325 - Diesel tank Sealing ring for topplate

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Diesel tank Sealing ring for topplate

Printed From: myHanse.com
Category: Hints & Tips
Forum Name: 325
Forum Description: 352 Hints, Tips and News
URL: https://www.myhanse.com/forum_posts.asp?TID=12662
Printed Date: 26 March 2026 at 23:37
Software Version: Web Wiz Forums 12.06 - https://www.webwizforums.com

Topic: Diesel tank Sealing ring for topplate

Posted By: Poul J
Subject: Diesel tank Sealing ring for topplate
Date Posted: 12 April 2021 at 13:44

I have a leak at the topplate on the diesel tank. It look like that diesel oil is leaking from the topplate sealing ring.

Does anyone know where i can buy a sealing ring belonging til the topplate on the dieseltank?.

At hanse.boatoon.com i can buy the topplate including the sealing ring (TMK0065), but not the sealing ring alone.

Attached a photo of the dieseltank.

Regards

Poul Jørgensen uploads/6915/Hanse_325_dieseltank.pdf" rel="nofollow - uploads/6915/Hanse_325_dieseltank.pdf

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Poul Jørgensen

Replies:

Posted By: 32mike
Date Posted: 12 April 2021 at 21:11

Hello Paul,

I don’t have an answer for you but I was hoping to tag on a question on the same topic, almost , if you don’t mind.

I was wondering if the orientation of the tank sensor matters. Does it matter how it is rotated in the opening?

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Mike
S/V Dulces Sueños
458 #087
Tampa, FL

Posted By: Captain Cook
Date Posted: 12 April 2021 at 21:54

When mounting the topplate it is important, that the bolts are tightened crosswise, like 1-6-3-8-4-9-5-10-7-2. Tighten until the bolts are firm, and then do it all over again with a torque wrench. Clean the gasket before mounting, and apply a thin film of Vaseline on it.

My topplate has been off for inspection some 6-7 times the last 15 years. Still same gasket.

:Kjeld

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Freya H400 #27 (2006),2-cabin, 40HP 3JH4E, 3-blade Flexofold, Aries LiftUp Windvane, Exturn 300, Jefa DD1,Simrad NX40,Icom M603(VHF)+M802(SSB)

Posted By: kipwrite
Date Posted: 13 April 2021 at 02:15

So, I had a persistent leak at the top of my fuel tank, and was convinced it was the result of a slight warping of the tank at the sending unit. After replacing the gasket and snugging things up, twice, the leak promptly reappeared, twice.

Turned out that when the tank was full, it swelled at the top and bulged upward, and this created a small crack in the white plastic fitting at the fuel pick up line, where it was pressed against the steel tank retaining plate just above the tank.

Fuel would then collect at the sending unit indent, leading to the erroneous conclusion that the sending unit gasket was the source of the leak.

I’ve since replaced the cracked plastic fitting and installed a wooden wedge between the top of the tank and the steel retaining plate, so as the tank bulges at the top when full, there remains clearance for these fragile plastic fuel line fittings that are easily cracked.

Took me awhile to figure this out but no more fuel leaks. I can’t imagine that my boat is the only Hanse with this issue, and I hope this helps someone chasing a persistent leak at the top of a fuel tank.

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Kipwrite

Posted By: Fendant
Date Posted: 13 April 2021 at 04:04

Thanks for this hint concerning the full tank. I had this when we took the boat over and filled the diesel tank for the 1st time. Although the pump stopped we had about 2-3 lts of Diesel in the bilge under the tank with the resulting horrible smell.

Decision: never filled the tank over 90% and marked my calibration curve accordingly as I suspected a leak in the filler pipe or the vent.

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Frank

Posted By: Fendant
Date Posted: 13 April 2021 at 04:08

Mike,

you are right. The notoriously unreliable cheapo crappy automotive sensor must be mounted in a direction where the lever can move freely. I recommend to replace it by a magnetic sliding sensor 0-180 Ohm. They are a drop-in interchangeable.

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Frank

Posted By: Poul J
Date Posted: 13 April 2021 at 07:23

Hi Keld

Thanks for your reply.

I will first disassemble the top plate and inspect the gasket. Perhaps it is damaged due to improper tightening of the bolts by the previous owner or the Hanse yard. If the gasket is broken I have to buy the whole set as I apparently can not buy the gasket alone.

It's a bit challenging as I'll fill up the diesel tank completely due to the winter-season. :-). Perhaps this is the reason why the defect became visible, while the top of the diseltank is at a higher level than the topplate.

I will use Vaseline when I reassemble.

Regards Poul

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Poul Jørgensen

Posted By: 350Bob
Date Posted: 13 April 2021 at 12:16

Hi Poul,

I will confess that I have never opened up the diesel tank on our 350 so don’t know what material Hanse are using for gaskets, but if you do an internet search on “gasket material for diesel” you will find results for both paper gaskets or nitrile rubber. I would certainly try making your own using a similar material to the original before buying a complete new fitting. Using the original as a template this should be fairly easy.

Good luck

Bob

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H350 #205

Posted By: Poul J
Date Posted: 14 April 2021 at 07:17

Hi Bob

Thanks for your reply.

I have now pumped excess diesel away, loosened and checked the gasket. The gasket is OK.

Therefore, I just tightened the bolts again in the right way. Unfortunately, I can´t test if the leak is gone as the diesel level is now just below top plate height.

Now I´m going to cruise with this status until the diesel tank is half full. On that point I will give the gasket a little liquid gasket (that can withstands diesel) - also around the bolts.

Poul J

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Poul Jørgensen