Understanding AN - everything you need to know about aftermarket hose options

If you watched this maaad episode where Marty fitted an oil cooler to Keith The Kei Tip Truck then you'll have seen the lads making hoses to carry oil. This style of plumbing is loosely referred to as "AN plumbing", which comes from when the US Army and Navy standardised the plumbing on their vehicles during World War 2.

Hot rodders picked up on this after they returned home and the AN-sizing soon became used for plumbing cars for oil, fuel, coolant, and more. You can READ THIS story to learn more about how there are different pitches and thread styles before we get into the world of aftermarket plumbing...

MCM uses Raceworks fittings and hose on our project cars - we've seen these used on some of the fastest street cars in Australia and they haven't let us down once.

In the oil cooler video you'll hear Marty refer to "dash 10" hose, which is a reference to the size of the hose and fitting. There are several types of hose (cutter, PTFE, push lock, and more), and you pick which type of hose based on the fluid it will be carrying.

When it comes to fittings there are a huge range of aluminium options, and typically they are sold either as hose ends (in a range of degree bends, from 30 up to 180), or adapters to fit to manifolds, fuel rails, and dozens of other uses.

For oil and fuel (especially ethanol) PTFE hose, which has a plastic inner sleeve under the braid, is the go. You do need to be careful not to kink this hose when running it, or bending it around corners though - big, gentle curves are the way to go with PTFE.

Some push lock hose is also able to carry E85 but it needs to be rated for ethanol. It is simpler to assemble this 400-series push lock hose into the fittings as it is a basic push-on style, but we prefer the look of the braided 200 series fittings.  

Here, you can see the difference between a 400 Series Push Lock fitting (left), and the 200 Series PTFE hose end (right), which uses a compression-style to clamp onto the hose rather than the barbed end like the Push Lock. 

Running the hose is a tricky part of the job, because Murphy's Law says you'll work out one way to do it, order the parts you need, then work out a better or neater way to do the job.

It is always better to order too much hose just in case you have to remake a line if you kink it, or have some other kind of disaster. Buying a few extra options for fittings and spare ferrules (when using PTFE) is a good idea - you'll be surprised how often you'll need them.  

The best way to run the hose is to mount everything you need to connect, terminate one end of the hose, and then snake the other end up to where you need it to go. This also lets you see if there are neater hose end or adapter options for connecting the system together.

When running fittings into parts like oil coolers, fuel rails, surge tanks (or the catch cans below), you'll need what are referred to as "ORB" fittings, which use a rubber O-ring to seat securely against the part and often come with a male AN thread you can screw a hose end onto.  

You can also get "bulkhead" fittings when passing through firewalls or boot floors, plus there are all sorts of adapters you can use on push-to-connect parts like GM fuel filters and flex fuel sensors. It can be very handy to reach out to a friend who has experience in AN plumbing when mapping out how you want to run your system, as they may know of a fitting which can drastically neaten your hose beast. 

It also pays to grab a set of aluminium fitting spanners, a set of the soft jaws to hold the fittings in a vice, and an adjustable AN spanner so you can assemble your hose without marking the aluminium. 

I also keep a bottle of half decent car wash or silicon spray on hand to prevent the aluminium threads galling when tightening them up, and a can of compressed air to blow the lines clean of schmutz after cutting them to length.

Making the lines is actually fairly simple, and the hardest part of putting these fluid systems together is finding neat ways to run all the hose.  

To start, mark the first cut line based on the top of the shank of the fitting you'll use (not the tail end of the fitting), and don't be tempted to cut it extra-long because PTFE can kink if you try to jam too much into the space.

The best way to cut PTFE is to wrap the hose with some masking tape then slice through with an angle grinder - this keeps the braid trim neat, making it easier to assemble the hose end. Make a quick cut, ideally gently holding the hose in a vice - don't squeeze it too tight or you'll crush it!  

The biggest difference between standard rubber, cutter or push lock hose, and PTFE comes in the next step - the ferrule.

You slide the hose end over the cut part of the hose, with the internal thread in the hose end facing up towards the cut you just made. The Raceworks PTFE (200 Series) hose fittings come with a small alloy ferrule which seats the hose into the end of the fitting, and you push this ferrule between the braid and the teflon liner until it is fully seated. 

These are a one-use-only item so make sure you're confident you haven't accidently run your fuel line around your wheel or tailshaft before assembling the fitting. The good news is you can buy spare ferrules in packs of 5 to cover any stuff-ups (which we all make).

Once the ferrule is home you can slide the hose end up. At this point I typically wipe a little bit of car wash on the aluminium threads and into the end of the ferrule/PTFE line to make the next step easier. 

You push the shank end of the fitting into the PTFE line and, once you feel it bottom out on the ferrule, then start winding the hose end onto the fitting. Before test-fitting it to the car give the line a good blow-out with air because there will be schmutz inside from where you cut it, and you don't want that getting into your engine.

Once you have the line measured to perfection you just repeat these steps to terminate the other end, and you have yourself a custom hose ready for oil, E85 or various other fluids (even some drag racing fire extinguisher systems!). 

Don't sweat if the hose ends don't line up absolutely perfectly as you can loosen the hose end and swivel the fitting in the PTFE teflon liner, then tighten it back up.

When plumbing an entire car from scratch be prepared to spend a whole swag of time and money on AN lines as they can become an addiction. However, the security and aesthetic benefits of a well-made AN line are hard to beat!