Cummins/Onan — Cooling System Test (LAT calculation)
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan DFBF, Cummins/Onan DFCB, Cummins/Onan DFCC, Cummins/Onan DFCE, Cummins/Onan HDKAL/HDKAS engine, Cummins/Onan NT855 engine, Cummins/Onan NTA855 engine
Procedure
- Complete a representative installation.
- Load the genset to rated full-load using a load bank.
- Conduct the test at ambient >= 21 C (70 F).
- Measure engine coolant outlet temperature and shielded ambient air temperature with thermocouples.
- Expel air from the coolant system before testing; add coolant as necessary.
- Run at full-load and record temperatures at 15-minute intervals until stable.
- Calculate LAT = T(max) 107C - T(test) + T(amb); goal LAT >= 40 C (104 F).
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- T(max) = 107 C (225 F); nominal engine shutdown 110 C (230 F)
Full service-parts list: Cummins/Onan DFBF →, Cummins/Onan DFCC →, Cummins/Onan DFCE →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.