This has bugged me for some time and I thought it worthy to ask if anyone has ever noticed or has the same setup or has dealt with it if it was a problem.....My Onan 5500 sits in the front of my trailer as most gens normally are. Under the trailer there's an area directly under the Gen which is a large inlet for the air cooling the unit. You can feel it sucking in a massive amount of air too. But just to the right of the cool air inlet is a hole about 14"-16" long and 6"-8" wide which is the hole for hot air exiting and also where the exhaust muffler is plumbed through as the exhaust pipe runs out to the side of the trailer and exits the exhaust fumes.My concern is that I've noticed on hot days, and really any time the gen is running, that the cool inlet air is pulled so forcefully that it "seems" that its pulling in some of the hotter air from the exit side. If this is the case then that cant be good. On a triple digit summer day running the A/C that would seemingly cause the gen to run unnecessarily hotter. No? Instead of 105* air passing through the gen box, there would be more like 130*+ air passing through the gen box as its sucking in a considerable amount of air from the hot side.I've thought about getting some sheetmetal made to screw up to the bottom of the trailer somehow separating the inlet and outlet and having and angle placed in the metal in order to more direct the hot air out away from the cool drawing inlet.Has anyone noticed this before or addressed it before or am I over thinking this?

You are over think it. I have pointed a fan at the area to keep the hot air from blowing towards the patio area.

My Onan 3600LP draws air through the ventilated compartment door and blows the heat out the floor. Your rig seems like a poor installation.

Mine draws from the bottom too. No ventilation in the door.Additionally, one may be tempted to run your generator with the cover off. Onan says that will actually decrease cooling.

My set up is quiet different from yours.. The genny exhausts to the side, near the black water bay. BUT the problem is the same,, Exhaust fumes rise into the motor home via assorted routes, I am starting to find a few of them.Hoever there is a cure... It is made by Camco and it is called a GEN-TURIThis uses the venturi principle it consists of a bag of adapters so it fits yoru exhause, one or more of these clamp on the exhaust pipe Then we have a SWEEP ELBOW (large radius elbow) that has 3 prackes on the end of it, these hold a polycarbonite pipe Very light weight, black in color and much larger then the sweep.... Exhaust "Jetting" out the sweep sucks in cool air via the Gen-turi principle so the pipe remains fairly cool.. HOW cool, after several hours of operation you can hold it in your bare hand with generator still running for several minutes.. (Though one time it got too hot to handle.. but it was SUNLIGHT, not Generator that made it that way)This takes the exhaust fumes up above the roofline, from there they continue their upward journy up-up. and away from your living quarters. Some folks yammer about the rootop air conditioenrs sucking in this exhaust.> Two answers to thatFirst.. The rooftop A/C is in the center of the RV, at the minimum six feet from the Genturi.. So by the time the exhaust gets over to where the A/C is it's already at lest 12 feet ABOVE the A/C. 2nd the A/C does not move air from Outside to inside, if anything it's the other way around.

wa8yxm wrote:My set up is quiet different from yours.. The genny exhausts to the side, near the black water bay. BUT the problem is the same,, Exhaust fumes rise into the motor home via assorted routes, I am starting to find a few of them.Hoever there is a cure... It is made by Camco and it is called a GEN-TURIThis uses the venturi principle it consists of a bag of adapters so it fits yoru exhause, one or more of these clamp on the exhaust pipe Then we have a SWEEP ELBOW (large radius elbow) that has 3 prackes on the end of it, these hold a polycarbonite pipe Very light weight, black in color and much larger then the sweep.... Exhaust "Jetting" out the sweep sucks in cool air via the Gen-turi principle so the pipe remains fairly cool.. HOW cool, after several hours of operation you can hold it in your bare hand with generator still running for several minutes.. (Though one time it got too hot to handle.. but it was SUNLIGHT, not Generator that made it that way)This takes the exhaust fumes up above the roofline, from there they continue their upward journy up-up. and away from your living quarters. Some folks yammer about the rootop air conditioenrs sucking in this exhaust.> Two answers to thatFirst.. The rooftop A/C is in the center of the RV, at the minimum six feet from the Genturi.. So by the time the exhaust gets over to where the A/C is it's already at lest 12 feet ABOVE the A/C. 2nd the A/C does not move air from Outside to inside, if anything it's the other way around.I think you are confused. The discussion is not about the engine exhaust but rather the air that is sucked in to cool the radiator and then exhausted.

Hot exhausting air from Gen being sucked in by cool inlet

11 Replies

KATOOM
Explorer
Jul 24, 2014
I hear ya but water cooled and air cooled engines are apples and oranges. Water cooled engines run thermostats to assure a more constant working temperature which is why water cooled engines run more consistent power levels than air cooled engines do. Air cooled engines must have air passing over the cooling fins otherwise the cylinders gets hot and the running temperatures become more inconsistent too. This doesn't mean an air cooled engine will run at 195* either since if its running in a 195* environment it would quickly overheat because dissipation temps would be even higher and the working temps would be outrageous.

All engines are generally OK up until around 140* ambient temperatures and then it just becomes too hot for optimal combustion, heat dissipation, and oil temperature dissipation for everything to work properly. Diesels will actually work in hotter temps than gasoline engines will but nonetheless, I think I'd rather try to and keep my generator from having to run at maximum operating temperatures since reliability and longevity is what I'm after.
opnspaces
Navigator II
Jul 24, 2014
the part you (and I) don't know is what is an acceptable temperature range for the cooling air. It might just be that the specs allow for 160 degree air before the engine is affected.

Think about the temps in a liquid cooled engine. Most are running a 195 degree thermostat which means the coolant in the engine is 195 degrees which is hotter than the generator cooling air.
KATOOM
Explorer
Jul 24, 2014
Thanks Chris. Thats it exactly. So Onan if I read that correctly Onan is only measuring a 25* increase in temp? That may not seem like much but if its 105*-115* outside, when you need the A/C most, and your generator is working overtime then that would mean the air passing over the engine trying to cool it would be well in the 130*-140* range. Thats a bit toasty. I think I'll try to rig something up to direct that hot air out and away from the cool inlet.
Chris_Bryant
Explorer II
Jul 24, 2014
Onan has a test for new installations using 2 measurement points- one 4' away from the genset, the other in the air inlet. They spec the max temp rise of 25 degrees F over ambient.
Baffles can be fashioned, which actually do a ton to quiet the genset, if they are done correctly.
KATOOM
Explorer
Jul 24, 2014
Thanks everyone but yes as Bill pointed out, this has nothing to do with exhaust fumes. Thats not a problem as the exhaust vents out and away from any open doors or windows.

The thread is about the hot air the generator engine creates while cooling itself. The inlet for cool air to cool the air cooled gen is potentially sucking in the hot air coming out directly next to it. That constant recirculation of hot air re-entering the cool air inlet has to warm the generator more than if it was only pulling fresh cool air away from that exiting hot air. It would be like the air coming out of your trucks radiator coming around the front and re-passing through the radiator again. That clearly wouldn't be good for dissipating more radiator heat would it?

And no, you cant run the gen with the cover off otherwise the air cooling fan cant pull air over the engine, but again this isnt the topic. Maybe I can post a picture if I get a moment.
Rvpapa
Explorer
Jul 24, 2014
One way to correct that is to use a mud flap (like from a dually) and make some type of bracket to hang it between the vents.
A piece of EMT fastened under the trailer and piece of rod on the flap. Just make sure to remove when packing up.
Art.
Bill_Satellite
Explorer II
Jul 24, 2014
wa8yxm wrote:
My set up is quiet different from yours.. The genny exhausts to the side, near the black water bay. BUT the problem is the same,, Exhaust fumes rise into the motor home via assorted routes, I am starting to find a few of them.

Hoever there is a cure... It is made by Camco and it is called a GEN-TURI

This uses the venturi principle it consists of a bag of adapters so it fits yoru exhause, one or more of these clamp on the exhaust pipe Then we have a SWEEP ELBOW (large radius elbow) that has 3 prackes on the end of it, these hold a polycarbonite pipe Very light weight, black in color and much larger then the sweep.... Exhaust "Jetting" out the sweep sucks in cool air via the Gen-turi principle so the pipe remains fairly cool.. HOW cool, after several hours of operation you can hold it in your bare hand with generator still running for several minutes.. (Though one time it got too hot to handle.. but it was SUNLIGHT, not Generator that made it that way)

This takes the exhaust fumes up above the roofline, from there they continue their upward journy up-up. and away from your living quarters.

Some folks yammer about the rootop air conditioenrs sucking in this exhaust.> Two answers to that

First.. The rooftop A/C is in the center of the RV, at the minimum six feet from the Genturi.. So by the time the exhaust gets over to where the A/C is it's already at lest 12 feet ABOVE the A/C. 2nd the A/C does not move air from Outside to inside, if anything it's the other way around.

I think you are confused. The discussion is not about the engine exhaust but rather the air that is sucked in to cool the radiator and then exhausted.
wa8yxm
Explorer III
Jul 24, 2014
My set up is quiet different from yours.. The genny exhausts to the side, near the black water bay. BUT the problem is the same,, Exhaust fumes rise into the motor home via assorted routes, I am starting to find a few of them.

Hoever there is a cure... It is made by Camco and it is called a GEN-TURI

This uses the venturi principle it consists of a bag of adapters so it fits yoru exhause, one or more of these clamp on the exhaust pipe Then we have a SWEEP ELBOW (large radius elbow) that has 3 prackes on the end of it, these hold a polycarbonite pipe Very light weight, black in color and much larger then the sweep.... Exhaust "Jetting" out the sweep sucks in cool air via the Gen-turi principle so the pipe remains fairly cool.. HOW cool, after several hours of operation you can hold it in your bare hand with generator still running for several minutes.. (Though one time it got too hot to handle.. but it was SUNLIGHT, not Generator that made it that way)

This takes the exhaust fumes up above the roofline, from there they continue their upward journy up-up. and away from your living quarters.

Some folks yammer about the rootop air conditioenrs sucking in this exhaust.> Two answers to that

First.. The rooftop A/C is in the center of the RV, at the minimum six feet from the Genturi.. So by the time the exhaust gets over to where the A/C is it's already at lest 12 feet ABOVE the A/C. 2nd the A/C does not move air from Outside to inside, if anything it's the other way around.
joebedford
Nomad II
Jul 24, 2014
Mine draws from the bottom too. No ventilation in the door.

Additionally, one may be tempted to run your generator with the cover off. Onan says that will actually decrease cooling.
beemerphile1
Explorer
Jul 24, 2014
My Onan 3600LP draws air through the ventilated compartment door and blows the heat out the floor. Your rig seems like a poor installation.