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I've been working on an e-fan conversion, and I've been trying to decide where to put the thermoswitch. My concerns are response time, and cleanliness of install and wiring. I have basically three options:
- Thermostat neck: Ideal placement for temperature response, but less than ideal when trying to keep wiring neat. Unfortunately takes a place that could later be taken by the sensor for a gauge.
- Drill and re-tap bleed screw at upper rad hose on radiator: Ideal for temperature response. Lose the utility of the bleed screw, though I've also never used it. Slightly obtrusive in terms of looks, but okay for wiring.
- Drill through blind sensor boss in lower driver's side corner of radiator: Sensor already fits threads, out of the way location, neat for wiring. Unfortunately, may not be ideal in terms of response time. Deletes the irritating 3000rpm warm up.
My question boils down to this: Would placing the sensor in the bottom driver's side of the radiator cause late response to temperature change? I'm using a 210 on, 195 off switch, meaning that once it's 210 in that corner it's hotter at the rad hose and in the engine. Also, does the two-pole sensor that normally fits there have any effect other than disabling the 3000rpm warm up?
I put mine in the factory location for Turbo and Auto cars which is on the water pump housing. If you have an auto pump housing there is already a tap for it. But you can certainly pull the housing and tap in the same location. I also use the stock sensor. It triggers the fan on at 185 and off at 180 in that location. Works perfectly. The response time for the fan is not necessarily temp critical but you will want it to be upstream of the radiator, because that is the engine temp you want to trigger the fan. The downstream temp is the cold side and not what your're trying to maintain. Also 210 is too hot in my opinion. Water seals can lose integrity at 220+...
I put mine in the factory location for Turbo and Auto cars which is on the water pump housing. If you have an auto pump housing there is already a tap for it. But you can certainly pull the housing and tap in the same location.
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Also 210 is too hot in my opinion. Water seals can lose integrity at 220+...
Thank you for the feedback. Yes, I'm going to change this switch out for a 185 on / 175 off switch. I was originally looking for a 195/185, but couldn't find one.
The reason I was hoping to find a good mounting solution on the rad is it lets me keep all of the fan control stuff (sensor, relay, fan itself) in one area. I'm leaning towards drilling out and tapping the bleed screw, since it's already a good place and it isn't the high point of the cooling system anyways (I always use a funnel at the thermostat neck to fill). I've never used that bleed screw before, and my OEM rad didn't have one there, so I don't really think it's necessary.
If you aren't using the air pump bracket, there is a boss on the front of the thermostat housing that can be drilled and tapped. It is before the thermostat, so an ideal location.
Otherwise there is plenty of room on the rear of the thermostat housing to drill and tap.
The sensor should be located before the thermostat. Pulling temp from the rad is not accurate as it represents the temp of the rad, not the engine. You want the fan to respond to engine temperature.
If you aren't using the air pump bracket, there is a boss on the front of the thermostat housing that can be drilled and tapped. It is before the thermostat, so an ideal location.
Otherwise there is plenty of room on the rear of the thermostat housing to drill and tap.
The sensor should be located before the thermostat. Pulling temp from the rad is not accurate as it represents the temp of the rad, not the engine. You want the fan to respond to engine temperature.
I still have a functional air pump. I'll probably put the switch in the water pump housing boss on the back near the stock sensor, if I'm already pulling that housing. I was hoping to avoid it since I'll need to replace gaskets and everything when I re-assemble, but if it's the best way to do it then I'll bite the bullet. I might be able to tap it while on the car, but I'd rather not risk it.
One last question. On the back of the thermostat housing there is no boss for the sensor that other Rx-7's received. I can see a location that seems suitable for the sensor, but the wall isn't particularly thick in that location. Is this a suitable place to tap? It would put the sensor probe right beside the stock ECU thermosensor.
I've also tapped the top of the thermostat neck, and I'm thinking that may be a better place for the fan switch since it only reacts once the thermostat is opened, whereas the position on the back of the thermostat housing is better for a gauge since it reacts even when the thermostat is closed. Either way, I'd like to tap it now since I won't want to pull this back apart in the future to re-do it.
Thank you, Chris
Last edited by WondrousBread; 12-26-19 at 11:34 AM.
The circled area is good, but I'd be concerned about the thickness of the metal there too. Simple solution to that is to weld a bung there to secure your sensor & drill through. You don't want to mount the sensor after the thermostat.
12-18-19, 04:47 PM
