Friday, July 14, 2023

Fuel Gauge Failure

 Our Fuel Gauge Failed 

On the last couple of trips, our Fuel Gauge became erratic. I would drop from showing 3/4 full to Empty or some other significant change in reading. I would normally put that down to a bad wiring connection however, I rebuilt the entire engine control panel in 2016 and I know I did a really good job ensuring all of the connections were solid. ( Crimped ! ) But still worth checking out the wiring.

The engine instruments are all on a common power supply and a common earth and the wires are connected to the instruments via ring terminals and nut and bolt attachments. All were secure. The other earth on the fuel gauge system is at the fuel tank itself, but that was solid too and using a Multimeter the resistance was less than 1Ω.

Next suspect was the Sender.

It's a pretty simple unit. The float opens/closes a series of reed switches as it moves up or down the shaft of the sender.

That changes the resistance of the sender and the gauge displays the fuel level dependent upon the resistance.

The tank is located on the Port side aft, Access is by removing the plywood bulkhead on the port side of the Aft Berth. 
I removed the sender from the tank and we tested it by moving the float up and down, ah ha! it would intermittently operate correctly, so I have to consider that one or more of the read switches is faulty.

Disconnecting the sender from the system and testing with a multimeter confirmed it was the sender.

I had ordered a replacement Sender and Gauge so that I was prepared if it turned out to be either of them.

The new sender did not work with the old gauge but the new gauge was the same size so it was a reasonably easy swap out.

The Gauge is not just a simple voltage meter!
When the power is applied, the gauge lights up to the selected background color choice then the needle moves from E to F, back to E and then it moves to indicate the current fuel level. It does this very smoothly. I found this a really nice feature, the needle moving in that way indicates that the system is working.

Once the system was wired in, all that remained was to replace the engine control panel, sealing the edges with Butyl tape - that makes it easy to remove if needed. Then secure the wiring at the tank end and replace the wooden bulkhead.

Most of the time taken was in testing the various components and wiring.

Kit details: 100TECH Boat Fuel Sending Unit with Gauge 11"(280mm) 
SUS316 Stainless Steel Marine Fuel Level Sender Sensor 240-33ohm

I opted for the 11" sender rather than the 12" that would still fit, if the gauge reads empty, then we have at least 1.5" of fuel in the tank. Consider it a reserve.

I purchased the kit from Amazon $69.

The only near hiccup was that the float on the new sender is slightly wider ( Dia. ) than the old unit but it fit snuggly. The kit included a new gasket, screws and butt connectors.

Just an FYI, we never fill the tank to Full - I really do not want to risk fuel overflow so when the gauge reads over 3/4 full we stop filling! We always carry at least 2 x 6 gallon fuel cans. So our normal capacity is 23 gallons in the tank plus up to 24 gallons in cans on deck. That gives us about 45 gallons and at 1 gallon per hour, we're good for 45 hours of motoring. 

One last thing: When we are motoring, we have a routine of 'checking the heartbeat'. About every 15 minutes, we'll check the engine status:- Look over the stern to ensure water is pumping out the exhaust, Check the engine Temperature and Fuel level.  If I'm in the cabin and Peggy at the helm, all I need do is tap my wrist with two fingers and Pegs gets the message then checks the Heartbeat.  

See you on the water.

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