Disclosure: This post contains affiliate links and I will be compensated if you make a purchase after clicking through my links. Learn More

Picking the right oil for your Generac generator directly affects how well it runs and how long it lasts. Many generator owners don’t know which oil to use or how much their model needs. This guide covers everything about Generac generator oil – from types and amounts to change schedules and best practices. Whether you own a small portable unit or a large standby generator, using the right oil will keep your power source running smoothly when you need it most.

Table of Contents

Understanding Generac Generator Oil Requirements

Official Oil Recommendations

Generac clearly states what oil types work best in their generators. Most Generac models run best with 5W-30 synthetic oil. This oil flows well in cold weather but still protects parts when the engine gets hot.

Our recommendation is to always check your owner’s manual first. While 5W-30 works for most models, some larger units might need something different.

The main goal of engine oil is to create a protective film between moving metal parts. This reduces friction, wear, and heat buildup. Oil also helps clean the engine, prevent rust, and seal the space between piston rings and cylinder walls.

Synthetic vs. Conventional Oil

Synthetic oil costs more than conventional oil but offers better protection:

It flows better in cold temperatures
It resists breakdown at high temperatures
It protects engine parts better
It often lasts longer between changes
It has fewer impurities that can cause deposits
It maintains viscosity better over time
It resists oxidation and sludge formation

Conventional oil works fine in most weather conditions but may need more frequent changes. For best results in extreme temperatures, synthetic oil is the clear winner.

Our recommendation is to use synthetic oil in your Generac generator. We’ve opened up generators after years of use with synthetic oil and found the inside parts looking almost new. This isn’t always true for generators running on regular oil.

Oil Viscosity Explained

Oil viscosity tells you how thick or thin the oil is. You’ll see numbers like 5W-30 or 10W-30 on oil bottles.

The first number (with W for Winter) shows how the oil flows in cold weather. Lower numbers mean better cold starts.

The second number shows how well the oil protects when hot. Higher numbers mean better protection at high temperatures.

For Generac generators, 5W-30 works well in most places. In very cold areas, try 0W-30. In very hot areas, 10W-30 might work better.

Our recommendation is to think of oil viscosity like this: When you start your generator in winter, you want oil that’s thin like water to flow quickly. But once the engine gets hot, you want it to thicken up to protect the parts better. Multi-viscosity oils like 5W-30 do both jobs.

Understanding API Ratings

Another important factor is the API (American Petroleum Institute) service rating. For most Generac generators, look for oils that meet:

SJ, SL, SM, SN, or SP for gasoline engines
CF, CG-4, CH-4, CI-4, or CJ-4 for diesel engines

Higher letters in the sequence represent newer, more advanced formulations. Using oil with at least the minimum rating helps ensure your generator gets the protection it needs.

Generac Generator Oil Capacity Chart

Knowing how much oil your Generac generator needs saves time and money. Here’s a simple chart for common Generac models:

Generator Model	Oil Capacity	Filter Change Add
8kW – 11kW	1.6 quarts	+0.2 quarts
12kW – 16kW	1.7 quarts	+0.2 quarts
17kW – 20kW	1.7 quarts	+0.2 quarts
22kW	1.9 quarts	+0.3 quarts
24kW	1.9 quarts	+0.3 quarts
25kW – 30kW	2.2 quarts	+0.3 quarts
32kW – 38kW	2.3 quarts	+0.4 quarts
45kW – 60kW	5.1 quarts	+0.5 quarts
70kW – 150kW	8.5 quarts	+1.0 quarts

Our recommendation is to always check your specific model in the manual. These numbers are general. Your model might be a little different.

Specific Model Capacities

11kW Generator Oil Capacity

The 11kW Generac generator typically needs 1.6 quarts of oil for a standard oil change. If you’re also replacing the oil filter, add another 0.2 quarts to account for the oil that will fill the new filter.

16kW Oil Capacity

For the popular 16kW models, you’ll need about 1.7 quarts of oil. These models use slightly more oil than the smaller units but still have similar engine designs.

20kW Oil Capacity

The 20kW standby generators also take approximately 1.7 quarts of oil. Despite the higher power output compared to the 16kW units, they often use the same engine block design.

22kW Generator Oil Capacity

Moving up to the 22kW models, the oil capacity increases to 1.9 quarts. These larger engines need a bit more oil to properly lubricate all components.

24kW Generator Oil Capacity

Like the 22kW models, the 24kW generators also require 1.9 quarts of oil. Both these sizes use similar engines with the same oil requirements.

“One mistake I often see is people not accounting for the extra oil needed when changing the filter,” our expert points out. “Always have a little extra oil on hand when doing a complete oil and filter change.”

Best Oil Options for Generac Generators

Top Oil Choices for Most Generac Generators

Generac Full Synthetic Engine Oil – Made for Generac engines, this oil meets all their specs. It works well in all weather conditions.
Mobil 1 5W-30 Full Synthetic – This high-quality oil protects well against wear and heat. It’s easy to find at most auto parts stores.
Shell Rotella T6 5W-30 Synthetic – This oil stands up well to heat and works great in heavy-duty uses.
Valvoline SynPower 5W-30 – A good mid-priced option that offers solid protection.
Castrol EDGE 5W-30 – Known for strong protection against deposits and engine wear.
Pennzoil Platinum 5W-30 – Made from natural gas rather than crude oil, it offers excellent cleanliness.
Amsoil Signature Series 5W-30 – A premium option with extended drain intervals and excellent high-temperature protection.
Royal Purple 5W-30 – Contains special additives that help clean and protect engine parts.

We’ve used most major brands of oil in generators over the years. While all quality oils work, we’ve seen the best results with full synthetic oils specifically made for small engines. They handle the heat cycles of generators better.

Specific Recommendations by Generator Size

For 22kW Generators

The 22kW models do best with full synthetic 5W-30 oil. These units run hot under heavy loads, so the synthetic oil helps protect the engine better. The larger engine in the 22kW models works hard when powering multiple appliances.

For 24kW Generators

Like the 22kW models, the 24kW generators need full synthetic 5W-30 oil. With their larger engines, good oil quality becomes even more important. These generators often power larger homes or small businesses.

Our recommendation is to use the best oil possible for 22kW and 24kW models. They cost a lot of money, and the price difference between cheap oil and good oil is tiny compared to the cost of engine repairs.

For 11kW Generators

The smaller 11kW models can use either synthetic or regular 5W-30, but synthetic offers better protection for these units that often sit unused for weeks. These generators typically power fewer circuits and may run less often.

For 16kW and 20kW Generators

These mid-sized units benefit from synthetic 5W-30 oil, especially in areas with big weather changes. These popular models for average homes need to start reliably in all weather.

Oil for Portable Generac Generators

Portable generators have different needs than standby models:

They often experience more temperature variations
They get moved around, sometimes over rough terrain
They may sit unused for longer periods
They often run for shorter durations but more frequently

For these units, a good synthetic 5W-30 oil works best. Some smaller portable models might specify 10W-30 in their manual, so always check your specific model’s requirements.

Our recommendation is to take special care with portable generators. They sit in garages for months, then get used hard during emergencies. Good oil is their best defense against this harsh usage pattern.

Generac Oil Change Guide

When to Change the Oil

For standby generators:

Change oil after the first 25 hours of use (break-in period)
After that, change it every 50 hours of use or once per year, whichever comes first
If you use the generator very little, still change the oil yearly
After running continuously for more than 24 hours, change the oil

For portable generators:

Change oil after the first 5-8 hours of use (break-in period)
Then every 50-100 hours or each season of use
At minimum, change yearly even if usage hours are low

Many homeowners forget their standby generator needs yearly oil changes even if it rarely runs. Old oil can damage your generator even when it’s not running.

The Importance of the Break-in Period

The break-in period for a new generator is crucial. During the first few hours of operation, metal parts seat against each other and small metal particles can enter the oil. Changing the oil after this initial period removes these particles before they can cause damage.

“Think of the break-in oil change as removing the ‘manufacturing dust’ from your engine,” our expert explains. “Skip this, and those particles will circulate through your engine for years.”

Oil Change Steps

Warm up the generator for 5-10 minutes to help the oil flow better
Turn it off and disconnect the spark plug wire to prevent accidental starting
Find the oil drain plug (usually near the bottom of the engine)
Place an oil catch pan under the drain plug
Remove the plug and let all the oil drain out (this may take 5-10 minutes)
While the oil drains, remove and replace the oil filter if your model has one
Apply a thin film of fresh oil to the gasket of the new filter
Install the new filter, tightening by hand plus a quarter turn (don’t overtighten)
Replace the drain plug
Remove the oil fill cap/dipstick
Add new oil slowly until it reaches the “Full” mark on the dipstick
Replace the oil fill cap/dipstick
Reconnect the spark plug wire
Run the generator for 1-2 minutes
Turn it off and check for leaks
Check the oil level again and top off if needed

The biggest mistake people make is rushing through an oil change. Let all the old oil drain completely. This might take 10 minutes, but it’s worth the wait.

What You’ll Need

The right amount and type of oil for your model
Oil catch pan (at least 2-quart capacity)
Funnel with a narrow spout
Rags or paper towels
Wrench for the drain plug
New oil filter (if your model has one)
Filter wrench (if needed)
Disposable gloves
Container for old oil
Torque wrench (optional but helpful)

Safety First

Let the generator cool a bit before changing oil – warm oil flows better but hot oil can burn you
Wear gloves to protect your hands
Clean up any spills right away – oil is slippery
Make sure the generator can’t start during service
Work in a well-ventilated area
Take used oil to a recycling center – never pour it down drains or on the ground
Wash hands thoroughly after handling oil

Special Tips for First-Time Oil Changes

If you’ve never changed oil before:

Take photos of your generator before starting to help remember where everything goes
Consider having someone experienced help you the first time
Keep your owner’s manual open to the oil change section
Move slowly and methodically
Double-check the oil level after adding new oil

Your first oil change might take 30 minutes. By your third one, you’ll have it down to 15 minutes or less.

Troubleshooting Oil-Related Issues

Common Oil Problems

Low Oil Pressure Warning Light

Possible causes:

Not enough oil
Oil sensor problem
Oil too thin for conditions
Oil pump issues
Clogged oil filter
Internal engine damage

Fix: Check oil level first. If full, have a technician check the oil pressure and sensors.

Oil Leaks

Look for:

Loose drain plug
Worn gaskets
Cracked oil pan
Loose filter
Damaged oil lines
Worn valve cover gaskets
Oil seals failing

Fix: Tighten loose parts. Replace worn gaskets or seals.

With oil leaks, clean the area thoroughly first. Then run the generator for a few minutes and look for fresh oil. This helps pinpoint exactly where the leak is coming from.

Smoky Exhaust

Blue/gray smoke often means oil is burning in the combustion chamber.

Possible causes:

Too much oil
Worn piston rings
Valve guide problems
Oil getting past the air filter
PCV valve issues

Fix: Check oil level first. If correct, you may need a professional repair.

Excessive Oil Consumption

If your generator uses more oil than normal:

Check for visible leaks
Look for blue smoke when running
Inspect air filter for oil
Consider whether the generator is being run at extreme angles
Check for overfilling

Some oil consumption is normal, especially in older units. But if you’re adding more than a quart between changes, something’s wrong.

Oil Color and Condition Issues

Healthy oil should be amber to light brown. Watch for:

Milky appearance (possible water contamination)
Very dark or black oil (excessive heat or overdue for change)
Metal particles (potential internal damage)
Foamy oil (possible air in the oil system)

The oil tells a story about your engine’s health. we can often diagnose problems just by looking at and feeling the oil during a change.

Seasonal Maintenance Considerations

Winter Care

In cold climates:

Use 5W-30 or even 0W-30 synthetic oil
Change oil before winter starts
Run the generator monthly to circulate oil
Consider a cold weather kit for very cold regions
Keep the battery charged, as cold reduces battery performance
Make sure the block heater works if your model has one

We’ve seen many generator failures during winter storms because people didn’t prepare their units for cold weather. Fresh oil before winter is cheap insurance.

Cold temperatures make oil thicker and harder to pump. This causes more wear during startup. Synthetic oils maintain better flow properties at low temperatures, making them ideal for winter use.

Summer Heat Tips

In hot climates:

Make sure cooling systems work well
Check oil levels more often (heat can cause faster oil use)
Consider 10W-30 if temperatures stay very hot
Keep the generator clean, as dirt acts as insulation and traps heat
Ensure proper airflow around the unit
Check that cooling fins aren’t blocked by debris

Heat is the enemy of engines and oil. In very hot areas, We sometimes recommend more frequent oil changes, especially if the generator runs for extended periods.”

Storage Tips

If storing your portable generator:

Change the oil before long storage
Run the engine for a few minutes to coat parts with fresh oil
Store in a dry place
Consider fogging the engine with storage oil
Add fuel stabilizer to the gas tank
Disconnect the battery or use a battery maintainer
Cover the unit to keep dust out

The worst thing for generators is sitting unused with old oil. The acids in used oil continue to attack metal surfaces even when the engine isn’t running.

Oil Change After Heavy Use

After running your generator for extended periods, such as during a multi-day power outage:

Change the oil even if you haven’t reached the normal change interval
Inspect the air filter
Check and clean cooling fins
Listen for any unusual noises
Check for leaks that might have developed

Long run times are hard on generators. They’re designed for intermittent use, not constant running. Fresh oil helps recovery from these stressful periods.

Oil Filters and Their Importance

Many Generac generators have oil filters that should be changed with each oil change. These filters remove:

Dirt particles
Metal fragments
Carbon and sludge
Other contaminants

Using a quality filter is just as important as using quality oil. Look for:

Correct size and thread pattern
Good quality filter media
Strong case that won’t collapse
Durable gasket

“Never reuse an oil filter,” warns our expert. “The few dollars saved isn’t worth the potential damage to your generator.”

Some smaller Generac models don’t have replaceable oil filters. For these, more frequent oil changes become even more important since there’s no filter to trap contaminants.

FAQs About Generac Generator Oil

Can I use car oil in my Generac generator?

Yes, you can use car oil if it meets the right specs (usually 5W-30). Generator-specific oils often have extra additives that help with the start-and-stop nature of generators. For best results, choose oil that meets API SJ or higher standards.

What happens if I use the wrong oil type?

Using the wrong oil thickness can cause poor lubrication, extra wear, hard starting, and poor performance. In the worst cases, it can damage your engine completely. Always use the oil type listed in your owner’s manual.

How often should I check my generator’s oil level?

For standby generators, check oil once a month. For portable generators, check before each use and after every 8 hours of running time. Regular checks help catch problems early before they cause damage.

Is synthetic oil worth the extra cost for generators?

Yes, synthetic oil is worth the extra cost, especially for standby generators that may sit unused for long periods. It resists breakdown during storage and protects better during sudden power demands. The price difference is small compared to the benefits.

Can I mix synthetic and conventional oils?

Yes, you can mix them safely if they’re the same thickness (like 5W-30). But you’ll lose some of the benefits of using full synthetic oil. If possible, stick with one type for the best performance and protection.

Do I need to use Generac brand oil in my generator?

No, you don’t need Generac brand oil. Any oil that meets the specs in your manual will work fine. Generac oil is good quality, but other brands meeting the same specs work just as well at similar or lower prices.

Why does my generator use oil so quickly?

Some oil use is normal, especially in new units during break-in or in older units with wear. If use seems excessive, check for leaks, blue smoke from the exhaust, or possible engine problems that may need professional repair.

How do I dispose of used generator oil?

Most auto parts stores accept used oil for recycling at no charge. Never pour it down drains, on the ground, or in trash. Store used oil in a sealed container until you can take it to a recycling point.

Can I use high-mileage oil in my generator?

Yes, high-mileage oils can help older generators. These oils often contain seal conditioners and additives that help aging engines. If your generator is more than 5 years old, consider high-mileage formulas for better protection.

What if I accidentally overfill the oil?

Drain the excess oil right away. Overfilling can force oil past seals into places it shouldn’t go, like the combustion chamber or air intake. This can cause smoke, fouled spark plugs, and poor running.

Should I warm up my generator before changing oil?

Yes, run it for 5-10 minutes to warm the oil so it drains more completely. Don’t let it get too hot, as hot oil can cause burns. Warm oil flows better and carries more contaminants out with it during draining.

My oil looks clean after a year. Do I still need to change it?

Yes, change it even if it looks clean. Oil breaks down chemically over time even when it looks fine. The additives get used up and acids form that can damage engine parts. Always follow the time-based change intervals.

Final Words

The right oil keeps your Generac generator running reliably for years. For most models, 5W-30 synthetic oil works best. Change it yearly or every 50-100 running hours. Always check your model’s specific needs in the owner’s manual.

Oil is the lifeblood of your generator. It reduces friction, removes heat, prevents corrosion, and helps seal the combustion chamber. Investing in quality oil and regular changes is the most cost-effective maintenance you can perform.

With proper oil care, your generator will be ready when you need it most – during power outages and emergencies. Regular oil changes are the single most important maintenance task for your generator.

In our many years working with generators, We’ve seen units last twice as long as expected with proper oil maintenance. And We’ve seen units fail early when oil was neglected. The choice is yours, but the smart money is on taking care of your oil.