Generac Generator Oil: Type, Capacity and Change Interval by Model
For a current Guardian or Next Generation unit, the answer is Generac's own 5W-20 full synthetic "gaseous engine oil" — part A0001412874 per quart — API SJ, SL or better, no additives. New units ship with 5W-30 conventional for the 25-hour break-in (20 hours on the 7.5 kW PowerPact); Generac's break-in article names A0001412874 for that first change and every change after. Capacities with the filter: 10 kW Guardian 1.1 qt; 14/18 kW 2.2 qt; 20–26 kW 1.9 qt; Next Generation 10 kW 1.4 qt, 14/18 kW 2.5 qt, 22–28 kW 2.2 qt; PowerPact 1.2 qt. Interval after break-in: every 2 years or 200 hours (Schedule A), dropping to every 100 hours when it runs below 40 °F or continuously above 85 °F. Older units have different viscosity charts — they're below, by generation.
What oil Generac specifies
Generac's oil FAQ is short and unusually direct. New home standby units ship with 5W-30 conventional oil for the break-in period. After break-in, Generac recommends its "proprietary synthetic 5W-20 Gaseous Engine Oil (GEO)" for ongoing use. The reasoning it gives: conventional oil "is more apt to pick up deposits and form sludge," while synthetic "contains additives intended to help keep engines cleaner" and offers "increased engine protection and performance at low and high temperatures." Mixing conventional and synthetic is not recommended but acceptable in an emergency — if you do, "perform a full oil change as soon as possible."
The current 10–26 kW owner's manual adds the standard that any substitute has to meet: "All Generac oil kits meet minimum American Petroleum Institute (API) Service Class SJ, SL, or better," and "do not use special additives." "Gaseous engine oil" means what it says — a formulation Generac specifies for its natural-gas and propane engines.
The one case where Generac tells you to use something else: a unit that hasn't reached 25 hours after a full year. Its break-in article gives two options — run the unit under load in MANUAL to reach 25 hours, or change the oil to "5W-30 conventional oil (not synthetic)" as a temporary measure until the break-in hours are reached. That is the only official endorsement of conventional 5W-30 outside the factory fill.
Oil capacity by model
Generac's oil-capacity article and the owner's manuals give these, all including the filter. Fill to the FULL mark on the dipstick, not to the number — the article warns that "overfilling can lead to increased pressure within the engine, which can cause leaks and damage."
| Line | Model | Capacity with filter | Oil (after break-in) | Source |
|---|---|---|---|---|
| Next Generation (2025+) | 10 kW | approx. 1.4 qt (1.3 L) | 5W-20 full synthetic GEO | Oil-capacity article |
| Next Generation | 14 / 18 kW | approx. 2.5 qt (2.4 L) | 5W-20 full synthetic GEO | Oil-capacity article |
| Next Generation | 22–28 kW | approx. 2.2 qt (2.1 L) | 5W-20 full synthetic GEO | Oil-capacity article |
| Guardian (2017+, Evolution 2.0) | 10 kW | approx. 1.1 qt (1.03 L) | 5W-20 full synthetic GEO | Manual A0001846499 |
| Guardian | 14 / 18 kW | approx. 2.2 qt (2.1 L) | 5W-20 full synthetic GEO | Manual A0001846499 |
| Guardian | 20 / 22 / 24 / 26 kW | approx. 1.9 qt (1.8 L) | 5W-20 full synthetic GEO | Manual A0001846499 |
| Guardian (2020 manual revision) | 10–24 kW | as the Guardian rows above | "Synthetic SAE 5W-30 for all temperature ranges" | Manual A0000973303 Rev. A (2020) |
| PowerPact | 7.5 kW | approx. 1.2 qt (1.1 L) | SAE 30 above 32 °F; 10W-30 to −10 °F; synthetic 5W-30 all temperatures | Manual 10000021790 |
| Evolution 1.0 era (2013–2016) | 9 kW | approx. 1.1 qt (1.03 L) | Synthetic SAE 5W-30, all temperatures | Manual 0L6629 |
| Evolution 1.0 era | 11 kW | approx. 1.7 qt (1.6 L) | Synthetic SAE 5W-30 | Manual 0L6629 |
| Evolution 1.0 era | 16 / 20 / 22 kW | approx. 1.9 qt (1.8 L) | Synthetic SAE 5W-30 | Manual 0L6629 |
| 2017 20 kW 3-phase | 20 kW | approx. 1.9 qt | Synthetic SAE 5W-30 | Manual 10000003882 |
| Nexus era (pre-2013) | 8 kW | approx. 1.5 qt | SAE 30 above 32 °F; 10W-30 from 40 °F to −10 °F; synthetic 5W-30 at 10 °F and below | Nexus-era manual |
| Nexus era | 10 kW | approx. 1.7 qt | as above | Nexus-era manual |
| Nexus era | 14 / 17 / 20 kW | approx. 1.9 qt | as above | Nexus-era manual |
Two things to notice. First, capacity does not scale with kilowatts — the 14/18 kW twins take more oil than the 20–26 kW engines. Buying "two quarts for a 22 kW" leaves you with a spare; buying two for a 14 kW leaves you short by a splash. Second, the viscosity spec changed twice: Nexus-era manuals give a temperature chart with SAE 30 as the warm-weather default, Evolution-era manuals (through the 2020 revision of the 10–24 kW manual) specify synthetic 5W-30 for all temperatures, and the 2023 revision moved to 5W-20 GEO. Generac's own pages date the Nexus-to-Evolution transition variously; the manual that shipped with your unit is the one that applies. Use the chart for your unit's generation — the newer oil is not wrong in an older engine, but the manual for your serial number is the document a warranty claim is judged against.
Change intervals
- Break-in: 25 hours (20 hours on the PowerPact 7.5 kW), oil and filter — Generac's article says "no earlier, no later." Metal particles in that first drain are normal. Valve clearance is inspected at the same service, except on 14 and 18 kW Guardians and Next Generation units with hydraulic lifters.
- Schedule A: every 2 years or 200 hours, whichever comes first — oil and filter, plus a battery inspection. The controller lights the yellow LED and shows SERVICE A when it's due.
- Extreme temperatures: every 100 hours. Generac's Schedule A article and the owner's manual agree: units operating below 40 °F or continuously above 85 °F need oil and filter every 100 hours (the manual says "every year or 100 hours"). A unit that ran through a week-long winter outage has likely used most of that.
- Schedule B: every 4 years or 400 hours — oil and filter again, plus air filter, spark plugs and valve clearance. That's what the maintenance kit is for.
- Older generations had shorter intervals. The 2016 manual (0L6629): Schedule A annually or 200 hours, Schedule B every 2 years or 400 hours. The 2017 20 kW manual: oil yearly or every 2 years/200 hours depending on climate. Nexus-era: oil, filter, air cleaner and plugs every 200 hours or 2 years. Read your own manual's table.
- During a long outage: check daily. Generac's oil-level article says to check the level every day while the unit is running an extended outage. A 1300 Low Oil Pressure shutdown in the middle of a storm is the alternative.
How to check and change the oil
Checking, per Generac's article: set both the utility main and the generator's MLCB to OFF; if the unit was running, let it run five minutes with no load, then cool five to ten minutes; pull the dipstick, wipe, reinsert fully, read; add to FULL, never above. Clear the yellow maintenance reminder afterwards if one was showing — on Evolution units, press ENTER when the reminder is displayed, arrow to YES, ENTER; the maintenance timer resets itself.
Changing it is inside most owners' reach, and Generac sells the kits on that assumption. The sequence that Generac's post-maintenance article expects you to finish with: reminder cleared, panels reinstalled, the 7.5 A fuse back in, Install Wizard completed if the controller asks, AUTO pressed (green light), MLCB ON, lid closed. If you're doing it during an outage, run one minute with the MLCB OFF before switching it ON.
Generac's oil-filter article identifies the filter for your serial number (070185ES in the current 10–26 kW manual). The parts table below has the oil; the filter and everything else are on the maintenance-kit page.
Parts and consumables
| Part | Part number | Fits | Where verified |
|---|---|---|---|
| 5W-20 full synthetic GEO, 1 qt | A0001412874 | All current air-cooled home standby | Generac break-in maintenance article |
| 5W-20 full synthetic GEO, case of 12 qt | A0001412864 | Same | Dealer listing (Gensys Parts) |
| 5W-20 full synthetic GEO, case of 12 qt (alternate listing) | A0001412868 | Same | Dealer listing (The Modern Shop) |
You may see "0J5993" quoted online as a Generac oil part number. No Generac or dealer listing under that number could be found; the quart is A0001412874. Oil filter numbers vary by engine and are listed with the kits on the maintenance kit page.
Repair or replace?
Not a question here — oil is the cheapest thing you will ever put in this machine, and the low-oil-pressure shutdown on every air-cooled model exists because running it dry is the most expensive. The relevant version of the question: a unit that has gone several years past Schedule A and now knocks or smokes has earned an inspection before the next outage, not just an oil change.
When to call a dealer
- You're not sure which generation your unit is — the serial-number lookup on Generac's site or a dealer settles the viscosity question.
- Oil level rises between checks, or the oil smells of fuel — a fuel-system fault, not an oil question.
- The unit has crossed 400 hours without a valve-clearance service and you don't own a feeler gauge.
- Milky oil — water intrusion; the manual's yearly inspection exists for this.
- Generac support: 1-888-436-3722.
Parts and supplies mentioned on this page
Keep two quarts of A0001412874 on the shelf — enough for one change on any Guardian, with a top-up left for a long outage.
- Generac 5W-20 full synthetic GEO, 1 quart (A0001412874)Check price on Amazon
- Generac 5W-20 full synthetic GEO, case of 12 (A0001412864)Check price on Amazon
Related pages
Everything else in a Schedule B service — filter, plugs, air filter, kit numbers by model: Generac maintenance kit. The other wear item: battery replacement. The shutdown that low oil causes: code 1300.
Not sure the generator can carry the load?Generator Wattage Calculator Running watts, the largest starting surge, and a generator class from manufacturer charts.Frequently asked questions
What kind of oil does a Generac generator take?
Current Guardian and Next Generation units: Generac 5W-20 full synthetic gaseous engine oil (A0001412874), API SJ/SL or better, no additives. Evolution-era units (2013–2016) specified synthetic 5W-30; Nexus-era units used a temperature chart with SAE 30, 10W-30 and synthetic 5W-30.
Can I use regular 5W-30 in my Generac?
Generac ships new units with 5W-30 conventional for break-in and, in its break-in article, allows 5W-30 conventional temporarily on a unit that hasn't reached 25 hours in a year. For ongoing use it recommends its 5W-20 synthetic GEO; mixing is acceptable only in an emergency, followed by a full change.
How many quarts of oil does a Generac 22 kW take?
Approximately 1.9 quarts (1.8 L) including the filter, per the owner's manual for 20–26 kW Guardians. Fill to the dipstick's FULL mark rather than to the number.
How often should I change the oil in a Generac standby generator?
First at 25 hours (break-in), then every 2 years or 200 hours (Schedule A). Below 40 °F or in continuous heat above 85 °F, every 100 hours. Check the level daily during an extended outage.
Is synthetic oil required in a Generac?
Generac recommends it and its kits contain it. The manuals' hard requirement is API SJ, SL or better with no additives; the synthetic recommendation is about deposits and temperature range.