1969 Cherokee run up/fuel valve

R

RonP

Pre-takeoff checklist
Joined
Jan 6, 2019
Messages
216
Display Name
Display name:
RvP
I have been talking to other Cherokee owners regarding the fuel valve use during run up. There seems to be 2 schools of thought:

1) Taxi to the run up spot on the lowest tank and run up on the fuller tank. Leave the fuel valve on the fullest tank for takeoff. This verifies you can pull fuel from both tanks.

2) Start, taxi, run up and takeoff on the fullest tank. This way you know you are really pulling fuel from the tank and not running off fuel stored in the line and the gas collator given a clog in the fuel tank. If indeed you were running off gas stored in both you could have the engine die during takeoff.

The checklist does not specify either but states fullest tank for takeoff. What is the best and safest method prior to takeoff?
 
Number 1 is stupid. If you switch tanks at altitude and there is something clogging the other tank you have plenty of time to switch back. If you switch just before takeoff and there is something wrong with the tank you are close to the ground and have no time to diagnose, let alone fix, the problem
 
From memory - the POHs I’ve read from Piper suggest proving one tank via the run up, then switching to the second tank for takeoff. If that’s bad, switch back to the first tank that you known is good. Seems sketchy to me.

personally I don’t switch tanks until I have altitude.
 
I don't switch tanks before takeoff. Startup, run up and takeoff is on the fullest tank. I switch tanks once in cruise for the first time at a point where I know that I can reach an airport with the fuel left in the first tank, just in case the second tank doesn't work.
 
Some pilots seem to have an obsession with switching tanks (especially Piper drivers!). I've seen people on here that insist on switching at runup, switching every 15 minutes in the air, switching off when parked. They are going to wear that valve out!

I think this is definitely a case where less is more. Every time you switch that valve, there is a very small chance it could fail. I personally limit switching tanks to what is necessary, and at points in flight that it is safe to do so. In the Comanche, only verify it is on a main tank that has good quantity during preflight, taxi, and takeoff. 30 minutes after takeoff, switch to opposite aux tank. 60 minutes switch to the other aux tank, 60 minutes back to opposite main, etc. The aux tanks happen to hold about 61 minutes of fuel if you are good, the mains 121 minutes, hence the 60 minute switching cycle.
 
I have a Cherokee 140B owners handbook right here. It does not address the fuel tank selection in the before-takeoff instructions. Personally, I like to have it on the fullest tank, and if I am alone and both are full it will be the left tank due to my weight on the left side.

One easy way to manage fuel tank selection is to use a wristwatch with an analogue display. When the minute hand is on the right side between 12 and six, be on the right tank. When it is between six and 12 on the left side of the watch, be on the left tank.

I made a whole lot of trips between Kalamazoo and central Wisconsin, across Lake Michigan. At first, I was reluctant to touch the fuel selector in my Bonanza when over the water, but I got over that. The flight was about 90 minutes, and the halfway point in time was halfway across the lake. As time went on, it wasn't a concern. I crossed the lake more than 230 times.
 
I also start and take off on the fullest tank. It should go without saying, but I check the sumps before startup, and always visually check fuel level in each tank. I'm not too concerned about the valve, or accidentally switching to 'off', but I really don't want to switch to a tank that's starting with water.
 
ateamer said:
Do this: Start your plane up, turn the fuel off and see how long it runs. That could help you decide whether to switch tanks right before takeoff.
Click to expand...

Also confirms the fuel valve actually shuts off. Recently found one leaked internally in the off position enough to taxi, run up, but wouldn’t provide enough fuel for full power.

Brian
 
ateamer said:
Do this: Start your plane up, turn the fuel off and see how long it runs. That could help you decide whether to switch tanks right before takeoff.
Click to expand...

Is it ok to exhaust your engine of fuel? I guess that would give you an idea of rough running and then engine stopping. Or put the fuel back in as it’s running rough and see if it kicks back on? Or does all of this happen too quickly for that?
 
mandm said:
Is it ok to exhaust your engine of fuel? I guess that would give you an idea of rough running and then engine stopping. Or put the fuel back in as it’s running rough and see if it kicks back on? Or does all of this happen too quickly for that?
Click to expand...
You do shut off your motor by cutting the mixture? That's running it out of fuel. Only difference is the lines from the valve to the engine are emptied.
 
midwestpa24 said:
Some pilots seem to have an obsession with switching tanks (especially Piper drivers!). I've seen people on here that insist on switching at runup, switching every 15 minutes in the air, switching off when parked. They are going to wear that valve out!

I think this is definitely a case where less is more. Every time you switch that valve, there is a very small chance it could fail. I personally limit switching tanks to what is necessary, and at points in flight that it is safe to do so. In the Comanche, only verify it is on a main tank that has good quantity during preflight, taxi, and takeoff. 30 minutes after takeoff, switch to opposite aux tank. 60 minutes switch to the other aux tank, 60 minutes back to opposite main, etc. The aux tanks happen to hold about 61 minutes of fuel if you are good, the mains 121 minutes, hence the 60 minute switching cycle.
Click to expand...

I’ve heard of the 60 minute switch, I probably do mine every 30-45 minutes as I set a timer, typically want to be near an airport or have an idea of an emergency landing site in case of an issue (I’ve read about the valves cracking midway causing fuel exhaustion), also I don’t want to forget to swap tanks, and the airplane tends to get out of balance especially with my weight on one side when going for more than 30/40 minutes on one tank. The idea of using the fullest tank I thought came from the idea of when you’re banking at slower speeds you don’t want fuel to float/tilt away from the inlets, no idea if that assumption is correct or not. As for water in the tank, that’s what we sump the tanks for so that should be no factor?
 
Hang 4 said:
You do shut off your motor by cutting the mixture? That's running it out of fuel. Only difference is the lines from the valve to the engine are emptied.
Click to expand...

Gotcha basically same thing then.
 
Maybe I misunderstand what happens when the engine is shut off by leaning it as part of the shutdown procedure. I thought leaning it for shutdown decreases the mixture to the extent the engine won’t run even though the fuel bowl is still full. Running the engine out of fuel by shutting off the fuel will drain the bowl and any fuel lines draining into the bowl of all gas. So does leaning for shut down actually drain the carb or merely create a mixture that the engine will not run?
 
It does not drain the carb. Fuel cannot leave the carb with mixture in ICO.
 
Thanks for the clarification. There is then a big difference between leaning for shut down and actually running the engine out of fuel by shutting off the fuel valve.
 
My Warrior (-161) POH under Normal Procedures:
Before Starting Engine: Fuel Selector: Desired tank.
Before Takeoff: Proper tank.

Personally, I start on the fullest tank and leave it there for the first 60 minutes (by timer). I switch tanks every 60 minutes to keep appropriate W&B.
 
Domenick said:
Personally, I start on the fullest tank and leave it there for the first 60 minutes (by timer). I switch tanks every 60 minutes to keep appropriate W&B.
Click to expand...
In my Archer, I personally did this as well. While the first hr works well, since getting a fuel totalizer, I now use the 10 gallon mark. As someone who has experienced fuel valve lock-up in cruise, and from a common sense perspective, I minimize cycles on that fuel valve when unnecessary. So, when the second hour, or 20 gallon mark, comes up, I take note of that to check the gages, but, since it makes no significant difference at that point to wing balance, I leave the fuel tank valve alone until the following 3rd hour, or 30 gallons.

I used to look at which side the valve was on on run-up when flying alone, thinking it would be better to burn off the left side first, since I’m sitting in that side. But I believe, if whatever tank it is on is full/almost full, it is more important to have confidence in an uninterrupted fuel supply that existed at the end of the last flight, for takeoff.
 
bflynn said:
From memory - the POHs I’ve read from Piper suggest proving one tank via the run up, then switching to the second tank for takeoff. If that’s bad, switch back to the first tank that you known is good. Seems sketchy to me.

personally I don’t switch tanks until I have altitude.
Click to expand...
What ya do if the second tank is bad is switch back to the good tank, taxi back to the hangar, tie down, FBO or mechanics hangar and find out WTF is wrong with your airplane.
 
Many of you are missing the nuances. You start and taxi on the lower tank. Shows you can draw fuel.

You switch tanks and THEN do the run up. If you can do the runup on that tank, you are drawing fuel, so you proceed to take off.

You DO NOT change tanks just before take off.
 
So I learned in a 180D and my CFI was adamite that the tanks were switched every 15min and at the same time the engine gauges would be checked as well. So of course after my checkride the DPE made it a point to explain to me that while he admired my dedication to the tank switch and gauge check, it wasn't a good idea to change the tanks before I took off. He also stated that I was giving myself extra work and recommended I switch them every 30min which is want I do now.
 
I have my gps set to remind me to switch every 15 min. But it's really just a reminder to "check your fuel situation and do the needful". This allows me to completely ignore the reminder if I'm in a critical phase of flight, or in the middle of something more important, but get another reminder fairly soon. In reality, I only switch every 1/2 hour, but I'm checking my fuel status every 15 min.
 
bflynn said:
From memory - the POHs I’ve read from Piper suggest proving one tank via the run up, then switching to the second tank for takeoff.
Click to expand...
I do not see that [ie - switching tanks during ground check] in the Archer POH nor the Archer checklist.
The Seneca does have this in the runup checklist. Switch left engine to cross-feed for 30 seconds then back to ON (ie - left). Switch right engine to cross-feed for 30 seconds then back to ON (ie - right). Do not run both engines on cross-feed at the same time. For the Seneca, I assume not so much checking the fuel tanks [which are obviously already being checked during ground runup] as it is checking and/or clearing the cross-feed hoses? And although still no idea why not to run both engines on cross-feed at the same time... I just blindly follow the POH on that one. lol.
 
Salty said:
I have my gps set to remind me to switch
Click to expand...
I do similar in my Archer although with different times and I use the transponder, GTX345, for the timer. When it hits zero, it starts counting backwards so similar to @Salty if it is not a good time to be messing with the fuel, I can put that off but I still have the timer counting backwards to both remind me and let me know how long it is past "switch time".

When starting with tanks both equal, for me in the Archer, first switch is @ 30 minutes. After that it is 60 minutes for subsequent fuel tank switches.
 
Last edited:
Pinecone said:
Many of you are missing the nuances. You start and taxi on the lower tank. Shows you can draw fuel.

You switch tanks and THEN do the run up. If you can do the runup on that tank, you are drawing fuel, so you proceed to take off.

You DO NOT change tanks just before take off.
Click to expand...
That's exactly how I do it. I'm not sure it's the best way but at least I know both tanks and the selector valve work.
 
Pinecone picked up on the first procedure the OP (which is me) stated. This first procedure: I.E. taxi on lowest tank, run up on the fullest and take off on the fullest verifies the fuel valve is not stuck and you can pull fuel from both tanks. If you start on the fullest and never move the fuel selector from startup, thru taxi, thru run up and takeoff how do you know the fuel valve is not stuck and the other position will pull fuel? The problem with this procedure is if the engine starts to sag during climb out is not the time to find the fuel valve is stuck or the other position does not allow pulling fuel. Bear in mind when during climb out is not 100 feet or 500 feet, you have other issues to deal with that low. But at the altitude you are leaving the pattern and the engine sags you may not know or be able to run on the other tank if you did not check it on the ground.
 
I’ve received input from different CFIs suggesting both methods. I guess choose which method is better for you?

Does anyone know how long it takes for an engine to stop running if fuel is contaminated or there is a blockage of some sort? Two or three minutes on the ground I would think should be enough.

If so I’ll probably stick with switching tanks prior to runup to guarantee both tanks are providing gogo juice.
 
bflynn said:
From memory - the POHs I’ve read from Piper suggest proving one tank via the run up, then switching to the second tank for takeoff.
Click to expand...

I just checked the POH for my Cherokee and Arrow, and an Archer and a Dakota and all of them say that on pre-flight or before starting engine
FUEL SELECTOR....desired tank

The before takeoff checklist includes:
BEFORE TAKEOFF...proper tank

Similar with slightly different wording in a Warrior AFM.

So your memory is probably off a bit.
 
woodchucker said:
I

Does anyone know how long it takes for an engine to stop running if fuel is contaminated or there is a blockage of some sort? Two or three minutes on the ground I would think should be enough.
Click to expand...

You may be surprised how long an engine will run after the fuel is turned off. The way to find out is easy. Next time you shut down, instead of pulling the mixture, turn the fuel selector to OFF and note the time.

Years ago a friend asked me to fly his 172 while he was away for a few months. The first time, as I did the checklist, I merely felt the fuel selector between the seats and thought it was in the 12 o'clock position (BOTH) when it was actually in the six o'clock position (OFF). After a long taxi, and during the runup, the engine died. If I had requested an intersection takeoff, the engine would have died shortly after takeoff.
 
woodchucker said:
Does anyone know how long it takes for an engine to stop running if fuel is contaminated or there is a blockage of some sort? Two or three minutes on the ground I would think should be enough.
Click to expand...

At take off power from about the start of the ground roll to 50 feet. At least that is how long the engine runs with the fuel shut off. Don't ask. :D
 
No idea how they set the valve, but see page two, second column for an example possibility:

https://www.ntsb.gov/Advocacy/safety-alerts/Documents/SA-076.pdf

My run-ups do not typically take as much time as the climb out to 50', re Pinecone's post above, so I'm not changing my answer or procedure.

From another source, 10' of 1/2" tubing is about .1 gal, which would be a bit over a minute longer at 5 gph. I'm guessing at the tubing size, length, and leaned idle burn rate...but there would be a difference between the "off" to engine stop, and water in tank to stop, assuming the water is in the tank bottom and not the line.
 
Pinecone said:
Many of you are missing the nuances. You start and taxi on the lower tank. Shows you can draw fuel.

You switch tanks and THEN do the run up. If you can do the runup on that tank, you are drawing fuel, so you proceed to take off.

You DO NOT change tanks just before take off.
Click to expand...

woodchucker said:
Does anyone know how long it takes for an engine to stop running if fuel is contaminated or there is a blockage of some sort? Two or three minutes on the ground I would think should be enough.
Click to expand...

Albany Tom said:
My run-ups do not typically take as much time as the climb out to 50', re Pinecone's post above, so I'm not changing my answer or procedure.
Click to expand...

I read a story about someone doing their run up after switching tanks, and then their engine quit on climb out. Albany Tom’s post addresses that. The precise time that fuel exhaustion occurs at takeoff power may vary among aircraft, and I don’t care to experiment. For me, it is far safer to leave the valve on the tank that it was on on previous day’s arrival since I’m invariable topping off both tanks on departure anyway.

JScarry said:
I just checked the POH for my Cherokee and Arrow, and an Archer and a Dakota and all of them say that on pre-flight or before starting engine
FUEL SELECTOR....desired tank

The before takeoff checklist includes:
BEFORE TAKEOFF...proper tank

Similar with slightly different wording in a Warrior AFM.

So your memory is probably off a bit.
Click to expand...

I have not looked at my Archer2 POH, but keep something in mind. Piper makes revisions from time to time about what is in the POH. They want you to remove the old pages and insert the new in its place. I’m not saying for sure on this one, but your memory may be correct before the wording/phrasing/data was changed.

Also, I’ve stated that on cross-countries, I change after 1 hour, or 10 gallons when on my totalizer. If one were to find the valve stuck, or fuel unable to be taken from the other tank for some other reason, how much fuel is left in the tank I’m using. So in the case of my totalizer, I have 14 gallons of useable fuel left. In the case of using 1 hour, I could have anywhere from approximately 17 to 13 gallons properly leaned,( or much less available if not leaning properly.) So how far can I go to get to an airport that has fuel? This is more than enough fuel for IFR reserves as well. Now, the only time this would have created an insurmountable problem for me is if the unplanned fuel stop was low IFR and would require an emergency approach, or I was flying to Alaska on the Alaskan Hwy VFR. But in the latter case, I’d have the highway itself to land on if needed.
 
midwestpa24 said:
In the Comanche, only verify it is on a main tank that has good quantity during preflight, taxi, and takeoff. 30 minutes after takeoff, switch to opposite aux tank. 60 minutes switch to the other aux tank, 60 minutes back to opposite main, etc. The aux tanks happen to hold about 61 minutes of fuel if you are good, the mains 121 minutes, hence the 60 minute switching cycle.
Click to expand...

That's similar to what I did with my Cherokee. Taxi, runup, and takeoff on fullest tank. Switch after 30 minutes, giving plenty of fuel to return to departure point if it doesn't work. Thereafter, switching every hour never leaves more than a 30 minute unbalance in tanks.
 
At idle, the carb's fuel will let the engine run for no more than a minute. The lines contribute very little to that, since no air is being allowed into them when the fuel valve is shut off. Air has to enter them via the float valve in the carb, the same valve that is letting the fuel into the bowl, and that valve is too small to allow any significant flow that way.

So, idle the engine, shut off the valve, and see how long it runs. Turn the valve back on, restart the engine, then lock the brakes, go to full power, and turn the valve off again. It will die real soon. You wouldn't get off the ground unless the valve was defective, and you'd find that on the idling test. It wouldn't quit.

Depending on the valve type, they get stiff as the lube in them is gradually washed out over years and hours. When they get stiff, the actuation get stressed and can fail. I had one break in a Citabria when someone shut it off. I have found Cessna 150 valves real stiff, too, risking the same thing. Those are plug-type valves that need the lube to survive. That's what Fuel Lube, now known as EZ-Turn, was designed for. Fuel-proof grease.

I once replaced the fuel selector control shaft in a higher-time 172. It's a short thing that has two tiny U-joints that wear out. If one breaks, you lose control of the valve. If there's much slop in the selector, suspect that wear.
 
woodchucker said:
Does anyone know how long it takes for an engine to stop running if fuel is contaminated or there is a blockage of some sort? Two or three minutes on the ground I would think should be enough.

If so I’ll probably stick with switching tanks prior to runup to guarantee both tanks are providing gogo juice.
Click to expand...

Regarding contamination, based on quite a few instances I've read about where a piston engined (both single and twin) aircraft crashed rather quickly after departure and being misfueled with Jet A, long enough to get in the air.
 
3393RP said:
Regarding contamination, based on quite a few instances I've read about where a piston engined (both single and twin) aircraft crashed rather quickly after departure and being misfueled with Jet A, long enough to get in the air.
Click to expand...

Different situation. It will run on the low octane mixture at low power. At high power you get detonation and then the engine fails. So it based on applying takeoff power, not time.
 
You must log in or register to reply here.
Back
Top