Fuel Gauges

Post by **GAHorn** » Mon Mar 13, 2006 4:35 pm

The original gauges were made by Scott. Rochester bought the product line. They are located in Dallas. I've talked to them extensively about this over the years. Their gauges (the ones re-sold by Spruce) are what are in my airplane, after having been modified by the installer. They work perfectly and look identical to the originals. (They may have been easier to install while the airplane was disassembled for rebuild, or while the tanks were removed.)

Rochester still makes the gauges for Cessna, for replacement use in a 170's. They are expensive when acquired thru Cessna, but they are the genuine product, and not all that out-of-line when compared to other, current prduction aircraft gauge prices. (Superceded PN is: 7083-00022 and costs about $260. Hill Aircraft: 1-800-998-7832 )

Rochester will not sell you the -00022 gauge directly, as they are committed to providing that exact model only to Cessna. They are basically made up from the Rochester 7083-5H76 gauge, and the 5-00894 Dial. The gauges purchased thru Spruce and others are a minor variant of the Rochester 7000 Series gauge (a 7080 actually), which can be used in both the vertical or horizontal positions.
The last number I had for Rochester was 800-982-0030 or 214-241-2161. They are insistent they will not sell direct for contractural and liability reasons. Perhaps thru them you might locate a local dealer who might be able to provide overhaul for your gauges, but that's only an idea.

N170CT · Post by **N170CT** » Tue Mar 14, 2006 3:41 pm

George....confusion reigns supreme

....I am simply incredulous

. The "original" fuel tank guages in my airplane are much different from the one I recently purchased from Spruce. For openers, the original had a red zone which is marked "No Take Off", the Spruce replacement has no red marks at all. This ain't identical. Second, the original guage appears to be one piece with a cork float on a thinner rod. The replacement guage is in two pieces apparently with a magnetic drive/coupling and a different float on a thicker rod. And as I explained in an earlier post on this thread, the gear ratios are different requiring a shorter float rod on the replacement guage.
As an engineer, I cannot understand how these two guages could possibly have even similar part numbers. Shucks..I would be amazed if they are manufactured by the same company. Where am I going wrong here

??

N5474C · Post by **N5474C** » Tue Mar 14, 2006 9:27 pm

FWIW...

I purchased / installed the Rochester gauges from A/C Spruce. They were marked with the red "No Take Off" zone. The rod for the float needed to be shortened and the correct bend made but otherwise they were a perfect fit and still work great nearly three years later.

Bruce

Post by **Bruce Fenstermacher** » Wed Mar 15, 2006 1:17 am

Remember the fuel gauges DO NOT need to be marked with the no take off range.

Post by **GAHorn** » Thu Mar 16, 2006 4:20 am

N170CT wrote:George....confusion reigns supreme ....I am simply incredulous . The "original" fuel tank guages in my airplane are much different from the one I recently purchased from Spruce. For openers, the original had a red zone which is marked "No Take Off", the Spruce replacement has no red marks at all. This ain't identical. Second, the original guage appears to be one piece with a cork float on a thinner rod. The replacement guage is in two pieces apparently with a magnetic drive/coupling and a different float on a thicker rod. And as I explained in an earlier post on this thread, the gear ratios are different requiring a shorter float rod on the replacement guage.
As an engineer, I cannot understand how these two guages could possibly have even similar part numbers. Shucks..I would be amazed if they are manufactured by the same company. Where am I going wrong here ??

Chuck, Chuck, Bo-Buck, Bananna Nanna Fanna Fo.... Uh... Charlie! ...,

... there's a lot of assumptions being made here. You don't specify which gauge you have acquired from Spruce. They sell a lot of gauges. As you can see, Bruce and myself, and several others have not had the problem you are experiencing. We must not be talking about the same product for the same airplanes.

Have you called Rochester yet?
If you'll PM or email me your fax number, I'll send you the Rochester info sheet I have on this.

N170CT · Post by **N170CT** » Thu Mar 16, 2006 3:40 pm

George,
You are right, I think. Immediately after posting the last message, it dawned on me that we are describing different fuel guages

. Unforturnately, I am in Virginia

and airplane/fuel guages are on the left coast in So. Cal so I cannot reach out and touch either. But I will check this out as soon as I can get back there.

And, YES, I do embarrass myself often.

Thanks for all your and others comments and help. chuck

Post by **GAHorn** » Thu Mar 16, 2006 4:05 pm

N170CT wrote:George, ...
And, YES, I do embarrass myself often.

... chuck

Hey! I claim the title "Most Often Embarrassed in the Forums!"

lowNslow · Post by **lowNslow** » Thu Mar 16, 2006 5:21 pm

The big difference with the new gauge is the gear ratio. The old gauge went thru a much smaller arc to achieve full range so you could put the rod straight in. The new rod requires a larger arc so requires a much short arm to achieve full range within the confines of the tank. I measured the depth of the tank (can't remember what it was, but 8" comes to mind) and played around with it alot before cutting the rod. I also bent the rod tip so the float sits 90 degrees to the rod to achieve full range. It takes a little monkeying around and a little cussing to get in, but it will go in. They look original and work great.

Post by **Bruce Fenstermacher** » Thu Mar 16, 2006 5:34 pm

If I recall correctly a fuel gauge in an aircraft only has to be accurate when the tank is empty. In other words a gage can read full when the tanks are not, they can read half full when there is more than half left but when the tank is empty the gage needs to read empty.

So if this is the case if one was adjusting a new gauge and mechanisim you would shot for accuracy at emtpy and best you can in other positions.

George do you know anything about this?

lowNslow · Post by **lowNslow** » Thu Mar 16, 2006 6:32 pm

From CAR_PART3:

Â§ 3.672 Fuel quantity indicator. Means
shall be provided to indicate to the flight
personnel the quantity of fuel in each tank during
flight. Tanks, the outlets and air spaces of which
are interconnected, may be considered as one
tank and need not be provided with separate
indicators. Exposed sight gauges shall be so
installed and guarded as to preclude the
possibility of breakage or damage. Fuel quantity
indicators shall be calibrated to read zero during
level flight when the quantity of fuel remaining in
the tank is equal to the unusable fuel supply as
defined by Â§ 3.437.

Since part of the requirement is to " indicate to the flight
personnel the quantity of fuel in each tank during
flight" I don't think having it show 1/2 full when it is actually full meets the requirement.

cessna170bdriver · Post by **cessna170bdriver** » Thu Mar 16, 2006 7:06 pm

N9149A wrote:If I recall correctly a fuel gauge in an aircraft only has to be accurate when the tank is empty.

So I guess I was legally OK to fly my airplane after that time some residual mogas evaporated and the residue glued the float to the bottom of the tank.

Post by **Bruce Fenstermacher** » Thu Mar 16, 2006 9:58 pm

Karl
I see this as agray area. Imagine that a gray area regulation. The only thing the CAR definitly says is

Fuel quantity
indicators shall be calibrated to read zero during
level flight when the quantity of fuel remaining in
the tank is equal to the unusable fuel supply as
defined by Â§ 3.437.

It does not specify how accurate they need to be in any other phase of flight or level of fuel.

lowNslow · Post by **lowNslow** » Thu Mar 16, 2006 10:06 pm

Weellllll, I'll let you stretch that point with the FAA. It does say "indicate to the flight personnel THE quantity of fuel quanity" not ANY quanity. As Miles so slyly points out, if your point is true, the gauge could just always read zero and still meet the criteria.

Post by **Bruce Fenstermacher** » Fri Mar 17, 2006 1:02 am

Karl
I suppose you and Miles have me there. I can only tell you what my experience has been when talking to maintenance people.

From time to time I've had aircraft like the one I fly now which doesn't have very accurate gages. When I have asked to have them calibrated they tell me they only have to read 0 when the usable fuel is gone.

Know assuming your gages in your 170 do indicate full at the instant they actually are and not before and they tell you when they are empty and not before, why don't you tell me how actuate they are in the middle while they are bouncing from 3/4 to 1/4. Would that be a 1/2?

In my experience of flying about 10 different small GA type aircraft and about 5 different helicopters only 2 helicopters the UH-1H and the Astar come close to having accurate gages all the time. And then only when the electrical system is running and adjusted as specified. Other wise they read high or low depending on the voltage.

lowNslow · Post by **lowNslow** » Fri Mar 17, 2006 1:29 am

N9149A wrote:Karl
Know assuming your gages in your 170 do indicate full at the instant they actually are and not before and they tell you when they are empty and not before, why don't you tell me how actuate they are in the middle while they are bouncing from 3/4 to 1/4. Would that be a 1/2?

In my experience of flying about 10 different small GA type aircraft and about 5 different helicopters only 2 helicopters the UH-1H and the Astar come close to having accurate gages all the time. And then only when the electrical system is running and adjusted as specified. Other wise they read high or low depending on the voltage.

I agree with ya here. When the gauges are bouncing around they aren't that accurate, but judging it against tach time, they are darn close when there settled down. I have always used small aircraft gauges as rough estimates and always backup with the tach time.