The underside of engine hatch coated with "Silent Running"
In the last few years, both Mary and I have gotten hearing aids. As anyone with hearing aids will tell you, they not only increase the volume of people's voices, but also increase the background noise. With hearing aids on so we could hear each other, our coach suddenly got so noisy that we were yelling at each other in our effort to overcome the engine noise. We were used to traveling with our multi-disc player on but the increased engine noise made using the CD player useless. The search was on to reduce engine and header noise.
The normal method that most GMC owners use to quiet the noise was adding a sound reducing layer under the engine cover rug. This would have meant that our rug would have to be pulled up, and maybe even a new rug laid since it had been glued down for over 12 years ago. The other option is putting the layer under the engine cover, but all were too thick to fit in that space on our coach. Our friends had a new engine cover made of aluminum so that the sound reducing material would fit between it and the engine. But our headers on the passenger side extend past the cover, so it also would need some form of sound reducer. The next problem was fire danger since most of the sound reducing layers were not self extinguishing, because they were often made of layers of foam.
We live in San Diego and many sailboat owners have diesel motors, so we searched the sailboat service industry for their solutions. "Soundown Corporation" who makes sound reducing mats suggested that I contact "Silent Coating Corporation" They make a sound reducing coating that they advertise as: "The best performing and cost effective soundproofing and vibration dampening product. Our liquid-based sound proofing coatings utilize a space-age viscoelastic polymer system that virtually eliminates unwanted sound and vibration problems. The viscoelastic properties of Silent Running liquid-based coatings absorbs the noise and vibration and converts it into low-grade heat, which is dissipated throughout the applied surface. It adheres to any surface and since it’s a liquid, it goes on easy like paint with a brush, roller or spray, and takes up less space and weighs less than existing sound proofing technologies like mats and wraps. Just paint it on and and feel the difference." It is also self extinguishing so it can be safely be used in an engine compartment. It sounded too good to be true. I could leave our existing rug in place. More information can be viewed on the manufacturer's web site at www.silentrunning.us
I chose the 500 series for industry use and gasoline engines and bought one gallon and had it shipped from the factory on the east coast to San Diego for about $80. (The local boat supply dealer only uses the 1,000 series for Diesel motors.) A coating thickness gauge was included with the shipment.
I cleaned the underside of the engine compartment cover, chiseled some of the wood away to add more space and coated it with a paint brush and small roller. The coating is thick and goes on in about ten thousandths of an inch thick layers. I put in on in the sun and it dried for the next layer in less than half an hour at 70 degrees and low humidity. It is water based, so humidity changes the drying time. The complete fifty thousandth thick minimum coating was applied in one afternoon. I covered the rubber seal area with one thin coat. I let it set up for a week before I put the engine cover back in. Everything fit with no changes needed. Since I used less than half a gallon to do the engine cover, I could also do under the floorboard on the passenger side to quiet the headers with my original $80 purchase. The engine headers on the drivers side are under the engine cover.
Doing the passenger side coating was more difficult and time consuming. I had to jack up the coach, pull the front wheel, remove the wheel cover, cover the motor to seal off any cleaning and rinse water spray, and clean off the thirty-four years of dirt,oil and grease before coating the wood and metal underside. Everything was coated with at least fifty thousandths of the Silent Running. I still had an 1/8 gallon of solution left.
Since the Silent Running application, we can now listen to the radio/music again, talk to each other with our hearing aids on, all this at up to 75 mph. We are both very satisfied with the improvement. It may be the best $80 we have spent on our GMC.
Chuck and Mary Botts, Remodeled, 10,000 lb. 23′