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Guest Technical Article:

Designing and Installing An Oil
Cooler System on Your 914

Pete Dubler
pete@dublerfamily.com

So you now know that your 914 runs a bit hot, now that you have added that oil temperature gauge? It is said that lowering the oil temperature by just 20 degrees Fahrenheit will double your engine life, so why not get the oil temp down closer to 180 degrees. You just have to add one of those $35 oil coolers, right? Well, it’s not quite that simple. The cooler itself is just part of the story... A true "closed-loop" oil cooler system needs to control oil temperature, not just cool the oil.

After much research, I have deduced that it is best to run your oil between 180 and 210 degrees Fahrenheit, with the lower end of that range being favored. Running synthetic oil, like Mobil 1 synthetic, certainly helps, but once the oil starts to get hot, like on a hot day, it is hard for the little cooler in the 914 to keep up. It seems that the temperature just kinda runs away and is soon up to 240 or 250 degrees.

SYSTEM DESIGN CONSIDERATIONS

An external oil cooler would be great if it could get good cool (that is, atmospheric) air running over and through it. Not many of us want to hang the cooler on the outside of our 914’s or punch ducts in the side, although a NACA duct in the side of a 914 might not look too bad if you could figure out where to put it. Alternately, putting the cooler up front in an air dam means a lot of plumbing and each foot of additional oil line is a further invitation for disaster. The solution is to add a fan to your oil external oil cooler. That $35 cooler, just went to $105 as a quality fan will run $70, but we’re still just getting started.

We’ll come back to the fan, which will keep the cooler from getting too hot, but what about getting the oil up to a serviceable 180 degrees in the first place. I live in Colorado and so I have to deal with air temperatures between zero and 100 degrees over the year, but you California cruisers are not exempt here either. Even on a 70 degree fall day, it can take quite a while for the oil to get to 180 degrees with an external oil cooler. The solution is to control the bottom end of your oil temperature is a mechanical oil flow thermostat. This device limits, but does not completely cutoff the flow of oil to the cooler. Installed in-between the engine and the cooler, this device shunts the oil flow back to the engine until the oil temperature reaches 180 degrees, at which point the total flow is directed though the cooler.

Connecting the external cooler to the engine is another small mystery and an area of potential disaster. For the life of me, I could not figure out how to install a "sandwich" adapter and still have room to get an oil filter on and off the car without removing the longitudinal engine support bracket. What’s more, there is so much heat at the base of the engine and around the heat exchangers, plus road debris kicking up, that a standard rubber oil line would be an invitation for leaving a long black streak on the road, followed by a large puff of smoke and a complete set of expletive phrases in the air. The solution I came to was using a "spin-on" adapter and Teflon-stainless braid hose. "Wow", you say, "that must have cost a ton of money". Here is a secret: If you can turn away from the automotive racing world for a moment and stop saying "AN fittings", you can save a ton of money. W.W. Grainger sells dash 8 (that’s 1/2" to the rest of us) Teflon hose with stainless braiding and brass (not stainless, sorry race fans) fittings for a fraction of the cost of those "racing hoses". They are rated at 450 degrees continuous and 1500 psi! The trick is that you have to think "hydraulic" instead of "automotive" and use JIC instead of AN fittings. No problem here really as JIC to pipe thread adapters are also available from Grainger and they too are cheap. (See parts list)

Now that we have a way to get the oil out of the engine without spilling it, and a way to make sure it is not too cool before it goes to the cooler, we need a place to put our oil filter. To this end, a remote oil filter holder is needed. Unless you want to run a lot more hose or mount your oil filter upside down and spill a lot of oil every time you change the filter, you will need a filter holder with side ports instead of top ports. The Perma-Cool model 1791 is perfect as it will allow you to take oil in one side and let it out the other, where you will attach your mechanical oil thermostat. (See photos and diagrams).

Finally, we need to consider controlling the top end of the temperature range. This means, we need to be able to turn the fan on and off. A switch next to your oil temperature gauge would work just fine but the overhead of "heal, toe, shift, double clutch, switch oil cooler on" is just a little too much for me, so an electrical thermal switch (a.k.a. thermostat) is in order. Some folks use a radiator fan switch off a VW Rabbit for this purpose, but that has large metric threads which means some custom parts machining. I prefer sticking with fitting I can find at the local hardware store, like 1/2" pipe thread. The AC/Delco (don’t worry, using an American part will not effect your lap times), "thermo switch" I found works great. (The tiny screw in the top can be tightened to lower the switch-on temperature a few degrees, if needed). I imagine there are lots of other similar parts out there if you cannot find this one. (NOTE: I have a few available for $12.00 including shipping in the US just e-mail dublerfamily@earthlink.net to see if they are still available.) The electrical thermostat should be installed as close to the engine as possible so you are measuring the hot oil leaving the engine. The input to the oil filter is the perfect location and a brass Tee fitting works great here and turns the corner from the filter to your hose all at the same time. While we’re on the subject of brass, I suggest using brass fittings throughout as they are smooth, won’t shed or rust, and tend to stay in aluminum castings, like the oil thermostat and filter holder.

The fan current should not be switched through the electrical thermostat, unless you want to replace them often. Also, you probably don’t want the fan running in the garage after you turn off the engine, so a relay is in order. The electrical diagram shows a simple and straight forward way to address all of these matters.

If you are keeping track, your $35 cooler, is now up to about $250. A cheap insurance policy for your $3000+ engine. Parts selected, design completed, let’s move on to installation.

INSTALLATION

First, wash the bottom of the car with engine cleaner, soap and water. You will appreciate this extra effort later.

To get the big picture on the whole system, check out this photo.

The cooler is mounted on four long 1/4-20 modified carriage bolts to the right of the tranny, slightly behind the drive shaft. This is roughly adjacent to the tranny fill and drain plugs. My approach to this was to raise the car a bit for elbow room, position the cooler against the underside of the trunk marking two outer most diagonal holes, using the oil cooler flange as a template. WEAR EYE PROTECTION, even after washing, stuff is still falling on you constantly. Do this step before mounting the fan to the cooler. I then drilled two small (1/8" or smaller) pilot holes, got out from under the car, and did all the rest of the drilling from the inside of the trunk. Just lay the cooler flange holes over the pilot holes, mark the remaining two holes, and drill all four holes to no larger than 17/64". You want a tight fit for these bolts. "Wait", you say, "Carriage bolts have those nasty square ends under their heads. They will never fit in those holes." This is where the "modification" of the bolts comes in. If you have a lathe, chuck up each bolt in turn (no pun intended) and file off the square part of the bolt, down to 1/4". If you don’t have a lathe, put the bolts in a vice and file away. (This will give your gasket sealer time to dry, see below). The bolts are mounted to the trunk with sealing washers or a washer and some silicone sealer, followed by a lock washer and nut. A quick wipe around the holes with carb cleaner or some similar solvent will assure a good watertight seal. Don’t worry if the bolts don’t line up perfectly with the cooler flange holes, these 1/4-20 bolts are easy to bend into position.

The fan should be mounted on the cooler using two short (~1") 1/4-20 bolts and nylock nuts in diagonal corners with on the flange side of the cooler. Have the wires from the fan come out on the same side as the oil ports of the cooler. You will have to slightly ream or drill out the appropriate flange holes on the cooler to align with the fan holes. Be sure to place four of the rubber pads provided with the fan between the fan flange and the oil cooler to keep it quiet. Press the fan in place then remove it, leaving impressions in the rubber pads. Trim the pads around the impressions to remove the part of the pad that would be in the air flow of the fan, then mount the fan firmly to the cooler. I used some high temperature silicon gasket sealer around the edge of the fan to "seal" the air flow and improve the draw through the cooler. You want to pull air through the cooler, not push it, as this is significantly more efficient (don’t ask me the physics of this). Plan on mounting the fan to the cooler the night before you do the rest of the work so the gasket sealer is nice and dry before you handle the fan/cooler assembly again.

Assemble the adapter, thermoswitch, oil filter holder, oil thermostat, plumbing contraption on the bench, tightening all fittings to about 25 ft lbs and using Teflon tape on all threads except the hose connections. The diagram and assembly photo will help you visualize this.  The order of assembly is a bit tricky. Here are two hints. 1) connect the street elbows in the thermostat outputs, C1 and C2, before connecting the barb adapters to the elbows and 2) completely assemble the oil return line from the thermostat, E2, all the way to the JIC adapter, before assembling the brass fittings at the input of the oil filter holder. The tee with the thermo switch in it should set further away from the oil filter holder than the input elbow, allowing room to turn and tighten it. This will make sense if you just dry assemble everything once.  This photo, looking straight up from the floor will help you see this.

Install the JIC to MPT adapters to spin-on adapter and attach both Teflon hoses to the adapter. I suggest marking the output (from the engine) hose with a ring of electrical tape at the far end for later reference.
 

Mounting the filter/thermostat assembly involves drilling three slightly bigger than 5/16" holes in the vertical sheet metal behind and above the number 3 cylinder. My sheet metal already had one hole here which I used for the lower outside hole. Make a quick cardboard template to help you mark the holes in the sheet metal from underneath the car. (Notice how much easier it is to see your pencil marks since you washed the bottom of the car first) Drill pilot holes, then drill to size. A bit oversized helps for (mis-)alignment later. The final mounting of the filter/thermostat assembly is a bit tricky and best completed by asking helper to spin the nuts in the engine compartment. Push the bolts in from the underneath side and fasten with nylock nuts on the engine compartment side. (This took me a good half hour doing this without assistance, but would take less than a full minute with a helper). This is also a good time to mount your relay in the engine compartment above these holes and to the center of the car. Same size hole and bolt.

Before mounting the oil cooler, install the 1/2" MPT x 1/2" hose barb fittings with Teflon tape. The cooler is mounted with the barbs facing forward by running a regular nut a little way up each of the 4" bolts, followed by a lock washer, the oil cooler flange, and finally a nylock nut. It probably does not have to be said, but after putting on the regular nuts on each bolt, do the rest one flange hole at a time, and wear goggles for catching the lock washers that you might drop. Don’t tighten any of the nuts until they are all in place and the cooler is level to your content.

Get out the oil pan and rags and remove and dispose of the old oil filter. Might be a good time to change the oil now while you are down there. Be sure to purchase two quarts more oil than usual. Once the dripping has stopped, moisten all sides of the spin-on adapter o-ring with fresh oil and install the adapter, with the braided hoses already in place, as mentioned earlier. Depending on how high the car is jacked up, you will need to bend and manage the hoses. Avoid every temptation to use the hoses as your leverage point when tightening the holder. If necessary, a long screwdriver between the two JIC x MPT adapters on the spin-on adapter works to turn it. Tighten as you would an oil filter. If you are lucky, the hoses will end up in a straight line, one directly in front of the other. The stainless lines can now be connected to the filter holder, et al, assembly. This is a good time to install your new extra big, V8 type oil filter. (PH-8A or equivalent), filling it with oil first. (Glad you mounted the holder so the filter hole is on top?)

The stainless hoses now form a graceful arch that is probably too close to the ground. To secure the these lines, I fashioned a 3/4" wide strip of 1/8" aluminum with a through hole at one end and a 6mm x 1.0 threaded hole at the other. The holes are spaced to accommodate the two hose tie downs placed on the aluminum strip like two "Ps" lying with their heads together. ( _OO_) The through hole accommodates the 6mm x 1.0 bolt that holds the inner hose tie down and the aluminum bracket to the base of the engine where the air guide plate goes, if you have one. The threaded hole at the other end of the aluminum strip holds the outer hose tie down. I went to the trouble to use a metric thread here so there will never be a problem if the two bolts are exchanged.

The hoses from the oil thermostat output to the cooler are relatively short and protected so I just used high quality oil cooler rated hose here. I did go ahead and place these inside braided nylon protective sleeves for good measure (and because it only cost 20 cents a foot at the surplus store). If you use the braided nylon sleeve, be sure to melt the ends after cutting and try to put your hose clamps over the sleeve. One of these hoses was an almost perfect straight run of about 5". The other forms a graceful "S" curve of about 15".

Now for the electrical.   Refer to the electrical diagram.  I got my power from the starter, ran that 12 or 14 gauge wire through one of the sheet metal grommets on the left side of the engine, then over to the relay. An inline fuse holder with a 30 amp fuse is added to this line right before the relay.   The ground wire from the fan was extended and routed to the multi-ground tie off on the top of the engine using one of those nifty female slip-on connectors that also provides an extra male connector so you don’t run out of connection points. A similar connector is used to connect the "key on" power from the positive terminal of the coil. The positive wire from the fan is extended and routed with a wire from the thermoswitch though a grommet in the sheet metal (with the negative wire) near the relay above the oil filter holder. Connect per the schematic and we are ready to get cool!

STARTING PROCEDURE

Add a full extra quart of oil to the engine. The first time you start the engine after installing the cooler may be a shock as the oil pressure takes what seems to be forever to come up. To avoid this, remove the wire from the coil to the distributor and crank the engine for several seconds, resting the starter every 15 seconds or so if necessary, until the green idiot light turns off. You have now filled your cooler system with oil. Reconnect the coil wire and fire it up! Check for leaks immediately, then every once and a while for a few days. Turn off the engine after a few minutes, lower the car from the jacks, wash your hands, have a cool (nonalcoholic) drink, and then check the oil level (wiping the dipstick and then measuring). Add some more oil to bring the level up to where it belongs. Be sure to check the level one more time the next time the engine is cold.

RESULTS

As soon as I was done installing the system, I immediately drove the car hard to see how the cooler would perform. Right away I noticed that my oil pressure was, if anything, slightly higher than before the system was added. This was a pleasant surprise considering all the extra plumbing. Studying the routing of the oil flow in the Hayne’s manual, I confirmed that the oil pressure is measured after the oil returns to the case, thus any increase in pressure is not due to any constrictions or added resistance in the new cooler system. Good news! I also observed that no matter how hard I drove the car, the oil temperature never exceeded 210 degrees, and hardly ever got above 200. Call me delighted! I think you will be too.

[Diagram 1]     [Diagram 2]

914 Oil Cooler System Parts List

     [Quantity Part Name Source P/N Price (aft Shipping/Handling)]

  • 1 Mesa 48 Plate Oil Cooler Latest Rage (none) $35 ($48)
  • 1 Permacool Oil Thermostat CB Perf 1724 $37 ($42)
  • (includes 3/8 x barb fittings) (also available from Jegs, but does not include fittings)
  • 1 Permacool Remote Oil Jegs 771-1791 $20 ($22)
  • Filter Mount, Dual Ports
  • 1 Permacool Spin-on Adapter Jegs 771-111 $11 ($13)
  • 1 Permacool 8" - 10 blade fan Jegs 771-19128 $70 ($77)
  • 2 -  24" Teflon/Stainless Hose Grainger 4HM67 $29
  • 3 - MPT x 3/4 JIC Adapter Grainger 6W438 $4.50
  • 1 - 3/8 MPT x JIC Adapter Grainger 6W437 $1.50

Local Auto Parts Store

  • 1 AC/Delco Thermo Switch 1-6490970 (1/2" MPT) $10.00
  • 1 Automotive SPST (horn type) relay w/ mounting tab $4.00
  • 1 fuse holder and 30AMP fuse $2.00
  • 3 feet 1/2" ID Oil Cooler Hose (and braided cover if you wish) $7.50
  • several feet each Red 12ga, Black 14Ga ,Red 14Ga., Yellow 14Ga. $3.00
  • Automotive primary wire

Local Hardware Store

  • 2 - 1/2" (-8) rubber bushed hose tie downs Your H/W Store $0.50
  • 4 Stainless Hose Clamps for hose Your H/W Store $2.00
  • 4 - 1/4-20 x 5" Full Thread Carriage Bolts Your H/W Store $1.20
  • 4 each 1/4-20 nylock nuts, lock washers, " rubber seal washers $1.00
  • 8 - 1/4-20 nuts $0.25
  • 3 each 5/16-28 nylock nuts, 1" bolts $1.00
  • 2 - 6mm-1.0 x ~20mm bolts $0.40
  • 1 - 3/8" ring 12-16 gauge crimp-on electrical connector $0.15
  • 7 - " insulated 12-16 gauge female crimp-on connectors $1.00
  • 1 - " insulated 12-16 gauge male crimp-on connectors $0.15
  • 2 - " MPT x " Barb fittings $3.00
  • 2 - 3/8" Brass Street Elbows $3.50
  • 1 - 1/2" Brass Tee $3.50
  • 1 - 3/8" Brass Elbow $1.75
  • 1 - 1/2" x 3/8"brass bushing $0.75
  • 1 - 3/8" close nipple (brass) $1.00
  • 1 - 3/8" x 4 1/2" brass nipple $3.00
  • 1 - 1/2" x 2 1/2" brass (or galvanized) nipple $1.50
  • some... Silicone RTV sealer, Cable Ties, " Teflon Tape $2.00
  • 1 1/8" x 1" x ~3" aluminum (scrap) $0.00

Supplier Contacts

  • Pelican for all your Porsche parts needs...
  • W.W. Grainger - see your local phone book or www.grainger.com
  • Jegs 800-345-4545  or www.jegs.com
  • CB Performance (outside California)  800-274-8337 (in CA 559-733-8222)
  • Latest Rage  619-445-7553

UPDATE: May 2000

Many folks have built the cooler system described in this article. Here are a few notes to save you some money and to hopefully keep you from falsely saving money on the wrong cooler element.

There have been a few price changes and now you can get all of the key parts from Jeg’s

You can now get the mechanical thermostat and a comparable cooler from Jegs.
Here are the part numbers and prices, per Jeg’s May 2000 catalog:

  • 8” Perma-Cool Fan (now lower price) P/N 771-19128 $58.99
  • Mechanical Oil Thermostat P/N 771-1060 $38.99
  • B&M 6” cooler 130-70264 (11” x 6” X 1 ”) $49.99

NOTE: The cooler includes barbed fittings and some hose (for cooler to filter assembly run), so you can cross those off the parts list.

All together, by ordering all these parts (plus the oil filter spin-on adapter and remote mount) from one source, you can save some money and hassle over using the three sources listed in the original article.

IMPORTANT NOTE: I have been asked if using a less expensive, single tube, multi-pass, fins-like-a-refrigerator, type cooler would work as well as the multi-plate cooler recommended in the article. I believe not. The multi-plate cooler is many times more efficient because it 1) exposes much more oil surface area to cooling surfaces, 2) creates turbulance in the oil, to mix the cool and hot oil and bring the hot oil to the cooling surface, and 3) provides more cooling time, in that the oil moves slower through a multi-plate cooler. Also, the multi-plate cooler is much more rugged, so you can feel safe mounting it under the car. I have been nothing but happy with this system and believe if you follow the details in the article, you will be also.


Update: I no longer have any of the electric temperature switches. I have found that the modern aftermarket units have a set temperature that is too high for our purposes. The GM/Delco part still has the adjusting screw. You can get these through a GM dealer's part's counter. The Delco part number is: D1879, the GM part number is 25036512. They cost about $13. Be sure to turn the adjustment set screw about 1 and 1/2 turns clockwise to lower the cut-in temp to about 180 deg F. (Don't go crazy on this screw or might loose it as it falls into the switch body).


UPDATE Oct 2001: NEW IMPROVED TEMPERERATURE SWITCH

The temperature switch recommended above is not a “snap” switch so it tends to short cycle the fan when the oil temperature is near the turn-on point.  It also takes some guesswork to get the switch adjusted to the right turn-on point.  A precision snap switch with some hysteresis would be preferred.  I have had one prototyped just for our purposes.  The turn-on and turn-off temperatures are about 10 deg F apart.  This makes for more consistent operation of the system.  In order to have these manufactured, I must order a lot of 100 units.   If you are interested in receiving one of these improved switches, for $25 including shipping, please let me know as soon as possible.

pete@dublerfamily.com


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