2020 and Newer L5P Duramax Maintenance: What to Service and When
The 2020 and newer L5P Duramax is a stout engine, and the trucks tell you a lot about their own maintenance. Most of what goes wrong on them starts with fuel: water, contamination or a filter left too long, all of which are hard on the high pressure pump. Here is what to service, when, and the parts that make each job easier.
GM's oil life monitor and fuel filter life monitor track the two most important services for you. Use the intervals below as a guide, and check your owner's manual for your year.
Normal or Severe Schedule?
Every manufacturer publishes two schedules. Towing, hauling heavy, long idling, short trips, dusty roads and very hot or cold weather all count as severe duty, and that describes how most diesel trucks actually get used. If you are not sure which one fits your truck, follow the severe schedule. It costs a little more in filters and fluid and a lot less in parts.
Engine Oil and Filter
Change the oil when the oil life monitor calls for it. Towing and idling bring that interval down. GM lists SAE 15W-40 above 0 degrees F and 5W-40 below it, in an API CK-4 diesel oil. The L5P takes about 10 quarts with a filter change.
- Schaeffer's 9000 SynShield OTR Plus 5W-40 full synthetic diesel oil. Whatever oil you run, check that the label meets the spec in your owner's manual.
- Wehrli billet oil fill cap
Fuel Filter and Water Separator
This is the most important service on the truck. The L5P's Denso HP4 high pressure pump needs clean, water free fuel. Change the fuel filter when the fuel filter life monitor calls for it, which usually lands around 22,500 miles, and drain the water separator at the same time. Drain it right away if you get a water in fuel warning.
- Easier filter changes: Fleece fuel filter upgrade kit for 2020 short bed trucks switches to a spin on canister. Wehrli makes fuel filter housing kits for 2020 to 2024 short bed and long bed trucks, and H&S makes a billet fuel filter housing. Add a FASS billet fuel filter cap.
- Lift pump: the FASS Drop In Series for 2020 to 2023 crew cab short bed. See our lift pump guide.
- Fuel additive: Schaeffer's Diesel Treat 2000 adds lubricity to ultra low sulfur fuel.
- If the pump does fail: the Exergy L5P HP4 pump is a direct replacement. Find out what contaminated the system before you install it.
Cooling System
The L5P uses GM DEX-COOL mixed 50/50 with clean water. Never mix it with other coolant types. Check the level cold and look over the hoses, pipes and reservoirs at every oil change.
- Wehrli upper coolant pipe for 2020 to 2025
- Wehrli aluminum coolant tank kit and auxiliary coolant tank kit for 2020 to 2025 trucks
Air Filter
GM's engine air filter life monitor will tell you when it is due. Look at the filter every oil change if you run dirt roads or job sites.
Transmission, Transfer Case and Axles
2020 and newer L5P trucks use the Allison 10 speed. GM's interval gets much shorter if you tow, so check the severe schedule in your manual. The same goes for the transfer case and axles.
DEF
Keep the DEF tank topped up with fresh, sealed, API certified fluid. DEF breaks down in heat and age, so do not stockpile it. Never put DEF in the fuel tank. If it happens, do not start the truck.
Quick Reference
| Item | Interval |
|---|---|
| Engine oil and filter | Per oil life monitor |
| Fuel filter | Per fuel filter life monitor, usually around 22,500 miles |
| Water separator | Drain at every fuel filter change and any water in fuel warning |
| Air filter | Per air filter life monitor |
| Coolant | DEX-COOL; check level cold every oil change |
| Allison 10 speed | Per manual; much shorter if you tow |
Shop L5P Duramax parts and fuel system.
FAQ
How often should I change the oil on a 2020 and newer L5P Duramax?
When the oil life monitor calls for it. Use SAE 15W-40 above 0 degrees F or 5W-40 below it. The engine takes about 10 quarts with a filter change.
How often does the L5P fuel filter get changed?
When the fuel filter life monitor calls for it, which usually lands around 22,500 miles. Drain the water separator at the same time and any time you get a water in fuel warning.
What coolant does the L5P Duramax use?
GM DEX-COOL mixed 50/50 with clean water. Do not mix it with other coolant types.
Not sure what fits your truck? Send us your VIN or call 865 640 2097 and we will help you pick the right parts.
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