Cooling System Flush

Cooling System Flush

The no-hassle, drain-and-fill drill

Draining and filling your cooling system used to be a whole lot simpler. Back in the early days of ethylene glycol coolant/antifreeze, all you had to do was reach for the drain petcock at the bottom of the all-metal radiator and let it dribble into the drain pan. Then you refilled the radiator with a fresh 50/50 mix of coolant and water until you could see it at the "Full" line embossed into the radiator tank. After tightening down the radiator cap, off you went, with nary a need for a second look at your work. Try that procedure on a modern passenger car or truck today and you will likely end up with an abbreviated drive and maybe a "cooked" engine to go along with it!

New-Age Cool

Lots of changes have been made to vehicle cooling and heating systems in recent years, such as reverse flow (bottom to top of radiator) for more even cylinder block/head temperatures. This new system allows for a faster warm-up, thereby reducing exhaust emissions (and complaints from passengers on those cold winter days). New designs also promote increased engine durability since aluminum radiator and heater cores are more efficient than copper and allow for more compact packaging and lighter weight. Moreover, the use of computer-aided design, coupled with thermoplastic technology, allows engineers to boldly go where no slide rule ever allowed them to go before.

Rear heater units are becoming commonplace in minivans and larger SUVs. Other advancements include dual-stage thermostats for tighter temperature control, electric fans actuated by the engine management computer (not a dedicated fan switch circuit), complex climate controls, long-life coolants, and so on. Many of these technologies have had a negative impact on serviceability. Radiator drain plugs are less accessible and "air locks" inhibit easy draining/filling of the system. These new designs may also block visual inspection of critical components as well as access to routinely replaced components (thermostats, hoses). With a little time, patience, and know-how, however, these obstacles can be overcome. Here's a quick checklist of tips for dealing with your new-age cooling system:

Drain the System

Determine if you can reach the drain plug by hand. Bear in mind that not all drain plugs are created equal and take different techniques to operate correctly. For instance, some plastic GM types turn 90 degrees, hit a stop and then must be pulled outward, so pay attention and don't force anything! If the drain isn't easily reached, then you'll have to remove the lower radiator hose. Fortunately, plastic radiator tanks make this process easy, as hoses usually don't "weld" themselves to this material. Direct the coolant into a large collector with at least a two-gallon capacity (similar to those used in transmission service). To insure maximum drainage, carefully remove the uppermost heater or bypass hose (there are special tools for this so damage doesn't occur in case you're especially heavy-handed) and loosen any "bleeder screws" provided.

Inspect for Sludge

Drain out any coolant in the reservoir (overflow bottle) as well and check sludge deposits in the bottom. It may be necessary to remove the reservoir to accomplish both of these tasks. Usually, half-filling the reservoir with clean water and shaking it (rock 'n roll or bartender-style, take your pick) will loosen the sludge. Dispose of this funky mixture and the used coolant in a responsible, legal way (usually outlined on the new coolant container). Next, inspect the radiator cap for seal damage and sludge packed in the spring area. Replace it if signs of either are present.

Know Your Stats

If you're changing the thermostat at this time, keep in mind that all 'stats are not created equal, either. Carefully compare your replacement to the original one. If you're not using the exact original replacement part, the replacement part you have should exactly resemble the original, especially in the number of "stages" it has (one or two-check the center area) and other features like a "jiggle valve." This valve is essential for quicker and more thorough initial filling of the system. Its absence will be replaced by your grief during the run-in procedure.

Picking Coolant

Make sure that you have the correct type of coolant for your vehicle. There are at least several distinct coolant types commonly used today, and using a type incompatible with the coolant recommended in the owner's manual (or on the underhood label) is inviting disaster (no exaggeration here). Whatever the type, it should be added in a 50/50 coolant/water concentration (well, at least some things haven't changed!). If the lower radiator hose had to be removed for drainage, reinstall using the factory "spring-type" clamp. Hopefully the original one didn't get distorted so you can reuse it. If you must use a "worm-gear" type clamp, be very careful not to over-tighten (an easy thing to do with a plastic tank) as the tank fitting can crack, which will require replacing your radiator!

Refill Procedure

Check for refill instructions printed on any underhood labels and follow those instructions. Otherwise, slowly pour the coolant mixture into the radiator. As the tank fills up, take your hand and repeatedly squeeze the lower radiator hose. This action activates the "jiggle valve." Continue filling until coolant comes out of the dislodged heater/bypass hose, its companion fitting or the bleeder screw(s)-or it reaches the top of the filler neck and stays there. Reinstall the hose, tighten the bleeder screw and install the radiator cap. Fill the reservoir to the "Full" mark. You're now ready for the run-in procedure.

Run-in Procedure

Turn interior temperature controls to "hot," or equivalent, and start the engine. Within about a minute, the heater/bypass hoses should be warming. After two minutes, there should be some heat noticeable at the heater air outlets (fan set to slowest speed). Check that the temperature gauge does not go past the halfway point without heat present at the heater outlets. If there is no heat present, shut the engine off and wait about ten minutes. Turn the ignition key on and check the temperature gauge. If it's dropped significantly, go to the radiator cap and slowly and carefully, preferably with a padded glove, relieve any built up pressure. Only after that can you then gingerly remove the cap. Perform the refill procedure again, but this time fill the radiator extremely slowly, as engine damage may occur otherwise. Continue with this run-in procedure until the heater functions normally, the radiator cooling fans (if so equipped) operate normally and the coolant level remains full in the radiator and reservoir. Certainly, this tedious fill procedure isn't as easy as in the "old days," but then again, when it comes to servicing modern vehicles, very little is.

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