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a.s.elliott(at)cox.net
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 Posted: Fri Oct 10, 2008 5:27 pm Post subject: Problem with fuel level senders |
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I very carefully bent the fuel level sender arms in accordance with the instructions before fitting them to the factory fuel tanks on my 601XL with 15G tanks. I (duh?) did not calibrate the senders before putting the wings on the plane. I did check the resistance and both went from 73 to 10 ohms.
Unfortunately, I found today, when calibrating the senders for my EFIS, that the right tank sender doesn't register the 1st gallon and then maxes out at 8.5 gallons. The left tank starts right away, but maxes out at 6 gallons.
I am really not looking forward to trying to extract and adjust the bends in the float wires through the access hole, but I really don't want to have displays that only register 1/2 the fuel in the plane. (Even though it will be OK at low fuel levels.) I do have a fuel flow and totalizer function.
Anyway, I am looking to hear if anyone else has had this problem, and what the fix was? Maybe I installed them upside down?
Andy Elliott, Mesa, AZ
N601GE (registered)
601XL/TD, Corvair, finishing...
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ashleyw(at)gvtc.com
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| Posted: Fri Oct 10, 2008 6:07 pm Post subject: Problem with fuel level senders |
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Try calibrating the EFIS again.
The float does hit the top of the tank at about 10.8 gallons so it will be against the top of the tank above 10.8 and you cannot make it read correctly above that.
My Dynon 180 seems to be extremely accurate between 0 and 10.8 gallons.
I made a dip stick to check the fuel level on preflight. It takes about 7 gallons in the tank for it to be visible through the filler port.
Floyd Wilkes
601XL O-200
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bryanmmartin
Joined: 10 Jan 2006
Posts: 1018
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| Posted: Fri Oct 10, 2008 7:07 pm Post subject: Problem with fuel level senders |
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Because of the geometry of the fuel tanks and dihedral of the wings, a single float type sender can not read accurately at both full and empty. The important thing is that the gauges be accurate at the low end in order to indicate when you are getting short on fuel. The "fix" is to make a calibrated dipstick to tell you how much fuel you start out with for fuel planning purposes. The gauges will give you a reality check on your fuel planning. Once you get your fuel totalizer function calibrated, that will most likely become your primary fuel monitoring device with your dip stick to verify the starting point and the gauges as a reality check.
I have the 12 gallon tanks on my Zodiac. My fuel gauges can only read the last nine gallons or so in the tanks and my dip stick can only read the first nine gallons. If I have less than three gallons in the tank, the bottom of the tank directly below the filler cap is dry. With the 15 gallon tanks, you will probably have the same situation, the float will hit the top of the inboard end of the tank with about nine gallons in the tank and the bottom of the tank below the filler cap will be dry after about nine gallons are used.
On Oct 10, 2008, at 9:25 PM, Dr. Andrew Elliott wrote:
| Quote: | I very carefully bent the fuel level sender arms in accordance with the instructions before fitting them to the factory fuel tanks on my 601XL with 15G tanks. I (duh?) did not calibrate the senders before putting the wings on the plane. I did check the resistance and both went from 73 to 10 ohms.
Unfortunately, I found today, when calibrating the senders for my EFIS, that the right tank sender doesn't register the 1st gallon and then maxes out at 8.5 gallons. The left tank starts right away, but maxes out at 6 gallons.
I am really not looking forward to trying to extract and adjust the bends in the float wires through the access hole, but I really don't want to have displays that only register 1/2 the fuel in the plane. (Even though it will be OK at low fuel levels.) I do have a fuel flow and totalizer function.
Anyway, I am looking to hear if anyone else has had this problem, and what the fix was? Maybe I installed them upside down?
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Bryan Martin
N61BM, CH 601 XL,
RAM Subaru, Stratus redrive.
[quote][b]
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Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive. |
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jgswartout(at)gmail.com
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| Posted: Sat Oct 11, 2008 6:50 pm Post subject: Problem with fuel level senders |
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Andy,
I made the same mistake--not testing them with the gauge before sealing them into the four tanks on my CH-801. I installed them exactly according to the instructions, but the gauge (when I finally checked them) read full when full, but 1/12 full when they were empty--not a good situation. I had sealed them to the tank flanges with PR-2 instead of using the rubber gaskets because I had a clearance issue with the center terminal being too high and interfering with the access cover. It was quite a job to drill out the rivets in the access cover and not letting any of the rivets disappear into the wing bays, then heat the VDO sender to probably 250 degrees until the PR-2 softened enough to pry it loose. This of course melted the nylon part of the sender, destroying it. I replaced them with Stewart Warner 240-30 ohm senders, which have a bit lower profile, at about half the price of VDO's, but of course then I couldn't use the Mitchell gauges because they go from about 8 to 185 ohms. I replaced them with Chief gauges (2 1/4"), which are compatible with the Stewart Warner senders, at about $40 each for the two. And I tested them before final installation, using the gaskets this time. Total cost of my error: about 6 hours and $180.
If you made an access hole in the top skin of the wing over the senders--with nutplates or rivets--it's not that big a deal to pull them out and re-adjust them. It sounds to me like your float arms are too long (which doesn't allow the variable resistor to realize its full range) and the pivot pin is located above the vertical mid-point of the tank, so travel below the horizontal is adequate but travel above the horizontal is not.
John
On Fri, Oct 10, 2008 at 9:25 PM, Dr. Andrew Elliott <a.s.elliott(at)cox.net (a.s.elliott(at)cox.net)> wrote:
[quote] I very carefully bent the fuel level sender arms in accordance with the instructions before fitting them to the factory fuel tanks on my 601XL with 15G tanks. I (duh?) did not calibrate the senders before putting the wings on the plane. I did check the resistance and both went from 73 to 10 ohms.
Unfortunately, I found today, when calibrating the senders for my EFIS, that the right tank sender doesn't register the 1st gallon and then maxes out at 8.5 gallons. The left tank starts right away, but maxes out at 6 gallons.
I am really not looking forward to trying to extract and adjust the bends in the float wires through the access hole, but I really don't want to have displays that only register 1/2 the fuel in the plane. (Even though it will be OK at low fuel levels.) I do have a fuel flow and totalizer function.
Anyway, I am looking to hear if anyone else has had this problem, and what the fix was? Maybe I installed them upside down?
Andy Elliott, Mesa, AZ
N601GE (registered)
601XL/TD, Corvair, finishing...
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