Toobuilder

Toobuilder

Well Known Member
The RV marks it's territory with some oil drops wherever I park. There are a few spots on the engine that I'm finally tracking down with the use of dye and a UV light source, but one I can't seem to stop is the dipstick. The tube is the plastic unit and is leaking from the cap, not the base. This despite the fact there is no apparent damage to the tube, cap or O ring. I've tried really smoking down the cap; I've tried running it just barely tight... Nothing changes.

Before I take it off the airplane and start really digging at the problem, is there some kind of known problem with the plastic outer tubes? This is the first airplane I've ever seen with one and thought I'd ask here first.
 
Be certain your oil pressure regulator is tight. If it leaks at its base, oil ends up all over the dipstick. Took me a while to find that one. The air going through the top of the engine keeps the oil from showing up anywhere but at the very bottom of that regulator, have to wrap your finger around its base to find it. Mine took an 1/8th if a turn and that fixed it.

If that's not it, make sure the rubber O-ring at the top of the tube is new and that the base is tight and safety wired tight. No need to crank down the dipstick, but if you've done so in the past and the base moved even a tiny bit...you likely broke the seal and it's leaking at the base. My guru had to straighten me out on that one as well. (thanks Ryan!). Remove tube, new gasket with permatex on it, tight, check tight, check again...safety wire so it can't move even if you get manly on the dipstick (no need).

Worked for me, your mileage may vary, I'm no expert but I know one, advice worth what you paid for it.
 
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My oil dipstick is also out of plastic and it also not a tight seal. It shows an oil slick by it after 20 hours or so. I tried to proseal it with a stock paper gasket and it's wet around it again. Will try permatex trick next time.
 
Tite-Seal

I used a copious amount of Tite-Seal on my dipstick tube as it was leaking a very fine trickle. Seems to have done the trick so far.

Don
 
dipstick

The dipstick is three parts, the dipstick itself, the cap which is a casting and a roll pin to join the two parts. If there is any looseness between the rod and the cap a slight amount of oil may leak out. The roll pin can be pressed out, clean everything up and reassemble with some epoxy on the end of the dipstick rod. Or you can make a new rod out of aluminum round stock that is a light press fit into the cap, then drill for roll pin. Of course the new dipstick will have to be marked.
 
For leaks at the bottom of the dipstick tube, using an o-ring instead of the flat paper gasket will stop the leaks completely. Just don't tighten the tube too much, you don't want to squeeze the o-ring out of place. Make sure to safety-wire the tube so it can't loosen. Even though this is not an approved thing, I've seen an o-ring in this application last more than 10 years totally leak-free. I put an o-ring on mine because the flat paper gasket was leaking like a sieve... and it solved my leak!
 
Neal@F14 said:
For leaks at the bottom of the dipstick tube, using an o-ring instead of the flat paper gasket will stop the leaks completely. Just don't tighten the tube too much, you don't want to squeeze the o-ring out of place. Make sure to safety-wire the tube so it can't loosen. Even though this is not an approved thing, I've seen an o-ring in this application last more than 10 years totally leak-free. I put an o-ring on mine because the flat paper gasket was leaking like a sieve... and it solved my leak!
Click to expand...

Or use an approved Real Gaskets silicone part.

RG-72059

http://www.realgaskets.com/files/horizontal.htm#lycoming

rg-72059.jpg


It has to be better than that paper thing that Lycoming uses.
 
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I got this tip on a previous post some time back. Safety the base of your tube in both directions as when tightening the cap can turn the base (tighter) and when you remove the cap the base will turn back against the safety wire. This movement will cause a base leak over time. Safety wired in both directions will stop this movement. This might apply to the REAL gasket more than a paper gasket as the silicone gasket well easily squish.
 
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