Heavy-Duty Coolant Maintenance: Testing, Topping Off and Avoiding Cooling Failures

In heavy-duty diesel engines, coolant protects against freezing, overheating and corrosion inside the engine. Poor coolant maintenance can lead to water pump failures, clogged radiators and liner pitting — some of the most expensive repairs a fleet can face.

Test coolant regularly

Check coolant at every PM service:

• Freeze point — with a refractometer or test strips.
• Condition — look for oil, rust, debris or a change in color.
• Additive level — conventional heavy-duty coolants need supplemental coolant additives (SCAs) or extenders on a schedule. Test strips show when more is needed.

Top off with the right product

Use the same type of coolant that is already in the system, or a product approved to mix with it. Use premixed 50/50 or mix concentrate with distilled water. Adding plain water dilutes freeze protection and additives.

Know your coolant type

Many newer heavy-duty engines use extended life coolant (ELC). Conventional coolants need more frequent additive service. Read more in our antifreeze and coolant types guide.

Signs of cooling trouble

• Coolant level dropping between services
• White smoke or a sweet smell from the exhaust
• Overheating under load
• Oil in the coolant or coolant in the oil

Save with bulk coolant

Fleets and shops that service many vehicles save by buying coolant in drums or totes and dispensing from the shop.

Frequently asked questions

How often should heavy-duty coolant be tested?
At every PM service, and any time the level drops or the engine runs hot.

Can I mix different heavy-duty coolants?
Only if the products are approved to mix. Mixing can reduce corrosion protection.

Should I top off with water in an emergency?
Only in an emergency. Restore the correct mix as soon as possible, because water lowers freeze protection.

Coolant we carry

Shop ShellZone Green Antifreeze Concentrate 55 Gallon Drum or browse the full Antifreeze & Coolants collection for Peak, Pride, All Season and OEM coolants.

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