Converting Oil Cooler Lines To AN Stainless Braided Hose - PeachParts Mercedes-Benz Forum

mach4 · #1 05-07-2014, 02:46 PM

A common and recurring question on the forums has to do with leaky or aging factory oil cooler hoses. Aftermarket hoses can be a problem due to quality and changing lines can be a pain. The idea of using aircraft quality AN fittings and stainless braided hose has been documented in various places on the forum, but not all in one place. This post rectifies the situation.

Here is how to make the conversion, if desired.

The oil cooler needs to be converted to an AN fitting as do the hard lines coming from the oil filter.

The first question is what size hose to use. I determined that the -10 size is an almost perfect one for this application based on the following research data.

There are two potential ways to modify the oil cooler end of the line to use the AN fittings.

The first method is to use the standard metric fitting from the stock hose and braze on a -10 AN fitting. This is the easiest and most straightforward method, but the downside is that the hose length is reduced, resulting in a tighter radius and more stress on the fitting. In addition, there is a longer effective lever on the fitting that could cause a problem. Here is how that strategy might look.

I rejected this solution, opting instead to modify the cooler to take a 90 degree fitting which is 1/2NPT on one end and -10 AN on the other.

It should be clear how much cleaner the 90 degree adapter is.

To use the 90 degree adapter, the cooler must be modified to take a 1/2NPT fitting. To do this it is necessary to cut off the old fitting and drill out the stock port to the size needed to tap for 1/2 NPT. This is easily done using a 3/4" step drill. (Note: do not attempt to use a standard twist drill for this operation as it will grab and likely damage the cooler) A common question is whether there is enough "meat" to handle the fitting. The answer is definitely yes - in fact the Mercedes repair kit for stripped fittings also calls for drilling out this fitting in the same manner and replacing it with a screw-in adapter.

Then carefully tap the fitting with a 1/2NPT tap

Test the fitting to make sure it fits properly

The next step is to modify the hard lines from the oil cooler. Just cut off the barb portion of the line and braze on -10 steel bungs. Note: I've removed the stock R4 Harrison compressor and bracket, so I've used a custom support bracket for the hard lines so this may be different from your own setup.

Then just make up the hoses...

...and install.

There is plenty of clearance

A question that occasionally comes up has to do with possible flow restriction using a 90 degree fitting. It turns out that the flow is actually quite low and any potential restriction is likely offset by the slightly larger -10 hose and fitting ID.

Making up AN hoses can be done with hand tools and is extremely simple.

There are countless links on the net for how to assemble braided steel hoses using AN fittings. Here is one to start with - How to Assemble Braided-steel Hoses

Sources for materials are numerous. I got mine by shopping on eBay, but hot rod shops, off road shops and other custom automotive suppliers are also good.

I don't have the expertise or tools to braze so I used a local radiator/air conditioning shop to do the brazing. It was very reasonable.

The beauty of using this system is that replacing a hose is a DIY job and there is no need to source new fittings as the fittings are designed to be reusable.

While this howto is focused on 617 MB engines the basic techniques should be able to be adapted to other engines as well.

Hope this helps for those contemplating a custom setup for oil cooler lines.

uberwasser · #2 05-07-2014, 03:15 PM

I will do this on my '85 soon, as the upper hose is weeping. Thanks for sharing, super informative.

EJHumber · #3 05-07-2014, 04:34 PM

are the hard lines steel or aluminum? Also, did you use any sealant on the threads of the elbow were it goes into the oil cooler? Thanks

mach4 · #4 05-07-2014, 04:41 PM

Quote:

Originally Posted by EJHumber

are the hard lines steel or aluminum? Also, did you use any sealant on the threads of the elbow were it goes into the oil cooler? Thanks

Hard lines are steel. This is why you must use steel bung AN fittings for brazing onto the lines.

I used Teflon tape on the threads of the 90 fitting where it went into the cooler - this is upstream of the filter so there is no danger of a loose strand clogging an oil galley.

Stretch · #5 05-07-2014, 04:50 PM

Great stuff mach4

I just hate the thought of mixing metric with non though - I've been trying to find a non AN metric alternative for a long time now and I keep on coming up with zip. I must be using the wrong search terms - all I want is a cheaper alternative to the bloody expensive fuel line on my W201...

mach4 · #6 05-07-2014, 05:12 PM

Quote:

Originally Posted by Stretch

Great stuff mach4

I just hate the thought of mixing metric with non though - I've been trying to find a non AN metric alternative for a long time now and I keep on coming up with zip. I must be using the wrong search terms - all I want is a cheaper alternative to the bloody expensive fuel line on my W201...

There may not be a metric equivalent system. AN stands for Army/Navy and was a milspec standard created during WWII to standardize hose fittings across the services. After the war, the racing community and custom builders started using the surplus fittings in their application and later there became a whole industry around providing new AN fittings for the various markets. Most fittings are the classic Blue/Red setup with red being the hose end and blue being the screw on fitting.

Is the hose you're looking for high pressure FI hose or low pressure diesel hose?

Ben D · #7 05-07-2014, 05:16 PM

Fancy work

minsk · #8 05-07-2014, 06:14 PM

wow.
nice work mach.
holy poop.

wow this forum is amazing.
but you guys all knew this already.

Stretch · #9 05-08-2014, 04:41 AM

Quote:

Originally Posted by mach4

There may not be a metric equivalent system. AN stands for Army/Navy and was a milspec standard created during WWII to standardize hose fittings across the services. After the war, the racing community and custom builders started using the surplus fittings in their application and later there became a whole industry around providing new AN fittings for the various markets. Most fittings are the classic Blue/Red setup with red being the hose end and blue being the screw on fitting.

Is the hose you're looking for high pressure FI hose or low pressure diesel hose?

It is a weird combination of high pressure fittings on one end of a pipe and then randomly placed jubilee clips at certain junctions. It is such a bizarre set up. Essentially it is high pressure with the odd low pressure joint chucked in for good measure!

I just need a cheaper flexible hose solution - the local hydraulic shops and tractor people get all in a bunch about the strange Mercedes parts and the dealer wants about 400 euros for about 50cm of flexible pipes and connectors. I've decided not to pay that.

I have found a place on ebay that sells metric straight converters to AN fittings so I could rig something up but I'd rather have an all metric system on a metric car.

mach4 · #10 05-08-2014, 08:06 AM

Quote:

Originally Posted by Stretch

I have found a place on ebay that sells metric straight converters to AN fittings so I could rig something up but I'd rather have an all metric system on a metric car.

Sounds like maybe you're letting a philosophical preference stand in the way of an economical solution

funola · #11 05-08-2014, 09:45 AM

Quote:

Originally Posted by mach4

Sounds like maybe you're letting a philosophical preference stand in the way of an economical solution

Then he must also convert the AC system from SAE to metric lol.

Stretch · #12 05-08-2014, 01:46 PM

Quote:

Originally Posted by funola

Then he must also convert the AC system from SAE to metric lol.

I've heard mention of this thing called AC - you'll have to enlighten me.

{I've never owned a car with electric windows}

Stretch · #13 05-08-2014, 01:47 PM

Quote:

Originally Posted by mach4

Sounds like maybe you're letting a philosophical preference stand in the way of an economical solution

I don't think there's any may be about it!

I've just spent ages trying to find some metric T pieces - pain in the arse...

ROLLGUY · #14 05-08-2014, 01:53 PM

Quote:

Originally Posted by Stretch

I've heard mention of this thing called AC - you'll have to enlighten me.

{I've never owned a car with electric windows}

You are in the right place for all information A/C related. Just do a search, and you will find everything you need to know. A/C is a very COOL invention!

Cejpat · #15 05-11-2014, 04:18 PM

i don't always rate a thread "EXCELLENT" ... but this is one of them