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Mirax Fuel Tanks
auburnbuilder	#1  Posted on 04/03/10 - 5:31 PM
Member Posts: 34 Comments: 0 Joined: 06/13/07	I purchased new Mirax tanks in the fall (2 -12 gallon ) for my Montauk. Do most people vent them or just plug off the vent port. I am worried more about over pressure due to temperature changes. I know the caps vent for withdrawal or suction of the fuel but I believe they do not vent excess pressure. I have noticed that it builds pressure and do not want it to cause a leak in the fuel system ( hoses and connectors ). Maybe a different cap? Thanks any help would be appreciated!
Tom W Clark	#2  Posted on 04/03/10 - 6:29 PM
Member Personal Page Posts: 4280 Comments: 7 Joined: 09/30/05	The fuel tank caps should let pressure out as well. Plug the accessory NTP ports.
bmw90w	#3  Posted on 04/03/10 - 7:18 PM
Member Personal Page Posts: 328 Comments: 1 Joined: 09/08/09	I asked Brian at Mirax about it, and he said the fuel caps will vent thm adequately. I plugged my npt hole as well with bronze dead caps. 1984 Montauk
auburnbuilder	#4  Posted on 04/03/10 - 8:35 PM
Member Posts: 34 Comments: 0 Joined: 06/13/07	Thanks for the info, I was concerned because I am getting some leakage at the mercury connectors to the fuel hose, only when under pressure. Maybe I just have to tighten up the connections more, they seem pretty tight though. I was not sure if it was bad for the fuel system to be under that much pressure. Does anyone know what pressure the caps vent at? Fram caps came with the tanks. Thanks
bottomfish	#5  Posted on 04/03/10 - 10:22 PM
Member Personal Page Project Albums Posts: 198 Comments: 32 Joined: 01/07/09	I used the vent on my 28 mirax. 3/8 solid line to a stainless fuel filter. Keeps fuel from spilling out and lets tank breath completely. May not be needed but I had a concern and that is the way I went. Works great no leaks, no pressure.
mattgeiger	#6  Posted on 04/04/10 - 5:29 AM
Member Personal Page Posts: 310 Comments: 2 Joined: 02/22/07	My 25 year old Mirax tanks are plugged. My new pair is due here next week, and I plan to plug them, as Debbie at Mirax has confirmed that the caps do vent both ways. Anyone know what size fittings I need in order to plug? Cape Dory 28 Hobie 20 Miracle A Class Catamaran
auburnbuilder	#7  Posted on 04/04/10 - 8:08 AM
Member Posts: 34 Comments: 0 Joined: 06/13/07	I believe you need 1/4" NPT. That is what I used to plug mine, in stainless steel.
auburnbuilder	#8  Posted on 04/04/10 - 8:11 AM
Member Posts: 34 Comments: 0 Joined: 06/13/07	Do your old Mirax tanks have a screw vent in the cap? Could you post a pic of them? Thanks, Gary
mattgeiger	#9  Posted on 04/04/10 - 1:14 PM
Member Personal Page Posts: 310 Comments: 2 Joined: 02/22/07	auburnbuilder wrote: Do your old Mirax tanks have a screw vent in the cap? Could you post a pic of them? Thanks, Gary One old cap did have a thumbscrew vent. The other was plain. I had to swap caps when I swapped tanks. Cape Dory 28 Hobie 20 Miracle A Class Catamaran