If the system is leaking down and all the hose connections dont leak and the cylinders test ok then your problem is the 30psi pressure relief valve. Its mounted on the air pump. Ive had two fail on me. Bad part is they are $90 bucks from Merc and are about the size of a peanut. I tried several other valves from different industrial suppliers and wound up buying the Merc.

Good luck

Ron

Nice work Formula.

What did you use for a compressor. My merc unit is on it's last leg.

Mike

I used the cheapest $12 auto type air compressor I could find. Mounted it under the helm station (so spark suppression wasnt a problem). Its loud but only on for 10 seconds or so to switch the cylinder. Has survived for 13 years now. Used a 2 position switch,(off and momentary) for the pump and a manual lever type air switch to switch the cylinders and mounted it just under the helm out of view. If you want to get fancier, you could use an electric solenoid to switch it but I figured that was just one more thing to break. I have a list of all the components around someplace if you want them.

Alot of great info here, thanks guys! Anybody know the mercruiser part# for the relief valve?

Silent Choice Relief Valve


Sure you don't want to just clean it with soap and water? Once you unscrew it, which you will have to do anyway to replace it, you will see how simple it is. Spring loaded rubber valve. Nothing more as long as the rubber isn't dry rotted.

I was able to see that mine wasn't sealing just by holding my thumb against the rubber seal and noticing that the leak 'disappeared'. Might check it 1st to make sure this is your problem.

Cleaned mine first and that slowed the leak. Priced the Merc part and went into shock. There is a lot of industry, chemical plants, around where I live and several friends help me find a couple of replacements but they never resealed fast enough to keep the flappers open. Fought it for a while then bucked up for the Merc part.

Another option is to remove the valve and cap the fitting off. Just be sure that your diverters work smoothly and never run the pump longer than required to open the valves. I ran this way also for a while.

Reading your post it brings back old bad memories of the air operated system. I have the Corsa electric valves on my boat now and they have been trouble free. I know that I will be kicking myself later but I just bought CMI's and their diverters are air operated. So here I go again!

Ron

Fantastik advice, very helpfull information here! Off to work I go.