on the road today should generally adhere to the severe service schedule, requiring the engine oil and lube oil filter to be replaced at 2,500 mile intervals or every 3 months, whichever should come first.

Engine Oil Capacity

All civilian 6.2 engines and 6.5 engines model year 1998 and older have a 7 quart oil capacity with filter change. All 1999 model year and newer 6.5 engines have an 8 quart oil capacity with filter change. These capacities are applicable for all C/K series trucks, G series vans, and SUVs (Tahoe, Suburban, Blazer, etc). Note that the 6.2 and 6.5 diesels have been employed extensively in marine applications where the engine oil capacity may vary. Military vehicles equipped with the 6.2 or 6.5 diesel may also have alternative engine oil capacities. After changing the engine oil, always verify proper oil level on the dipstick.

Fuel Dilution in 6.5 Diesel Engines

Fuel dilution is an entirely normal, unpreventable occurrence in every diesel engine since the seal between a piston, piston rings, and the cylinder wall is imperfect. Fuel dilution is generally accepted as "excessive" and of concern when it exceeds 5% by volume. In extreme cases, excessive fuel dilution is referred to as "making oil" as it is detectable via an overfilled crankcase oil level. Ordinarily, however, fuel dilution is detected and monitored as part of a routine regiment using an oil analysis service.

Fuel dilution below 5% is not cause for concern. Excessive fuel dilution can be caused by a number of contributing factors, including:

• Excessively lugging an engine (heavy engine loads at low RPM)
• Frequent driving in stop-and-go traffic
• Frequently taking short trips that prevent the engine from reaching operating temperature (especially in cold weather)
• Malfunctioning CDR valve preventing fuel fumes from being extracted properly
• Poor initial warm-up routine during frequent cold weather operation
• Leaking fuel injector(s)
• Severely worn piston rings resulting in excessive blow-by

Oil Consumption in 6.5 Diesel Engines

Engine oil consumption is an entirely normal byproduct of the process by which cylinder walls are lubricated. What is considered "normal" oil consumption and what is considered "abnormal" or "excessive" oil consumption is largely speculative and widely dependent on a number of variables. Engines operated at high speed and load are likely to consume oil at a greater rate than engines operated at lower engine speeds and loads. Operating temperature and component condition are also crucial factors in overall oil consumption.

We suggest that a healthy 6.5 diesel should not lose more than 10% of its oil capacity between 2,500 mile oil change intervals. This would represent 0.7 quarts for 7 quart systems and 0.8 quarts for 8 quarts system; approximately 3/4 of a quart regardless of capacity. The 6.5 liter has a relative small engine oil capacity and engine oil plays a critical role in cooling components it comes in contact with. Additionally, if fuel dilution is present, its effects may become more prominent as the oil supply decreases. If an engine uses more than this between service intervals, monitor and add as necessary to keep the supply replenished.

The greatest source of oil consumption is a severely worn engine. Worn piston rings and valve stem seals are common sources of excessive oil consumption. Assuming an engine is in good overall condition, turbocharger oil seals are another probable source. Lubricating oil is pumped through the turbocharger while the engine is running. A poor shaft seal can allow oil to seep into the intake air charge or exhaust pathway. Note that blue smoke is generally indicative of excessive oil burning in the combustion chamber.

The CDR valve on a 6.5 liter diesel can also be the source of oil consumption. The CDR valve is designed to recycle crankcase fumes (a combination of fuel/oil vapors and exhaust gases) through the intake air path. When functioning properly, oil vapors are consolidated and settle in the CDR valve before draining back into the crankcase through the valve cover. When not functioning properly, excessive oil vapors may be pulled through the CDR valve where they will ultimately be consumed in the combustion chamber.

6.2 & 6.5 Diesel Engine Oil Selection

The 6.2 and 6.5 liter engines are compatible with SAE 30, 15W-40, and 10W-30 engine oils depending on the anticipated ambient temperature for which the vehicle is to be operated. Ambient conditions play a significant role in engine oil selection, particularly at start-up and during the initial warm up period. GM specifies a diesel engine oil meeting API CF-4/SH specifications is preferred for all 6.5 liter applications. This classification has since been superseded (several times) and any diesel motor oil meeting modern API specifications will suffice.

Engine Oil Viscosity Charts

The 6.5 (figure 1 above) and 6.2 (figure 2 above) Detroit diesel engine oil viscosity charts are similar with the exception of the temperature range for which a SAE 10W-30 engine oil is acceptable. Note that some early 6.5 diesel service material uses the 6.2 viscosity chart. However, later material reflects the viscosity grades and temperature ranges depicted in figure 1. In either instance, SAE 15W-40 is a preferred engine oil in ambient temperatures above 0° F and should be used unless temperatures are well below freezing.

For cold weather operation, GM has specific requirements for block heater usage. Employing the engine block heater is crucial to easy starting in cold weather, but more importantly provides essential protections by preserving or restoring oil flow properties and ensuring proper lubrication at these extremely low temperatures. The table below details when and for what duration the engine block heater should be used prior to starting based on ambient temperature and oil viscosity.

[1] - SAE 30 is not listed as a compatible engine oil viscosity grade in temperatures below 32° F; this guidance is technically redundant
[2] - SAE 15W-40 is not listed as a compatible engine oil viscosity grade in temperatures below 0° F; this guidance is technically redundant

Engine Oil Recommendations

We highly recommend a full synthetic diesel motor oil for all 6.2 and 6.5 liter diesel applications. Modern synthetic motor oils are far superior than conventional oils, providing greater protections against wear, oil contamination, and the breakdown of engine oil resulting from mechanical, chemical, and thermal exposure. Additionally, they offer greater resistance against oxidation in vehicles that are parked for long periods and/or driven infrequently.

Diesel Hub recommends the following Amsoil products for GMC and Chevrolet vehicles equipped with a 6.2 or 6.5 diesel:

Amsoil Max Duty Signature Series 15W-40 diesel oil
Premium full synthetic motor oil for severe duty service and maximum wear protection

Amsoil Heavy Duty 15W-40 diesel oil
Economical engine oil option offering advanced wear protection

Amsoil Max Duty Signature Series 10W-30 diesel oil
Premium full synthetic motor oil for maximum protection in cold temperatures

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

• Advanced protection for vehicles that stored periodically or driven in-frequently

Amsoil is a leading manufacturer of synthetic oils and lubricants, including a line of engine oils engineered to meet the stringent demands specific to diesel engines.

Oil Change Parts List

[3] - Part can be reused if not damaged
[4] - Part not intended to be reused; replace with each oil change

How to Change the Engine Oil on a 6.5 Diesel

Click any thumbnail to view fullsize, detailed image

• Place a suitable container (minimum 8 quart capacity) beneath the oil pan drain plug.
• Note - do not attempt to change the oil on a hot engine; engine should be allowed to cool completely prior to draining the oil.

• Locate the engine oil fill cap at the top of the engine.
• Loosen the engine oil fill cap, but leave the cap in place. This will allow air to enter the crankcase as the oil pan drains, allowing the oil to drain smoothly, freely, and completely.

• Remove the oil pan drain plug with a 14 mm socket/wrench.
• Allow the engine oil to drain until the stream becomes a steady drip and the oil filter is accessible.
• Reposition the drain pan so that it catches oil dripping from the oil pan, but will also catch oil leaking from the oil filter.

• Loosen the engine oil filter by rotating counter-clockwise (when looking from the bottom of the filter upwards) until oil begins to run down the sides of the filter canister.
• Once oil stops draining down the side of the filter, clean it off and completely remove it from the filter mount.

• Clean off the oil filter mount (specifically the gasket contact surface) and ensure that the old oil filter gasket did not stick to the mount.

• Thoroughly clean the engine oil pan drain plug. If using an OEM drain plug gasket, lightly coat the silicon portion with clean engine oil. Note that these drain plug gaskets are intended for a single use; once they have been torqued to spec, they should not reused.

• If desired, prefill the engine oil filter with clean motor oil.
• Generously lubricate the oil filter gasket with clean motor oil.

• Reinstall the engine oil pan drain plug with a new drain plug gasket.
• Torque the engine oil pan drain plug to 18 lb-ft (216 lb-in).
• Install the new engine oil filter. Once the oil filter gasket contacts the mount, tighten an additional 1 to 1-1/4 turns.

• Using a clean funnel, add the appropriate amount of engine oil for your application to the crankcase through the oil fill at the front of the engine (7 quarts for 1998 and older engines, 8 quarts for 1999 and newer engines, less what has been added to the oil filter if it was prefilled).
• Replace the engine oil fill cap.

• Verify the engine oil level using the dipstick.
• Check the drain plug for leaks.
• Start the engine, then check for leaks around the drain plug and oil filter. If oil filter leaks, turn off engine and tighten filter.