The International Cessna^® 170 Association

I have a 48 170 with the original C-145-2 with no modification to the fuel system. At the annual in January, when we dropped the lower cowling, we noticed some blue die from 100LL on the bottom right side (while facing forward) of the lower cowling. It appeard that a small amount of fuel was dripping from somewhere in the area of the #1 cylinder (the cylinder on the right side of the engine nearest the firewall).

We looked everywhere and could not find the source of the leak. The primer fuel line goes into the left side fuel manifold (sp?) so we don't think the leak is coming from the primer plumbing.

Since we coudn't find the source, and since it appeard to be a small leak that was dripping down onto the lower right cowling after shutdown, the mechanic signed off on the plane with the admonition to "keep an eye on it."

Today, in pre-flighting the plane, I opened up the right upper cowling for a look-see and the fuel stains were back with what also appeard to be a spattering of fuel stains (probably blown by air forced through the engine while in flight) on the right lower side wall of the bottom cowling.

Whatever the rate of the leak, it isn't enough to view any dripping in progress. Nor is there enough that it ever reaches the floor of the hangar. However, any amount of fuel stain showing up within the engine compartment has me concerned so I'm going to take it to another mechanic next week to get a second opinion.

You fellow association members have been so helpful in the past, I was wondering if anyone 1) had any ideas of where we should look for a leak? and 2) is it normal for something like this to be happening on our older aircraft?

On the right side of the engine, I believe the only "pipes" that carry fuel to the cylinders is the fuel manifold off of the carburator.

Other than from the fuel manifold, could fuel be dripping from where the cylinder bolts to the case? Could it be leaking from the rubber tubes that appear on the pushrod tubes?

Sorry if I'm getting some of this terminology wrong...I'm not a mechanic.

Thanks for any ideas in advance.

Sincerely,

Curt

Curt; You failed to mention if the stain appears after the plane has set for a time after you have cleaned off the stain.Or does the stain appear after a flight?
Check the plumbing at your fuel pump (front of # 5 Cylinder) ,also check the fuel line from the fuel strainer line to the carb.It may be a fitting lose or a pin hole in the line only showing up when the engine is running with
pressure from the fuel pump.
Leaks such as oil or gasoline are always difficult to find unless they are sizeable leaks. I had a like problem with my 1948 C170 smelling gas fumes upon starting .After exhaustive search I discovered fuel spewing
from the primer line when I had a friend work the primer prior to starting.
I don't know if this was any help ,but find that leak before any future flying.
BOB

Bob:

Thanks for the tips. The stains only appear after the plane has set awhile, after flying. If I clean it up and don't fly, no stains appear. Immediately after a flight, no stains either.

Curt

Took the plane to a very experience A&I today and he found the source of the leak(s) immediately. There is a hose between the intak manifolds and each of the cylinder intake elbows and a couple of these hoses are allowing a small amount of fuel to drip on the bottom cowling after shutdown. The A&I said that this is normal as these hoses deteriorate with time like any rubber hose. We ordered 6 new hoses and clamps and will install within a week, although the A&I said that there was no danger of fire, etc. at this point.

Regards,

Curt