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MG MGB Technical - Early fuel tank sender unit. Problem or not?t

Can anyone help on this one? I'm in the process of changing to a stainless steel fuel tank on my 1964 Mk1 Roadster. The Smith's fuel sender unit, works perfectly and has been removed from the old tank ready for re-use in the new one. A general inspection of the sender unit revealed that the workings (presumably a winding and wiper arrangement) sit inside the tank and are shrouded in a soft aluminium cover. At each end only, this cover is lightly pinched to the outer body of the unit. I believe this unit to be the original, as over a period of time this shroud has become thin and in some places perforated, a number of holes being clearly visible. The orientation of the unit when installed, would indicate that when the tank contains a large quantity of fuel the sender unit is in fact submersed and fuel which is therefore entering the workings. The question is are these perforations a problem because the construction of the unit would suggest that fuel has always been capable of entering the workings through the edges of the lightly fitting shroud any way, as well as via the float spindle? Can this be correct? I would appreciate any ones thoughts.
Thanks
Chris
Chris Woodfield

Further to my original posting, in order to aid identification, I have done some more investigation. The Haynes maintenance manual shows an image of the type of sender unit that I have. They refer to the type of sender unit as 'Early Modified' and link it to the early design of strap-on tank (the same as on my car).

Any comments gratefully received.
Chris
Chris Woodfield

Chris, it is normal for the unit to have fuel in it's innards. Despite all evidence to the contrary in movies and TV shows, it is next to impossible for the fuel tank to explode under normal conditions.

Tony
Tony Oliver

Hello Tony
Many thanks for your very welcome response. I have never come across the phenomenon of electrics in fuel before. I guess it doesn't matter how much you think you know about your classic car, how much experience you have or how many different jobs you undertake to keep it running properly, there is always something new to learn. Thanks for your help.
Chris
Chris Woodfield

Fuel can only burn when there is an adequate supply of air available, the mixture in the tank is far too 'rich' to explode. I well remember starting a bonfire with petrol (I know I know), standing back and seeing a flame on the open filler neck - it was only burning outside where there was sufficient air, not inside (thank goodness).
PaulH Solihull

Paul
Thanks for the info. I guess its pretty obvious really but it had me scratching the old cranium for a while. I suspect that your impression of a flame thrower was an experience you will not want to repeat too often.
Chris
Chris Woodfield

I have always wondered about the sender unit in my early car. I recently bought one of those new replacements to see how it goes and the guage is now more stable.
Chris, how is the gear lever going?
Ian Buckley

Ian, the moving gauge is part of the measurement! If the gauge suddenly shows empty on right hand bends, the tank is half full. If it shows part full on left hand bends it's three quarters full. If it doesn't move at all, it's time to look for a petrol station....

So much more informative than the modern gauges which have are fiddled to give you peace of mind. E.g. temperature gauges showing the same temperature over a broad range.

Mike
Mike

Mike, I read you... hahaha.

True of course. I must admit I zero the tripmeter every time I fill the tank to be sure I don't run out. Oh for a 12 gallon tank. It would be a lot more practicable but I won't make the change.
Ian Buckley

*Are* the gauges fiddled with? Or is it simply that cooling is so much more efficient and stable? Some years ago I saw an RV8 idling, and the cooling fan going on and off every few seconds, with the temp gauge absolutely stable. Very different from my V8 which can vary between N and half-way to H as the fans come on and off. I commented on it and was told that the temp gauge is run through the ECU, which does fiddle with the reading, only letting higher readings through when it's time to do something about it (i.e. little more than a warning light). I took that at face-value, my Celica and ZS were and are the same, but the schematics show no conenction with the ECU. Has anyone actually monitored the voltage on the wire from sender to gauge, to see if that *does* go up and down while the gauge stays still?
PaulH Solihull

The gauges are fiddled, and I verified this on my Mazdas, as the real temp did not match the gauge readings. I thought it was ECU controlled, and it may be in some cases. There are multiple temp sensors, and at least some of them do go through the ECU; I got to the point that I couldn't figure out more without knowing exactly what the ECU is doing. But, evidently there is a way of doing it in the gauge - and ways to fix it.

Link here but you need to sign up for the forum:
http://www.clubprotege.com/forum/showthread.php?54637-how-to-linear-water-temp-gauge&p=717855

This should be the source for this (might have to sign up here too): http://www.miataforumz.com/showthread.php?t=245

And more: http://www.tyrion.net/miata/tempgauge/90-93-MTGLP.mht

Most important Q I think is does the ECU set off disaster signals when things go wrong that you can't see because the gauge is lying?
I know Jaguar did similar on oil pressure, to keep owners from complaining about low hot idle pressure. Always assumed the ECU was keeping track of the real situation by comparing temperature, engine speed, and pressure, but maybe not.

FRM
FR Millmore

This thread was discussed between 04/09/2011 and 16/09/2011

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