Generac GTH/GTV 990 Engine oil

[jonnied1]

I have the Generac GP-1500E generator with the GTH/GTV 990 Engine. The engine manual and owners manual state not to use 10-40W oil or diesel oil.
I see many on the forum recommend using Rotella T5 15-40 or T6 5-40.
What would make the 30HP GTH/GTV 990 Engine different that Generac would say not to use the above mentioned oil?
Copied from the engine manual:

Recommended oil type:
Using the proper type and weight of oil in the crankcase
is extremely important. Check the oil before each use and
change the oil regularly (see Figures 1-1 through 1-5). Failure
to use the correct oil, or using dirty oil, can cause premature
engine wear and failure.
Use only high quality detergent oil rated with an API service
classification SJ or higher (example: SL or SM). Do NOT use oil
designated "for diesel engines only" (example: CD).
The recommended oil weights include the following:
• During summer months: SAE 30. An acceptable substitute
is SAE 10W-30. After first oil change, synthetic oil is
acceptable.
• During winter months: SAE 5W-30 or synthetic 5W-30. DO
NOT USE SAE 10W-40. After first oil change, synthetic oil
is acceptable.

 

[CharBaby]

I'm going to shoot from the hip here and say that, the MFG specs a 5W30 oil(dino/syn) due to the fact that most generators don't get used as often as a motor vehicle so, they(MFG) wants quick(er) lubrication at startup due to generators sitting idle so often.
And that most 5W30 have the proper additive package to meet their specification. Whereas not all of the other oils listed in the "DON'T USE" list, may not have the proper add pkg.

 

[old1]

It says , do not use oil marked for diesel engines ONLY. Rotella is for diesel or gas engines. The do not use 10-40 is for WINTER use.

 

[mattwithcats]

I run Castrol Edge 0W-30 in my generator.

Expensive (around $10 a quart!), and hard to find,
but I bagged ten quarts during the AutoZone December $2 clearance...

I change it every 200 hours or two years.

 

[NormanBuntz]

I have the GT-990 engine on my 16KW Generac, 10 years old. I have used Napa 5w-30 synthetic and QSUD 5w-30 since it was new. Both have worked fine with not much oil consumption unless the unit runs under load for 36+ hours.

Because of the manual recommendations and your WV climate, I'd stick with your personal choice of 5w-30 synthetic.

 

[jonnied1]

How many hours do you have on that engine now?

 

[NormanBuntz]

Originally Posted By: jonnied1
How many hours do you have on that engine now?


About 240 hours on the GT-990. About 110 hours of that comes from the weekly exercise cycle that it runs.

 

[jonnied1]

Thanks, I only have 30 hours on mine. Just want to make sure it lasts.