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Ferrari 360 Heat Exchanger Failure Analysis

I've been examining a failed heat exchanger sent in by a fellow Ferrari 360 owner and it appears that the problematic side is from the oil and not the coolant, at least in this case.

Three leaks were detected by running water from a hose through the oil side. I used a set of banjo bolts (M16x1.5) purchased on Amazon for $13 to connect to the oil side. In addition, the HE oil side appeared to be literally packed with debris. I haven't analyzed it yet but it appears to be more than just oil mixes with coolant.

I removed one of the tubes that had a leak by using a tapered reamer on a drill press. The tapered reamer would be self-centering so I wouldn't have to be concerned with being slightly off center, which would be an issue with straight bit. The stops were set at a very conservative place and when I reached the stop, progress was checked and if no sign of cut through, lower the stop a bit and repeat. Once cut through was detected, and that was pretty easy to see, the HE was flipped and the same thing done on the other side of the tube.

It wasn't totally cut and dry to get the tube free. It took some jiggling and coaxing, plus a little swearing and it finally came free. The tube slid out of the hole quite easily once it was loose.

Here's what the tube looked like when I cleaned it up. I have a new tube above for comparison. The outer tube is corroded to the point of being completely gone. That's why it leaked. The tube just eroded or corroded away.

Old: 5.5-5.7mm OD ~5.0mm ID walls: 0.25-0.35mm
New: 6.3mm OD 4.7mm ID walls: 0.8mm (I guessed at the new material based on what sticks out of the HE)

Here's an end view. Note how thin the walls of the tube are. The inside of this tube is cruddy because it has a leak but the ones without a lear were pristine on the inside with no apparent wear or corrosion. I think blaming heat exchanger failure on a lack of coolant changes may be misguided.

I can conclude that in this case, the oil side of the HE was the one that caused the failure. There does appear to be some slight erosion of the inner tubes but they are still shiny so it's very slight.

The outer tube is obviously corroded or eroded. They're rough, have a varied surface, and the wall thickness varies quite a bit. The tubes are made of copper. The housing for the HE is made from brass and it appears that the ends that hold the tubes are brass as well. Brass is a harder metal that copper and less subject to corrosion or erosion. The copper alloy they used appears to be quite soft. It was easy to machine out the tube without generating heat.

From this cursory investigation, I would conclude that the reason why the 360 heat exchanger is failing is because the oil is corrosive to copper. It could be that people who used oil that isn't corrosive to copper have pristine heat exchangers. I doubt that oil by itself is erosive to copper. Oil by its very nature is unlikely to erode anything. So it's likely to be a corrosive force. In addition, this tube is buried in the heat exchanger and not subject to the high flow from the ports.

The debris lodged in the oil side was difficult to remove and consisted of more than just oil and coolant. It appears that the corrosion process produces a precipitate of some sort that appears in sand sized particles and not adhered to the copper. These particles can probably be found in the screen of the transaxle filter as well as the heat exchanger core.  

The debris in the heat exchanger accumulates around the tubes, blocking the flow of oil and insulating them from doing their job of exchanging heat. What effect does this reduced flow of oil have on the transaxle? 

Another conclusion I can draw is that repairing this particular heat exchanger would be difficult. Every tube would have to be replaced and there are a lot of them. 

The problem is that the rest of the heat exchanger can be degraded to the point that repairing it just kicks the failure down the road a bit. If the oil issue isn't corrected, it could lead to the case failing, which would be messy and cause the vehicle to be stuck on the side of the road.

A 3D printed heat exchanger would likely be the answer but the cost for such a device would be in the thousands. I have a quote for $2500 for one printed in aluminum. An aluminum heat exchanger would likely solve the corrosion problem once and for all but at 3 times the price of the original.

The real solution is to manufacture an aluminum heat exchanger using traditional means.


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