My Diff Cooler Build

[GTP]

I had success on track running without a diff cooler by double-wrapping my exhaust near the differential, and running 140 weight gear oil

But I finally got the Axle Overtemp warning at the 32 minute mark during an open track day. So I decided to design a fan-less diff cooler.

I worked with the Setrab applications engineer via email over a few weeks. He advised that -6AN lines were sufficient as was their small ~1gmp pump. I agonized the most over which cooler to choose. I planned to bolt a wide, short cooler to the underside of the spare tire well in a lateral and vertical orientation. I settled on their 9-series 15-row cooler because its width spanned the flat spots of the body the best and had the most cooling rows without extending below the ground clearance plane of the car. I positioned it about halfway between the roll bar and black fuel system box.

I considered both flow directions of oil from the diff to the cooler then the pump, versus the diff to the pump and then the cooler. The reason for the latter scheme is only because the suction load is lower. I chose the former to run cooler oil to the pump, and after being assured by Setrab that the suction would be high enough.

Another interesting feature to my build is the Setrab thermo-switch. This 180F switch is rated at 10 amps. The pump draws about 1 amp, and is fused at only 3 amps. Therefore I saw no reason for the complexity of a full 5-wire relay setup. With crossed-fingers, I proceeded to build this fan-less and relay-less design.

Pretty much everything was available from Improved Racing. Here is the flow scheme:

• Diff lower port
• Temp switch
• Hose #1
• Check valve, flapper style
• 150-micron filter
• Hose #2
• Setrab 915 cooler
• Hose #3
• Marco pump
• Hose #4
• Diff upper port (I did not drill/tap a new fill port for the obvious reason.)

This setup uses only 4.5 feet of hose! I squirted some gear oil into the pump gears, then hooked up all the hoses. I rigged up 3/8” clear vinyl tubing, two -6AN/barb adapters, and a stainless salad bowl for the pump to prime the system. (To run the pump I only had to jumper the thermoswitch and switch on the car. Once oil came out of the second tube, I connected the supply-side hose to the diff lower port (i.e. swapping input and output), and further filled the diff to the proper level using the pump. Then I connected the two hoses as they should be.

Back to another open track day, I tested it out on a 45-minute run. Temp remained steady at 230F. Mission accomplished!

Detail of checkvalve, filter, hose2, hose3, and a supporting strap for 3-point cooler mounting.

The little Marco pump, and wiring harness passed through the rubber grommet.

Thermoswitch, hose1, and hose4.

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[GTP]

Electrical path is

• interior fusebox fuse #37 for switched power
• Thermal switch
• Pump fuse 3A
• Pump
• Ground screw above fusebox, via black return wire

There are two sizeable holes with rubber plugs in the spare tire well. I cut a slit into the passenger side plug so as to route the pump wires.
Incoming power harness and 3amp pump fuse.

Source end of the 2-wire power harness.

I ran a dedicated ground wire which was screwed down to the ground point above the interior fusebox. Fuse #37 was the only other switched power I could find there.

I used a fishtape to install the harness behind this big interior cover. That prevented trouble removing and replacing the cover.

Verifying 12V switched power when the thermal switch is jumpered out.

Jumper also used to run the pump for priming and filling the system.

 

[GTP]

This photo is on the "ground clearance plane", i.e. the elevation of the lowest parts of the car. You can see that the two Setrab 90 elbows are about 2" above this plane.

 

[Optimum Performance]

You really want to run a fan, not really good airflow. At Daytona the thermostat never turns the fan on but you are at 150mph twice per lap, on normal tracks the fan is always on.

Laying it horizontal rather than vertically also keeps it from damage due to debris.

FYI, Kenny Brown has a differential cooler kit that is almost an exact replica of the one we designed and have run since about 2016-2017.

 

[Ewheels]

With the inlet and outlet ports on the bottom of the heat exchanger, won't that trap air inside? Otherwise, very nicely done! I'm curious how testing goes. It doesn't seem like that area gets great air flow but if it works enough, that's all that matters. I suppose same could be said for the trapped air

 

[luc]

With the inlet and outlet ports on the bottom of the heat exchanger, won't that trap air inside? Otherwise, very nicely done! I'm curious how testing goes. It doesn't seem like that area gets great air flow but if it works enough, that's all that matters. I suppose same could be said for the trapped air

A lot if factory mounted coolers have the fittings at the bottom so I don’t think that is really an issue

 

[GTP]

With the inlet and outlet ports on the bottom of the heat exchanger, won't that trap air inside? Otherwise, very nicely done! I'm curious how testing goes. It doesn't seem like that area gets great air flow but if it works enough, that's all that matters. I suppose same could be said for the trapped air

Yes, I was aware of the "upside down" mounting potentially trapping air. And I brought that up in my discussions with Setrab, who assured me that that wouldn't happen.

The prime and fill proceded quite slow and steady and there was not a single bubble in the clear outlet tube. (I had too small of diameter tubing which I have since corrected with 3/8" tubing and -6AN-to-3/8 barb adapters just for filling, pictured below.)

Also by removing the return hose4, the zip tie method to check final oil level still works.

As for air flow, since the cooler is fully exposed, does anyone really think that warm air will "cling" to the cooler and not be carried away by turbulent air, regardless of road speed?

 

[Optimum Performance]

This is the KB plug and play kit.

https://kennybrown.com/collections/...022-mustang-rear-irs-differential-cooling-kit

 

[GTP]

Also interesting (to me) was that I replaced the drained fluid (it had just been changed), and then added another 1.8 quarts. I suppose the small/short hoses hold more oil than I expected.

 

[GTP]

This is the KB plug and play kit.

https://kennybrown.com/collections/...022-mustang-rear-irs-differential-cooling-kit

Fascinating similarities, but I swear I figured out my build before ever seeing this kit for the first time just now!

 

[Optimum Performance]

We did this one, the day before a 3 day Daytona event, quick and crude to see how it worked. We do not like running high current wires inside the cabin so they are all through the subframe and in the rocker plastic to the engine compartment over the wheel liner.

We thought about making a kit but did not think the market would support it when Mustangs were still $30K. Now $1000 kits are reasonable being the same car is $50k.

The KB kit is all quality components.

 

[Therealmattlex]

Very nice

 

[Bossdog]

Quote:
"This setup uses only 4.5 feet of hose! I squirted some gear oil into the pump gears, then hooked up all the hoses. I rigged up 3/8” clear vinyl tubing, two -6AN/barb adapters, and a stainless salad bowl for the pump to prime the system. (To run the pump I only had to jumper the thermoswitch and switch on the car. Once oil came out of the second tube, I connected the supply-side hose to the diff lower port (i.e. swapping input and output), and further filled the diff to the proper level using the pump. Then I connected the two hoses as they should be."

How do you swap the in and out hoses after the Diff is full of fluid without all the fluid draining out the lower hole?

 

[GTP]

What you quoted is the procedure when the diff is empty but the rest of the system is primed.

I like those flexible bags of gear oil (eg Valvoline 75w140 with friction modifier). But there wasn't room to put the spout into the upper diff port adapter. So I just used the pump to fill the diff by connecting the return hose to the lower port. I could wait to see fluid coming out of the top port, or else use the vent zip tie method to check the level.

But to your point, I do have to swap hoses at the lower port quickly to prevent losing fluid and making a mess!

Clearer?

 

[Bossdog]

Yes, thank you. What is the “vent zip tie method? My guess is to place the head of a zip tie facing down in the fill port to attain the proper level below the fill port opening ?

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