A coolant change will ready your truck for thousands more miles without overheating or radiator trouble

There are two types of truck diesel engine coolant out there these days: extended life coolant (ELC) and fully formulated antifreeze, to which you add supplemental coolant additives (SCAs) as needed. Regardless of which you use, your coolant eventually will need to be changed. With ELC, it’s necessary to replenish the carboxylates. These protect the system from corrosion and eventually begin to deteriorate. With other coolants, a change is needed to remove acids or solids that build up in the coolant and can’t be removed on the truck.

Consult the literature your supplier provides to determine when it’s time to change. The interval is normally from about 600,000-1,000,000 miles. You also can get your coolant lab-tested periodically and let the lab tell you when to change.

To collect the coolant, get a good-size drain pan and make sure you have a place to store the old antifreeze for proper disposal – perhaps some used antifreeze jugs. Coolant capacity for a heavy-duty diesel is normally about 12 gallons.

Also, make sure you have a basic set of open-end or box wrenches as well as some sealer designed for cooling systems. Get a radiator cap tester if you don’t have one already. And, unless you plan to use 50/50 pre-mixed coolant, get a refractometer or coolant strength test strips.

Throughout the process, make sure to get the engine full of water or coolant before operating it and that you shut it down before draining.

The Job
Drain the system. To prevent scalding yourself when you remove the radiator cap, shut the engine off and allow it to cool until it’s at about 160 degrees F. Set the parking brake, chock the wheels and make sure the transmission is in neutral and the two valves to the heater are open (A).

Remove the radiator cap (B). The photo shows a Kenworth overflow tank that has a separate filler opening with a solid cap that has been removed; on most trucks you’ll just be removing the radiator cap.

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Place your drain pan under the drain cock and open the cock, normally done by turning it counter-clockwise so that it screws inward. Open the cock all the way and drain the coolant (C).

Many engines also have a drain plug located low on one side of the block or on or near the water pump. Removing the plug will make it much easier to get all the old coolant out and also to keep it for proper disposal.

Once the coolant stops draining, close the drain cock. If you removed the drain plug, coat it with a little sealer to lubricate it and reinstall.

To flush the system, refill with plain water, leaving just an inch or two at the top of the radiator top tank or overflow tank (D). When it is full, start the engine and then set the throttle to idle at 1,300 rpm, but leave the radiator cap off (E). Have water handy and watch the level. When the thermostat opens, air will be expelled, and the water level will drop. Keep refilling the overflow or top tank. You’ll see a fair amount of old antifreeze in the coolant (particularly if you weren’t able to remove the block’s drain plug). When the level remains constant, install the radiator cap. Allow the engine to run for about 15 minutes to circulate the coolant, then shut down.

Allow engine to cool to 160 degrees, then repeat the draining process. If the coolant is still obviously either red or green from the old antifreeze, repeat step 6 until it’s almost clear. This is essential to get the most out of your new antifreeze, especially if converting to ELC, as left-over SCAs can interfere with ELC’s corrosion-protection system.
Coat the drain plug with sealer and reinstall it, tightening until just snug (you may find a torque spec in the engine repair manual if you have one, in which case you can use a torque wrench). Also, retighten the drain cock (but only finger tight).

If converting from traditional coolant to ELC, replace the water filter with a “blank” or “zero-charge” filter having no coolant additive. You can also simply plug the coolant filter connections if switching to ELC. If using traditional coolant, replace the coolant filter with the same type you’ve used in the past. The best systems add SCAs from the filter using a method of controlled release. The filter pictured is a Need-Release filter from Penray (F).

Refill the system with 50 percent water, as antifreeze must never be used alone. The best procedure is to buy 50/50 premix, as the right amount of pure water is already there. If using straight antifreeze, make sure the tap water in your area meets the cleanliness standards required by the engine manufacturer. If you live in a climate with temperatures below -34 F, you can use up to 60 percent antifreeze, 40 percent water.

Refill using the procedure in Step 6. If you’ve mixed your own water in with pure coolant, check the freeze point with a refractometer or freeze point test strip [Refractometer and ELC Coolant]. Adjust the freeze point if necessary to -34 F (or the lowest temperature needed in your area) by draining coolant and adding straight antifreeze or water. Keep some extra coolant with you and check the level (after the engine cools to 160) over the next few days.

Note the time and miles and, with ELC, add a bottle of extender halfway through the approved life of the coolant. Test ELC for proper coolant strength annually and adjust as necessary. With conventional coolant, test the coolant for SCAs and coolant strength and change the filter as advised by the manufacturer. If you run a small fleet, make sure any hired drivers add only the same brand of ELC or fully formulated coolant you originally installed.