Oil for a generator

[Jerry1]

I have a generator that is liquid cooled and basically a small 4 cylinder engine. It runs off of natural gas. I'm looking to change the oil and the recommended oil is 15W40. I'd like to switch over to a synthetic oil. Any 15W40 I find is labeled as being for a diesel engine. I know we have some people on this forum that are knowledgeable of cars/engines and I'm wondering what you would do.

1. I can just go ahead and use the 15W40 synthetic that is labeled for diesel engines.

2. I could go with a 10W40 synthetic (plenty of brands with a synthetic option in that weight).

3. I could just continue to use 15W40 conventional oil.

I've always understood that oil thickens up with temp and that the synthetic oil does this quicker/better than conventional oil. So I'm thinking 10W40 in synthetic should be no problem. However, I'm inclined to stick with the manufacturer recommendation but I'm not sure if the "diesel" designation actually means anything.

FWIW, the generator has an engine warmer so it will never be super cold even in the winter.

 

[RobbieB]

It'll work fine.

 

[Sunset]

Usually the manual says what standard the oil needs to meet to be considered the proper oil, cars have many standards..

Strangely, I have always had the opposite view of OP, I think oil thickens when cold and the lower the first number means it's thinner at a lower temp than a higher one.
So 10W40 is better in Canada than 20W40 for winter time.
A thinner oil in the cold will allow the engine to start easier.

My Toyota van uses 0W40 and that oil is thin like water, runs down the stick so fast it's hard to see the level, even without running the van.

My other understanding is the last number means the oil can handle (less breakdown) at higher temps , so in my mind, a 10W40 is better than 10W30.

 

[Koolau]

I am no expert. My understanding is that synthetic is typically used for relatively extreme engine conditions (lots of driving, heavy load, etc.) and to extend the life of the oil (easily a year or more IIRC). My question would be, why use synthetic in an application like a generator which starts (what?) once a month for 30 minutes? The fuel is natural gas (primarily methane) which is way cleaner than gasoline or diesel. IOW, most home generators would be considered light duty. Synth. oil seems like overkill unless you know something I do not. Keep in mind that synth. oil is typically more expensive as well. Just spit balling, so YMMV.

 

[njhowie]

Either conventional or synthetic 15W40 will be fine. That it is labeled for diesel makes no difference.

Before switching to the synthetic, I would drop an email to the support folks for your generator and just run it by them if they would recommend, or specifically not recommend switching to synthetic. The high likelihood is that they're going to say it really doesn't matter. However, in this day where everyone is connected and it's so easy to get information, it doesn't pay not to get input from the generator manufacturer before doing it.

 

[Jerry1]

Strangely, I have always had the opposite view of OP, I think oil thickens when cold and the lower the first number means it's thinner at a lower temp than a higher one.
So 10W40 is better in Canada than 20W40 for winter time.
A thinner oil in the cold will allow the engine to start easier.

My understanding is the same. I used poor phrasing. Oil wants to be thick in the cold. The lower the first number is, the thinner it is at startup. Then, as heat is experienced, the oil will thicken to operating thickness. It’s kind of counter intuitive.

I am no expert. My understanding is that synthetic is typically used for relatively extreme engine conditions (lots of driving, heavy load, etc.) and to extend the life of the oil (easily a year or more IIRC). My question would be, why use synthetic in an application like a generator which starts (what?) once a month for 30 minutes? The fuel is natural gas (primarily methane) which is way cleaner than gasoline or diesel. IOW, most home generators would be considered light duty. Synth. oil seems like overkill unless you know something I do not. Keep in mind that synth. oil is typically more expensive as well. Just spit balling, so YMMV.

When the generator runs, it runs at 3600 rpm. The one thing you’re not accounting for is the actual power outage. Our last power outage was for 4-5 days. That’s kinda of like getting in a car and going cross country round trip in a low gear with never stopping. That’s heavy duty.

 

[street]

You should be fine using that oil.

 

[Winemaker]

My Generac generator, natty gas powered, runs about 5 minutes every week for testing. The oil does absorb/gathers moisture and the engine doesn't run long enough to boil it out. I strongly advise going to a synthetic, as it is more slippery, and have seen the benefits of synthetic in terms of much less heat generated during operation.

 

[jazz4cash]

I agree it should be fine with the synthetic, esp with the engine warmer. The oil spec should be defined by the engine mfr, not the generator mfr (although they could be the same, it’s not likely). Engine mfrs may be reluctant to endorse a product they haven’t tested. Look for the API designation in addition to the viscosity grades. There are lots of old wives tales about switching over to synthetic that I do not adhere to. Synthetic in a generator seems ideal (expensive) for a generator as it could run many many hours after sitting many many weeks. It’ll depend a lot on the application. Is it standby? Does unit get exercised periodically? Etc.

 

[Jerry1]

The oil spec should be defined by the engine mfr, not the generator mfr (although they could be the same, it’s not likely).

The engine is a Mitsubishi 4 cyl. However, the information I get is from the manual that came with the generator. If there is not consensus between the OEM’s, I guess they should have dealt with that before writing the manual. The manual just says an SAE oil rated at 15W40. Given that it was manufactured in 2003, there may have still been some reluctance to recommend a full synthetic. Also, I doubt they would have included an engine heater if they were committed to a synthetic oil.

 

[JRon]

You should be fine with synthetic 15W40. Synthetic oil with the same rating will perform as well or better than conventional oil and last way longer before breaking down.

You do need to change the oil before switching. Do not add synthetic oil to conventional oil to top it off.

 

[OldShooter]

What problem are you trying to solve?

 

[Jerry1]

What problem are you trying to solve?

Just trying to change to oil and want to use the best product for the job. Not really a problem, but if it helps to keep engine temp lower or use less oil, those would be good benefits.

 

[OldShooter]

Just trying to change to oil and want to use the best product for the job. Not really a problem, but if it helps to keep engine temp lower or use less oil, those would be good benefits.

Oil will not affect engine temp unless you don't use any. Oil consumption will probably not change either. Why don't you contact the engine manufacturer and ask their advice? Or find a more recent version of the engine manual and see if there is a synthetic listed. Check here for more information on oil specs: https://www.api.org/products-and-se...d-classifications/oil-categories#tab-gasoline

Truth be told, oil doesn't matter that much if you have the right spec and are in the ball park viscosity-wise. My racing engine builder tested them all on his dyno and his advice was "Use whatever you can get for free." That said, I ran Red Line 30W synthetic because I found that it left me with less ash on the back side of my exhaust valves. That would be after about 2 hours of running or a little less, as I freshened the head after every weekend. Junk-filled garage still has a couple quarts of that stuff as there is no reason to use it in street cars.

With a generator, engine temps should be well controlled and risk of oil breaking down approximately zero. Actually the worst service is short runs as in automatic generator testing if the oil does not reach and hold temperature long enough to boil out the evil combustion byproduct juices. That is why street car oil change intervals are specified in miles and in time. The time spec is assuming lots of short runs and hence likely poisoned oil even if low miles.

 

[Texas Proud]

I am no expert. My understanding is that synthetic is typically used for relatively extreme engine conditions (lots of driving, heavy load, etc.) and to extend the life of the oil (easily a year or more IIRC). My question would be, why use synthetic in an application like a generator which starts (what?) once a month for 30 minutes? The fuel is natural gas (primarily methane) which is way cleaner than gasoline or diesel. IOW, most home generators would be considered light duty. Synth. oil seems like overkill unless you know something I do not. Keep in mind that synth. oil is typically more expensive as well. Just spit balling, so YMMV.

It is light duty until you are actually using it, then it is heavy duty.


I just got a generator so had talked to a few people who had one. One guy was out of electricity for a week. Now, you are supposed to shut it down every 24 hours, but running an engine for a week is not light duty.




Edit to add... the air cooled ones run at 3600, the water cooled like the OP runs at 1800.

 

[OldShooter]

... running an engine for a week is not light duty. ...

Depends on the engine. The Kohler engine in our 13.5kw lake home genset specifies an initial break-in period of 500 hours. It is designed for continuous-duty industrial use. Once the engine temperatures have reached equilibrium it really doesn't know or care how long it's been running.

$300 Chinese generators, probably not so much.

 

[38Chevy454]

The 15w-40 is typically a diesel spec. The synthetic diesel equivalents are 5w-40. Because synthetic flows better at cold temperatures.
There is a difference between gas engine and diesel engine oil. Diesel oil is made to hold more blow by contaminants. It is a good oil, even for gas engines.

 

[Texas Proud]

Depends on the engine. The Kohler engine in our 13.5kw lake home genset specifies an initial break-in period of 500 hours. It is designed for continuous-duty industrial use. Once the engine temperatures have reached equilibrium it really doesn't know or care how long it's been running.

$300 Chinese generators, probably not so much.

Hmmm, will have to read the manual as I got a 20kw Kohler generator and the techs said to 'rest' it every 24 hours of use to check the oil... so about 20 to 30 minutes off...


I got my first use out of it a week or so back... lost electricity for a bit over an hour and it came on without a hitch...


I am surprised how loud mine is... I will have to take a DB measure to see but it seems much louder than the show models... I am wondering if having it behind the garage and near 2 fences makes it sound louder as the sound is being contained for a bit..

 

[steiny]

it is best to check with the manufacture for oil specs.


here is a rabbit hole for ya , a fourm all about oil


https://bobistheoilguy.com/

 

[Jerry1]

it is best to check with the manufacture for oil specs.


here is a rabbit hole for ya , a fourm all about oil


https://bobistheoilguy.com/

Thanks

 

[Big_Hitter]

I would stick with the conventional oil if you can't get synthetic without zinc

 

[OldShooter]

Hmmm, will have to read the manual as I got a 20kw Kohler generator and the techs said to 'rest' it every 24 hours of use to check the oil... so about 20 to 30 minutes off...

Well, I wouldn't run mine for a week without checking/tracking oil consumption, but "the techs" for the genset vendor are unlikely to know much beyond OWTs about the engine. If you're set on synthetic and or anything not listed in the manual, just call Kohler tech support and see if there is a recommendation for other oils. Have your engine model, serial number, and run hours for them. FWIW I don't have an opinion on your oil choice except to know that just because I have used oil that fact does not make me a lubrication engineer.

I got my first use out of it a week or so back... lost electricity for a bit over an hour and it came on without a hitch...

Then you're still in the break-in period. While you're reading the manual be sure to check the time to first oil change.

 

[Texas Proud]

Well, I wouldn't run mine for a week without checking/tracking oil consumption, but "the techs" for the genset vendor are unlikely to know much beyond OWTs about the engine. If you're set on synthetic and or anything not listed in the manual, just call Kohler tech support and see if there is a recommendation for other oils. Have your engine model, serial number, and run hours for them. FWIW I don't have an opinion on your oil choice except to know that just because I have used oil that fact does not make me a lubrication engineer.


Then you're still in the break-in period. While you're reading the manual be sure to check the time to first oil change.

Thanks.... I have not read anything yet... but they said that synthetic 'comes with' the generator...


I do find it a bit suspicious that they recommend changing the oil out every 6 months with synthetic... I would think that it could go years if not worked that much...

 

[Walt34]

I do find it a bit suspicious that they recommend changing the oil out every 6 months with synthetic... I would think that it could go years if not worked that much...

As I understand it merely being exposed to the open air (which it is in a crankcase) allows the oil to absorb moisture which in turn creates undesirable compounds to form. I know nothing of the chemistry involved but the manuals for every engine I have ever owned said to change out the oil at least once a year even if it wasn't used much, so I assume that's the reason.