Oberdorfer update and stuck fuel guage

[Kent & Jane Overbeck]

   We just completed a 150 mile trip on the TN river from Chattanooga, upstream to Watts Bar Lake and back.  I mostly ran around 1800 RPM (slower boats were in the group)but jacked it up to 2500 for a while to see how the new pump would perform.  The lake water temp was in the high 80's.  The water temp in the engine stayed at a consistant 170 degrees.  I was a happy camper and am glad I made the change.
   I filled up with fuel (Fuel spilled out of the vent), proceeded to do the trip and noticed the fuel gauge seemed to be stuck on "full".  There was no change at the end of the trip even though I used about 9 gallons. 
Any explanations or suggestions would be appreciated.

We are relatively new to the group and would like to express our thanks to the guys that make this website possible.  It has been a great assistance in learning about our new, to us, boat.  We plan to depart Oct. 2012 for the Gulf Coast and then possibly do the Loop.

Kent

[Stu Jackson]

Kent,

Glad we could help.

Sounds like a dead sender in the fuel tank.  Pretty time consuming but simple once you get to the tank.  I'll look for some links for you.

Here are some:

http://c34.org/bbs/index.php/topic,439.0.html

http://c34.org/bbs/index.php/topic,4358.0.html

http://c34.org/bbs/index.php/topic,5134.0.html  (excuse my rant in this one! )

http://c34.org/bbs/index.php/topic,2824.0.html

I found these doing a search on "fuel sender" by Ron Hill, who has, along with others, "written the book" on this subject.  You'd find many more just doing a regular search on that phrase, but these have all you need.  

If you think the gauge is faulty based on the tests suggested in one of these links, then try that first before you dive into the aft cabin, but it's usually the senders.

Most reports are of gauges that stay at zero, rather than full.  I personally haven't heard of that failure at the gauge.  It could well be a stuck float as noted on one of the links.  Mine's been showing empty for 12 years.  It's good for you to have known about your fuel consumption.

All the best, sounds like you have a great plan and a lot to look forward to.

[John Sheehan]

Kent,
This spring I also had the experience of filling my fuel tank and then the gauge staying at full.  Went through the various tests and they showed the sender to be the problem.  Changed out the sender and the gauge still showed full.  Then got a new gauge from Seaward Products (part number 1853.1 - $61.52 including freight and taxes) and that solved my problem.  As a side note, for some reason I had been getting eratic tack readings and changing out the gauge solved that problem.  I had checked out all the usual suspects such as bad connections and grounds and could not find anything wrong.  When I hooked a sender directly to the old gauge at the panel and moved the float, the gauge would travel from "F" to above "F".  You would suspect the sender as being the problem as Stu suggested but it is not always the case.  My old sender would show some lack of smoothness with an ohm meter so it was also getting tired.

Hope this helps.

John

[Ron Hill]

Kent : Interesting that you have an Oberdoffer on a MK II?  Confirm that you have a M35BC engine!

On the fuel gage, remember they are like light bulbs - some last for years and other "blow" sooner.  As Stu mentioned most gages go to "0" when the sender goes out.  Try my checks and make sure it's the gage before ordering a new one.
 
On the fuel gage also remember the fuel tank is asymmetrical (larger at the top than at the bottom) so it will NEVER measure accurately on the gage!!
 
What you need to do is check your fuel consumption against time.  If you have an M25XP you could figure .5 gal/hr.  If you have a M35 BC engine try using .65 gal/hr as a starter and then refine it (RPM makes a big difference)

A few thoughts

[Stu Jackson]

Kent : Interesting that you have an Oberdorfer on a MK II?  Confirm that you have a M35BC engine!

As I recall, Kent did a fine writeup of his switch to the Oberdorfer pump from the Sherwood OEM.

Here it is:  http://c34.org/bbs/index.php/topic,6100.msg39068.html#msg39068

[Kent & Jane Overbeck]

Thanks Guys for all the info.  I guess I have a new project!!
Ron, I used right at .4 gal/hr on this trip running 1600-1800 rpm. This pushed me along around 5.5 - 6MPH.  Overall I figured I got 14 MPG.

Kent

[BillG]

look in the tech wiki under"Fuel" and then "Gauges"
you will find the test procedures from seaward located there

[Kent & Jane Overbeck]

Thanks Bill

[Ron Hill]

Kent : As a suggestion, you really need to calculate fuel consumed against time to be meaningfull.
 
A head/tail wind or current movement will change your time/distance fuel consumption.  Where as time against fuel consumption remains constant  - if the same engine RPM is used.

A thought.   

[Kent & Jane Overbeck]

Ron,  Thanks for the input.  However, I took the total hours of the trip ( upstream and down)
, and the fuel it took to top off at the end of the trip to arrive at my figures.

Kent

[Stu Jackson]

Thanks Guys for all the info.  I guess I have a new project!!
Ron, I used right at .4 gal/hr on this trip running 1600-1800 rpm. This pushed me along around 5.5 - 6MPH.  Overall I figured I got 14 MPG.

Let's not confuse Kent's reading of gallons per hour with his 14 MPG.  He did them both.  And we all know MPG is just a funny aside...

My 0.463 gallons per hour on our vintage M25 engine is based on the spreadsheet I've shared and  includes the average of ALL kinds of motoring since it is what happens from fuel refill to fuel refill, using whatever RPMs I'd been doing between refills.  FWIW, we usually motor at 2500 RPM, but sometimes I go slower (into the slip?!?) or faster (just to see how clean the bottom is!).

That's why it's called an average.

Spending time figuring the difference between running at 1800 RPM or 2500 RPM or 3000 RPM is kinda waste of time.  Unless you like doing that kinda stuff...

[Ron Hill]

Guys : I forgot to mention that if you haven't done it - take a stop watch and check the watches time against your hour meter on the engine tach!   
You might find that Teleflex makes great instruments, but not so great a time piece ! 

A thought