Fuel flow

[N4027v]

Just completed my first cross country flight with instructor in my 1948 170 and had a fuel flow issue. A little background
First. Last night I drained the fuel from the left tank to replace the drain cock that had been leaking but even with fuel selector in off position, the fuel continued to transfer from the right tank. I drained both tanks, replaced both drain cocks and both fuel cap gaskets, filled both tanks and returned selector to both in prep for today's flight. My plane has the vent in center of fuselage for both tanks. After through preflight inspection, we departed Winona MS for Vicksburg Tullulah LA. About 3/4 the way I noticed the left tank on half and right tank full. After landing we checked the caps and the vent both seemed fine. I blew into the vent while instructor held hand over fuel opening and he confirmed tank was venting. I switched the selector from both to off and after about 30 mins the tanks equalized. Back to both and after lengthy run up we took off back to winona. When at safe altitude and over airport, we switched to right only tank but continued to draw from left tank and maybe some from right but clearly used more from left. Any suggestions on what to check much appreciated.

[N4027v]

I'm not sure that there is flow to the carb in the off position, only sure that there is flow between right and left tanks in the off position. I will check Gascolator in off position. Thanks.

[Waterboy]

I believe the earlier 170's have a different fuel valve. My A model has the brass valve. When I park on a side slope and turn the fuel off it still drains from the up hill tank to the down hill. When checked at the carburetor, at annual, the fuel does turn off when its in the off position. My valve when in the both position draws fuel evenly from both tanks. I do not have an exploded view of the valve. Someone else here might be able to fill us in if this is normal for the early model fuel valves.

Ken

[sfarringer]

The 48 does have a different (simpler) valve design than Aryana shows.

Left and right tanks are interconnected when the valve is either on "Both" or "Off".
But there should not be any interconnection when the valve is either on "Left" or "Right".

[N4027v]

Went back to hanger to check a few things:
Selector in off position - no flow at Gascolator.
Selector in right, left and both - flow at Gascolator.

[N4027v]

Selector

[Kurt Aichele]

Do you have (2) 12.5 gallon tanks in each wing?

[Bruce Fenstermacher]

First it must be understood we have 3 models of aircraft, two completely different fuel storage systems and 2 different fuel valves by part number but I think three actual different valves which I will explain. The '48 has only one thing in common with the other two models and that is the center goose neck vent. The tanks are different as is the fuel lines and the way they run. The valve itself is not the one Arayna posted for the B model but is the same for the A model according to part number but it starts to get cloudy from here.

The valve is a lapped cone in a seat type valve. There are no o-rings or seals that can be replaced. There will be a packing at the valve stem. You might be successful in removing, disassembling the valve and lapping the cone and seat.

According to the IPC the first 574 170s had the valve under the floor similar to the later A and B, with a arm connecting it to the control handle. Serial numbers after 18574 had the valve mounted under the instrument panel and a different control selector system. If I remember correctly at least the later system selection pattern was left-right-off. No both. It would stand to reason the first 574 also had the same selection but yours on the floor says it has a both position. A '48 guy with the under panel selector will have to confirm the existence of lack thereof in that set up. Strangely enough the Cessna 140 had what looks to be the same valve with the same selector sequence but not the same part number, instead using the Imperial the manufacturers part number 44703. According to the IPCs the 48 and the A model and about the first 30 B models have the same selector. Problem is that in the A and B models this valve is capable of selecting left-both-right and off then back to left. What this would require is a hole drilled straight through the selector creating a T rather than an L hole.

I believe the 140 valve and the valve in the early valve found in the 170, 170A and those first 30 or so B models are all the same valve with the A and B models modified. But there is not enough documentation printed to prove that. So if you find the valve can not be made serviceable Univair has a valve that is PMA'd for use in the Cessna 140. I've told them several times it is likely the same valve as the 170 and 170A they should include it in their documentation but they haven't. Their valve only have left-right-off. So to use it you (or you mechanic) would have to determine it is the same part and or modify it to be. The Univair part is just over $400.

Now as for your tanks not draining from the selected tank or fuel being used from one tank more than the other or fuel passing from one tank to another, than is a very common trait among all 170s no matter the model.

[Bruce Fenstermacher]

And what Kurt is alluding to is the stock 48 did not have 25 gal each side as your selector is marked but it is a very popular mod to add the second tank same as the right side.

[N4027v]

Yes my 170 has been modified with a second tank on the left side to match the configuration on the right.
So Bruce are you saying I likely do not have a problem? Although 170's all exhibit this problem of using more fuel from one tank, would you not think it excessive to have burned half a tank from left and right still full? If left on both would it have used all left fuel and then consume the right? Is there a procedure that will help keep the tanks equal?

[DWood]

My 48 (later sn 18608) does have off - right - both - left

They don't drain equally but 1/2 from one tank and still full on the other is not what mine does. That seems excessive. Might want to take a container and measure one or two minutes of draining from left v. right to see if one side might be restricted. You might check to make sure your fuel valve hasn't been changed as the plate is different from original.

Dan

[Bruce Fenstermacher]

Dan is the 48 expert having two of them and having an early and a late one at that.

It seems every 170 has a unique fuel burn pattern. Just when you think you have yours figured out, it does something different.

Check your flow at the gascolater. You should have the same flow from each side if there is the same amount of fuel in each side. In both there should probably be a bit more as the head pressure is theoretically doubled but you may not see it. Then with the fuel off you should have no flow. Make sure off is really off and there is fuel all other selections.

[blueldr]

Bruce,
I believe head pressure is only a function of height and not volume.

[Bruce Fenstermacher]

Bruce,
I believe head pressure is only a function of height and not volume.

Ahererrrrrrrrr. Dam you may be right. In which case the flow should not change between left-both-right.

[DWood]

After thinking about this overnight, I think the best way to test is by measure volume per time for each tank.
If there is a significant difference, then it could be due to a restriction or venting issue. You could remove the caps for a second test to eliminate the venting.

I also think that since your selector plate is not original, you need to make sure that the valve and plumbing hasn't been changed or modified. a picture of the original selector is in the attachment.

Note: I didn't see a cotter pin retaining the lever.

There is a screen in the fuel tank that could be restricted is everything else checks out (also see attachment)

Dan