Why generators show "low oil pressure": 58 documented causes and brand-specific fixes, compiled across 23 manufacturers.
Oil viscosity too light or oil is diluted
3 brands- Bgm/Nhm: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
- Cummins/Onan: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.; 1. Drain oil and refill with correct viscosity oil. 2. Add oil as required. 3. Replace oil pressure switch (see Engine Block Assembly section). 4. Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section.).
- Marquis: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
Low oil level
3 brands- Bgm/Nhm: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
- Cummins/Onan: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.; 1. Drain oil and refill with correct viscosity oil. 2. Add oil as required. 3. Replace oil pressure switch (see Engine Block Assembly section). 4. Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section.).
- Marquis: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
Low oil pressure switch defective
3 brands- Bgm/Nhm: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
- Cummins/Onan: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.; 1. Drain oil and refill with correct viscosity oil. 2. Add oil as required. 3. Replace oil pressure switch (see Engine Block Assembly section). 4. Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section.).
- Marquis: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
Faulty oil pump
3 brands- Bgm/Nhm: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
- Cummins/Onan: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
- Marquis: 1. Check and adjust oil viscosity. 2. Refill oil to proper level. 3. Replace low oil pressure switch if defective. 4. Check and replace faulty oil pump.
Shutdown Low oil level Oil leaking from engine Oil pressure sender
2 brands- Generac: Verify oil level on dipstick. Add oil, if needed. Visually inspect the engine for leaks. Restart unit and verify loss of pressure. Shut down immediately if pressure does not reach 5 psi (34 kPa) within five seconds. Refer to OEM engine operator’s manual to identify corrective action.
- Marathon: Verify oil level on dipstick. Add oil, if needed. Visually inspect the engine for leaks. Restart unit and verify loss of pressure. Shut down immediately if pressure does not reach 5 psi (34 kPa) within five seconds. Refer to OEM engine operator’s manual to identify corrective action.
Oil too light. Oil badly diluted. Oil too low. Oil relief valve not seating. Badly worn bearings. Sludge on oil screen. Badly worn oil pump. Defective oil pressure gauge.
2 brands- Cummins/Onan: Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean, or replace, Replace. Remove and clean. Replace. Replace.; Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean, or replace. Replace. Remove and clean. Replace. Replace.
- D.W.Onan: Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean, or replace, Replace. Remove and clean. Replace. Replace.
Oil too light. OH badly diluted. Oil teo low. ODl reef valve aot seating. Badly worn bearings. Sludge on oil screen. Badly worn oi} pump. Defective oi] pressure gauge.
2 brands- Cummins/Onan: Drain, refill with proper oil. Drain, reGill with proper oil. Add oil. Remove and clean, or re- eplace. Replace. Remove and clean. Replace. Replace.
- Prestolite: Drain, refill with proper oil. Drain, reGill with proper oil. Add oil. Remove and clean, or re- eplace. Replace. Remove and clean. Replace. Replace.
Oil too light. Oil badly diluted. Oil too low. Oil relief valve not seating. Badly worn bearings. Sludge on oil screen. Badly worn oil pump.
2 brands- Garretson: Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean, or replace. Replace. Remove and clean. Replace.
- NEC: Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean, or replace. Replace. Remove and clean. Replace.
Low crankcase oil level, Clogged oil cooler or filter, Excessive oil temperature, Defective oil pump, Incorrect oil, Oil pressure regulating valve failure, Broken piston spray jet, Clogged oil pump screen or cracked pick-up tube, Excessive main or connecting rod bearing clearance
2 brands- John Deere: Fill crankcase to proper oil level., Remove and inspect oil cooler. See your John Deere engine distributor or servicing dealer., Remove and inspect oil cooler. See your John Deere engine distributor or servicing dealer., Remove and inspect oil pump. See your John Deere engine distributor or servicing dealer., Drain crankcase and refill with correct oil., Remove and inspect oil pressure regulating valve. See your John Deere engine distributor or servicing dealer., Replace piston spray jet. See your John Deere engine distributor or servicing dealer., Remove oil pan and clean screen/replace pick-up tube., Determine bearing clearance. See your John Deere engine distributor or servicing dealer.
- Katolight: Fill crankcase to proper oil level., Remove and inspect oil cooler. See your John Deere engine distributor or servicing dealer., Remove and inspect oil cooler. See your John Deere engine distributor or servicing dealer., Remove and inspect oil pump. See your John Deere engine distributor or servicing dealer., Drain crankcase and refill with correct oil., Remove and inspect oil pressure regulating valve. See your John Deere engine distributor or servicing dealer., Replace piston spray jet. See your John Deere engine distributor or servicing dealer., Remove oil pan and clean screen/replace pick-up tube., Determine bearing clearance. See your John Deere engine distributor or servicing dealer.
Operating oil pressure drop below approximately 10 psi
1 brand- Generac: None provided in text
Low oil level Improper type of oil Partially plugged oil filter
1 brand- Northern Lights: Fill crankcase to proper level. Drain and fill crankcase with correct oil. Replace filter.
Low coolant level, Defective thermostat, Temperature gauge not working properly
1 brand- Northern Lights: Fill crankcase to proper level, Fill tank or radiator to proper level, Check thermostats, Check water temperature with thermometer and replace gauge if necessary
Low Oil Level, Improper type of oil, Partially plugged oil filter
1 brand- Northern Lights: Fill crankcase to proper level, Drain and fill crankcase with correct oil, Replace filter
Low oil level, Improper type of oil, Partially plugged oil filter
1 brand- Northern Lights: Fill crankcase to proper level, Drain and fill crankcase with correct oil, Replace filter
Improper grade of oil or engine running hot
1 brand- Headquarters, Departments Of The Army, Air Force And Headquarters, U.S. Marine Corps: Check for improper grade of oil (refer to end item Lubrication Order). If proper grade of oil, check for engine running hot. Refer to Malfunction 7. If engine not overheating, check for defective regulating valve (inspect oil pressure regulating valve, refer to paragraph 3-17.2.). If setting is normal, check for clogged oil pump strainer (remove and clean strainer, refer to paragraph 3-21.2.). If not clogged, check for defective oil pump (remove and inspect oil pump for defective parts, refer to paragraphs 3-21.1. and 3-21.2.). If not defective, check for worn rocker arm bushings (replace rocker arm bushings, refer to paragraph 3-33.). If not worn, replace engine.