Installation of a Bumper-Mount Oil Cooler

Background

With summer fast approaching, and with it, Track Season, which added together mean "High Engine Temps." The car is a 1977 911 Cab with a 1990 3.6L 964 engine. I primarily use it for street driving including commuting to and from work, as well as track days every other month or so, and the occasional autocross. The engine was rebuilt in the Fall of 2001.

Cooling History

When I first did the 3.6L conversion, the only oil cooling was via a stock Carrera cooler with a fan, mounted in the stock location (front right fender). A 964 engine does not have an oil cooler mounted on the engine, like a 3.2 and earlier engine does.

I had modified the stock setup by cutting a hole in the Turbo valence in front of the cooler, and fabbed a fiberglass 'pan' across the bottom. I also used strips of polyeurethane foam to fill in all of the gaps between the ccoler and the body. The net result was all air that came in thru the duct was routed through the cooler.

With ambient temps were in the high 80's to mid-90's, the oil temp ran in the 210-230 range on the street - too high by my opinion. The temperature would drop while under way, but would shoot right up again once I stopped.

To counter this, I added a Mocal cooler in the driver's side fender, with a similar hole and ducting in the valence. This brought temps down to a maximum of 210 on the street. During a track day in February with ambient temperatures in the high 60's/low 70's, with a professional instructor driving, the maximum temperature observed on the guage was between 220 and 230. For the next track event in March, I enlarged the opening a bit more and removed the foglights to improve airflow, and with ambient temperatures in the mid 70's, the highest temperature was between 210 and 220.

I still didn't think this was good enough, so I bought an RSR bumper with brake ducts and an oil cooler opening, and a Setrab oil cooler. The cooler measures 24" across, 2 3/4" deep, and 6" high. It's a single pass cooler, meaning the oil goes in one end and comes out the other, and can take fittings on the front or the sides. The cooler is available at PatrickMotorsports.com and the price is comparable to a stock Carrera cooler or Mocal cooler.

Installation

The installation is somewhat more complicated than that of a stock Carrera cooler or other fender-mounted cooler, for that matter. For effective cooling, there must be a pathway for the air to escape after it's picked up the heat from the cooler. With the RSR bumper, and with the cooler mounted just less than flush to the cooler opening, there was less than 1/2" of space between the body and the cooler. This is not sufficient. To install the cooler properly, I cut a 'notch' into the trunk approximately 5" high and 3" deep at the center. The depth of the opening at the edges is slightly more due to the curvature of the front trunk. I then fabricated a 'box' to close off the trunk, forming a channel for the air to travel down and under the car. For a street car and occasional track car, this is acceptable, but for a race car, you should consider routing the air over a specially-made hood. The box was constructed from simple 16ga sheet metal and MIG welded to the body. The cutting of the trunk, box construction and welding took two solid afternoons of work.

The cooler is attached directly to the body via bolts thru the mounting flange of the cooler. The cooler is isolated from the mounting hardware and the body by 1/6" firm rubber washers - 3 between the cooler and body, and 1 under each fastener.

Plumbing

All lines and fittings are AN-12. I routed the inlet to the top, and the outlet through the bottom. I don't know if cooling would be more effective if the hot oil went in the bottom and came out the top. I was going to do it that way, and got the hoses mixed up and ended up with it backwards. The new cooler is in series with the Carrera cooler.

Observations

So far, the oil temperature has yet to break 205 degrees in mid-80's street and freeway driving. It gets close to 200 when stopped in traffic, but as soon as the car starts moving again, the temperature drops like a rock. The temperature delta between the 'inlet' and 'outlet' of the cooler is significant, although I've only done 'by touch' tests so far. I'm close to having "too much" cooling!

Another thing you could do would be to make the box deeper on the battery side (ie farther into the trunk) and mount a SPAL fan immediately behind the cooler, with the extra trunk incursion used to duct the air from the fan.


A test-fit of the cooler with the mounting flange on top of the bumper. This was an experiemntal fit in a attempt to get sufficient airspace without cutting the trunk.


A test fit with the mounting flange facing forward, to block airflow. I decided against this methodin favor of a more stable mount with the flange closer to the body.


The trunk area prior to cutting - you can barely see the cut line marked on the original yellow paint.


A view of the trunk immediately after cutting.


A test-fit of the cooler over the new opening.


A view of the cooler from inside the trunk.


Test-fit with the cooler and the bumper.


A view of how close the cooler comes to the bumper, and this was with the cooler hanging loose!


Here's the 'box' made up to be welded in. 2 pieces of 16ga sheet metal welded together @ a 90 degree angle because I don't have a brake.


The box tacked in. Be very careful when welding on the battery-side of the car. Even though I'd cleaned my trunk thoroughly with baking soda and water, there was still acid residue from prior battery leakage. This burned when I welded in that area, and made an acrid smoke that burned the lungs.


The trunk view of the box. I left plenty of room to get the spare tire in and out. I could have taken almost another 1" into the trunk and still have been able to squeeze the tire in and out.


Side view of the box welded in. I hand cut end caps with a pair of tin snips and welded them in.



Test fit of the cooler with the box tacked in. In this picture I'm holding the cooler up at the angle where it will eventually ride.


Top mounting bolts installed after all welding completed.



Simple 1/8" x 2 1/2" flat stock for lower brackets, just because I didn't have anything narrower laying around.


View of the rubber isolation washers.


In order for the side fitting to clear the bumper, I had to cut a 2" x 3" hole in side side, and this was after I used a low-profile 3/4" NPT brass elbow (available at any hardware store) to bring the 90-degree bend closer to the cooler. There are other aftermarket bumpers available that have a larger area behind the lip, making this hack unnecessary.


The finished install, awaiting paint.