So as the title says, how tight should AN fittings be?

oil cooler lines? (I broke a Mocal cooler by over-tightening)

turbo oil feed lines?

Fuel system lines?

I'm specially paranoid about the fuel system, leak, die in a fire, etc...

 

depends on your strength and what you are using to tighten them?
if you use the aluminum wrenches it helps

 

I just use the "mechanic's feel" technique. Tighten until I feel it tighten up with just the slightest amount of yielding. If you work on stuff a lot you know what I mean. And I've never ruined a fitting or had one leak doing this in 30+ years working with AN fittings. It does take a bit of finesse.

BTW, I like longer wrenches than the aluminum ones - a longer wrench gives me more precise control. If you are straining, it's hard to be gentle.

One of the techniques I use a lot is to squeeze 2 wrenches (1 on the nut, 1 on the "stationary" part of the fitting) opposed to each other with one hand. That also gives more control.

 

Here is a table from Summit Racing:

 

Thanks for the table. It gives an excellent reference for what torque to use.

The issue I have, however, is that it's often difficult or impossible to get a torque wrench (with socket or even a crow's foot) into where you need it to torque oil or fuel fittings. So from experience, I found my technique above to be far more practical.

 

On all the oil coolers I've seen, there's always a caution about torquing fittings and supporting the cooler side hex, - murphy sure to intervene if you don't!

I'd agree with DaveW, invariably no room more than half the time to torque to a spec, educated feel is the best you'll do.....unless you're using Chinese fittings, then you're using a bit of pot luck with dodgy wall thickness, heat treat, etc.

 

I go finger tight then use one of the alu spanners to nip it up maybe half to 3/4 of a turn? I'm ham-fisted as anything though, I've lost count of the amount of fittings I've twisted clean off by my dumb meat hands.

You should always pressure test new fittings anyway. Fuel I'll always short the pump for a few seconds to get some pressure in the lines and carefully check for leaks. Same with oil, I'll crank the engine for a few turns then check fittings. Also check fittings after you run the engine and let it cool.

 

There is another advantage to this technique even on things other than fittings that I forgot to mention - it saves a lot of scraped knuckles from wrenches slipping off. It's my preferred method when using open-end or box wrenches when an exact torque is not required.

 

I was taught in engineering school: Torque it until it strips, then back it off a quarter turn. :-P