6.5 GM Diesel Oil Change Guide

Applicable Models:

1992 - 2002 Chevrolet & GMC C/K series trucks, Suburban, C3500HD, etc

Applicable Engine(s):

6.5L GM diesel (turbocharged and naturally aspirated)

Oil Change Intervals:

Change engine oil and filter every 5,000 miles under normal conditions, 2,500 miles under severe service conditions (includes towing)

Engine Oil Capacity:

7 U.S. quarts with filter change for 1992 - 1998 model years, 8 U.S. quarts with filter change for 1999+ model years

The older an engine gets, the more important it becomes to adhere to the "severe" maintenance intervals. Routinely changing the engine oil at OE specified intervals is imperative to the life of your engine. Since diesel engines suffer from fuel dilution and soot contamination, one could argue that this service procedure is more critical than it is in other engine types.

6.5 Diesel Oil Change Parts List

Part Description

Part Number(s)


Engine oil filter

ACDelco PF1218


Oil pan drain plug gasket

ACDelco 14090908


Oil fill cap



Engine oil

Refer to viscosity chart below


6.5 GM/Detroit Diesel Oil Selection, Requirements, & Recommendations

The 6.5L GM diesel has a relatively small engine oil capacity at 7 quarts (8 quarts for 1999+) with a filter change. For comparison, the 6.6L Duramax has a 10 quart system. Even though the 6.5L has an oil cooler, the oil in these engines may have a tendency to degrade quicker and have a relatively low resilience to fuel dilution and other forms of oil contamination due to the limited capacity. Heat also plays a large role in the degradation of engine oil, which ultimately modifies its properties.

A synthetic oil is your best choice for any engine, and thus remains our recommendation for the naturally aspirated and turbocharged 6.5L diesels. There's no special procedures for converting to a synthetic engine oil and synthetic service fluids are far superior to conventional petroleum based "dino" oils. Albeit slightly more expensive, synthetic oils tend to provide a greater level of protection for your engine.

6.5 GM Diesel Viscosity Chart


Ambient Temperature Range

SAE 15W-40

> 0° F (preferred)


> 32° F (15W-40 preferred over 30W)

SAE 10W-30

< 32° F (cold weather viscosity)

While a straight 30 weight oil is acceptable in ambient temperatures greater than 32° F, 15W-40 is largely preferred and recommended in place of a SAE 30W. 10W-30 must be used when the engine is operated in ambient temperatures below 0° F and can be used in place of a 15W-40 when the ambient temperature is in the 0 to 32° F range. Engine oil should be changed every 5,000 miles under normal conditions and 2,500 miles under "severe" duty conditions, which includes frequent towing, extended periods of idling, off-road use, etc.

6.5 GM Diesel Engine Oil Recommendations

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

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.

How to Change the Oil in a 6.5L GM Diesel

Click any thumbnail to view high resolution, fullsize image w/ details (where applicable)

engine oil pan

• Place a suitable container beneath the engine oil pan (minimum 8 quarts capacity) to catch the oil as it drains.

• Remove the oil pan drain plug with a box end wrench (in this case a 9/16" or 14mm wrench, however the actual size of your plug may vary - it may have been replaced, etc) and allow the engine oil to drain completely. The drain plug points to the driver side of the vehicle.

oil draining from oil pan

• While the oil is draining thoroughly clean the drain plug with a lint free rag. Inspect the drain plug gasket and replace as required. The best practice is to replace the drain plug gasket at every oil change. Replace the drain plug and tighten snug once the engine oil has drained completely.

• Reposition the drain pan as necessary and remove the engine oil filter. An oil filter wrench may be required to loosen it. Another method of getting a better grip on the filter is to wrap it with emery cloth or sand paper - especially useful if the filter is slick with oil.

engine oil fill location

• The engine oil fill cap is located at the front of the engine, just to the passenger side of the thermostat housing. Removing or loosening the cap may help the oil drain quicker, but make sure to place a rag over the fill tube if you remove the cap completely.

oil filter location

• Using a lint free rag, clean the oil filter mount where the gasket of the oil filter seals against the oil filter mount. Inspect the mount and make sure that the old oil filter gasket did not stick to the sealing surface; this is very common and will result in a compromised seal when the new oil filter is installed.

filling new oil filter with clean motor oil

• Fill the replacement oil filter with roughly 3/4 of a quart of oil. The filter will hold approximately 1 quart of oil, however if it is filled to the brim you are likely to spill it when installing the filter.

• Thoroughly lubricate the oil filter gasket with clean engine oil.

• Reinstall the oil filter. Hand tighten snuggly; do not tighten with oil filter wrench.

oil dipstick location

• Add 7 quarts for pre-1999 and 8 quarts for 1999+ model year engines (minus the amount added to the oil filter) of new motor oil to the crankcase through the oil fill tube at the front of the engine.

• Verify the engine oil level using the oil dipstick.

• Ensure the oil fill cap is secure and that the engine oil drain plug is not leaking, then start the vehicle and check for leaks at the drain plug and oil filter.

oil filter and Amsoil diesel oil

• You can't go wrong with an OEM ACDelco oil filter. This truck received 7 quarts of Amsoil Heavy Duty 15W-40 motor oil and is ready for severe service.