A diesel makes a lot of heat, and in Central Florida the air it uses to shed that heat is already hot. Add a heavy trailer or a full load and the cooling system works at its limit. When something in it slips, the gauge climbs or the coolant disappears. RDI Power repairs diesel cooling systems at our Brooksville shop for pickups, work trucks, tractors, buses and diesel pusher RVs.
The cooling stack
Most diesel trucks have several heat exchangers stacked at the front: the A/C condenser, the charge air cooler, the radiator and sometimes a transmission or fuel cooler. Behind them, a fan clutch pulls air through. On pickups, that is usually a viscous or electronically controlled viscous clutch. On heavy trucks, it is often an air-engaged fan drive that is either on or off. Inside the engine, a water pump circulates coolant, a thermostat controls flow, and on many diesels coolant also passes through an EGR cooler and an oil cooler.
Overheating warning signs
- Temperature gauge climbing under load or at idle
- Coolant level dropping, or a low coolant warning
- A sweet smell, steam or residue around hoses and the radiator
- White smoke from the exhaust with coolant loss
- Fan running loud all the time, or never engaging
- Weak A/C at idle, since the condenser shares the same airflow
Where coolant goes when you cannot find it
External leaks drip, crust or evaporate off hot parts. Internal leaks are harder: an EGR cooler that cracks sends coolant into the exhaust; an oil cooler that fails mixes coolant and oil; a head gasket can push combustion gas into the coolant and coolant into a cylinder. The 6.0 Power Stroke is known for oil cooler and EGR cooler failures, and the 6.4 for radiator leaks; see our Power Stroke service page. EGR coolers sit on the emissions side too, covered on our exhaust and EGR page.
Cooling system tests
- Pressure test the system cold to find external leaks, and check the cap.
- Combustion gas test on the coolant to detect a head gasket or cracked component.
- Coolant condition: strength, additive level and contamination with oil or fuel.
- Fan clutch engagement checked hot, and airflow through the stack.
- Temperature readings across the radiator to find clogged sections.
- EGR and oil cooler testing when coolant is going somewhere it should not.
Debris and duty cycle
Trucks working farms, groves and job sites pull grass, seeds, dust and mud into the cooling stack, and the gap between coolers fills up where you cannot see it. Bugs do the same on highway trucks. A truck that only overheats in the afternoon heat with a load is often a cleaning job. Agriculture and construction fleets see this more than anyone.
Cooling system repairs
- Radiator replacement or repair, and charge air cooler leak repair
- Hoses, clamps and the degas or overflow bottle
- Water pump and thermostat replacement
- Fan clutch or air fan drive repair
- EGR cooler or oil cooler replacement, with the cause of the failure addressed
- Flushing and refilling with the coolant type the manufacturer specifies
Prevention
Coolant wears out. Testing its strength and condition at each preventive maintenance visit, and cleaning the cooling stack on trucks that work in dirt, prevents most overheating calls. RVs and buses that sit should have hoses checked for age as well.
If the gauge is creeping or the coolant level keeps dropping, bring the truck in before a hot afternoon turns it into a tow.