356B T5 Fuel sender unit issues

356 Porsche-related discussions and questions.
Post Reply
Message
Author
User avatar
Ian William Stockwell
356 Fan
Posts: 50
Joined: Sat Feb 07, 2015 2:36 pm
Tag: 356 not just a number
Location: Andover, Hampshire, UK

356B T5 Fuel sender unit issues

#1 Post by Ian William Stockwell » Sun Apr 15, 2018 1:52 pm

I have recently fitted a new fuel tank, made by Dansk, and rubber fuel lines in the car and swapped the sender unit to the new tank.
I filled up with petrol, about 10 litres and went for a drive to check all was ok.
As usual the fuel gauge needle was fluctuating wildly, but no smell of fuel so all seemed ok until the car started stuttering as if firing on 2 cylinders.
In the blink of an eye I noticed that the fuel gauge needle was not moving but stuck at about one third full so switched the tank onto reserve and headed for the nearest petrol station.
When I got there I looked in the tank and the sender unit was stuck to the bottom of the tank, I released it and filled up with an extra 30 litres.
When I got home and investigated further. I found I could push the sender unit to the bottom of the tank and it stayed there as if magnetised, it is not absorbing fuel.
I removed the unit and rubbed the float smooth with sand paper and placed it back in the tank but once again I could press it to the bottom of the tank and it would stick, when I say press there was no pressure at all.
I then played around bending the wire between the sender and the float so that if it sticks, the needle on the gauge shows empty.
When the tank has more than 20 litres, about 2 gallons, then the needle fluctuates as normal without sticking.
Does anybody know what is happening?
Porsche engine DNA is Flat Four, Flat Six & Flat Twelve NOT Flat Battery Packs :(

Dick Weiss
356 Fan
Posts: 2997
Joined: Sun Apr 20, 2008 12:54 am

Re: 356B T5 Fuel sender unit issues

#2 Post by Dick Weiss » Sun Apr 15, 2018 2:42 pm

Ian,

Most likely your float arm is too straight and not having an upward bend on it, it'll tend to stick like you said.
Changing the tank (and hope it's bottom is the same shape as original), the proper way to get a gage reading is to add 5-gallons
and check the gage reading if it reads 1/2 full; If not--pending if it reads higher or lower, reach in (or remove the sender) to bend
the arm upward to read higher toward 1/2 or lower to read 1/2. NOTE: The arm should have its bend in the middle of its length and the float should not leak--is it plastic or a cork material? You didn't say which tank you have--A/B or C? Hope it isn't a bottom sender on a T6B.

BTW, I didn't ask if the sender's pivot action is not sloppy; Have you checked its action and readout? Slop of the pivot may get stuck, too.
Also, if an A/B tank exists, the fuel reading will be kinda erratic due to not having baffles like the later tanks.

Dick

User avatar
Ian William Stockwell
356 Fan
Posts: 50
Joined: Sat Feb 07, 2015 2:36 pm
Tag: 356 not just a number
Location: Andover, Hampshire, UK

Re: 356B T5 Fuel sender unit issues

#3 Post by Ian William Stockwell » Sun Apr 15, 2018 3:27 pm

Hello Dick

The car is a B T5 so the tank is a B tank.
The float is cork.
My concern is that I removed the sender from one tank and fitted to the replacement tank without damaging it and now it sticks.
I purchased the tank from a very reputable Porsche specialist and to all intensive purposes is the same as the original, it is manufactured by Dansk, the only difference being that it does not have the brass drain plug like the original tank.
As regards the slopping fuel, a neighbour fixed up some resistors to stop the needle flicking about but this was not refitted so I must get around to buying the proper fix.

Ian
Porsche engine DNA is Flat Four, Flat Six & Flat Twelve NOT Flat Battery Packs :(

User avatar
Vic Skirmants
356 Registry Member
Posts: 6759
Joined: Tue Oct 27, 2009 5:02 pm
Location: SE Michigan

Re: 356B T5 Fuel sender unit issues

#4 Post by Vic Skirmants » Sun Apr 15, 2018 6:13 pm

BRASS DRAIN PLUG?? Never seen one of those.

User avatar
Ian William Stockwell
356 Fan
Posts: 50
Joined: Sat Feb 07, 2015 2:36 pm
Tag: 356 not just a number
Location: Andover, Hampshire, UK

Re: 356B T5 Fuel sender unit issues

#5 Post by Ian William Stockwell » Mon Apr 16, 2018 1:51 pm

Hello Vic

Yes a brass drain plug but it is toward the top of the tank on the right at the back. see attached photo.
The tank has a plate behind the breather pipe stamped with the word "Schmid", I guess this is the manufacturer, is it an original tank?

Ian
Attachments
20180416_183822_resized.jpg
Porsche engine DNA is Flat Four, Flat Six & Flat Twelve NOT Flat Battery Packs :(

User avatar
Al Zim
356 Fan
Posts: 1691
Joined: Fri Mar 14, 2008 9:14 pm
Location: FT.WORTH/DALLAS TEXAS

Re: 356B T5 Fuel sender unit issues

#6 Post by Al Zim » Mon Apr 16, 2018 8:13 pm

I would replace the cork gasket with a rubber one, this is available on the 911 gas tank and oil tank sending unit. Zim's sells a device that stops the erratic movement of the fuel gauge needle. It does not require any cutting or soldering of wires to install. But you have to be on your back under the dash. al zim Zim's Autotechnik 800.356.2964
 

User avatar
Ian William Stockwell
356 Fan
Posts: 50
Joined: Sat Feb 07, 2015 2:36 pm
Tag: 356 not just a number
Location: Andover, Hampshire, UK

Re: 356B T5 Fuel sender unit issues

#7 Post by Ian William Stockwell » Tue Apr 17, 2018 2:42 am

Hi Al

Thanks for that. We can get these devices in the UK and that is what I intend to do.
Do you know why the sender cork float should stick to the bottom of the tank after simply swapping from the old tank to the new one?

Ian
Porsche engine DNA is Flat Four, Flat Six & Flat Twelve NOT Flat Battery Packs :(

User avatar
Ian William Stockwell
356 Fan
Posts: 50
Joined: Sat Feb 07, 2015 2:36 pm
Tag: 356 not just a number
Location: Andover, Hampshire, UK

Re: 356B T5 Fuel sender unit issues

#8 Post by Ian William Stockwell » Tue Apr 17, 2018 2:43 am

Hi Al

Forgot to mention, that the new gasket is the rubber one.

Ian
Porsche engine DNA is Flat Four, Flat Six & Flat Twelve NOT Flat Battery Packs :(

Post Reply