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Dr. Hess
Dr. Hess MegaDork
6/27/19 2:11 p.m.

I've been piddling with the Locost lately.  Not like I don't have other things to work on, like the 429 Desert Eagle, ZAV, maintenance stuff, etc., but I've been piddling with it.  Wiring specifically.  I have the front of the car almost done.  Headlights, turn signals, etc.  I'm using the MR2 front relay/fuse box.  The radiator fan is now run by one wire to the relay.  Put 12V on it and it turns on the fan relay.  I need some way to control that +12V. 

 

The 20V's ECU doesn't run the fan.  I was thinking of adding one of these:

https://www.jegs.com/i/Speedmaster/746/PCE184.1005/10002/-1

or

https://www.jegs.com/i/Derale/259/18748/10002/-1

to switch the relay, but then I got to thinkin'...  Where should the temp sensor be?  I mean, the fan is there to move air across the radiator when insufficient air is moving over it otherwise.  So, should the temp sensor be on the radiator output?  Engine output of hot coolant to the radiator, cooled in the radiator, then out the radiator and back to the motor.  If the radiator isn't cooing sufficiently, then you want the fan on.  Not necessarily just when the motor is up to 185F, as the motor could be there but the radiator could have enough air to not need the fan on.  What should normal temp be on the radiator output?  Probably not ambient, but at what point do you switch on the fan?  Maybe two thermistors, one on radiator in and one on out, and if the differential is insufficient and above 185F then turn the fan on.  Then maybe an Arduino to monitor the thermistors, make a decision and turn on the relay?   Or wait for the motor itself to get over 190F?  Seems rather crude to me.  I mean, wait for the motor to overheat, then turn the radiator fan on and hope for the best?  That seems to be the approach commonly used, but it just seems like a sub-optimal solution.


I dunno.  Maybe just wire the fan to a switch on the dash, like Lotus used to do, and not worry about it.  Hey, dummy, if your car is overheating, you should have turned the fan on.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
6/27/19 2:19 p.m.

Driver controlled fans are an excellent source of dead motors.

The 1.6 Miata turns the fan on with a thermoswitch that's mounted on the radiator side of the thermostat. Simple. I'm not 100% sure what the switching temperature is, but it's higher than thermostat temperature because, well, you only turn the fan on when the thermostat can't keep the car at its normal temp.

The aux fan on my Mini is similarly triggered with a universal unit. It's reading off the temperature of the radiator fins. I can adjust the on temperature with a screwdriver, and I have it set to turn on only when the thing is starting to struggle.

NAPA has the Big Book Of Thermoswitches behind the counter that will give you a huge choice in trigger ranges, threads, type of switch, etc.

It doesn't really matter exactly where the switch is as long as you have it tuned to match. If it's on the outlet of the radiator, you'll want it to trigger at a lower temp than if you have it at the inlet.

rslifkin
rslifkin UltraDork
6/27/19 2:29 p.m.

Thermostat on the output of the radiator is better IMO.  That triggers the fan on airflow need (to keep radiator temp down) rather than based on engine temp.  So when idling for a while the temp swings as the fan cycles tend to be smaller.  

1988RedT2
1988RedT2 UltimaDork
6/27/19 2:31 p.m.

The fans on the RX-7 and the truck are mechanically driven, so if the motor is running, the fan is moving air.  It's extremely effective, reliable, simple and cheap.  Years ago, virtually every vehicle on the road used this same method.  That's the way it was, and we LIKED IT!!

 

TurnerX19
TurnerX19 HalfDork
6/27/19 2:38 p.m.

Some OEMs do it at the radiator outlet, some do it at the inlet. Like 1998RedT2  I prefer radiator outlet temp and trigger on just above the thermostat temp, trigger off about 10% lower.

dean1484
dean1484 GRM+ Memberand MegaDork
6/27/19 2:44 p.m.
rslifkin said:

Thermostat on the output of the radiator is better IMO.  That triggers the fan on airflow need (to keep radiator temp down) rather than based on engine temp.  So when idling for a while the temp swings as the fan cycles tend to be smaller.  

I did this and I set up the rad fan so when the rpm was under 1500 It came on if under this amount for more than 10 seconds. The off was also on a 10 second delay for over 1500 rpm. This way it would always come on in the pits as drivers always forget to turn the fan on when pitting. The temp sensor I don’t think turned on the fan when the car was at speed. We did have a manual override to turn the fan on and a yellow light would come on when the fan was on. But there was no way to turn the fan off if under the 1500 rpm or if the temp sensor called for the fan to be on. This set up was also a kind of alarm that if it came on when the driver was at speed it probably meant that there was some sort of obstruction on the air inlets or junk on the rad. Once I put this setup on the car no more overheating in the pits due to drivers forgetting to turn the fans on when they came in. 

dean1484
dean1484 GRM+ Memberand MegaDork
6/27/19 2:52 p.m.

Thinking about this mor I think I had the sensor in the outlet from the motor to the rad so the rad would cool things as it came in to the rad. Not sure if this was the best but it worked. 

In another car that came with two fans I wired one as noted above and the second was manually controlled. I am not sure if the manual one was ever used or not. 

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
6/27/19 2:53 p.m.

+1 for radiator output, that's the ideal location.

Jumper K Balls (Trent)
Jumper K Balls (Trent) PowerDork
6/27/19 2:58 p.m.
Keith Tanner said:

Driver controlled fans are an excellent source of dead motors.

 

Once again Keith puts the truth in simple terms. I cringe at the sight of a toggle switch on the dash labeled fan.

 

I keep a M22-1.50 tap handy at all times. I make bungs in either aluminum or steel to weld into aluminum radiators or solder into others. I put them in the exit tank. The VW fan switch from the late 70's to the early 90's is available in multiple temp ranges. I like the on at 195 degrees and off at 180 for most cars. It is robust and can handle up to a 40amp fan without a relay. Makes for easy simple wiring that will continue to run after the car is shut off.

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
6/27/19 3:01 p.m.
Jumper K Balls (Trent) said:
Keith Tanner said:

Driver controlled fans are an excellent source of dead motors.

 

Once again Keith puts the truth in simple terms. I cringe at the sight of a toggle switch on the dash labeled fan.

I have one in my Samurai in an on/off/auto configuration. I need to be able to turn it off for deep wading. Still, on one of my more recent offroad rallies I turned it off when the engine stalled during a long uphill climb, to try to give the starter a voltage boost. Forgot to turn it back on for a minute and definitely added some drama to the event...

Jumper K Balls (Trent)
Jumper K Balls (Trent) PowerDork
6/27/19 3:22 p.m.

Since I am in the process of putting an electric fan in my mini I have a VW  switch on the toolbox

This is a 2 speed switch but single speed is more common. 22mm thread. I have seen too many of the "spear the fin" probes become dislodged to trust them. I prefer direct to coolant contact.

rslifkin
rslifkin UltraDork
6/27/19 3:31 p.m.
Jumper K Balls (Trent) said: Makes for easy simple wiring that will continue to run after the car is shut off.

Personally, I hate fans that run after key off.  The engine isn't running, it doesn't need airflow for cooling.  All that does is draw the battery down a bit for no real benefit.  

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
6/27/19 3:50 p.m.
GameboyRMH said:
Jumper K Balls (Trent) said:
Keith Tanner said:

Driver controlled fans are an excellent source of dead motors.

 

Once again Keith puts the truth in simple terms. I cringe at the sight of a toggle switch on the dash labeled fan.

I have one in my Samurai in an on/off/auto configuration. I need to be able to turn it off for deep wading. Still, on one of my more recent offroad rallies I turned it off when the engine stalled during a long uphill climb, to try to give the starter a voltage boost. Forgot to turn it back on for a minute and definitely added some drama to the event...

My old Land Rover runs the fan when wading because some weirdo attached it to the crankshaft with a belt :)

A fun way to implement this would be to put in a momentary button that triggers "fan shutdown". Use it to trip a relay that will only stay energized while the ignition power is on, so it resets as soon as you shut down the car. Also light up a big crazy warning light.

Or use a water sensor that shuts down the fan when it's submerged :) Ooo, this is a fun problem.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
6/27/19 3:52 p.m.
rslifkin said:

Thermostat on the output of the radiator is better IMO.  That triggers the fan on airflow need (to keep radiator temp down) rather than based on engine temp.  So when idling for a while the temp swings as the fan cycles tend to be smaller.  

I'm not sure it makes a difference as long as the water pump is running. The thermostat is doing the bulk of the work, if the engine is adding more heat than the radiator can shed then the engine temp will keep climbing at both the inlet and the outlet, and temperature at the engine is what really counts.

Are there any OE applications where the temp sensor is at the radiator outlet? Serious question, as I only know anything about one car :)

TurnerX19
TurnerX19 HalfDork
6/27/19 3:59 p.m.

Volkswagen Volvo 240 and (old) Fiat have radiator outlet fan switches. I know nothing of Fiat after 1987cheeky

Stefan
Stefan MegaDork
6/27/19 4:07 p.m.
rslifkin said:
Jumper K Balls (Trent) said: Makes for easy simple wiring that will continue to run after the car is shut off.

Personally, I hate fans that run after key off.  The engine isn't running, it doesn't need airflow for cooling.  All that does is draw the battery down a bit for no real benefit.  

Actually, it does help as the water continues to cycle via a thermosiphon effect, it also helps cool the entire engine bay.  If your battery is that weak, then you have bigger issues.

Dr. Hess
Dr. Hess MegaDork
6/27/19 4:07 p.m.

If I had thought of this when I did the cooling system, I think I would have welded a bung to something for one of those screw in switches.  I didn't, and welding on the cooling system now is going to be a major PITA.  So I am leaning towards a sensor based system.  What are this through the fin things?  I didn't see anything on Jegs like that. I just need a low current switch to control the relay, not something to switch 20 amps. 


So water comes out of the radiator and back to the motor, picks up heat, dumps it in the radiator.  Seems to me that the radiator exit temp should be considerably below engine temp so that the water has some heat capacity in it to pick up more heat.  Don't know where, but maybe have fans come on at like 120F? 140? on the radiator outlet. 

My schematics show that Toyota just kinda put a switch somewhere, but I don't think there's one on the motor, and I don't have a full 4AGE20v AE101 car schematic, just the engine section.  On the MR2, it was controlled by the AC computer.  Not on the AE101, at least not from the schematic I have.  It might still have been by an AC computer, but all the pinouts I see are going straight to the ECU and I don't have that anyway.

boulder_dweeb
boulder_dweeb Reader
6/27/19 4:07 p.m.

Hey,

I used something similar to the Speedmaster on my last V8 Vega. The probe went into the top radiator hose, and with a health dose of RTV sealed fine. Car never overheated. Easy-Peasy.

Rog

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
6/27/19 4:24 p.m.
rslifkin
rslifkin UltraDork
6/27/19 4:30 p.m.

For the battery thing, having a lead acid battery (especially a typical engine start battery that's not meant to be cycled) sit at even 95% charged rather than 100% has a definite negative effect on its lifespan.  So the battery draw after shutdown isn't about not being able to start it again, it's about shorter battery lifespan for no real benefit.  Yeah, some water will still circulate for a bit, but unless you're shutting it down with it running very, very hot, there's no real benefit to running the fan after shutdown.  No OEM I know of does it. 

In reply to Keith Tanner :

BMWs with electric fans (including the electric pusher fan on your M5) are controlled at least partly based on radiator outlet temp.  Engine temp is only used to trigger the fan to go into "oh E36 M3" mode from what I remember. 

The idea of controlling on rad outlet temp is that much like a clutch fan, you're aiming for making sure the engine is getting cool enough water for the thermostat to regulate effectively.  When you stop, rad outlet temp climbs, fan comes on. 

Triggering on engine temp works, but it's not as smooth, as you generally wait until the engine heats to the upper end of the thermostat temp range before the fan kicks on and then it drops a few degrees.  My Jeep is done this way, the E38 (converted to electric fan using the stock DME aux fan control) is triggered on rad outlet temp.  Left idling with the A/C off, the Jeep will see about a 5* coolant temp swing as the fan cycles (and it stays at the upper end of the thermostat temp range, so noticeably warmer than when moving under light load).  The BMW only varies about a degree as the fan cycles, as it can stay near the bottom of the thermostat temp range (but without the fan running almost all the time like it would if I set the trigger point colder on the Jeep). 

Stefan
Stefan MegaDork
6/27/19 5:06 p.m.
rslifkin said:

For the battery thing, having a lead acid battery (especially a typical engine start battery that's not meant to be cycled) sit at even 95% charged rather than 100% has a definite negative effect on its lifespan.  So the battery draw after shutdown isn't about not being able to start it again, it's about shorter battery lifespan for no real benefit.  Yeah, some water will still circulate for a bit, but unless you're shutting it down with it running very, very hot, there's no real benefit to running the fan after shutdown.  No OEM I know of does it. 

In reply to Keith Tanner :

BMWs with electric fans (including the electric pusher fan on your M5) are controlled at least partly based on radiator outlet temp.  Engine temp is only used to trigger the fan to go into "oh E36 M3" mode from what I remember. 

The idea of controlling on rad outlet temp is that much like a clutch fan, you're aiming for making sure the engine is getting cool enough water for the thermostat to regulate effectively.  When you stop, rad outlet temp climbs, fan comes on. 

Triggering on engine temp works, but it's not as smooth, as you generally wait until the engine heats to the upper end of the thermostat temp range before the fan kicks on and then it drops a few degrees.  My Jeep is done this way, the E38 (converted to electric fan using the stock DME aux fan control) is triggered on rad outlet temp.  Left idling with the A/C off, the Jeep will see about a 5* coolant temp swing as the fan cycles (and it stays at the upper end of the thermostat temp range, so noticeably warmer than when moving under light load).  The BMW only varies about a degree as the fan cycles, as it can stay near the bottom of the thermostat temp range (but without the fan running almost all the time like it would if I set the trigger point colder on the Jeep). 

My Porsche does it.  They also wired the circuit to run the fan slower when the ignition is off.

Dr. Hess
Dr. Hess MegaDork
6/27/19 5:36 p.m.

That's an interesting gizmo, there, Keith.  Not real sure I have room for it.  It's tight.  I'm kinda leaning towards a through the radiator switch or a bulb switch clamped on to the radiator output line.  I have sanitary tubing running back from the radiator to the motor.

dean1484
dean1484 GRM+ Memberand MegaDork
6/27/19 6:09 p.m.

One time we added a temp sensor to a car by soldering a brass nut to the side tank of the rad. The sensor was screwed in to it with a little thread locker of some sort. I remember that using a two wire sensor was critical as the rad was not grounded. 

daeman
daeman Dork
6/27/19 6:30 p.m.

You should be able to get a 4age thermostat housing with a hole for a thermo switch.

Otherwise has the radiator got a plugged sensor hole or drain bung? I've used a drain bung to fit a thermo switch in the past.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
6/27/19 6:40 p.m.
Dr. Hess said:

That's an interesting gizmo, there, Keith.  Not real sure I have room for it.  It's tight.  I'm kinda leaning towards a through the radiator switch or a bulb switch clamped on to the radiator output line.  I have sanitary tubing running back from the radiator to the motor.

Drill that sanitary line and put a threaded boss in it for a sensor. You'll need to ground the pipe.

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