g/auto • Posted by u/scan_tool_sam • 1 days ago

Detroit DD15 oil consumption — 1 quart per 1,500 miles, normal or not?

Customer came in with a 2017 Freightliner Cascadia DD15, complaining about oil consumption. Driver is adding a quart every 1,500 miles. Engine has 680,000 miles. No visible smoke, no coolant in oil, no oil in coolant.

DD15 consumption spec from Detroit is 0.1% of fuel consumption. On a long-haul truck burning 6 MPG and driving 100,000 miles/year, that works out to roughly 1 quart per 1,000-1,500 miles.

Is this truck actually consuming oil at the normal limit, or is it worth digging deeper for a cause?

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3 replies

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u/transmission_ted • 1 days ago

Also verify it's actually consumption and not a slow leak that only appears under operating temperature and pressure. Turbo oil seals on a high-mileage DD15 can weep at operating pressure and look clean when cold. A dye test rules that out.

u/wrench_monkey • 1 days ago

At 680k miles, a quart per 1,500 is pushing the acceptable limit but not dramatically. Detroit's 0.1% spec is the maximum, not the target. Before condemning the engine, do an oil analysis — Blackstone Labs is $35 and will tell you if you have combustion blowby products, coolant, or metal content that indicates where the oil is going.

u/diesel_dan • 1 days ago

Check the intake manifold and inlet charge cooler for oil. DD15s with EGR running can accumulate oil mist in the charge air system. If the charge cooler is saturated, that oil is going somewhere — sometimes out the exhaust, sometimes not. Clean the charge system and recheck consumption over 15k miles.