Perhaps one of the most overlooked items of diesel truck maintenance involves the various fluids that are the lifeblood of these vehicles. Proper maintenance of oil, coolant, transmission fluid, and fuel are all crucial to a long and happy lifespan. However, there is some dispute about how often you should maintain or change fluids and filters, as well as the type of fluids used. In this section of Basic Training, we'll try and clear the air and give some sound advice regarding fluid maintenance.
| fluid Basics Diesel Service Schedule wrenching On Cummins Engine
Engine Oil
While diesel engines have very large capacity oiling systems that allow them to run much longer between changes than their gas counterparts, that doesn't mean you never have to change it. For oil changes, the frequency is largely dependent on the usage, make, and model of the vehicle. 6.0L Power Strokes, for instance-which use oil to lubricate the engine, fire the injectors, and are very sensitive to oil contamination-should observe the severe service change interval at the very least (5,000 miles). However, for the best peace of mind, we'd change the oil every 3,000 miles (and the same goes for 7.3L owners). By contrast, a newer common-rail engine that burns very clean may be able to be extended to 7,000 or even 10,000 miles, if the usage is freeway, and non-towing. As far as the type of oil used, most still run conventional 15W-40 weight oil.
| Although conventional 15W-40 engine oils are the norm for diesels, lighter weight and synthetic oils have become much more popular. For example, the lower viscosity of Shell’s Rotella 5W-40 synthetic (shown) helps aid cold weather startups and performance, and its synthetic blend has much better shear stability and engine wear protection properties than its conventional counterparts.
5.9L Cummins: 5,000 miles
6.7L Cummins: 7,500 miles
6.6L Duramax: 5,000 to 7,500 miles
7.3L Power Stroke: 5,000 miles normal, 3,000 miles severe
6.0L Power Stroke: 7,500 miles normal, 5,000 miles severe (but we'd do 3,000 miles)
6.4L Power Stroke: 10,000 miles normal, 5,000 miles severe or 200 hours
"Fluids other than oil are perhaps the most overlooked maintenance item on any diesel."
Gear Oil
Many people forget that the oil in their axles should be regularly changed. Gear oil is probably the most neglected of the fluids, possibly because in lighter-duty cars and trucks, it is virtually never changed. The weight, power, and general work use of diesels makes for a different situation, and gear oil should be changed every 20,000 miles in heavy towing applications, and about every 50,000 miles in mixed-use driving.
5.9L Cummins: 15,000 miles
6.7L Cummins: 15,000 miles
7.3L Power Stroke: 100,000 miles normal, 30,000 miles severe
6.0L Power Stroke: 97,500 miles
6.4L Power Stroke: Only when a leak is detected, 50,000 miles severe
Coolant
Today's diesel engines put out a lot of heat, as they deal with emissions- related exhaust gas recirculation (EGR) and regeneration cycles. EGR is extremely hard on coolant, as antifreeze is used to cool exhaust gases from as much as 1,200 to 1,300 degrees to roughly 350 degrees, so it can be reintroduced into the engine's intake tract. This makes keeping an eye on the health of your coolant and observing the correct flush intervals paramount.
| Motorcraft’s Premium Gold Engine Coolant is recommended for all 6.0L and 6.4L Power Stroke engines. This coolant uses a hybrid organic acid technology (HOAT) makeup that includes silicates (to protect aluminum) and nitrites (to guard against cavitation on cylinder walls).
On 6.0L Power Strokes, Ford recommends testing the coolant every 15,000 to 20,000 miles (when running a traditional coolant), even though the original coolant is stated to last up to 100,000 miles.
5.9L Cummins: 24,000 miles
6.7L Cummins: 100,000 miles or 60 months
6.6L Duramax: 150,000 miles
7.3L Power Stroke: 15,000 miles
6.0L Power Stroke: 45,000 miles
6.4L Power Stroke: 50,000 miles
Transmission Fluid
As transmissions and fluids have advanced, the interval between changes has gotten longer and longer. However, since most enthusiasts don't leave their diesels alone horsepower-wise, it's a good idea to change the fluid and filter more often when the vehicle is producing more power than stock-especially while towing. Heat is also a big factor in transmission and fluid life, so extra-capacity pans, finned pans, and external coolers can all help extend the life of your fluid.
| fluid Basics Diesel Service Schedule draining Oil
5.9L Cummins: 24,000 miles
6.7L Cummins: 120,000 miles normal, 60,000 miles severe
6.6L Duramax: 50,000 miles normal, 25,000 miles severe
7.3L Power Stroke: 21,000 miles
6.0L Power Stroke: 30,000 miles
6.4L Power Stroke: 30,000 miles
Fuel and Filter
How often should you change your fuel and fuel filter? Seems like a weird question, but it is an important one. First off, when filling, try and use a high-traffic filling station in order to get a good batch of fuel. If fuel sits too long underground, it can be contaminated by moisture. Water in diesel fuel can have exceedingly bad results for a diesel engine (including taking out the injectors, or even complete destruction if it is run long enough), so if you suspect contaminated fuel, drain your tank immediately. If you're running biodiesel, try to mix it in with regular diesel fuel so that it doesn't gum up injection system components. In cold weather, special attention must be paid to keep the fuel from gelling, and a fuel heater is very common, as temperatures dip into the single digits or below zero. As far as filters go, nearly all the OEM engine manufacturers recommend you change them every 10,000 to 15,000 miles.
5.9L Cummins: 15,000 miles
6.7L Cummins: 15,000 miles
6.6L Duramax: 15,000 miles
7.3L Power Stroke: 15,000 miles
6.0L Power Stroke: 10,000 miles
6.4L Power Stroke: 10,000 miles
Transfer Case Fluid
Due to essentially only being a case fitted with gears and chains, the transfer case and its fluid is definitely a neglected component on four-wheel-drive trucks. But think about it, your transfer case fluid has no cooler or any real way of seeing a temperature drop. This is why it's often black or extremely dark in color when you finally drain it. It can get hot!
| While it’s probably inconvenient for most of us who own four-wheel-drive rigs, changing your transfer case fluid at the recommended interval is good practice. While newer GM trucks come with a lengthy, 100,000-mile change interval recommendation, many aftermarket companies suggest changing the fluid annually, or every 50,000 miles.
We're not surprised that some trucks go their entire lifetime without seeing a fluid change, but how important is four-wheel drive to you?
5.9L Cummins: 60,000 miles
6.7L Cummins: 60,000 miles or 48 months
6.6L Duramax: 100,000 miles
7.3L Power Stroke: 60,000 miles
6.0L Power Stroke: 60,000 miles
6.4L Power Stroke: 60,000 miles
