Detroit D40, D50, D60 Difficult Cold Start


Problem: Stiction, poor fuel quality, or glow-plug problem.

Solution: If you suspect poor fuel quality, treat with Diesel Extreme.

Solution: In winter, treat with a half-dose of Diesel Extreme and a full dose of Diesel Winter Anti-Gel.

Solution: Check the glow plugs (see below).


Poor fuel quality can make the truck hard to start in the mornings. Treating with Diesel Extreme should clear out the fuel system.

If you are still having trouble with cold starts, it’s likely the glow plugs are not operating correctly.

Look at the glow plug relay. If you listen closely to it, you will hear an audible “click” when the key is turned on.
Check all of the wiring leading to the glow plugs for breaks or cracks in the insulation. A single chaffed wire can throw out a whole system.
If the wiring looks good, measure the resistance across the glow plug to see if it within specification. An “OL” reading on your DMM means that there is no continuity in the circuit, and the glow plug is bad.
If you have any questions, feel free to contact one of our diesel experts.

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