Need help picking correct oil for my 25 year old 19hp twin Generac generator

[Robin Veerman]

What is the correct oil to use in my 25 year old 19hp, twin cyl, air cooled Generac generator. This is from the old days with higher ZDDP in the oil and I don't want to screw up my house generator with modern oil. The generator has test run more than actual use and only has maybe 15 hours of non-test use. So the rings aren't even seated yet.

Here's my engine, front ID tab and owner's manual oil requirement
View attachment 857278View attachment 857279 View attachment 857280
What I have been using is some ag gas engine oil that correct for the but is 30W and I want to go lighter like 10W30 or even synthetic for the winter. I could also use modern oil and just add a little ZDDP additive. I have done this with other gas engines and know the % mixture from company instructions

But, here's what I saw the other day in a shop but I know nothing of these oils. Does anyone know anything about these?
View attachment 857281

My plan at the moment is confusing. Should I just use modern synthetic gas engine oil if OK for rings seating, add a little ZDDP and call it good or go with a pre packaged oil as shown in the pictures? Are they really different? Any knowledge or help appreciated.

I’ve used Amsoil Synthetic Small Engine Oil for years. Good stuff in various grades. I personally use the 10w40 in most of my small engines, except the 10w30 in my Honda 2200 inverter. My research indicates Anti-wear ingredients are Moly 72, Phos 722, Zinc 778 ppm. See link below for info.

4 Stroke Power Equipment: Shop Oil for 4 Stroke Equipment - AMSOIL

Shop for 4 Stroke Power Equipment at AMSOIL. Find the full line of premium AMSOIL products and buy online for delivery to your home.

www.amsoil.com

 

[Willie B]

I have a different opinion.
I sold, installed & did service on Generac standby generators when yours was new.
For reasons take too long to express, I stepped away from Generac, (then Guardian)
10 years ago, my son wanted to get back in. We are electricians, and hobby mechanics. These days we install 15 a year on average.
Generators get oil changes at least annually. Oil does not "wear out". It gets contaminated. No difference between dirty synthetic & dirty fossil oil.
Some generators seem to inhale small amounts of water, I think in the form of tiny snow crystals. Oil gets milky.
Generac no longer specifies oil to use. We choose Rotella Diesel oil in 10W-30. Slightly thicker oil does make starting a hint slower, but air cooled engines heat the oil quickly. I find oil consumption is reduced. The diesel oil has more zinc in it, helps valves resist wear.

 

[Fxfymn413]

I once had the opportunity to attend a forum where the chief lubrication engineer for Ford spoke. In a nut shell his point was that any motor oil produced today is superior to those made previously.

I use 5-w30 synthetic in all of the small engines including a 2002 Generac generator.

I agree the Generac's are basically reliable, but mine had the butterfly valve fall off once. Apparently a not unheard of failure. Fortunately the engine did not swallow it and after a few hours of disassembly it was easily fixed.

 

[5030]

I have a different opinion.
I sold, installed & did service on Generac standby generators when yours was new.
For reasons take too long to express, I stepped away from Generac, (then Guardian)
10 years ago, my son wanted to get back in. We are electricians, and hobby mechanics. These days we install 15 a year on average.
Generators get oil changes at least annually. Oil does not "wear out". It gets contaminated. No difference between dirty synthetic & dirty fossil oil.
Some generators seem to inhale small amounts of water, I think in the form of tiny snow crystals. Oil gets milky.
Generac no longer specifies oil to use. We choose Rotella Diesel oil in 10W-30. Slightly thicker oil does make starting a hint slower, but air cooled engines heat the oil quickly. I find oil consumption is reduced. The diesel oil has more zinc in it, helps valves resist wear.

I keep the starting battery on my whole house Generac heated in the winter with a 110 volt heating pad that I bought not from Generac but from another source and yes, heavier weight oil causes the engine to turn over more slowly (slightly) but nothing fatal.

Just about ready to strip everything out of the old corroded steel enclosure and re-install everything in the new powder coated aluminum enclosure I bought from Generac. Wasn't cheap but in reality, much less than buying an entirely new unit. The new one is very complete right down to all new fasteners. Looking forward to renewing the enclosure, my old steel one is looking very ratty. I am going to pour a new concrete pad as well. The old pad is cracked so it gets replaced as well. I hope it all just remove the components and install in the new enclosure, looks to be anyway. I'm not an electrician by any stretch.

Been a good unit all these years. It does use a tiny bit of oil but I change it yearly so that is inconsequential for me. While I have it out of the old enclosure and readily accessible, I'll adjust the valves as well. I checked my records and I have been using Rotella 15-40 T5 in it. Need to order a tune up kit anyway and change the filters (air and oil) as well.

 

[showcattle]

I'd run Rotella T5 10W-30 diesel oil in it

 

[sixdogs]

I have a different opinion.
I sold, installed & did service on Generac standby generators when yours was new.
For reasons take too long to express, I stepped away from Generac, (then Guardian)
10 years ago, my son wanted to get back in. We are electricians, and hobby mechanics. These days we install 15 a year on average.
Generators get oil changes at least annually. Oil does not "wear out". It gets contaminated. No difference between dirty synthetic & dirty fossil oil.
Some generators seem to inhale small amounts of water, I think in the form of tiny snow crystals. Oil gets milky.
Generac no longer specifies oil to use. We choose Rotella Diesel oil in 10W-30. Slightly thicker oil does make starting a hint slower, but air cooled engines heat the oil quickly. I find oil consumption is reduced. The diesel oil has more zinc in it, helps valves resist wear.

My engine doesn't sit outside but in the heated garage and I roll it out to a shed to run and a cord to plug into the house when needed. It was made in 1999 and I would have no problem running an oil with higher ZDDP in it. It has hardly any hours on --maybe 15 to 25 so I don't want to run synthetic in it because tat was the practice back then.

For summer, I have 30W diesel rated Kubota oil I could use or I could use the T5 Rotella 10W30 or even the straight 30W T-1 (?) Rotella made for older diesel engines. Can I run diesel oil in a gas engine? I can get 10W30 gas engine oil with or without higher ZDDP so what about that?

Tell me more about the things you know and learned from working with these now older engines.

 

[5030]

I'd run Rotella T5 10W-30 diesel oil in it

No reason to as I prefer not to stock all sorts of different lubricants and 15-40 works fine for me. I do run the larger oil filters on mine versus the small ones. Same with the diesel standby by the barn.

Can I run diesel oil in a gas engine? I can get 10W30 gas engine oil with or without higher ZDDP so what about that?

I have been using and will continue to use T5 15-40 in all my engines including the buggies. Been doing that for years now and I don't see any obverse conditions arising either.

Just got delivered 2 cases with 3 gallons in each I purchased from Amazon and the cost per gallon was appreciably less than any of the brick and mortar stores around here, Tractor Supply included and it's free shipping as well. I have in the shop, at least 10 gallons as well. I never have enough.

 

[MMC]

I will offer only a couple of suggestions. First, I personally find value in the synthetics for small engines that we use here on the farm. Most any brand name synthetic that gets close to original weights should suffice and help with winter ops. Second, smaller air cooled engines appreciate supplemental heat for winter starting.

I am fortunate to have an old school propane boiler for heat (with several efficient mini-splits added). Circulator pump for the boiler requires only small amps to drive its six zones, so I can get away with a small propane Generac house generator, powering several essential circuits. It's a 2009 model - As 5030 said about his larger one, I have only replaced one starter in all these years and did the original install myself. I did add a battery wrap heater and a small magnetic crankcase heater on a thermostat. After these mods, never fails to start and run. Switched to a 5-30 syn after a couple of years. Not as conscientious as 5030 - change my oil, filter, and air filter every two or three years. No oil consumption that I can visually see at this point...

But, it runs so well, I am thinking about buying a replacement electronic brain for it after all these years - afraid Generac might not stock some of this old stuff in the future.

 

[Robin Veerman]

My engine doesn't sit outside but in the heated garage and I roll it out to a shed to run and a cord to plug into the house when needed. It was made in 1999 and I would have no problem running an oil with higher ZDDP in it. It has hardly any hours on --maybe 15 to 25 so I don't want to run synthetic in it because tat was the practice back then.

For summer, I have 30W diesel rated Kubota oil I could use or I could use the T5 Rotella 10W30 or even the straight 30W T-1 (?) Rotella made for older diesel engines. Can I run diesel oil in a gas engine? I can get 10W30 gas engine oil with or without higher ZDDP so what about that?

Tell me more about the things you know and learned from working with these now older engines.

No reason to not run synthetic oil in such a low hour machine. Most equipment built after 1980 (seals etc) are compatible with synthetic lubricants. My 1998 Honda 5000 Generator ran exclusively on Amsoil synthetic 10W40 since new and never used oil between changes. I'm doing the same with my newer 2022 Honda 6500... ;>)

 

[YoungMark]

One other difference between diesel oil and gasoline oil other than the zinc content is that they have higher detergent levels to help with the sooty blowby. If you put it into an older gas engine, it'll clean up deposits better than just doing a regular oil change - in fact you possibly may need to do another oil change soon after to avoid choking the filter. YMMV.