The International Cessna 170 Association

iowa wrote:could really smell the gas in the cabin as well
is this due to the vent as well?

Could be one or both of the short sections of rubber tubing connecting the gooseneck vent to the aluminum vent tubes from the tanks is beginning to fail or one of the clamps is loose. May have leaked or weeped slightly to create the smell when the fuel was transferring. When those hose sections on my plane failed a few years ago, i smelled fuel in the cabin, then fuel started dripping on me. Caught my attention pretty quickly. Changing those hose sections is kind of a pain, but do-able. There's at least one thread detailing how to do it.

iowa wrote:also, my exhaust gauge doesn't work
my radio man, Spencer Avionics in Spencer Iowa,
says its probably the sensor in the exhaust.

where is this located?
and where does one purchase a new one?

I have an Alcor dial-type EGT gauge and the sensor probe is on the exhaust pipe of the right rear cylinder (looking from the cockpit) right below where it attaches to cylinder. It looks like a standard hose clamp wrapped around the exhaust pipe with a wire coming from it. (When I open the top right cowl cover in my '52 B model similar to your A model, it's right there in front of me.) The probe extends from the hose clamp portion into the exhaust pipe through a hole in the pipe. The wire goes from the end of the probe at the clamp to the gauge in the cockpit. Replacements are readily available from Spruce. The clamp and probe are sold as a single sensor unit.

iowa wrote:could really smell the gas in the cabin as well
is this due to the vent as well? ... .

My guess is that the gas you smell is fuel that went out the tank with the cap off. Probably still a good idea to change the crossover vent tube connector hoses since they may be decades old but I doubt that is where you are getting the fuel vapors from if you didn’t notice the smell before flying without a fuel cap. Always a good idea to look at the inboard wing trailing edges after takeoff for fuel. Don’t ask how I know!

iowa wrote:... My exhaust gauge doesn't work
my radio man, Spencer Avionics in Spencer Iowa,
says its probably the sensor in the exhaust. ... .

Before you start replacing parts willy-nilly you might want to do some troubleshooting. Not sure if yours is an Alcor EGT but Alcor calls for 0.8 ohms resistance between your probe leads.

I hate to admit it, but I left a fuel cap off once after filling the tanks and flew for about 1/2 hour and didn't notice a thing until after I landed and saw the open cap as I was walking away from the plane. No fuel smell in the cabin, no noise from the cap aganst the top of the wing, no excessive fuel drain (but it was only a 1/2 hr flight). (This occurred about a year after I changed the rubber vent lines at the gooseneck.) So I would check those rubber vent lines, just in case. They may not get enough cross flow to leak (or weep) during normal use but there may have been enough cross flow with the cap off to create enough of a leak to create the smell. I'm just guessing at this point, of course. But it's worth checking out.

Your EGT probe is most likely clamped to your exhaust riser about 1.5" below the cylinder flange.

The fuel smell could be a couple of sources.
1-If the tanks are full and you perform a wheel landing and heavy braking.... fuel may vomit out of the cabin overhead gooseneck onto the cabin roof/windshield.
2-If the tanks are full ...the vent line above the headliner may have old/rotten rubber hose connections which have shrunk and/or leaking.
3-The fuel selector valve may have a leaking O-ring where the selector-handle-shaft enters the fuel valve.
4- (rare)- The fuel lines in an A or B model which pass up the rear doorposts may have control cables, hardware, or upholstery hardware which has chafe'd thru the fuel lines which are inside the doorpost cover.

I did have occasionally the smell recently and to George’s post it was the fuel valve o'ring and the valve gasket

I love the smell of aviation fuel in the morning.

Just not in the cabin.

My C180 had an aluminum fuel line in the belly from the right tank chafe where it crossed a longitudinal stringer to the point it was almost worn thru. Had it failed, the entire contents of the fuel tanks would have emptied into the belly. It was found at annual.

Once removed, one slight bend by hand broke the tubing in half showing almost no wall thickness left in the chafed area. No telling how much longer it would have lasted before starting to leak.

good morning
could s.t. tell me how to find
copies of the C170 newsletters online
thanks
dave

Hi Dave,

The Flypapers and 160 News are on the members only page of the Association website. You need to be a paid member to get access.

I have now heard /experienced this fuel leak that Richard had. The fuel line from the right hand tank travelling under the floor . We had 2 early model Cessna,s come through the shop about 3 years ago that had the same issue in various degrees of leakage. So when I was doing my cessna SIDS inspection , that area was all open and to my surprise I had a leak . I hadn’t experienced any smells in the past. On removal [not a easy job] the pipe fractured. I manufactured a new pipe with thicker wall and routed a little differently and supported on the structure a little more evenly.

Maybe we all should be having a detailed look at this pipe .

Those fuel lines between the tanks and the fuel selector valve should be inspected along their ENTIRE LENGTH at EVERY ANNUAL inspection because if they become loose, entangled, or some object becomes loose and rubs against them this can cause a fuel leak that the fuel selector valve CANNOT STOP. In flight this could be a real tragedy.

Good flashlights and mirrors help this inspection and doorpost covers/wing-root fairings and upholstery must be removed to accomplish it. If your annual inspector doesn't do this you're not getting what you're paying for...or you're not paying for what you should be getting....or you may get what you didn't want when you don't want it.

I do all my own 100hrly/12 month and SIDS check and sign for all of it ,but the Rh pipe wear issue is when you are looking back,just after the pipe is connected to the fuel shut off valve there is a bulkhead with a clamp to support the pipe ,it’s in this immediate area that pipe just touches the bulkhead. Then there is no support until the pipe bends up towards the door pillar. However the pipe had become age hardened and brittle .the clamp was Attached on the forward face of the bulkhead and looking behind this area is very hard to see. There a very small mark on the pipe and this where it cracked on removal.
When manufacturing a new pipe I changed direction of the pipe as it is now supported in 3 places and travels closer to the fuselage skin and with less bends.

I don't know about Australia but in the U.S. changes to the fuel system design are major alterations and in every case need to be documented.

here is my EGT
what kind is it?
what sensor would I need?
thanks
dave

iowa wrote:here is my EGT
what kind is it?
what sensor would I need?
thanks
dave

Iowa, you'll need to access the rear of the gauge and see what the dataplate tells you. It will likely give you the info you need, such as "type K" and/or provide a mfr'r type/part number you can identify the gauge. Then an instrument shop can point you to the correct probe.