Within the past month I have been getting sewer gases sucked into my evaporative cooler.
I have lived here for ten years and never had this happen before. The vent is about two feet from the coller. I went on the roof and the smell at the vent is horrible. What can I do to stop this?

The smell at the vent above the roof is supposed to stink, that's where sewer gas is designed to exit. Is the roof smell identical to the smell from the cooler, you could have some mold or bacteria growing inside the evaporator.

The smell is the same smell and comes and goes depending on the wind. I also smell it at times on the patio in the backyard if the wind is blowing that way.

Vented gases can sometimes be detected in a yard if the wind conditions are right. Sewer gas should rise but can be swirled down by wind. Is there an air intake or anything on your evaporator that could be pulling in the vented gases? If the evaporator has a trap make sure it has not gone dry as well as any other plumbing traps.

The smell at the vent above the roof is supposed to stink, thats where sewer gas is designed to exit. Is the roof smell identical to the smell from the cooler, you could have some mold or bacteria growing inside the evaporator.

The evaporative cooler is the air-condtioner that has three sides with pads that water flows theough to cool the house. It sucks air in on three sides-one of which is twc feet away from the vent.

I'd try rerouting your vent termination up higher or several more feet away from the evaporator. Is this in your attic or on roof?

I agree with Balangerb1: reroute the vent. I my area, the vent would have to be 10' away from the cooler.

Another option, ( I like lotsa options) would be to install a Ordor Hog(see image) on the vent. Check them out at; OdorHog(tm), roof vent pipe filter that stops septic tank odor. 1-800-963-6746 (http://www.odorhog.com/) Good luck, Tom