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Generac 10W30 Engine Oil (1 Quart)

Generac Electric Generators and Accessories
Model: 0J5139
(Based on expert analysis, manufacturer ratings and customer reviews)
5.0 out of 55.0 out of 55.0 out of 55.0 out of 55.0 out of 5
2 Reviews
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Generac 4-Cycle Engine Oil - 10W30
Formulated with an advanced additive technology

Low Friction Formula
Helps improve generator performance

Longer Engine Life
Protects against the formation of sludge & varnish deposits

Recommended for Use In All Gasoline Engines
Exceeds API SN service classification requirement

*Note Always Follow Recommended Oil Weight In Your Owner's Manual
Product Specs
60 Hertz
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  2 Questions
Q: I purchased a Generac generator from you a few months ago. The directions say that below 40 degrees, 10W-30 oil should be used. I presently have 30 weight oil in the generator. With the weather below 40 degrees, can I still leave the 30 weight in or is it best to actually drain it and replace it with 10W-30?

by Howard Tolk from Connecticut on February 04, 2014

A: Thanks for your inquiry.

All oil should meet minimum American Petroleum Institute (API) Service Class SJ, SL or better. Use no special additives. Select the oil's viscosity grade according to the expected operating temperature.

Above 40 F, use SAE 30
Below 40 F and down to 10 F, use 10W-30
Below 10 F, use synthetic 5W-30

Multi-viscosity oils are those denoted by two numbers with a 'W-' in between (for example, 10W-30 or 20W-50). The 'W' originally stood for winter, as oils were developed to compensate for the wear due to the vast temperature ranges then. They're almost exclusively used today rather than straight-weight (monograde) oils. Multi-viscosity oils use polymer additives to change the natural consistency of oil as its heated, preventing it from thinning out as much as it otherwise would.

The only downside to this is that some of the additives used to improve viscosity at high temperatures can also leave sticky deposits. Oil companies have mostly eliminated such problems by adding detergents to oil, along with rust inhibitors and antioxidants. Some precise performance engines will still require straight-weight oil, but all newer vehicles are designed for multi-viscosity oil and require it, else your warranty will probably be void.

What the numbers mean.

The numbers in motor-oil nomenclature refer to the viscosity (thickness) of the oil. A higher number corresponds to thicker oil, while a lower number refers to thinner oil. The numbers themselves are supposed to correspond to a set of real, measurable qualities in the oil, one of which is the viscosity index. In multi-viscosity oils, the left number refers to cold behavior of the particular oil, while the right number refers to its hot (100 degrees Celsius) behavior. So, for instance, 5W-30 oil would flow well when cold like 5-weight oil, but protect at high temperatures like 30-weight oil.

Do oils vary much by brand? Yes. The 5W-30 oil from one company might equal 10W-40 oil from another company in viscosity, because there might be a difference in some of the other properties of the oil, like its flash point (at what temperature it ignites). The numbers in multi-viscosity oil also don't tell anything about how viscous the oil is at normal engine operating temperatures, as opposed to extremes. The best advice here is to choose a familiar brand, and experiment with other major brands if you think it's too thin or too thick. Never mix brands or different weights. Wait until an oil change.

What about synthetics?

Synthetics are better in every way, but they are much more expensive. They offer better high-temperature resistance and better low-temperature flow, and they leave nearly no deposits. Prices for synthetics are coming down, though, and there are also blends that combine synthetics with traditional mineral oils. Because synthetics flow and penetrate much better than regular oils, a change to synthetic oil will sometimes reveal leaks you didn't know existed.


The American Petroleum Institute (API) assigns letter ratings to motor oil. The category ratings correspond to industry standards for various qualities like viscosity, thermal protection, and preventing deposits and sludge. Every few years, the currently awarded rating is changed. Currently, SL (Spark ignition, Category L) is the top rating. SJ was introduced in 2001 and SH in 1996.

As your car ages and becomes a high-mileage vehicle, many experts recommend that you change to thicker oil than is normally used. Over time, gaps between parts in the engine become larger, enabling less oil to reach critical parts. Ask a mechanic familiar with your model vehicle or ask the dealership if you should change the type of oil for your vehicle beyond 100,000 miles.

The underlying message is that all oil is not the same. Making sure you use the correct viscosity rating is just the start. The quality and characteristics of oils can vary greatly by brand, too.

by Mike, Product Expert
Q: I own a generac 7500watts I have not used it . I would like to know how much oil to put in the crank case? The stick reads half now. Do I fill it up?
by Harvey Denis from New York on December 21, 2013

A: The oil level should be at the full mark on the oil stick. If you currently show half full you will need to top it off.

Generac does not provide an exact amount of oil on their portable units. So, you will need to fill a little and check the level and repeat as necessary until the level is at the full mark on the oil stick.

by Mike, Product Expert
Generac 0J5139 Reviews & Ratings
Overall Rating
5.0 out of 55.0 out of 55.0 out of 55.0 out of 55.0 out of 5
I'd Buy It Again (1)
Reliable (1)
Exceeded Expectations (1)
Quiet (1)
Expensive (1)
100% of respondents would recommend this product to a friend
2 Reviews  Sort by 
Richard C.
Cheboygan, MI
Purchased from Electric Generators Direct
Purchased 7/5/17
Most Helpful Positive Review
5 out of 55 out of 55 out of 55 out of 55 out of 5
General Oil
So far so good.
Pros: Quiet, Exceeded Expectations, Reliable, I'd Buy It Again
Cons: Expensive
Richard Recommends This Generac Product
Richard's Experience With Electric Generators Direct
Web Site


"Just changed the oil in my General generator, and it operates good so far."
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Bobby M.
Shelbyville, KY
Purchased from Electric Generators Direct
Purchased 11/6/14
5 out of 55 out of 55 out of 55 out of 55 out of 5
I was very surprised about the fast delivery. The order was correct. I would recommend Generators Direct. I will be ordering again. Thank you.
Bobby Recommends This Generac Product
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