ENGINE CONDITION

The 6.5 is a strong and durable engine design. However, as is the case with any turbo diesel engine, high coolant temps will shorten engine life and must be avoided.
GM did its customers a great disservice by placing the high-temp, red warning mark at the high-end of the coolant temperature scale on the dash gauge. It more rightfully should have been placed at the 210* mark. These engines will provide a substantially long service life if the coolant temperature is maintained at or below the 210* mark on the gauge. Excursions above the 210* mark will have a detrimental affect on the engine, shortening its service life.

The most common issue we find when a 6.5 wants to run over the 210* mark is a dirty radiator and or air conditioner condenser core. These will accumulate bugs, dirt and weed seed, which affect cooling efficiency, resulting in excessive coolant temps.
When the radiator and or a/c core are dirty, the radiator cannot efficiently dump heat into the pass-through air. This results in pass-through air that is relatively cool and cool enough to not trigger the viscous fan drive---------so, the coolant temp gauge reads high and the fan does not kick in to cool things down.
The first step in correcting for a high coolant temp problem is to clean the radiator and a/c condenser.
The only way to properly clean the radiator and a/c core is to remove the radiator from the vehicle. Put the radiator over a bucket or box, so you can see through it then clean the heck out of things--------it simply has to be spotlessly clean—no shortcuts!
While the radiator is out of the way, you must clean the a/c condenser core. These will often plug just behind the oil coolers. The oil coolers are configured in a way that allows the crud to go through them and lodge in the a/c core. Often there will be a solid mat of junk packed into the a/c core that is not visible until the oil coolers are loosened and tipped forward. Usually, one can use a pressure washer to flush the crud back out the way it came in. In some cases, we have to remove the grill and loosen the oil coolers to affect a thorough job of cleaning the a/c core.
Commercial grade a/c coil cleaners are available from heating and a/c stores. An acceptable alternate is Scrubbing Bubbles tub and shower cleaner. Spray this stuff into the radiator and a/c cores, let it soak, then blast it out with water. Repeat as necessary to get these units clean, really clean.

If the radiator and a/c core are CLEAN and if the engine is equipped with genuine GM AC Delco thermostats AND if the viscous fan drive is in good shape, this cooling system will do a very good job of maintaining temps at or below the 210* mark.


Towing with high mileage fuel injectors (typically miles exceeding 90,000) can damage pistons, leading to complete engine failure. Under light duty driving conditions, injectors can often operate without apparent issue, to 180-200,000 miles. However, when working the engine hard, these old, sloppy injectors can kill the pistons.
Typically, as the mileage approaches 100,000, injectors develop poor spray patterns and they loose their ability to shut off cleanly at the end of the injection stroke. The poor spray pattern will affect starting and engine efficiency. The inability to shut off cleanly at the end of the injection stroke will cause individual pistons to overheat, which will result in piston / engine failure.
When the 6.5 is worked hard and or used for towing, it is always wise to replace injectors at 80-100,000 mile intervals.


Our performance upgrades are perfectly suited for use with a healthy engine and life expectancy is unaffected.

If the engine has issues, hard work can bring it to its knees sooner than if it were healthy.

It is always a good idea to perform a ‘crankcase blow-by’ test before doing upgrades as this will help to determine the relative health of the engine.
Checking the amount of ‘blow-by’ is a good way to determine the health of the 6.5’s cylinders.

Blow-by refers to the combustion gas vapor that pushes past the pistons and rings. When the pistons, cylinders and rings are worn or damaged, they will be less affective in maintaining combustion gasses and will allow these gasses to leak past and into the crankcase, resulting in blow-by vapors.
The blow-by vapor will puff up out of the oil filler tube when the oil filler cap is removed.
If the engine is healthy, there will be little or no visible blow-by vapor. As the miles accumulate, it is expected that an increasing amount of blow-by will exist.

The first step is to bring the engine to normal operating temperature by driving the truck.
With the engine idling, remove the oil filler cap to observe any blow-by vapor. This vapor, if it exists, will puff up out of the oil filler tube.
A healthy 6.5 will have little or no visible blow-by vapor puffing out of the oil filler tube. We have seen a great many 6.5’s that exhibit no vapor puffing even when they have accumulated 150-200,000 miles.
These are engines that have not suffered due to coolant overheat or by running worn injectors---the pistons, cylinders and rings are healthy.
In more advanced stages of cylinder wear, the blow-by vapor may puff out of the dipstick tube and past the dipstick handle. If you see vapor puffing out past the dipstick, there is considerable blow-by and possibly a scored cylinder----the engine is nearing failure.
If there is blow-by coming from around the dip-stick handle and if the engine is knocking and running rough at idle, this would suggest that it has a failing or failed piston, likely due to overheat conditions.

We recommend a simple blow-by test that you can do in the driveway. It goes like this:
Obtain a 5’ section of clear 3/8” id tubing from the hardware store.

After removing the oil dipstick, slip this tube over the dipstick tube. Drape the clear tubing over the fender and place the end of it in a container of water.
With the engine fully warmed up and idling, the water level in the clear tubing should be level with the water in the container.

Rev the engine to around 2000 rpm. At this rpm, the water level in the clear tube should rise about 1” above that of the container.

If the water fails to pull up into the clear tubing, this would suggest either a failed CDR (crankcase depression regulator) valve or excessive blow-by pressure.
The first corrective measure would be to replace the CDR valve (GM part # 25098706). The CDR is the canister located on top of the passenger-side valve cover---it is easy to change.

With a new CDR in place, do the 2000-rpm test again. If the water fails to rise into the clear tube or worse, if the tube pushes air into the container, the blow-by is higher than it should be. If the engine fails this test and if there is blow-by vapor puffing out of the oil filler tube, this would suggest worn or damaged cylinders, pistons and or rings.
Adding performance upgrades to a 6.5 in this condition is not wise.

You must feel free to contact us with any questions you may have---we are dedicated to the 6.5 and are always happy to help.

Staff
Heath Diesel
877 894 6266 or email