# FYI running small engines in HOT weather



## exmar (Jun 29, 2015)

I've been having an issue with a 26HP twin cylinder Kohler engine on a Garden Tractor with deck which I use for mowing. Essentially, it runs great until the temp goes over 85 then gets weak. Suspected a coil was going soft but they both checked out fine and the engine only has 200 hours on it. Posed the question in another forum and got a very interesting response from a retired mechanic on there. He said to just unplug the headlights and lift off the hood and run it like that. I tried it and problem was solved. Here's his explanation:
"I think it is percolation of the fuel leading to 'bubbles' being fed to the emulsion tube and an incorrect fuel:air mixture" So, evidently elevated temps cause the percolation resulting in a sort of two phase flow instead of just gas. It also seems to be dependent on the carb, I have a 24 year old 26HP Briggs that doesn't care what the temp is. 

The west coast is roasting, we're looking at the next three days of very high heat here in SE Ohio which is very unusual. Generators are going to become more of a necessity and if high temps have a similar effect on them RPM and power would be impacted. While you can't lift off the hood on a generator, a small fan could be plugged into one of the 120V outlets and directed to help the cooling. 

Just thought this was interesting and could be useful when running a generator when it's Hot. IME most of our outages are in early spring due to ice or when winds and thunder storms move through, not high temp scenarios.


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## FlyFisher (Jun 30, 2018)

Yea we might be in for a "hot summer"... 

I do find it interesting that in California, although the temps haven't been "brutally hot" (like triple digits) they are already talking about necessitating rolling blackouts. How is that going to fare for all those that have switched over to electric cars when they don't have electricity? Let alone the ability to run their AC in the heat... Hopefully that all stays contained in CA, however anything is possible...

As to the percolation in the fuel - interesting thought. I have heard of too thin of oil getting air entrainment (I am not sure I would go so far as to call it cavitation, like when a boat prop sucks air type cavitation) and that causing excessive wear and heat build up. Of course that is bad for an engine, also, however it is irrespective of the type of fuel issue you mention. I can see where it could happen, though.

I agree with the fans on generators. I have been thinking through that and have a way to make it work (my large gen has a sole L14-50, I have split off of one leg inside the box to feed a 5-15R for power at the gen - tools and what not).


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## Dutchy491 (Sep 18, 2019)

Be careful if thinking about opening up the case of your generators because sometimes that actually distorts the airflow and causes higher temperatures. Use a small fan as suggested. Well we all know the arguments about oils and the associated dreaded oil threads that go on and on and on. It’s severe situations that separate the men from the boys, so to speak. This is where the argument comes to a point. Use the best synthetic oil to provide the best possible protection in the most severe situation. Just change the Oil more often doesn’t always work especially when things are going sideways. I like the Amsoil Synthetic Small Engine Oils. Specifically made for these types of engines in severe duty. Not some repackaged car Oil. Delivery right to your door is sweet too. pm me for a link. Dutchy


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## Airstreamer67 (Oct 3, 2020)

I'm 77 and so am an old coot, but in all my years I've never found the need for synthetic oil in any of my engines, and I've never had an engine problem related to oil as long as there was enough of it in the crankcase. My generators are used mostly in the summertime during tropical storms and hurricanes.

Edit: I do have a Mazda car that specifies 0-20 synthetic oil of a specific sort, so that's what I use in it. I always try to follow what the maker specifies.


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## speedy2019 (Jan 29, 2019)

I use semi-synthetic oil in my gen


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## iowagold (Jan 22, 2020)

this is a good argument for diesel as they like high heat.
and the same for LP and NG as they do not have the fuel issue in hot temps.
unless the tank vents on LP due to high pressure.

for racing they use a "cool can" setup with dry ice or just ice to help keep the fuel cooler.
also check to see if you have a carby warmer if it is liquid cooled. we block those off in the summer.
and yes with cold air induction!
a good duct fan would be a great idea to blow cooler air over the carb and engine.
you could get fancy and make it temp controlled like they do on cars and trucks with electric fans.


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## drmerdp (Apr 10, 2018)

exmar said:


> I've been having an issue with a 26HP twin cylinder Kohler engine on a Garden Tractor with deck which I use for mowing. Essentially, it runs great until the temp goes over 85 then gets weak. Suspected a coil was going soft but they both checked out fine and the engine only has 200 hours on it. Posed the question in another forum and got a very interesting response from a retired mechanic on there. He said to just unplug the headlights and lift off the hood and run it like that. I tried it and problem was solved.  Here's his explanation:
> "I think it is percolation of the fuel leading to 'bubbles' being fed to the emulsion tube and an incorrect fuel:air mixture" So, evidently elevated temps cause the percolation resulting in a sort of two phase flow instead of just gas. It also seems to be dependent on the carb, I have a 24 year old 26HP Briggs that doesn't care what the temp is.
> 
> The west coast is roasting, we're looking at the next three days of very high heat here in SE Ohio which is very unusual. Generators are going to become more of a necessity and if high temps have a similar effect on them RPM and power would be impacted. While you can't lift off the hood on a generator, a small fan could be plugged into one of the 120V outlets and directed to help the cooling.
> ...


You are more or less describing vapor lock. Gas turns to vapor and disrupts the normal fuel flow characteristics. In old cars it was a gas vapor disrupting the prime on the fuel pump or a vapor pocket preventing flow to the carb from the pump.

The float bowl is vented to atmosphere,through a port on the inlet track of the carb. I would assume fuel is vaporizing in the bowl, the vented vapors plus Liquid fuel being sucked into the Venturi would cause a rich condition and poor running. Looks like removing the hood is keeping everything cooler.


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## JJ Ranch (Apr 23, 2021)

Airstreamer67 said:


> I'm 77 and so am an old coot, but in all my years I've never found the need for synthetic oil in any of my engines, and I've never had an engine problem related to oil as long as there was enough of it in the crankcase.............


I'm catching up to you in age - I'm a somewhat younger old coot. I'm using 5W-40 full synthetic in my 13 Kw diesel generator mainly because of the wide temperature range for the Perkins diesel. I think it's good from below zero F to 120F. I use conventional oil in all of my other engines.


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## pipe (Jun 27, 2021)

Picked up recently from Wallyworld Shell RGT Full Syn all viscosities for $1/Qt. Similarly recently Pep Boys, NAPA, Autozone have a "throwaway bin" with 5qt jugs for $5. All our outdoor engines use high HTHS rated oils just for high temperatures. With water cooled engines it is less of an issue.

All our outdoor engines run Non-Ethanol E0 fuel


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## exmar (Jun 29, 2015)

Good discussion. Just shared an experience that I'd never had before and the resolution. 'course, I didn't make it a habit of mowing when the temp was 90 either. However, our weather pattern recently is very hot for 3-4 days followed by 2-3 days of rain and repeat. So, if your generator is acting up in high temp, think about air cooling air flow, location and perhaps a fan. Yes, the situation is reminiscent of vapor lock and is related except vapor lock usually prevented starting until engine cooled down. Anyone old enough to remember Wisconsin engines on balers and combines? You didn't shut them off when hot-period. I also wonder if the mystery gas we have to buy (Ethanol) is to blame somehow. As I understand it, the two don't really mix so you have a laminar flow.


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## Ground Fault (Jun 9, 2020)

And just like that, it became a thread about oil. 

Fan. On the exhaust side of the generator if closed frame. They got the airflow right when they designed it, just HELP them by sucking it out. PULL the heat out, because...you can't push a rope.


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## exmar (Jun 29, 2015)

Ground Fault said:


> And just like that, it became a thread about oil.
> 
> Fan. On the exhaust side of the generator if closed frame. They got the airflow right when they designed it, just HELP them by sucking it out. PULL the heat out, because...you can't push a rope.


 YEP! If you're at sea level the atmospheric pressure is 14.7 PSI, nature abhors a vacuum (except in the heads of our elected officials) so ambient temperature air will immediately rush in to the generator. Blowing air at the generator isn't as effective.


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## pipe (Jun 27, 2021)

Ground Fault said:


> And just like that, it became a thread about oil.


Some of us mentioned both fuel and oil 

Ok, on the stuff hitting the fan ... built one time a bypass system by having an open oil drain valve (QWIK valve), port connected to a tube that went into a motorcycle oil cooler mounted externally to a rack (not connected to generator so as to isolate any vibration). The oil cooler was connected to a remote oil filter also mounted externally and finally a small 12v oil pump at the end provided a suction & return to the oil filler port. Entire system increased the oil capacity of the generator by about 1.5 quarts and nicely cooled the entire system. A small portable fan (there! finally got to a fan!) was directed at the oil cooler fin assembly.


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## Dutchy491 (Sep 18, 2019)

Blame me for turning this discussion into an Oil thread. But like we used to change Oil in our cars every 3k miles now 5 k miles or more, things are always achanging.... 😬 Dutchy


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## billt (Dec 11, 2020)

Out here this time of year 115 F to 120 F is common most every day. (Today it's supposed to hit 121 F). What really helps for generator operation in that kind of heat, is to run a large box fan, to keep a good flow of air moving through the engine and dynamo.

They don't draw much power, even on the highest setting. (Which is where I run it). And they can make a big difference in keeping electrical and electronic component temperatures down. I set mine up about 6" away from the recoil starter, and have it blow directly into and through the generator frame. You'll be amazed at how much heat it pushes away from the unit.

It also helps disperse exhaust gasses, which are also very hot. A fan like this one is inexpensive and works perfectly.



https://www.walmart.com/ip/Comfort-Zone-20-3-Speed-Box-Fan-White/55555960


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## iowagold (Jan 22, 2020)

and shade helps as well...
those gen tents rock of you do not have severe wind.


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## drmerdp (Apr 10, 2018)

Generators usually have a rated ambient air temp, usually around 90 degrees.


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## iowagold (Jan 22, 2020)

yea the in the sun on a 100 deg plus day is hard on them!


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