Hi everyone—

I keep finding water in my 1956 170b's starboard fuel tank (not unusual for the wet coastal BC climate where I live).

HOWEVER, the water I'm sumping from the drain is rust coloured.




Old style fuel cap


Does this mean my tanks are rusting, or there is some other part within the fuel tank which is rusting? I've heard the top fuel cap and mount assembly or can rust causing these issues, but I didn't see any.

It's worth noting the tank is not leaking at all. The port side tank has a new venting style fuel cap and there is no rust coloured water in that tank.

Thoughts?

New cap in starboard tank is first thing I would do . Or swap them and see if problem follows. Na. Just get a new cap for offending tank

Tim

Pull out the 6 screws around the tank and replace them with stainless steel screws, also seal the screws with Blue Locktite (removable grade, not red locktite).

I’m guessing this is the quick drain which is steel. Buy a spare and swap it out, then put on a new o ring and keep the spare in the plane.

Nothing like 100ll running down your arm. Don’t drop anything when changing out.

And I would change both fuel caps for the red ones.

Cheers, I'll do this.

Do you know where I can find part #s for the drain valve, caps, and filler-neck hardware? I'm relatively new to aviation and aren't sure where to look

Any idea on the part # for these bolts or where I can find out?

The screws are easy, pull one out and measure it, then buy non-structural stainless screws from aircraft spruce. I don't remember the exact size, but probably 10-32 X 1/2 inch or something close to that. If you're new to ownership you should probably get a start on a small inventory of common size screws to keep in your tool box.

I would change one thing at the time to isolate the problem.

My guess is the fuel sump drain. That's where the water sits long enough to become discolored.

Caveat... I'm a flyer, not a fixer, so talk to your mechanic.

I had a similar issue on my old 170 and it would also get clogged with little rusty bits. I changed the sump drain and that solved the problem but it returned a few months later. I replaced it again, this time draining the tank and flushing out the gunk. That solved it.

Draining the tank can be dangerous.... don't do it in an enclosed hangar!

I bought my sump drains from Aircraft Spruce but I bet McFarlane has them too. Here is the link to the Spruce parts page, assuming your tank is original. These planes are old... some have had the tanks replaced. If that's the case, you will have to remove the drain valve and examine it to determine which one fits.

https://www.aircraftspruce.com/catalog/appages/f391.php?clickkey=4924028

reecewallace wrote:Hi everyone—

I keep finding water in my 1956 170b's starboard fuel tank (not unusual for the wet coastal BC climate where I live).

HOWEVER, the water I'm sumping from the drain is rust coloured.




Old style fuel cap


Does this mean my tanks are rusting, or there is some other part within the fuel tank which is rusting? I've heard the top fuel cap and mount assembly or can rust causing these issues, but I didn't see any.

It's worth noting the tank is not leaking at all. The port side tank has a new venting style fuel cap and there is no rust coloured water in that tank.

Thoughts?

First thing you need to do is get in touch with Hartwig and see if they still sell the old Monarch kit to “fix” that filler inlet. Sorry, I don’t have a photo, but Monarch made a sheet metal collar that fit tight to the filler neck, and covered that recessed area. Well sealed both at filler neck and top of wing. Then, add a raised cap....standard Cessna cap.

What’s happening there is the plane sits out in precip, and fills that little “moat” around your filler neck. Now, the water by capillary action, creeps up the neck, under the gasket and into your tanks.

Water in tanks is a VRY bad thing and hard to remove it all.

I had this problem on a 52 170B on floats, which lived outside. I nearly ALWAYS got water out of sumps till installed that kit, never got any after. I wouldn’t fly a 170 without that mod.

If Hartwig doesn’t sell the kit, maybe someone else does. If not, it’d be very simple to cut a donut shaped piece of aluminum that fits tight against the filler neck. Then install a better cap.

As to the rust, could be a number of things, but to me the WATER is the real problem that must get fixed. Don’t believe for a minute that you’re ALWAYS getting all the water out of those tanks every time you sump them.

Those little “moats” around your fillers are potential killers....

MTV

And if it ever gets cold, be very careful, the water will not come out when it is a solid.

Does anyone have a picture of what MTV is taking about? I have hated those filler necks for years and fought water for way to long. I don't think i have ever seen a 170 with that mod.
Greg

Some old caps had a chain on them, to not get lost. That chain will rust and fall off in the tank. It will then rust with dissimilar metal and cause little pin holes in the fuel tank and could show rusting signs in the fuel sump.

roamak wrote:Does anyone have a picture of what MTV is taking about? I have hated those filler necks for years and fought water for way to long. I don't think i have ever seen a 170 with that mod.
Greg

Never seen that, but I have seen people fill the sump around the neck with silicone. Its fugly. I built a hangar.

mtv wrote:.....First thing you need to do is get in touch with Hartwig and see if they still sell the old Monarch kit to “fix” that filler inlet. Sorry, I don’t have a photo, but Monarch made a sheet metal collar that fit tight to the filler neck, and covered that recessed area. Well sealed both at filler neck and top of wing. Then, add a raised cap....standard Cessna cap.....

I've never seen or heard of this kit.
Far as I know, Monarch / Hartwig just sells their racheting cap kit these days.
FWIW Atlee Dodge sells a couple kits to change the cap configuration,
looks like neither is STC'd for the 170 though.

http://www.fadodge.com/category/cessna/ ... ms-cessna/

It sounds like a great fix, but without a purchasable kit and STC, might be above my pay grade.

Look closely at the neck for any rust pinholes.
I recall replacing the filler neck on a customer’s airplane when it had rusted through. Similar deal, water in the tanks constantly.
I can’t remember the model of Cessna but it was a PITA due to corrosion.
I have vague recollections it was the screw-in neck style. Not sure what you have without looking at an IPC.
Cheers,
Dave

I agree with the previous post. Check for pin holes. I've changed a number of thefiller necks and have a special tool built for it. PM me if you want more info. I can also send you the tool to borrow if you need, I'm just over in Alberta so not to far away.

reecewallace wrote:It sounds like a great fix, but without a purchasable kit and STC, might be above my pay grade.

Maybe before you give up, you might call Hartwig. I’ve found in past that they often have stuff that’s not shown on their website.

Or, it’s easy to cut a circular piece of say, .040 or? aluminum in a circle to cover the “moat”. Then, cut a hole in that to slip down over the filler neck. The kit used some stuff like “steel in a tube” to seal both the filler neck and perimeter to the wing.

Easy for any mechanic to make, me thinks, and a “minor” alteration?

MTV

A1Skinner wrote:I agree with the previous post. Check for pin holes. I've changed a number of thefiller necks and have a special tool built for it. PM me if you want more info. I can also send you the tool to borrow if you need, I'm just over in Alberta so not to far away.

Appreciate this. My buddy is a retired AME an has the tool, so we're going to take a shot at doing it ourselves first.

reecewallace wrote:

A1Skinner wrote:I agree with the previous post. Check for pin holes. I've changed a number of thefiller necks and have a special tool built for it. PM me if you want more info. I can also send you the tool to borrow if you need, I'm just over in Alberta so not to far away.

Appreciate this. My buddy is a retired AME an has the tool, so we're going to take a shot at doing it ourselves first.

Right on. Mix up a bit of PRC and put some on the threads to seal them well, then I usually put a nice bead of it around the base and on the 6 screws as well.