oil leak from oil temp fitting

[N74DV]

We finished our annual and after having done a leak check engine run up we notice that there is a leak from the oil temperature bulb fitting. We've tightened the brass fitting into the oil screen adapter fitting as tight as it will go yet is seems that you can ever so slightly wiggle the oil temp bulb line.

This ability to wiggle tells me obviously this is the cause of the leak. The bulb is not tightening down all the way. What puzzles me is it was fine before the annual. Did we forget a seal or something? It was 3 months ago when we started the annual and removed the oil temp bulb. I can't recall if there were extra parts that perhaps we did not put back in.

[Bird]

Re: oil leak from oil temp fitting

Isn't there a thin brass washer that goes there?

[Hank Jarrett]

Re: oil leak from oil temp fitting

There are two types of bulb oil temps. One has a matched flat seal and a second has a tapered interface. If you mix them up, they leak. If you tighten the mixed up ones, you "may" get lucky and slow or stop the leak, but most likely you will ruin the interface or break the line.
Someone on the group had some pictures of the differences and I have an article somewhere in the mess.
Anyone else have the article? I may have gotten it from the Pietenpol site.
Hank

DON'T try to tighten it to fix the leak till you know for sure!

[3Dreaming]

Re: oil leak from oil temp fitting

There should be a crush gasket between the screen and the accesory case, and between the adapter and the screen. They should not be tightened as tight as you can get for the crush gaskets to work. Did you change the oil temp gauge or any of the hardware? I have seen clearance problems between the temp bulb nut and the adapter before, but this would be only if you changed something. Tom

[Buell Powell]

Re: oil leak from oil temp fitting

The part numbers are AN900-28 for the screen gasket and AN900-10 for the Thermometer to oil screen gasket and Aircraft Spruce has them.

[N74DV]

Re: oil leak from oil temp fitting

I tried the crush gasket but with it installed there was a tremendous about of slop in the bulb.... about 1/8". I'll try to shoot a video this week and post it up to show exactly what our problem is.

[NY86]

Re: oil leak from oil temp fitting

Anyone else have the article? I may have gotten it from the Pietenpol site.

This one?

[N74DV]

Re: oil leak from oil temp fitting

I'm going to the hangar today to investigate this further. That article is a big help. I don't suspect a mismatch of parts, as it has been flying for many years with no problems, but it'll be good to have a closer look and see.

[N74DV]

problem solved - I hope

I believe I found the cause.

My parts match up in terms of having all tapered bulb flange pieces so that doesn't appear to be the cause.

What I did notice is that over the years of tightening that bulb fitting nut it has slowly compressed the sealing flange to the point now where the bulb nut bottoms out on the adapter before it has had a chance to contact the sealing surface of the bulb.

So I've taken the adapter nut off and turned it down about .050" on my lathe. This should allow the bulb nut to turn at least another full turn if needed and compress and seal the bulb flange against the adapter.

the pics may help with understanding.

[Mark Julicher]

Re: oil leak from oil temp fitting

Or perhaps install an AN900 washer??!!

[N74DV]

Re: oil leak from oil temp fitting

no, that would be the opposite of what I need to accomplish. I need to shorten the adapter nut face. Adding a washer would lengthen it.

[N74DV]

Re: oil leak from oil temp fitting

oil leak issue appears solved. Turning down the adapter nut face allowed me to turn the bulb fitting nut an extra full turn which caused the bulb sealing surface to be properly pressed against the adapter nut.