Mark Doiron

In the past I've shared on this forum how to install an engine fan off relay for an sPOD that's useful for fording deep water. Ever since my solar eclipse expedition, I've had occasional engine overheating problems. Turns out it strongly appears to be due to this mod. The problem is the relay itself. From a post I'm sharing in another group ...



Well, this image pretty much seals the deal. This is a shot of the old relay--I used a Dremel tool to cut it open. In the normally relaxed position (as shown), the relay passes 12 VDC to the fan. In the powered position, the relay moves the power source to the other set of contacts (open in the image), which has nothing connected to it (it has the yellow or black shrinkwrap on it in the video above, depending on which relay you're viewing). This prevents the fan from running when the Jeep wants it to run.

See how the normally connected contacts are barely touching due to carbon buildup? I believe that buildup was due to the constant vibration, when powered on washboard roads and such. Carbon builds up and prevents proper relay contact, increasing resistance. As explained above, at the current we're drawing, it doesn't take much resistance to create problems. [In an earlier post on this forum I showed video of me bouncing the old relay and a replacement and how the resistance of the relay contacts on the old one kept jumping up to around 30-50 ohms--which is going to cause a huge voltage drop at 12 VDC when drawing 35-45 amps for the fan].

Here's an interesting work-around: Normally the powered on contactor is not used for anything (a bit backwards from a normal horn relay, which, ignoring the amperage issue, is why you can't wire this through an sPOD directly). I could have taken the terminal lug on terminal 87a and moved it to terminal 87. Then I could have activated the relay with the fan off switch on the sPOD. Except, this time instead of turning the fan off, it would have passed fan voltage from the Jeep to the fan motor whenever the fan was needed (as determined by OEM circuits). It would NOT have left the fan running all of the time--that decision still resides in the normal OEM circuits. But, it would have left this relay activated even if the Jeep was turned off (unless I turned off the fan off switch on the sPOD controller). That wouldn't have been any real problem since it's on an aux battery, and the relay draws minuscule current. The more you know!

A couple last thoughts: Mike's suggestion (also my engineering physicist daughter's) to use a solid state switch would prevent this. And I'm hoping that moving the relay off the fan shroud to something with a bit more vibration resistance will prevent a recurrence. But, at least now I know where to look first next time.

----------

Just FYI, if you buy this same relay today from Amazon, the new one is much better sealed. Not saying that was the entire problem, but letting dust into the relay would certainly contribute to carbon build-up. Suggest folks who have done this mod consider a couple changes:

1. Move the relay to somewhere more isolated from road vibration than the fan shroud I originally specified. Every time my engine overheated, it was a high vibration surface, from a ferry ramp at Lake Powell, to cobblestone streets in Guymon, OK, to washboard roads in Canyonlands and Capitol Reef.

2. Buy a new relay and replace your old one unless it is hermetically sealed.

3. Learn the work-around I've described above just in case you do experience this problem.