Jim Park

With summer almost upon us, the urge to keep things cool under the hood of your truck should be a strong one. If you’re smart, you’ll have your cooling system checked out next time Ol’ Betsy’s in the shop. And there’s a lot you can do yourself, even if you’re not a wrench.

Among the easiest is checking belts and hoses for cracks and bulges, but you can’t rely on just a look-see. You’ve got to feel for bulges and softness and anything else that seems awry. Look carefully at the clamps too, of course. Are they tight?

Radiator maintenance used to mean directing a high-pressure hose at the dirt, but not any more. Most trucks today have a three-part sandwich of radiator, air-conditioning condenser and air-to-air intercooler. That makes them harder to get at and more difficult to clean.

The first line of defence is to spec and maintain a bug screen either on the grille or behind the grille and ahead of the heat-exchanger group. This stops the bugs with their corrosive body fluids getting into the cores of the different heat exchangers. Keeping out bugs means there’s less for dirt to hang up on, too. But don’t forget that the screen also needs regular maintenance to keep it clear.

If there’s a blockage to a clear passage of air through the heat exchanger cores, you can try to clean all the cores out with a blast of air. Blow in the opposite direction to the natural airflow, of course, but don’t use more than 70 psi. You can remove the intercooler for better access, but this is dangerous as dirt can get into the heat exchanger or the hoses and pipes to ‘dust’ the engine when you fire it up.

High oil temperature, excessive fan cycling and maybe getting just a little warmth out of the heater often signifies a cooling system problem that may require a full cleanout.

Look in the top of the radiator. If the coolant is rusty and has a thick-looking consistency, or if there are deposits on the top tubes in the header, you or your mechanic should follow the recommended procedure to remove rust, solder bloom, corrosion byproducts and all the rest of the stuff that’s plugging the radiator tubes.

If you’re chucking out the coolant (properly, right?), and when the system is recharged, a pre-charge of supplemental coolant additive must be included according to the engine manufacturer’s recommendation. When recharging, remember to use new coolant filters.

Before recharging, ensure the check procedures allow for a look at fan belts and clutch. For radiator integrity the fan must be kept out of the core, so fan blades must be checked for cracks and runout, and the fan clutch inspected for play with the clutch released. Recommended maximum play for the fan is 3/16-inch at the fan blade tip.
To check the radiator for leaks, have the cooling system pressure-tested – but only when the engine’s cold because that’s when the system leaks most. And if it’s going to leak, it’ll come from the radiator core, the header tank face, or in hose joints. The radiator cap should be pressure-tested too.

The Water Pump

Heavy-duty diesels now last far longer than ever before, with time-to-overhaul now approaching or even exceeding a million miles for many models. But not everything on the engine will last that long, and among the most nagging problems are water pumps.

Fleet managers say pumps routinely fail at 200,000 to 300,000 miles on certain engines. Some failures are due to design and manufacturing defects, and about all you can do is replace the pump and maybe make a warranty claim. But try to get the latest pump available, not another copy of the same unit that will also fail early. For instance, the materials used in impellars, seals, shafts and bearings have been changed in a number of products in recent years to make them more robust.

Also, be sure the original pump has really failed before pulling it out. According to the U.S. Technology and Maintenance Council, the high priests of truck maintenance, a high percentage of water pumps are declared dead or dying when seepage is spotted at the pump’s weep hole. In fact, the hole is there to allow a bit of moisture to escape from the unit, so a few drips of coolant may be normal. Steady dripping, on the other hand, indicates an internal seal failure and the unit may indeed be bad.

Seal failures are one of seven causes of pump failure, according to TMC’s Recommended Practice 322. Other reasons: cavitation of parts surfaces (due to air bubbles beating on metal); erosion of surfaces (from contaminants or metal defects); seal overheating (when the coolant itself does); oil and grease seal failures (from using the wrong grease or installation mistakes); bearing failure (mostly from contaminated coolant); and drive failures (pulley or belt problems).

Many of those conditions stem from lousy maintenance practices. Dirty and rusty coolant, and too little or too much supplemental coolant additive (SCA), can turn the coolant into a brine that will attack and destroy the pump. How do you avoid that?

* Use the correct antifreeze. Engine builders publish recommendations on what to use, so ask your dealer for the recommendations and follow them. Don’t use consumer-type antifreeze formulated for cars and light trucks, because these will have too many silicates that form a green goo that damages the parts in heavy truck diesels.
* Use SCAs according to the builder’s recommendations.
These can be poured into the coolant or released gradually by special equipment, including filters. Ask about installing a coolant filter if your truck doesn’t have one, and if it does, keep it working.
* Use good water. Avoid hard water and water that runs through galvanized iron pipes.
* Monitor the coolant’s condition by visual and chemical inspection. Look for rust, dirt and discoloration. Periodically sample and analyze the coolant to find out exactly what’s in there.
* Drain old coolant at the engine builder’s recommended interval (for example, every 200,000 miles), flush the system, and refill it with the right stuff. This will be cheaper than replacing the pump.

If you take care of the cooling system at large, the pump will last a long time. If you don’t, the chances are good that you’ll have to find you way to a shop. And maybe at the end of an expensive wrecker’s hook.

What’s the Best Engine Temp?

You have a lot of time to think and ponder the details of your truck’s performance, like what the temperature gauge says. Assuming it’s accurate, does running at 190° or more hurt an engine that ‘should’ be running at 180°? No. The engine may run best at 180° to 190°, but it will take more – and must be able to – if ambient temps are sizzling.

One rule of thumb says an engine should operate about 100°F above ambient temperature. If it’s 120° in Death Valley, the temperature gauge might read 220° and be ‘normal’. The coolant doesn’t boil because it’s under pressure. Yes, this will be hard on the engine, but it’s hard on everything and everybody else, too.

Cooling systems and their components are designed to try to keep the engine in a specific operating range. Components will operate in sequence to try to maintain that rather narrow temperature band. An example:

1. Starting from cold, the thermostat remains closed, keeping coolant in the engine block until it warms up to 180°. Then it opens to allow coolant to flow through the radiator.

2. The fan stays off until coolant reaches 195°, then the fan turns on and stays on until the temp drops back down to 185° or so. (Staying on below its start-up point reduces annoying cycling of the fan.) The fan will also engage to keep A/C refrigerant within specified parameters, and this can cause repeated cycling.

When radiator shutters were used (they hardly are anymore), they stayed closed until after the thermostat opened and coolant began flowing into the radiator. Then the shutters would open as coolant temp climbed, allowing ram air to do its job. If this wasn’t enough, the fan would then come on.

Today’s cooling systems are designed to run with air flowing freely through the radiator.

Jim Park

Jim Park was a CDL driver and owner-operator from 1978 until 1998, when he began his second career as a trucking journalist. During that career transition, he hosted an overnight radio show on a Hamilton, Ontario radio station and later went on to anchor the trucking news in SiriusXM's Road Dog Trucking channel. Jim is a regular contributor to Today's Trucking and, and produces Focus On and On the Spot test drive videos.

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