Fuel guage not working, help!!

[rickjordan]

The other day my car was acting like she was running low on fuel. I had it in the past where my fuel guage would stick briefly on full. So I thought my fuel guage my have died. Well she took 16 gallons, so the guage is dead, or it's the sending unit. So, my question is how due to troubleshoot this. If it's the sending unit, it's $181. If it's the guage, it's $430 (fuel, oil, water).
When I shut the car off, the fuel guage goes dead. As soon as I turn the key, it goes straight to indicate full. Also to add to this, for a long while now, my water temp. has not worked either. So either I am looking at two seperate sending units or that gauge cluster is faulty.
Any help would be appreciated.

[Knightrider966]

I would start with the sending unit for your fuel tank first! Remove the first aid kit from your rear parcel shelf and disconnect your sending unit. If you fuel guage goes to empty, the sender is most likely the culprit. But if not you still have a short somewhere that will have to be traced down and located. Same thing with the engine temp gauge. Also measure how much voltage you are getting at the point where the plug fits the sender to ground. this is a good place to start.

[toomany MBZ]

Which car? I have replaced the sending unit on a 123, around $65.00. I had an intermittent temp gauge problem on my, since sold, '85 300D, never did figure out.

[rickjordan]

This problem is on my 83 TD. Since it's a wagon I will have to take the cargo area floor apart to get to the sending unit. I checked the price of the sending unit through our host here and it is listed at $182.
With my water temp gauge, it stays on zilch, notta, zero. Would disconnecting it at the temp sensor change anything. What kind of voltage numbers should I be reading..
I hope like hell, for the water temp problem is a temp unit, that's listed at $23. If it's the gauge, I have to replace the whole gauge along with the oil press and fuel level and that's $430