A couple of months ago, Part 85 of this blog told the long and convoluted story of installing a new, custom radiator in Beck TD from a manufacturer in China. I'm happy to say that I'm really pleased with the performance of that new radiator! Even on recent hot afternoons (temps around 88 F), on the road the car ran at 160 degrees, which is the temperature at which the thermostat opens. Basically, it runs as cool as possible, even in hot weather.
But, as always, there was one more thing to figure out - the best location for the sensor that controls the cooling fan for that radiator. I've just completed the third try, and I think it's the one that will remain. Here's the story of the wandering home for that sensor...
My first attempt was to try the "easy" location. The stock TD radiator has a bung in the top tank for the water temperature gauge. I had the manufacturer keep that location, thinking it would be a decent place for the sensor. Here's a photo of that bung, which I now have filled with a plug and rubber washer.
In early testing, it was obvious this wasn't a good location. My guess is that either coolant level or turbulence kept it from working right. For whatever reason, it didn't reliably turn on the fan. Time for round 2.
This location, at the front of the cylinder head, was round 2, and it was reported in Part 85. Even when that was written, I expressed doubt that the fan would turn off once it turned on, and that was the case. That location feeds the heater in the stock Volvo that sourced my engine, and is probably the hottest coolant location in the engine.
For round 3, I called my expert friend Jake, who suggested that I put the sensor on the "cool" side of the engine, and use a lower temperature sensor (180 on, 165 off). We brainstormed a few possibilities, and decided that the return port for the heater, which is built into the water pump, would be ideal. In the photo above, you can just see the plug at the bottom that I had previously made to fill that hole (reported in
Part 40). The photo below shows a mock-up from that post, rotated so that it matches the orientation in the engine.
Our idea was to make an adapter that is permanently epoxied into the water pump. I made this to match a used pump I had lying around. The hole for the sensor is tapped 1/8-27 NPT (pipe thread), and the larger hole on the back side allows coolant to surround the sensor. The screw on the side is for a ground wire, since epoxy is not electrically conductive, and the small grooves help the the epoxy firmly hold the part in place.
And here it is sitting in the junk water pump. After it fit, I assumed I was done, but when I went to install the adapter in the pump in the car, the hole was different and it wouldn't fit! It's because that hole was cast and never machined on the larger outer bore. The lesson, should I ever have to repeat this, is to buy a new pump and size the adapter to the pump. In this case, I had some very fussy trimming to do to reduce the diameter of the center part of the adapter.
And here it is installed and wired. The short black wire is grounded to the blocking plate where the sensor lived in round 2, and the green wire goes to the relay for the fan.
In early testing, it all works fine! When the engine temperatures reach the higher 190s on the gauge, the fan comes on, and 3-4 minutes later it has cooled enough that the fan cycles off. I'm calling it done!
In case I ever need to make another one of those adapters, I'll just leave the measured drawing here.
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