Fuel Sending unit

[TR674]

Hi all

I had a rear end accident a few years ago and my fuel sender unit no longer works.

Is it worth the trouble to get it our of the tank and repair or just replace with new?

[RobH]

Well you have to take it out of the tank either way,  so it's probably worth seeing if you can fix it before buying new?

[TR674]

Thanks Rob. I should be more specific. Order a new one and replace, or are they serviceable, worth the time to fiddle with it?

[Martin50]

I have just taken my fuel sender out of the tank and then refitted to a new tank. Sender appears to be very simple but not sure what is actually inside the box that the float arm goes into. I’m guessing some sort of rheostat/ variable resister. If the fix is on the arm or float my view would be this is easy / achievable. If the problem is on the box my worry would be making a fix / adjustment that allowed some electrical spark. I don’t know enough on exactly how it works but it does have a “live” and an “earth” connection hence the worry. It comes off the voltage stabiliser so again I’m guessing low volts. Personally I would replace if you can get access to new parts - also a lot of work to re access the unit once boxed up if subsequently goes bad. Just some thoughts.

[RobH]

 They are repairable within reason but it depends on what the fault is (Catch 22!).  If the resistance-wire track has broken somewhere in the middle that is more of a problem. This description of repair is from the 'dark side' but is useful as a general process thought the unit is physically a bit different from the TR sender, which is more 'bent-tin' in construction:

http://mgaguru.com/mgtech/electric/et214.htm

 

It's a bit counter-intuitive but as long as there is liquid petrol present in the tank, the vapour concentration in the tank is much too rich to ignite,  so sparks are of no consequence.  That is how they were able to use such a simple device as a sliding electrical contact on a wound resistance.  Petrol vapour only burns over a range of about 1.4% to 7.6% mixture with air at ambient pressure which is far weaker than is present in a partially-filled petrol tank. 

That certainly isn't the case near the filler pipe when re-fuelling though, as petrol going into the tank displaces vapour which is diluted by the surrounding air and is almost certainly in the flammable range.  It is also why an empty fuel tank is hazardous too as remaining vapour will be in the dangerous range, making 'hot' repairs an explosive experience. 

 

Edited March 25, 2021 by RobH

[BlueTR3A-5EKT]

4 hours ago, TR674 said:

Hi all

I had a rear end accident a few years ago and my fuel sender unit no longer works.

Is it worth the trouble to get it our of the tank and repair or just replace with new?

Is the earth wire connected ok to sender and body earth?   If you have had someone poking about repairing they may have disturbed the connections.

Peter W

[Martin50]

Rob,

Appreciate the comment on flammable limits and petrol tank. Good point. Does give me some peace of mind. I must admit I have flitted between the dark side and light and enjoyed both marques. 

My background and career triggers my over abundance of caution - its been ingrained in me. 

[TR674]

Thanks all. Peter, I've checked connections and all seem O.K. I'll take the unit out when the fuel level is low. Before the accident the sender did occasionally stop working. Turning the ignition off and on usually rectified this. But after the rear shunt it is completely dead. 

[Mike C]

"Before the accident the sender did occasionally stop working."- Much as I hate replacing original parts I hate intermittent electrical faults more- if the fault is not obvious I'd replace it.