fuel gauge

ghebbns · August 08, 2024, 02:17:48 PM

Hi all,
I noticed today that my fuel gauge is stuck fully to the left (empty). The tank is nearly full and it was working fine 2 days ago. It almost seems that the needle moves a little further left when I turn on the ignition.

I am working through the document I found on here (Fuel Gauge Test Procedure). I shorted the S and G terminals on the engine panel and the needle moved fully to the right. I am hoping someone on here might have a suggestion that does not require me to remove the aft cabin walls to get to the fuel tank (although I am almost positive I will have to do that.)

Any thoughts or suggestions?

Thanks

PS I should have added that all other gauges are working fine.

Ron Hill · August 08, 2024, 02:51:08 PM

ghe : You will only have to remove the port side aft panel to get at the fuel gage wiring connections.

A thought

AndyBC · August 08, 2024, 09:53:19 PM

Looks like you completed step 1 of 4 for the fuel gauge test procedure. Your gauge appears not to be the issue. You'll need to complete the other 3 steps to isolate the problem. I had this issue at the beginning of this season - I ended up replacing the fuel sender.

ghebbns · August 09, 2024, 04:58:22 AM

Thanks all. I have taken the port aft panel off and have access to the sender. I am having problems with step 2 of the trouble shooting procedure. It says to connect the pink (which in my case is purple) wire to a known ground. I am not sure where a nearby known ground is. Any suggestions?

I did try the next step (connect pink to ground on sender unit) and it tested ok. Does the fact that it passes step 3 mean that it would pass step 2? If so, then it is a bad sender.

Thanks,

Greg

scgunner · August 09, 2024, 05:47:40 AM

Greg,

I've had trouble twice with the fuel gauge both times it was the sending unit. Sending units are cheap and can be found at any chandlery.

Jim Hardesty · August 09, 2024, 06:20:21 AM

QuoteI've had trouble twice with the fuel gauge both times it was the sending unit. Sending units are cheap and can be found at any chandlery.

When I first bought Shamrock the sending unit was bad, replaced it with a generic one and it's been good for decades. Helps if you remove the existing one and take it with you when you buy the new one.
FWIW The hour meter is a much better and more accurate fuel gage. Log when the fuel is topped off, I also write it on a whiteboard at nav station, then it's hours run times your burn rate, mine is .7 gal/hour guessing yours is more like .5 gal/hour. Helps a lot with avoiding overfilling.
Jim

Ron Hill · August 09, 2024, 02:04:11 PM

ghe : Like Jim said use .5 gal/hr and the clock. You have an asymmetrical tank so the float cannot be accurate.

When you purchase a new sender it's the length that's critical. I believe that the MK II has a Beckson port in the floor of the port side lazarette - you'll have to remove that port to get the old sender out (because of length) and the new sender in!!

Welcome Aboard!!

A few thoughts

ghebbns · August 11, 2024, 02:09:04 PM

Thanks all for the help. I installed a new sender today and all seems to be good. As Ron said, there is an inspection port above the tank in the port lazerette that makes it much easier to get the old sender out and the new one in. The only real challenge was getting the screw holes lined up as they are not symmetrical. Took a couple of tries but think I am fine now.

Greg

scgunner · August 12, 2024, 07:35:00 AM

Ron,

The float is accurate when you realize it measures inches of fuel not gallons. Since there are fewer gallons in the bottom 25% of the tank than the top 25% it just means the needle on the gauge is going to move faster so it should be checked more often although I don't think too many people operate in that bottom quarter. You should probably consider the bottom quarter to be your reserve or time to find a fuel dock.

Ideally if you could start with a dry tank you could measure how many gallons it takes to reach the 1/4 mark then the 1/2 mark etc. The problem is nobody wants to run their tank dry so that most important bottom 1/4 can be accurately measured, it's also not a good idea with a diesel motor. So unless you prefer to do burn rate calculations probably best to keep a sharp eye on the gauge should you find yourself at the bottom side of the gauge.

Stu Jackson · August 12, 2024, 10:32:24 AM

Quote from: scgunner on August 12, 2024, 07:35:00 AM>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

So unless you prefer to do burn rate calculations probably best to keep a sharp eye on the gauge should you find yourself at the bottom side of the gauge.

Fuel consumption rates have been detailed for our engines since 1987. My M25 gets 0.5 gph, M35 use 1.0 gph.

You do NOT need to do your own calcs, others, many others, have done the work for you. Really. Please do so if you like, it's not hard to do, you simply have to keep track of hours between refills and gallons upon refills.

Fuel consumption is an important thing to know, gauge working or not. I find it's great to know how much you expect to need to refill to avoid spilling fuel all over the boat and into the water, because marine hoses are not like the ones at your gas station for your car, right?

Fuel Log 101

http://c34.org/bbs/index.php/topic,3841.msg21571.html#msg21571

Noah · August 12, 2024, 10:44:20 AM

For a bit of a cushion, I use an estimate of 3/4 gallons per hour for my M25XP engine.

Ron Hill · August 12, 2024, 02:43:29 PM

Guys : Most of us just go with .5 gal/hr I've used that with my M25XP and it's worked out just fine. I increased it to .6 gal/hr for the new M25xpB engine. I still use the clock rather than the gage!!

The gage is there and I just like to see that it's not pegged and stay at full or empty!!

A few thoughts