Viscosity and hours between oil changes in small air cooled engines.

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I have spent a fair amount of time researching oil - trying to pick one for my air cooled Honda EG2800i generator. It will likely be used for a few days straight when outside temps are in the 90-98 degree range. (Houston area hurricane driven power outage)

On one hand I think - use a 5W30 full synthetic and change it at least every day or even every 15 - 20 hours.

On the other hand I think, use something like 10W40 / 15W40 - to provide better protection in the extreme heat.

My research leads me to the conclusion that higher viscosity oils like 15W40 are recommended by many because using 10W30 oils have resulted in oil related engine failures -

But is that because they used a 10W30 conventional oil and ran the generator hard for 4 or 5 days straight without an oil change when it was 95 degrees outside?

With a 15W40 they can run for a few days on the same oil and still avoid oil related engine problems - so they choose the higher viscosity oil.

Is a better choice to just change the oil more often?

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If I start with the idea I will be changing the oil at least every day say 15-20 hours between oil changes -

Is a 5W30 synthetic a better choice over a 10W40 or 15W40 conventional oil or maybe even better than a 15W40 / 5W40 synthetic?

My theory is the 5W30 synthetic will provide a good oil film for at least a day - and since it is a lighter oil the engine will run cooler and maybe even have better fuel economy. Where a higher viscosity oil will cause the engine to work a little harder - making it run hotter and burn more fuel.

I totally understand why a heavier oil is required if you are going to go 150-200 hours between oil changes - the lighter oil will break down and stop providing the protection needed and it will result in a reduced engine life or total engine failure.

But does that change if you do at least daily oil changes?


It takes me 5 minutes to change the oil in my Honda EG2800i - I do it while refueling - the ~~16 ounces of oil costs less than $2 so I don't care about cost.

Maybe if I was running a commercial operation and I had a dozen air cooled engines running every day - a longer between oil changes system would be better - but that is not what I am doing.

So if 15-20 run hours between changes is the standard - which oil do you pick to keep your generator running for 4 days straight in 95 degree heat?
 
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although i don't think even a cheap 10w-30 could cause engine failure i wouldn't run that. But thicker oils dont necessarily last longer in terms of oxidation. thin oils do have a lower hths which can cause a failure in very high oil temps and engine load. Guys have spun bearings in their 5.0 mustangs from using 5w-20 instead of something thicker since heavy loads and high rpm's can cause that.

If i was using an air cooled engine severely at high loads id most definitely be using a diesel oil that has ford wss and volvo vds approvals. I'd change it every 30-40 hours or so. The oil wont break down in a day basically no matter what unless it was cooked to like 400f but air cooled engines have no filter and they start to contaminate quickly and that leads to more wear. I'd use just plain supertech diesel 15w-40. Has both good certifications and is the best priced. i get the 2 gal jugs. If you want to be fancy mobil delvac extreme syn diesel is the pick but thats pretty overkill and is 2x the price.

Also thicker oils don't really affect the heat and fuel consumption that much so i wouldn't worry. The oil being 30% thicker wont cause 30% reduction in efficiency. Probably like 3-5% in all honesty.
 

z71bill

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although i don't think even a cheap 10w-30 could cause engine failure i wouldn't run that. But thicker oils dont necessarily last longer in terms of oxidation. thin oils do have a lower hths which can cause a failure in very high oil temps and engine load. Guys have spun bearings in their 5.0 mustangs from using 5w-20 instead of something thicker since heavy loads and high rpm's can cause that.

If i was using an air cooled engine severely at high loads id most definitely be using a diesel oil that has ford wss and volvo vds approvals. I'd change it every 30-40 hours or so. The oil wont break down in a day basically no matter what unless it was cooked to like 400f but air cooled engines have no filter and they start to contaminate quickly and that leads to more wear. I'd use just plain supertech diesel 15w-40. Has both good certifications and is the best priced. i get the 2 gal jugs. If you want to be fancy mobil delvac extreme syn diesel is the pick but thats pretty overkill and is 2x the price.

Also thicker oils don't really affect the heat and fuel consumption that much so i wouldn't worry. The oil being 30% thicker wont cause 30% reduction in efficiency. Probably like 3-5% in all honesty.
I just had a 2 gallon jug of SuperTec 15W40 heavy duty diesel oil delivered to my home - $20.49 is hard to beat. Figured I would rather have it and not need it than need it and not have it.

Delvac Is $11.87 a gallon or $23.70 - but I was thinking of mixing in some 15W40 with the 5W30 SuperTec I already had was the main reason I went with SuperTec.

Cost is not my main focus - but I like to buy stuff on sale and when it is a deal.

My point was - lighter oil would run at a lower temp - that is the reason for better fuel economy -

If I ran some high end 5W40 like Chevron Delo (I have a gallon of it) I will still be changing the oil every day - I am a fanatic about it - and think the push to heavier oils is driven by people wanting to go a few days or longer between changes.

If a big truck takes 3 gallons of oil and multiple filters - sure I would want to extend the change interval out - but I am talking about 1/2 a quart and 5 minutes of time.

I know this is sort of narrow view - but does 1 day old 5W30 synthetic provide better lubrication than a 15W40 that is also 1 day old?
 
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What does the owners manual suggest for viscosity and change interval? I don't see any reason to change the oil every day myself. My first instinct without doing any research would be something like a 15w-40 and change it every 100hrs or so. Check at every fill up to make sure it doesn't need to be topped off though. Honda probably knows best though.
 
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Simply put, you cannot change the oil too often on small, air cooled gas engines. It's impossible because of several reasons.

1.) They all have a very limited oil capacity. (Most are under 1 quart, or only slightly above).

2.) They all run at high RPM all but constantly. (Lawn mowers, generators, pumps).

3.) They are all under a heavy load most all the time they are running.

4.) They run, for the most part, at higher than normal temperatures.

5.) Except for the larger V-Twin models, they have no oil filtration system what so ever. And are sling oiled with no pressure pump.
 
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I just got back last weekend from the races. I ran my generator for over 65 hours straight. The oil change had ~80 hours on it. My recommended OCI is 100 hours. I would not change the oil daily especially if you are using an HDEO oil. I currently run Super Tech 10W30 FS HM with good luck. I will be at it again this weekend with another ~48 hours of continues run time. One of these times I will do a UOA and see if it tells me anything.

On my next change I might go to 15W40 HDEO, IDK yet.

Just my $0.02
 
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40 year old Sensation Mower w/3.5hp Briggs Commercial featuring "rotating valves".
Been using 30W.
Bought 40 and the countermen asked, "why change the weight?"
I said, "It's 40 years old. Give the old machine some 'cush' ".
 

z71bill

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What does the owners manual suggest for viscosity and change interval? I don't see any reason to change the oil every day myself. My first instinct without doing any research would be something like a 15w-40 and change it every 100hrs or so. Check at every fill up to make sure it doesn't need to be topped off though. Honda probably knows best though.
Honda says 5W30 or 10W30 (of course Honda likes 10W30 Honda oil) - With continuous use in hot conditions change every 25 hours.

Owners manuals are the minimum amount of maintenance and a good place to start - but I want to go a little above the bare minimum required.
 

z71bill

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I just got back last weekend from the races. I ran my generator for over 65 hours straight. The oil change had ~80 hours on it. My recommended OCI is 100 hours. I would not change the oil daily especially if you are using an HDEO oil. I currently run Super Tech 10W30 FS HM with good luck. I will be at it again this weekend with another ~48 hours of continues run time. One of these times I will do a UOA and see if it tells me anything.

On my next change I might go to 15W40 HDEO, IDK yet.

Just my $0.02
What was the high temperature?

Big difference from 80 to 95. Which is why I am obsessing about it.

I broke my infrared thermometer - but may buy another and start taking readings on the engine where the piston is -

Just curious is that is 190 or 250 or what?
 

z71bill

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M1 15-50 in my Generac ...Risking a blown motor for negligable lower temp of thinner oil is folly.

Wouldn’t lower engine operating temp - all other things being equal - mean less friction?

Why would an engine experiencing less friction blow up more than one running with more friction?
 
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Chill bill….you’re seriously over thinking this to the point of being irrational! That little Honda will run forever on most anything you dump into it. If it were mine it would get Mobil1 15w50 annually or every 100 hours.
 
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which oil do you pick to keep your generator running for 4 days straight in 95 degree heat?

I ran mine a couple of summers ago when water leaked into my breaker panel. I was waiting for the new back plane to arrive and ran my Genny on Castrol HD30 for 5 days during a heat wave. I changed the oil once, using the same HD30. No issues.
 
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I would never use a 5w-30 in a generator in your climate. I wouldn't use it in my climate either !!! You could try Mobil1 10w-30 High Mileage or Rotella T6 15w-40. Look for higher HTHS viscosities. It's 3.5 on the former and at least 3.7 on the latter.
 
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What was the high temperature?

Big difference from 80 to 95. Which is why I am obsessing about it.

I broke my infrared thermometer - but may buy another and start taking readings on the engine where the piston is -

Just curious is that is 190 or 250 or what?

The high temperature was 75 the low close to 40. Regardless of the high temperature if it’s 75 compared to your 95 the delta is 20 degrees… I really think you are over thinking this IMO.

Just for reference this generator ran for ~4 days on 5w30 last summer after the derecho in Iowa. The weather was in the high 80’s during the day and low 70’s at night. This thing has run in all kinds of temperatures and has not missed a beat!

I’d suggest if you stay within the manufacturer’s recommendations you won’t hurt it. You are wasting money if you change the oil before the recommended OCI, especially if you run an HDEO or full synthetic oil.

Just my $0.02
 

z71bill

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Chill bill….you’re seriously over thinking this to the point of being irrational! That little Honda will run forever on most anything you dump into it. If it were mine it would get Mobil1 15w50 annually or every 100 hours.
Not sure if irrational fits - mild OCD maybe - I like things done right!

Plus - Over thinking stuff is in my DNA - 🤔 I consider it - Just exploring my options.


The Honda came with a 3 year warranty - I bought it in January on 2018 - the generator stayed in the box unused until February of 2021 when I got it out and ran it during the Texas deep freeze - since I am free from any warranty related requirements I am free do do whatever.

I have a bunch of 5W30 full synthetic if in any doubt I will use that -

I also have a few other heavier oils on hand - and it the outside temp goes way up I would use one of them.

But this stuff interests me - and curiosity makes me want to figure out what is best.

Far as a 50 weight oil - no way I will do that unless it is something the manufacturer recommends -

My view right now - I would rather change it more often VS using a 50 weight.
 

z71bill

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The high temperature was 75 the low close to 40. Regardless of the high temperature if it’s 75 compared to your 95 the delta is 20 degrees… I really think you are over thinking this IMO.

Just for reference this generator ran for ~4 days on 5w30 last summer after the derecho in Iowa. The weather was in the high 80’s during the day and low 70’s at night. This thing has run in all kinds of temperatures and has not missed a beat!

I’d suggest if you stay within the manufacturer’s recommendations you won’t hurt it. You are wasting money if you change the oil before the recommended OCI, especially if you run an HDEO or full synthetic oil.

Just my $0.02

That would be 5W30 or 10W30 every 25 hours -

The thing is it only takes 16 ounces of oil -

I have Mobile1 that cost me $12 for 5 quarts (after rebate) that is a $1.20 a change - but even if M1 is $25 a jug that is still only $2.50

If I do a change every day for a week it isn't even $20 -
 

z71bill

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I would never use a 5w-30 in a generator in your climate. I wouldn't use it in my climate either !!! You could try Mobil1 10w-30 High Mileage or Rotella T6 15w-40. Look for higher HTHS viscosities. It's 3.5 on the former and at least 3.7 on the latter.

I wouldn't either if my plan was to run it for 100 hours straight. But does changing it every day change the view?

While researching oil a while back I discovered that 5W30 has a higher viscosity at 100C than 10W30 -

Mobile1 5W30 Kinematic Viscosity @ 100 C, mm2/s, ASTM D445 = 11.1

Mobile1 10W30 Kinematic Viscosity @ 100 C, mm2/s, ASTM D445 = 10.4

High mileage M1 5W30 Kinematic Viscosity @ 100 C, mm2/s, ASTM D445 = 11.9 the 10W30 = 12.

I was thinking the 5W30 is an OK choice because it maintains a slightly higher viscosity at 100 C I am sort of pulling that out of my butt with no real scientific reason. I don't know much about HTHS and how it relates to viscosity at high temps -

I read some stuff about HTHS a while back - a lower number means it flows easier at extremely high temps - which gives you better fuel economy.

So 5W30 has a higher viscosity at 100 c VS 10W30

But 10W30 has a higher HTHS at 150 C VS 5W30

So does this mean running at high temps of 150 C the 5W30 would break down faster?

Do I care if I am changing the oil everyday? Right back where I started.

Does it really matter if one oil is 11.1 and the other is 10.4 at Kinematic Viscosity @ 100 C, or of one oil is 3.7 HTHS and the other is 3.5?

These differences seem small - when compared to something like a 0W20 with a Kinematic Viscosity @ 100 C, of 8.6 - IDN what the HTHS is but I will assume much lower than 3.7.

Deep stuff this oil analysis!
 
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Adjust the valves at 250 hours. Use any 10w30 oil. Setup a box fan to help cool the open frame inverter.
 
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