Cooling Fan Failure
Joe Angell
Back in July I joined North East Region DeLoreans to see Bill Shea’s Back to the Future collection. Our meeting place was about an hour from where I live. Everything went well until about a mile from the off ramp, at which point we hit some traffic and the car starting getting a little too warm. The engine temp crept up to about 240 before I got off the highway. When I made it to the rally point, I shut down the car and let it cool down. After a half hour, I put about half a gallon of coolant in it, but we didn’t know what had gone wrong.
The trek from there to the to the collection was uneventful until we arrived at Bill’s farm. We were sitting in the driveway arranging our cars, and the engine temp crept up over 240. I wound up turning the car off when I was stopped and turning it on again when I needed to move.
Only when we were about to leave did my friend figure out the problem — the cooling fans weren’t running. Luckily, the return trip was almost entirely on highways, so I drove home, toggling the A/C on and off to keep the temperature under control.
Back home, I pulled the fan relay and tried to apply power with a PowerProbe, but they wouldn’t spin. We put the car up and tested the fans directly, and they ran just fine.
The Culprit
I took a break and checked my EFI wiring diagram. I knew that MegaSquirt was controlling the fans now, and that it passed through what I called a “polarity flip” relay, and then to the power relay. Everything along that chain seemed fine. My diagram also mentioned an inline fuse between the power relay and the fans itself.
I had to pull the relay sockets to get access to the inline fuse. It seems I’d used a holder with awful short wires. What I found was that the fuse had melted, which caused the metal contacts to break. The holder also had a burn mark on it.
It’s not clear to me what caused this problem. I was able to install a jumper and run the fans without issue. I removed the inline fuse holder and installed a new one with longer wires and a new 30A fuse. This worked fine, but I felt like I should add a bit more redundancy.
The melted fuse.
The melted and burned fuse socket.
The old socket and fuse (left) and the new one (right), along with the long screwdriver bit I used to pop the pin out of the relay socket.
Dual Fuses
There are two wires going from the relay to the fans. I had inserted a single 30A inline fuse there. It seemed like I should add a bit more redundancy and switch to a pair of 15A inline fuses. That way I’d be more likely to only lose one fan instead of both. The engine temperature might still go up, but it would be slower and I’d be more likely to catch the failure.
I crimped two inline fuse holders onto a single relay pin, and the other end to the fan lines. The fans run fine, but I haven’t had a chance to test it beyond that, but my car has been cool so far.
Two inline fuse holders connected to a single relay pin.
The new inline fuses attached to the fan relay and the individual fans. I tucked them under the relays before putting the cover on.