Retrofit 911 oil cooler on 964 engine – here’s how

[billjam]

As part of the work involved in a long-running project 3.6 engine rebuild, I decided that I wanted to use a 911-style engine-mounted oil cooler rather than get involved with adding a new centre-mounted cooler up front. This engine will go in a G50 Carrera which already has the fender-mounted front cooler so I don’t anticipate any cooling issues for street use.

Fitting the oil cooler requires the following issues to be addressed:
1. Camshaft P/S drive boss
2. Thermostat
3. Top oil connections (in and out of cooler)
4. Bottom oil connection (oil pump supply)
5. Air ducting

Because the power steering pump drive usually occupies the space where the oil cooler fits, this must all be removed. Unfortunately, the drive boss on the end of the RH camshaft also pokes into this space and will need to be cut off flush with the end camshaft bearing journal. I got John at Dougherty Cams to do this for me while he was doing a DC-21 regrind for me.
I will plug the hole in the camshaft housing with the standard steel plug (93010516100).

A standard 911 thermostat will fit as a direct swap for the blanking plate that is used on 964, but the thermostat won’t work until the oil passages to/from the oil cooler are opened up.
Another related issue in this area is relocation of the oil temp and pressure switches/sensors. I haven’t looked at this in detail yet, but I don’t expect any problems here if I use the top breather housing from a 911 engine.
For some unknown reason, only the front oil passage between thermostat and cooler is correctly drilled and machined to take the usual rectangular seal but the hole is plugged. Drill and tap the plug so it can be pulled out.
The rear passage is not drilled or machined for the seal. I haven’t done this yet but it will be a relatively simple machining operation – just annoying that one passage is machined and one not – go figure!



I burnt off a few brain cells figuring out the best way to adapt the bottom oil cooler connection.
The problem is that there is precious little space in this area to work with and machining the crankcase to suit the rectangular standard 911 seal just won’t work because there isn’t enough metal there to start with.
The only real option was to modify the 964 fitting (to which the original inlet oil pipe attaches). The length of this fitting must be reduced considerably so it loses the 30mm hex. Fortunately, the 17mm bore of the fitting lends itself to being cut to an internal 17mm hex so that the fitting can be tightened with an allen key or allen socket.

A visit to the local seals specialist turned up an ideal O-ring size. The diameter of the recess in the oil cooler is 26mm, so that was a starting point. The ID of the O-ring was constrained by the size of internal hex that I planned to cut in the fitting. A standard section diameter of 2.62mm gave me enough room all round so I ended up with an O-ring 26 OD x 20.8 ID x 2.6 dia. I could have gone with a fatter O-ring but the resulting smaller ID would have meant machining the fitting with a flat face and doing away with the spigot that provides the O-ring with internal support. Because this is a suction line, I prefer to have the O-ring supported on the inside.

Maintaining correct compression of the O-ring is critical so it is important to machine the fitting to suit the actual dimensions of your cooler, crankcase and the aluminium sealing washer. See A and B dimensions below. The squash on a 2.6mm Viton O-ring should be 0.5 to 0.6mm.

I guess a few pictures and drawings might help.







Ducting air into the cooler was a major piece of work timewise.
Really, the processes are all quite simple, it’s just time consuming – especially if you are learning as you go!
I decided to follow the same general shape as the ducting on a 911 engine. I considered using a standard 911 duct at the oil cooler end and just making up the extra piece to adapt it to the 964 shroud, but in the end I decided to make a whole new duct from the fan to the cooler as the 911 part didn't fit the 964 shroud very well.

I built up the shape I wanted using foam blocks and filler, then used this as my mould for laying up the fibreglass duct. I had hoped to be able to get the part off without damaging the mould so I could make up one or two spares, but unfortunately that didn’t go to plan. At least I have one good part that I can reproduce a mould from if I really need to make another duct.











Continued ...

[billjam]

For airflow into the duct, I cut holes in the 964 shroud loosely based on the 911 shroud, but without taking away too much of its strength.





Attaching the fibreglass duct turned out to be quite simple, but I wasted some time trying to find a way to glue flanged M6 nuts to the inside of the shroud. NOTHING sticks to this plastic! A few different types of speed nuts and mechanical fasteners were considered and rejected because they didn’t sit flush with the top surface. The solution was actually staring me in the face all the time. The captive nuts that are used on the front side of the oil cooler proved ideal and were available from my local fasteners specialist.



When bolted up, there are no gaps between shroud and duct, however I may use a thin soft foam gasket just to get a 100% seal to ensure that all the cooling air in the duct actually gets to where I want it.
Enjoy.

[André 3.0]

Nice work

[DUK]

I'm sure you thought of this, but couldn't you use the bottom fitting and eliminate the alum. tube on the cooler? I've always been skeptical of the feed hose so maybe there's a way to improve on that? Of course you'd have to address the oil tank fitting and supply hose.

Just my .02.

[Bill Verburg]

very nice work!

[midlife]

Very nice write up. I love the trick of shaping the internal hex on the lathe. I have never seen that before.

Thanks.

[billjam]

Originally Posted by DUK

I'm sure you thought of this, but couldn't you use the bottom fitting and eliminate the alum. tube on the cooler? I've always been skeptical of the feed hose so maybe there's a way to improve on that? Of course you'd have to address the oil tank fitting and supply hose.

Just my .02.

DUK,
No I didn't think of that, but then I really wanted to stay with a stock oil cooler and hoses if possible.
I just went out and had a look at the oil cooler and I reckon it could be done by cutting out the whole pipe and centre of the bottom flange as you suggest.
There wouldn't be much of the bottom flange left behind for mounting, but enough to do the job.

[jpnovak]

Great Post! I like the work.

I would be interested in more information about cutting the internal hex on the fitting. I have not seen this done before.

[DUK]

Very cool Bill. That's what I was visualizing.

BTW- I really like your air duct.

[jpnovak]

I think I figured out your technique for cutting the hex notches by re-reading the description.

It appears that you use the lathe as a support for the "keyway" cut using a 120 deg cutting bit. The cross-slide or tail stock is what makes the cut while the part is stationary in the chuck. Very cool.

[Trackrash]

I think I figured out your technique for cutting the hex notches by re-reading the description.

I'd call that genius. I'm definitely going to remember that trick.

[Joeaksa]

Excellent work and excellent thread!

[billjam]

It's sort of off topic, but a few have expressed interest in the method of hex cutting so I just took a few pics to clarify.
It just came to me one day while I was trying to figure out how to cut the hex.
The same principle could also be used to cut internal square holes, internal and external keyways, and external hex's or squares.

[uwanna]

Bill,

I loved the home grown engineering that went into your oil cooler retrofit! Beautiful work! I did a 3.6 retrofit into my '80SC way back in 1992. Long before the "retro kits" and such. I had to do a lot "jerry rigged" engineering myself. I did retrofit on engine cooler by drilling out the oil galleries as you did, and installing a thermostat.
I also modified the cooler by removing the oil return tube as you showed in your pic, then used a 964 (modified)screw on return tube. My dilema, after installing the thermostat, I had to relocate the oil pressure sensor/switch to the threaded hole just to the rear of the thermostat. AOK so far, but now I needed a place the locate the temp sensor. I could not find an appropriate location anywhere on the engine, so I welded a nut onto the modified oil return tube, and installed the temp sensor there! My thinking was this, on the 964, the oil temp sensor (and pressure sensor) is located on the cover plate which replaced the thermostat,
so therefore the oil temp is sensed just after it returns from the tank and pump. So if I sensed the oil temp in the return line, it shouldn't be a whole lot different!
As far as cooling air flow, I did not do any type of cooling shroud like the beautiful one you crafted. Just relied on the limited "sideways" airflow coming across the cylinders.
I know this all sounds rather primitive, ( I'm not the machinist you are) but it has worked for the last 18 years. I have a front Carrera cooler w/fan (switched on/off from cockpit) and even in 95+ deg days with the AC on I don't run hotter than 210-215.
Here's my old post thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/453580-3-6-transplant-oil-cooler-question.html

By the way, subscribed to your other 3.6 rebuild thread, great work and imagination, can't wait to see how it all sorts out. You're my new HERO!