DeLorean Cooling Fan Relay Upgrade

I received a bunch of positive feedback about documenting repairing my DeLorean’s shorted electrical compartment, particularly quite a few people who were curious about what kind of work it takes to maintain a DeLorean. So I’m gonna try posting details of all my constant fix-it jobs/upgrades on here. Let’s see how this goes!

My DeLorean on display at an event inside Brisbane City Hall

The whole reason I was fiddling in the electrical compartment in the first place was to work out why my cooling fans weren’t turning on. Once the car was running again, I vowed to make sure I would never have that problem any more. In its original condition the car had an indicator light on the dash that lit up when the cooling fans weren’t working, however the way this circuit worked was SO fraught with problems that the circuit itself tended to die way more frequently than the fans did, and when the circuit died it also caused the fans to fail. The standard workaround for the last 30-something years was to just jumper past the fan fail circuit. Yes this was something people were bypassing even when the car was brand new, it was so problematic. When I went through my electrical compartment I noticed my (new when I bought the car, I might add) bypass wire had turned brown from excess heat and needed replacing, so I decided it was time to fix this in a way that not only gave me more reliability with my cooling fans but re-enabled my cooling fan fail warning light again.

My DeLorean’s cooling fan jumper bypass wire – browned from overheating, it needs replacing anyway

There’s a few options here – the main ones are to either replace it with another new jumper wire and forget about the light, or go back to the original configuration that’s fraught with troubles. Thankfully one of the people in the DeLorean community, Dave McKeen aka Bitsyncmaster, offers a much better solution. He’s put together a dual-pcb solid-state replacement with fuses on top. This replacement gives dual wiring with individual fuses per fan, which will to try and keep at least one fan operating if the other fails. And if one (or both) fans fail, the cooling fan fail light on the dash doesn’t just turn on – it flashes, which grabs your attention pretty well. What’s more, it also offers current sensing capabilities so if the current between the two fans falls outside a certain tolerance (user-configurable but by default it’s 20%), indicating that one of your fans either has a still-there-but-poor connection or is close to dying, the cooling fan light will flash too. The flashing pattern is different depending on the error code so by just looking at the warning light’s pattern, you can quickly tell that not only is something wrong with your cooling fans, but which one has the fault, and in what way it’s failed. And for some icing on the cake, the whole component is encased in watertight, airtight resin so it won’t corrode in the electronics compartment. Pretty swanky! I opted for the version with physical fuses instead of the one with resettable electronic fuses because, while I don’t doubt his engineering skills, the physical fuse version has a lot more use by other DeLorean owners.

The new upgraded fused fan fail relay. Apologies for the dirty hand; I still had liquid electrical tape on me from repairing wires!

I installed it then tested different failure modes by removing the fuses to simulate failed fans. The warning light blinked in the right pattern, indicating the circuit worked perfectly. Huzzah! 😀

Now for the next area in the cooling fan circuit that I thought could do with some love – the main enabling relay! This is just a standard automotive relay that is used to turn the fans on or off, but it can still be improved. The cooling fans turn on under two circumstances – the first is when the coolant temperature reaches a certain point – and as you can imagine, this can result in a little bit of fan cycling when things are right at the cutoff limit for the thermal switch. This means a large load is switched on and off repeatedly, which causes lots of spikes & sags in the car’s electrical system. The second time it turns on is when you turn on the air-conditioning of the car – at which point the air-conditioner’s compressor kicks on (another sudden huge momentary electrical load & corresponding spike), the engine’s RPM momentarily drops from the extra resistance of the compressor which means the alternator temporarily sags in its output, and the cooling fans both turn on (another huge sag of voltage plus enabling some of the largest constant loads in the whole car).

DM-eng offers a replacement smart Solid State Fan Relay as a drop-in replacement in the relay socket. Basically this is a solid state relay (which means is uses less power and can be more reliable), that delays turning on the fans by one second after the enabling signal is received (to allow the air conditioning compressor clutch’s sag and the engine’s RPM drop to settle itself), and then also guarantees the fans will run for a minimum of 20 seconds (to help eliminate constant on/off cycling). Again it’s encased in watertight, airtight resin for longevity and you can see an example of its construction on his website.

Super boring looking, but a super useful upgrade

Fitting this upgrade was as simple as doing a relay swap. Its operation was tested with an oscilloscope, both to check the delay function and its impact on the car’s electrical systems. The delaying actions worked exactly as they should, and there was a marked improvement in voltage smoothness when the AC was enabled or disabled thanks to its staggered approach. I’ll call this one a win! 🙂

You can buy both of these relay upgrades by getting in contact with Dave McKeen, also known as BitSyncMaster, via his website.

Now that my cooling fans seem to be working perfectly, it’s time for me to move on to other electrical areas…