Your cooling system is probably working harder than ever. Most of the new big-bore diesels using cooled exhaust gas recirculation (EGR) will be diverting up to 30% of the engine’s exhaust stream – which used to flow freely up the stack into the atmosphere – back into the engine. This significantly increases the amount of heat the cooling system must dissipate. The new engines won’t necessarily be running hotter (though some will), but there will be a lot more heat to get rid of, placing higher loads on the cooling system and its components.

On the average, midrange diesels will be rejecting 10% to 30% more heat, while heavy-duty engines will be at 15% to 40% more. Cooling demand will increase at low engine rpm (when the EGR cycle is at its peak), and at low road speeds when air flow through the rad is at a minimum. As well, we’ll see increased pressures on the engine’s air-intake system, such as charge-air coolers and the ducting
downstream of the turbo.

Many engines will have higher-pressure radiator caps than before, and top-tank coolant temperatures will be up, too. Anywhere high temperatures and high pressures combine with fluid or air-containment apparatus, you run higher risks of
leaks in cores, hoses, and fittings. PM services and daily checks should focus on leaks.

These changes, of course, will affect more than just the radiator.

Some manufacturers have developed controllable viscous-drive fans, which turn faster the hotter it gets. A viscous drive is never completely off. On/off fan clutches will be cycling more frequently, putting increased loads on bearings, seals, clutch facings, and belt drives. Gene Wantuck from Borg Warner Cooling Systems says that with viscous fan drives, it’s important to make sure drives aren’t permanently locked up or freewheeling. Any sign of bluing indicates excessive heat.

Horton’s Jim LeClaire says fan size and fan rpm will have an impact on fan-clutch loadings. He says that if fan speeds increase only 10%, the horsepower ‘pull’ goes up 33%. Increased fan-on time will affect fuel economy. He also voices concern about short fan-cycling intervals, which put greater loads on the fan clutch and shortens life. He also says that under-hood inspections should focus on air leaks and loose or under-tensioned belts, which can slip. Drivers should be on the lookout for both when doing their pre-trips.

Ken Bridges from Gates Rubber says a good belt drive system, properly maintained, should give 60,000-mile V-belt life and 150,000 miles for the new V-ribbed belts.

Automatic belt tensioners should go for 350,000 miles. Maintaining factory-recommended belt tensions is critical, as is proper belt alignment, especially on ribbed drives. Belt tensioners should be checked regularly to see if
they spin free and are wobble-free. A properly maintained belt drive system should be noise- and vibration-free.

The Problem’s Core
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 but 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. Bug screens need regular cleaning too.

If there’s a blockage 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 air flow, 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.

A proper cooling-system check demands that you also 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 run-out, 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, pressure-test the cooling system. With the engine cold – this is when the system leaks most – pressurize the system to 15-18 psi and verify that there are no leaks, either in the radiator core, header tank face, or in existing hose joints. Pressure-test the radiator cap. It should hold a minimum of five psi, but check with the manual regarding correct system pressure.

Whether or not you’re running an EGR engine, a thorough cooling system maintenance and inspection is critical this time of the year. It’s a long way from 40-below to 100-plus degrees, and you can bet it gets a lot hotter down in the
engine room.

Fan Clutch Maintenance
Summer’s heat means more work for your fan clutch, and a clutch failure can cost a bundle. If the fan fails to cycle off, the increased horsepower draw will suck up fuel like there’s no tomorrow, and if the clutch fails to engage, you run the risk of overheating.

And let’s not forget the added stress from the fan cycles required by your air conditioner. Now is a good time to inspect the fan clutch and do a little R & R if needed.

* Check for air leaks or bearings that are on their last legs: you’ll hear hissing or rattling sounds coming from the center of the fan hub.

* Check for cycling frequency: if the fan is constantly cycling on and off, you could have a bad temperature sensor or some other electronic fan trigger might be on its way out.

n High operating temperatures: if the fan doesn’t come on when needed, it might be either an electrical or an air system problem.

* Fan always on: a fan clutch that fails to disengage can also indicate trouble with the electrical system, air problems, or a problem with the clutch mechanism itself.

* If the fan clutch seems to be cycling properly, yet the operating temperature remains abnormally high, you may need to look for restrictions at the front of the rad, such as debris, leaves, bugs, etc., jamming up the cooling fins, or a problem with the coolant circulation, such as a bad thermostat or a failing water pump.

One of the most expensive on-road repairs this time of the year is the air conditioning compressor. AC systems are being turned on for the first time in months, and when the vents fail to deliver comforting cool air, it’s pretty annoying. A roadside compressor replacement can cost nearly $1000, but a scheduled at-home repair or replacement can cost less than half of that.

Low system pressure increases cycle frequency – up to 300-400 times per hour – which places a heck of a strain on the bearings, belts, clutch, etc. There’s at least one answer, from Index Sensors & Controls of Stanwood, Wash. It’s the ACX-10 ‘Air Conditioning Life Extender’.

The ACX-10 is simply a passive pressure-monitoring switch that prevents rapid cycling of the compressor. When persistent high or low system pressure is detected, it disengages the AC clutch until the pressure returns to a normal, safe operating range. The ACX-10 permits limited operation of the AC compressor in a limp-home mode, rather than a total shutdown. This allows the truck to return
home for a more cost-effective repair rather than taking your chances with a roadside shop. The sensor sells for about $100. For more information, call your truck dealer.