When climbing mountain grades,...
When climbing mountain grades, it's important to keep your cooling system in optimum condition to prevent overheating.
Proper cooling is critical to any engine. Without some way to remove the heat created during the combustion process, the engine will quickly become a lump of scrap metal. But today's coolants provide many other functions: They prevent cracked engine blocks in freezing weather and add corrosion and scale inhibitors, water pump lubricants, and other additives essential to efficient operation of the engines. The original term "antifreeze" was gradually replaced by coolant, which really is a more accurate term.
What They Do
Diesel engines place greater demands on coolants than a typical gasoline-powered engine. Diesel fuel has much more BTU per gallon than gasoline. This gives a diesel engine the potential to create more power and torque than an equivalent-size gasoline engine. Of course this extra energy also creates more heat, so the cooling system requirements of a diesel engine will also be greater.
Engine blocks used in automotive applications have cylinders that are bored into a one-piece casting. When they are worn out or damaged, the engine block will need to be scrapped. Heavy-duty engines that are used in trucks are designed to last for many miles, so they use replaceable cylinder liners that can be removed from the engine block and replaced when worn or damaged to minimize operational costs over the life of the vehicle. A motorhome typically does not rack up as many miles as a daily-driven truck, but the engine is still in the heavy-duty class so its construction will be similar.
Many diesel pushers utilize...
Many diesel pushers utilize a rear radiator with a charge air cooler for the turbocharger stacked directly above it.
Cylinder liners come in two designs: dry-sleeved and wet-sleeved. Dry sleeves are inserted into the engine block and surrounded by outer walls cast into the block that contact the coolant so the coolant never touches the actual cylinder liner. Wet sleeves are inserted into a block that does not have any outer cylinder wall. The coolant in the engine actually contacts the cylinder liner itself. The liner has flanges and counterbores on its outside diameter that are used to hold O-ring seals so that the coolant stays in the engine's water jackets and doesn't leak down into the engine's oil sump.
Typically, dry sleeves are used on smaller engines, while wet sleeves are used on larger engines. The reason for this is that larger engines create more heat, and the wet sleeve does a much better job of conducting that cylinder heat to the coolant because the wet sleeve is in direct contact with the coolant. Engines like the 5.9-liter Cummins ISB and 7.2-liter Cat C7 use a dry sleeve, while larger engines like the 8.3-liter Cummins ISC, 8.9-liter Cummins ISL, etc. all use wet sleeves. Dry sleeves aren't as picky with coolants, but wet sleeves do have unique requirements and coolant selection and maintenance are critical. This all has to do with cavitations and liner pitting.
This cylinder liner has numerous...
This cylinder liner has numerous pits and pinholes and has failed from the effects of cavitation.
Liner pitting is a result of something best described as "cavitation." Wet cylinder liners are held in place in the engine block with O-ring seals and the clamping pressure of the cylinder head upon the upper flange of the liner. As the piston moves up and down, there is also side-to-side force being exerted on the cylinder due to the throw of the crankshaft. This lateral force causes these liners to vibrate back and forth. When the cylinder moves in one direction, it moves away from the coolant, creating a small air bubble in its wake. Eventually this air bubble bursts and the coolant, which is under pressure, bursts through and impacts the cylinder liner. This sudden jet of high-pressure coolant can pit the liner, and if allowed to continue, will create a pinhole through it. In wet-sleeved diesel engines, this vibration and air bubble popping happens repeatedly whenever the engine is running. Eventually, these pits deepen and cause pinholes, which will allow coolant to pass into the combustion chamber. When this happens you'll find your coolant level going down, increased operating temperatures, and white smoke coming from your exhaust. By the time you see this it's too late, and you'll be in for some expensive engine overhaul costs.
Regular coolants just can't handle the effects of cavitation, so don't put Dexcool into your large wet-sleeved diesel. There are a number of heavy-duty coolants available for diesel engines, and each has its own specific formulations and specifications. Couple this with the fact that Cat and Freightliner have their own private-labeled coolants, and things get really confusing for the average RVer.