Venting diesel tank - Maxum Boat Owners Club

gregorys · 07-06-2017, 04:34 AM

Now I can't fill my port diesel tank. I put a camera down the full up hose and there is no obstruction. The vent tube is so small on the outside and doesn't seem to be Removable. Any suggestions?
Scott

mmwjr · 07-06-2017, 04:43 AM

It's common for the vent screen to become clogged with wax or bugs. Access it from inside, remove the hose then you can unscrew the large nut holding it on. Remove the vent and install a new one.

gregorys · 07-06-2017, 04:51 AM

I can't seem to find how to access that part of the inside of the hull. It is a 1999 4100 SCA. I am bringing my air compressor to the boat this weekend and see the if I can blow it free from the outside or if I have to disconnect the hose from the tank and blow air out. It is just really hard to access!

shrew · 07-06-2017, 01:58 PM

Have you located the fuel tank vent on the outside of the hull? That is where I would start. Can you locate the STBD tank? The Port would be exactly opposite to trim the boat properly.

The screens corrode over time as well if in a saltwater environment.

gregorys · 07-06-2017, 03:35 PM

I have found both of them. They are so small and protected I cant see into them. They look clear from what I can see. I am in freshwater on Lake Michigan.

shrew · 07-07-2017, 02:13 PM

Locate the vent lines on the inside. Make sure there is no kink or trap in the vent line. I would remove and inspect/replace the vent through hull itself. These get easily clogged. insect nests and the like. You won't be able to see inside of it. It will need to be removed.

remove the hose clamp and hose on the inside. Then remove the lock nut. Break the caulk binding the exterior flange to the exterior of the hull (I use a razor blade to cut the caulk then a 2" putty knife to pry it off (wrap putty knife in painters tape to protect the gelcoat)). Then wrestle to pop the through hull off. You can then open the interior and exterior part to expose the screen. The screen is always clogged with junk.

This is the root cause and solution to 97% of fuel fill problems.

gregorys · 07-08-2017, 02:27 AM

The problem I have is that I cannot access the locknut part of the vent hose. There is no access to it! I did put an endoscope camera up the hose and didn't see or feel any kinks.

Quote:

Originally Posted by shrew

Locate the vent lines on the inside. Make sure there is no kink or trap in the vent line. I would remove and inspect/replace the vent through hull itself. These get easily clogged. insect nests and the like. You won't be able to see inside of it. It will need to be removed.

remove the hose clamp and hose on the inside. Then remove the lock nut. Break the caulk binding the exterior flange to the exterior of the hull (I use a razor blade to cut the caulk then a 2" putty knife to pry it off (wrap putty knife in painters tape to protect the gelcoat)). Then wrestle to pop the through hull off. You can then open the interior and exterior part to expose the screen. The screen is always clogged with junk.

This is the root cause and solution to 97% of fuel fill problems.

dbriceno · 07-12-2017, 01:17 AM

I couldn't access mine from the inside either. I drilled a hole through the middle of the vent from the outside. Worked like a charm. Start with a small bit and move up to 1/4" - 3/8". Every couple years you may need to run the drill bit through again. After drilling out the vent (I also needed to do it on my water vent) I noticed there was wood shavings stuck in the vent/line.

gregorys · 07-12-2017, 03:27 AM

What did you do not to protect water from entering the vent?
Scott

dbriceno · 07-12-2017, 01:17 PM

Actually, nothing. It would take some serious bad seas for water to enter through the small hole. For that matter, I didn't have much choice.

iantan · 07-17-2017, 07:51 AM

I replaced all mine on my 4600, when filling up with water I'd get a geyser splashing back at me and then once when it happened when filling diesel I decided to change the vents out.

In the 4600 2 are behind the settee and the other two on the port side are behind the fridge.

No issues after doing this.

shrew · 07-17-2017, 02:18 PM

Quote:

Originally Posted by gregorys

What did you do not to protect water from entering the vent?
Scott

The fuel vent line is looped with the loop going ABOVE the vent through hull. If water were to push into the through hull vent, it would not be able to climb the loop and dump into the tank. Instead it drains any water back out the vent again.

You can inside the vent from the exterior. The vent line needs to be located inside the hull. The hose reomved from the vent inside. The lock nut ont eh backside of the vent removed. Then the vent is pulled out from the outside.

You can pull the vent hose from teh top of the tank and try blowing into it. Usually the restriction is not complete.

Lonelouie · 01-28-2019, 06:30 PM

The port side vent is accessed behind the galley drawers. Don't know of anyone who ever got to the starboard vent. The drill through the existing vent is the only way I know. Water coming in has never been an issue....

Good luck!

gregorys · 01-28-2019, 06:45 PM

That is what I did. Drilled through it and the drill bit pulled out a bunch of grass/twiggs and I had air movement!!

iantan · 01-28-2019, 09:02 PM

As I said in an earlier post it’s easy to change the starboard vent, just a few screws and the seat back comes off in the saloon and the vent is then easily accessible. I swopped out the vent as not only was it blocked but the vent body had pitted and it looked a bit scruffy.