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Temperature Sensor Location....

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Alright, alright, I will give it to you. I concede that the best location for a temperature sensor to automatically activate an electric fan is indeed at or near the bottom of the radiator, i.e., in the coolest location of the stored coolant. Now, that said, there is a drain plug on the body of the TR6 block located right above the starter motor. Looks like it might be about 3/8 or even 1/2". What a great location, in my mind's eye, for a sensor to plug right into the coolant jacket. The manuals on the fan (Spal) say to plug the sensor into the head! Man, that's got to be hot coolant! Whatever, would the coolant behind this plug be under a constant state of flow when the thermostat is open (I would think there is no area of stagnant fluid) and what might the temp reading be of the coolant in this area? The beauty of this location is the sensor would be self-grounding, thus one less wire. It would be subjected to high heat from the exhaust manifold and the wire properly insulated and protected. The other option is to cut the metal down-pipe from (or to) the water pump near the short piece of hose into the radiator and put the StanPart pipe tee here with the appropriate sensor, grounded of course. Two more areas to leak.

Bill
 
I like the idea of using an existing access point to the water jacket, but cringe at the thought of all that heat from the exhaust. Why not add a tee fitting to the temp sending unit on the water pump housing. This is where Triumph chose to place their sensor for the temp guage. I realize this may simply be the same top vs bottom of the radiator discussion.
 
Hi Bill,

Well, I see the TR6 has a metal pipe in the lower rad hose, like my TR4 does. I was under the impression TR6 didn't and that you'd have to cut a lower hose and install a tee. I based my earlier recommendations on that.

Since there is a bottom pipe, I really think that's by far the easiest and best place to put the sensor.

Just remove the pipe, drill a hole in it and weld or have a bung welded (or brazed) into it. Tack weld a #10 bolt next to it for a short ground wire.

Piece of cake. The right size bung can be bought from www.summitracing.com or a variety of other places. If you take the pipe to a radiator shop to have the bung and ground bolt installed, they might even have a drawer full of the bungs. Just take the sensor along for a test fit. Being partly Scottish, I've even made bungs from cheap pipe fittings bought at the local hardware store.

My only concern would be whether that pipe is stainless steel or not. If it *is* S/S, a S/S bung and special welding would be needed. An exhaust system installation shop might be able to help. They also use NPT bungs for exhaust sensors and they need to weld S/S in some exhaust installations.

On the other hand, if it's mild steel, parts and welding are even easier to find and have done.

P.S. You could terminate the ground to the top of the steering box, where you will probably find other grounds. Or to the lefthand engine mount, which is normally fitted with a grounding strap. Both are close by the lower rad hose. BTW, I also added one more ground wire over to the radiator, for the fan relay that's installed on the side of the radiator.

Yes, the drain petcock on the side of the engine is a *possibility* that *might* work. But, I agree that radiant heat from the exhuast is a real concern. It could effect the sensor operation and/or possibly damage it or the wiring coming from it.

Another concern I would have with that sort of installation: The coolant in the block, particularly near the back, will probably warm up faster than anywhere else in the system and normally be a lot hotter than the return hose coming from the rad. There is a possibility that a sensor there will be in or near a hot spot and kick on the fan too early, before the thermostat has opened. That *might* cause pre-mature cooling from the fan, which in turn *might* delay or hinder t'stat opening. If that happened, it could really upset the function of the cooling system.

And, mounting back there on the block will probably mean running a longer wire than would be needed with a lower rad pipe installation, too. This assumes you are mounting a fan relay that will be pretty close to the radiator/fan/lower rad pipe.

All in all, I still think putting the sensor downstream from the thermostat is best and that lower rad pipe makes this particularly easy.
 
Thanks again, Alan. I wonder if my metal downpipe is stainless. Looks like stainless, but a large magnet willingly was attracted to it. Zero rust, so I might be some sort of alloy. The idea of using a tee inline sure looks easy, as seen below. It will just add two more joints that might want to leak. The tee does have lips on both ends that would hold the rubber hose on quite well though. You can see them bulging through the rubber.
bung.jpg

Just have to ground it. Got the Spal 16" fan in and am really, really impressed with the quality. Very sturdy, has a rubber gasket to rest against the fins and fits perfectly within the confines of the radiator frame. Their mounts are amazingly sturdy and can be modified for any application. That is the good news. Got my radiator back from the radiator shop and there was a distinct lack of communication. I now have a three-row (not what I asked for) radiator with diminished cooling capacity. In sheer frustration, I went ahead and ordered a Ron Davis aluminum radiator. It's just parts. Will delay the whole process about one month.

Bill
 
Bill, that is a nice clean setup. What model# Spal fan did you purchase as I am looking at them as well.
 
I got model #30102120, which is the 16" flat blade puller, with the gasket, metal mounting kit and wiring harness. You will be impressed.


Bill
 
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