Inline coolant temp switch

[zellamay]

Somewhere here I read about installing a temp switch in the radiator return line, for use with an aftermarket electric radiator fan. (I've done the fan delete with electric fan, wired to turn on with stock aux fan.) I've searched and can't find it. Sorry, I should have tagged it when I saw it. Does anybody have that thread or a recommended parts list handy? I found these, but hate to buy and then learn by trial and error.
https://www.amazon.com/Upgr8-Aluminu.../dp/B00FY2LWII & https://www.amazon.com/dp/B079633F11...ing=UTF8&psc=1 I question using that switch without a relay? ........thanks

[bluptgm3]

Additionally, some folks use an aluminum thermostat housing and drill and tap the housing for a temp sensor location.


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[zellamay]

Additionally, some folks use an aluminum thermostat housing and drill and tap the housing for a temp sensor location.

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Yes, that's the setup I'm talking about. The sites I referred to in first post are: an alum tstat housing with 1/8 npt thd and a sensor with 1/8 npt thd to go in it. Seems like it would work.

[Randy Forbes]

This happened to be an S-54 3.4 Ltr stroked engine, but the same principles are applied. In his case, the thermostat housing proved too thin to support an 1/8" NPT sensor (I don't know, maybe it was an M10 x 1.0, they're very close...) so a boss was added to provide more thread contact. Your results may vary.

[ProductUser]

Why wouldn't you put the water temp switch at or near the radiator outlet? If the outlet temp hits the target temp, the cooling fan(s) should kick in.

Just curious.

[BimmerBreaker]

This happened to be an S-54 3.4 Ltr stroked engine, but the same principles are applied. In his case, the thermostat housing proved too thin to support an 1/8" NPT sensor (I don't know, maybe it was an M10 x 1.0, they're very close...) so a boss was added to provide more thread contact. Your results may vary.

I think you guys may be talking about different things. Randy here is talking about putting a thermostat switch directly into the existing thermostat housing

But recently there was a thread where we discussed cutting the lower hose and adding a housing and switch there to control an electric fan. I thought this was what OP was looking for - that information is in the "Fan Delete and Overheating Question" thread. Starting with post #76

[ProductUser]

Gotcha. Thanks

[zellamay]

I think you guys may be talking about different things. Randy here is talking about putting a thermostat switch directly into the existing thermostat housing

But recently there was a thread where we discussed cutting the lower hose and adding a housing and switch there to control an electric fan. I thought this was what OP was looking for - that information is in the "Fan Delete and Overheating Question" thread. Starting with post #76

Right. I think I remember talk that it is not a good idea to simply attach the aftermarket fan to the stock aux fan wiring. I'm looking to control and power the aftermarket fan separately. I'll check out that thread ref you gave as soon as I have time. thanks.....

[gmushial]

Sorry for disappearing - dad ended up in the hospital for 5 wks, now is in hospice care, and is a 9hr r/t drive away, which I've been making 2 and 3 times a week [grateful the Z is a comfortable long distance driver]... so: one of those: I'd clearly rather be doing something else, about anything else things... and not having time at the moment to chase down the old thread - I'll post here: I made the hose up: it really was a 32mm adaptor ($4 dBay) [Reins sp?? hose is 30.5-31mm ID - so the fit is about perfect, a little bit snug without, and with clamps it will never leak :-) ]. everything else went per plan... but I don't have it installed yet [waiting for time to replace the heater hoses while I have the coolant out]... will post pics when I come up for air. I have the 210-195F switch installed, but also have a 190-205 switch if that proves more appropriate ($2.25 eBay each).

[rf900rkw]

This is setting the temp of the coolant being presented to the engine, so aim low. For a M54, and assuming the 15 degree spread is standard, 195-180. Maybe even lower.

[gmushial]

Thanks Randy - clearly you're the guru on this... with the switches being so cheap, and once the hose is in, can be swapped in about 2 mins - we can experiment... my first test will simply be to see how often the coolant temp is needing the 2nd fan to come on: so I'm going to just have an LED on the dash that comes on when the switch closes... and yes, 15deg is more or less the norm: though they're upside down in that: switch doesn't close until the upper temp, but stays closed until the lower one is reached. ... while I'm dealing with crazyville, I'll order up a 195/180 switch so it'll be here and ready to use when I have time. Thanks again. :-)

edit: though remember: in my model, this is for the backup fan, one that should only run if the AUX fan fails for any reason... if that's the case, do I want that much lower of a temp sensor, ie, isn't there a chance/likelihood that it'll be coming on before the AUX fan?

[rf900rkw]

Yeah, I didn't think about this being a back up to the back up. The BMW switches work the same, though I've never mapped the exact span. Opening point id's much lower than the closing temp.

[gmushial]

This is per the discussion in December (??)... where running fan-deleted is fine, and maybe 1-2% of the time the AUX fan comes on... but in the case that it has failed for whatever reason: fan, thermoswitch, relay etc died, this was to be an independent system that triggers off the water temp being fed back into the engine, where the hope was that it was never used, but if it was, it was there (*)... and to have a red LED on the dash telling one that the backup was forced into action, ie, the AUX fan system has failed.... probably I should dig up that old thread and continue there - just really time short at the moment... but given such: having the in the hose sensor trigger when that coolant temp is moving out of range was the goal, hence the 210-195 sensor/switch.

(*) though the inhose sensor could equally well be used as a replacement for the radiator sensor for those that didn't want the AUX coming on per radiator temp, but actual coolant back into the block temp

[zellamay]

I was thinking of the aftermarket fan coming on first; at a lower temp than the aux fan. Reason being: my present setup is the two fans wired together, controlled by the 81 C fan switch. They come on too late. This only happens when I've been on the highway, then come to a stop. The engine temp gauge is most of the way towards the 2:00 line by the time they come on. When they do come on, the temp goes down to normal operating temp in about 20-30 seconds. To avoid this, I keep the AC on so the fans stay on. It seems the 81C fan switch is not responding soon enough, so I will add a switch in the return line to turn on the aftermarket fan. (P.S.The system cools perfectly at any speed over 20 mph.)

[MartyBtoo]

If your fan switch is set up like my 2002 S54, it is a two stage switch that turns on the aux fan at low speed at a much lower temperature, then turns it on the high speed as you described. You should check to see if the fan switch is wired correctly (some weren't) and make sure it is hooked up correctly.

Marty

[gmushial]

I was thinking of the aftermarket fan coming on first; at a lower temp than the aux fan. Reason being: my present setup is the two fans wired together, controlled by the 81 C fan switch. They come on too late. This only happens when I've been on the highway, then come to a stop. The engine temp gauge is most of the way towards the 2:00 line by the time they come on. When they do come on, the temp goes down to normal operating temp in about 20-30 seconds. To avoid this, I keep the AC on so the fans stay on. It seems the 81C fan switch is not responding soon enough, so I will add a switch in the return line to turn on the aftermarket fan. (P.S.The system cools perfectly at any speed over 20 mph.)

I guess, from an engineering perspective, I would have what one thinks is the more reliable fan, come on first, and then the other as the backup.. and albeit from very limited data, I've had two of out AUX fans die over the years - though I'm suspecting they are likely actually the more reliable of the two [that vs a SPAL puller] ... so I would be inclined to flip-flop the sensors, ie, use the in-hose sensor to drive the AUX fan, and the in radiator sensor drive the 2nd less reliable one... this would also allow one to more easily tune the turn-on temp, in that the aftermarket sensors come in quite a range of trigger temps [165 -> 225F comes to mind in what I've seen in my looking]. [The other thing I've noticed in my looking for parts is: there are in hose sensor housings, which allow for two sensors, ie, one might think about two different temp sensors - with staggered turn on temps - and use one to drive one fan, and the other to drive the other.. ?? - though one might have to be careful in getting the orientation of the bottom sensor correct so as to not run into the a/c belt etc [I've actually seen two double sensor topologies: two side by side - but with our lower hose having limited straight sections, I'm not sure that could be made to fit; the other being two 180deg out of phase but in the same short single sensor housing - which would fit into our hose, but one would need to think about the orientation of the two so as to not collide with belts etc]].

[danomite]

I was thinking of the aftermarket fan coming on first; at a lower temp than the aux fan. Reason being: my present setup is the two fans wired together, controlled by the 81 C fan switch. They come on too late. This only happens when I've been on the highway, then come to a stop. The engine temp gauge is most of the way towards the 2:00 line by the time they come on. When they do come on, the temp goes down to normal operating temp in about 20-30 seconds. To avoid this, I keep the AC on so the fans stay on. It seems the 81C fan switch is not responding soon enough, so I will add a switch in the return line to turn on the aftermarket fan. (P.S.The system cools perfectly at any speed over 20 mph.)

It seems that people are still confused about how the system works in our cars, and I'm the one who described the set-up that I developed with the in-line back-up fan switch...so if I may: If you have the 81/88C switch installed for the aux fan, and you're nearing overheat situations often, then the temp switch for the fan is not your issue...either you have a blockage in the cooling system somewhere (most likely the radiator), you have air in your cooling system, or your t-stat is failing/malfunctioning. The "job" of the aux fan switch, mounted in the cold-side tank of the radiator, is to trigger once the water temp on the cold side of the radiator becomes too hot (not enough cooling air flowing through the radiator elements)...thus cooling the water in the radiator, allowing the radiator to supply "cooler" water back into the engine. Most of our cars have a wide "normal" operating temperature range, as far as the little needle on the dash is concerned. Our engines begin to "overheat" at about 120C/245F. If you're seeing the needle on the dash move, it means that you're in the 115C/240F range, and that shouldn't be happening! Remember that the temp you're seeing on the dash or on your OBD reader is the temp of the water IN THE ENGINE...not the temp of the water in the radiator! So, if your engine is nearing an overheat situation, and your aux fan switch works but seems to come on late, that means that for some reason the hot water coming from the engine isn't getting to the aux fan switch quick enough to trigger it sooner. It sounds to me like your have a blocked radiator or air in the system. I'd do a COMPLETE diagnosis of my cooling system if I were you, because the needle shouldn't be moving at all when the system is operating correctly (yes, even with the fan delete). Check your radiator for blockages, check all hoses, check all clamps, check your t-stat, check the fan, check the switch, check for air in the system, etc. Run all of the tests! Then, and ONLY then, will you know where you have the issues.

I guess, from an engineering perspective, I would have what one thinks is the more reliable fan, come on first, and then the other as the backup.. and albeit from very limited data, I've had two of out AUX fans die over the years - though I'm suspecting they are likely actually the more reliable of the two [that vs a SPAL puller] ... so I would be inclined to flip-flop the sensors, ie, use the in-hose sensor to drive the AUX fan, and the in radiator sensor drive the 2nd less reliable one... this would also allow one to more easily tune the turn-on temp, in that the aftermarket sensors come in quite a range of trigger temps [165 -> 225F comes to mind in what I've seen in my looking]. [The other thing I've noticed in my looking for parts is: there are in hose sensor housings, which allow for two sensors, ie, one might think about two different temp sensors - with staggered turn on temps - and use one to drive one fan, and the other to drive the other.. ?? - though one might have to be careful in getting the orientation of the bottom sensor correct so as to not run into the a/c belt etc [I've actually seen two double sensor topologies: two side by side - but with our lower hose having limited straight sections, I'm not sure that could be made to fit; the other being two 180deg out of phase but in the same short single sensor housing - which would fit into our hose, but one would need to think about the orientation of the two so as to not collide with belts etc]].

You can have the standard aux fan work as your primary fan (which is how I have it), or as your "emergency" fan. You need to decide how you want the system to run before you satrt setting things up though, other wise you'll be adding extra work, parts, and costs to your build. Here is how my system works:

I bought an 81/88C switch, an in-line hose connector, a Spal 16" 2021cfm puller fan, a Spal relay kit (which is not necessary, and had a custom aluminum shroud made. I mounted the Spal fan and relay to the shroud. I installed the in-line hose connector into the lower radiator hose near where it exits the radiator. I removed my OE 91/99C switch from my radiator, and installed it in the in-line hose connector (after testing and verifying it works correctly). I then installed the 81/88C switch into the side tank of my radiator (again, after testing it and verifying it works correctly). Next, I ran the wiring from the Spal and relay to the 91/99C switch in the in-line hose connector. Finally, I connected the wiring to the aux fan switch and refilled my cooling system.

As such, I have my aux fan set up as my primary fan, and the Spal is the "emergency" fan. You can set yours up the other way by simply swapping the 81/88C and the 91/99C switches...the your Spal fan will come on first (at 81/88C), and your aux fan will be your "emergency" fan (coming on at 91/99C).

So, decide which fan you want to perform which duty. One is your primary fan, and one is your "emergency" fan. I chose my set-up based on the simplicity and ease of assembly. I did not have to modify and wiring or connectors, which you will certainly have to do if you plan to have the aux fan run from the in-line hose connector circuit. It's not super complicated...just swap the 81/88C and the 91/99C switches from how I did mine, wire the aux fan connector to the in-line hose connector switch, and wire the Spal fan to the

*Important note: Always make sure you're using the correct gauge wiring for the application!!! DO NOT use wiring that is too small, or you risk short circuiting the system, or starting an engine fire (worst case).