40 weightoil make an air cooled engine runhotter?

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I have a Generac 16KW generator with a 32HP Generac V twin. The manual shows 30 weight above 40 degrees F. 10-30 from 10 to 40 degrees and Synthetic 5W-30 below 10 degrees.

I really like 5-40 Shell Rotella oil and I want to run that.

Seems I have read that 40 weight oil tends to make air cooled engines run hotter. It their any truth to that?

Thanks a ton!
 
Originally Posted By: callbay
I have a Generac 16KW generator with a 32HP Generac V twin. The manual shows 30 weight above 40 degrees F. 10-30 from 10 to 40 degrees and Synthetic 5W-30 below 10 degrees.

I really like 5-40 Shell Rotella oil and I want to run that.

Seems I have read that 40 weight oil tends to make air cooled engines run hotter. It their any truth to that?

Thanks a ton!



This isn't a cheap throw-away genny, so I'd be a little cautious.
You might contact the manufacturer and ask them.
I'd think that the T6 would hold up better during extended runs in any ambient conditions.
 
I have a quality (hahahaha) Harbor Freight thermocouple that I dip into the oil of my lawn equipment. I've tried various different viscosity oils. I have a rural couple of acres with trees, shrubs and lawn around everything. I mulch up all manner of stuff. So, my lawn equipment runs hard, really hard. The engines struggle quite a bit.

While I no longer use 10W-30 or 5W-30 oils due to 2 engine failures, I don't see any temperature difference between grades. Regardless of viscosity, oil temps hit just over 260 degrees in my Snapper Mower after a slog through the tall grass.
 
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I have a cheap pressure washer with a 4hp B&S that would get so hot it would diesel on shutoff with the speced SAE30. Using T6 is has never done that so it obviously runs cooler on 5W40.
 
Supposedly 40 weights will run a little warmer due to the increased friction in the reciprocating mass.

I won't run a 30 weight oil in a generator. 5W40 is perhaps the best oil you can run in a generator, in my opinion.

I'd use the 5W40 in complete confidence and not worry if it raises the engine temp 3 to 5 degrees.
 
What is also interesting is that the manual says change the oil and filter after 200 hours, 2 years, or "24 hours of continuous use".

So that means if we have a week long power outage I would have to change the oil & filter seven times.

Seems like the heavy duty 5-40 Shell Rotella would be a much better choice as the manufacturer seems to think the 24 hours will wear out normal duty oil.
 
Unless it is freezing a 15w-40 probably is a better choice. Why would you run 24/7?
 
Why go against the manufactures engine recommendations? Do you have some reliable data that suggest 40w is better than 30 in this application? I would run a synthetic 5w30 as recommended. Ed
 
Originally Posted By: moklock
I have a cheap pressure washer with a 4hp B&S that would get so hot it would diesel on shutoff with the speced SAE30. Using T6 is has never done that so it obviously runs cooler on 5W40.



One has nothing to do with the other.

I run small engines for a living and daily have at least a couple of generators and 12-16 air compressors running
I haven't noticed any differences in temp when using a 5w-30 or 15w-40. My charger actually runs 10-15f cooler at 70mph when using a 0w-40 vs the prescribed 20 grade.
And difference will be minor if any.
 
Originally Posted By: Eddie
Why go against the manufactures engine recommendations? Do you have some reliable data that suggest 40w is better than 30 in this application? I would run a synthetic 5w30 as recommended. Ed


Did you forget the Florida hurricanes of 2004? My house was without power for about 45 days. In July and August. In Florida. My house was over 110 degrees inside. People were running their free FEMA generators 24 hours a day, 7 days a week to run their refrigerators, cooling fans, and small window air conditioning units.

People that were using 30 weight oil were blowing their engines up within a week. On a heavy duty cycle engine, such as a generator, a 40 weight or 50 weight oil offers superior burn off protection. With a 30 weight you have to add oil to the engine every 10 hours of use, and people just were not doing that, and thus were blowing up their engines. 15W40 and 20W50 offered a large margin of protection for our severe usage pattern.

I am HIGHLY of the opinion that 15W40, 5W40, and 20W50 offer superior performance in generators, in the summer heat. I won't use a 30 weight oil in this application where I live. I dont have to worry about cold starts here.
 
Originally Posted By: callbay
What is also interesting is that the manual says change the oil and filter after 200 hours, 2 years, or "24 hours of continuous use".

So that means if we have a week long power outage I would have to change the oil & filter seven times.


They probably are tired of people not checking their oil and blowing up their engines. If the engine has a filter it would probably be OK to go the full 200 hours before changing it as long as you checked the oil at every fuel fill up.
 
With shipping, prices are much higher than I can find locally. Amazon.com prices are better. I believe Wal-Mart.com might even be shipping oil to your house/shop now (for free?), and that would be a better deal.

Edit: Yep, just checked wal-mart.com and you can get 5 quarts of Mobil 5000 (5 qrts for $12.88) shipped for free ($50 order gets free shipping) which comes out to about $2.57/quart.
 
I really believe that you can't harm almost any engine with T6. I run it in everything. A newer car with 5-20 (or 0-20) maybe not, but i still don't think it would do any harm.
 
Originally Posted By: Donald
What makes most air cooled engine run hot is old grass or mouse nests on/in their cooling fins.



Absolutely. Get a new-to-you mower that's at least 3 years old and clean it off. Looks great. Now remove the shroud, clean again. Remove the recoil, clean again. Think you got it? Now remove the flywheel and find all kinds of additional garbage. It's amazing to me how much a small engine can eat.
 
I'm with bubbatime on this one, but sometimes SAE 40 is hard to find so 15W40 should be the next best choice.

The flash point of an engine oil may give a hint to it's suitability to continuous high temperature operation, and possibly it's NOACK value too.

I change the oil in a lawnmower by letting it run out of gas then turn it upside down with the fill cap removed into a bucket.
There is no way I'm letting oil that hot run on to my hand (ever again) like I do when changing the oil in a car or truck.

For the purpose of this discussion, I would define the SAE 40 grade as 15W40, 20W40, 25W40 and SAE 40.

A full synthetic 10W40 may also be included.
 
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My mower and little generator calls for 10w-30, I run Rotella 5w-40 or Rotella 15w-40. They have had runs in triple digit outside temps... no issues yet.
 
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