Whaat is the best method for wiring a manual override switch for my cooling fans

[jacques]

My car is a 1980 400i with three fans in the system. I would very much like to override the thermal fan switch during oppressive
Florida summer conditions. Any and all help is greatly appreciated.Thanks. Jacques.

[greyboxer]

I don't know about the best way but a straightforward way is to wire a switched jumper across the radiator thermostat bringing the wires back into the cockpit and a little hidden switch - use household two core cable and spades with a spade splitter on each thermostat terminal so it is completely non-invasive/reversible - bring the cable round the engine bay and find a grometted entry to the cockpit to slip the wire thro - find somewhere to locate a switch or just use an inline mains light switch shorted accessibly dangling down

[PTFunk]

Originally Posted by greyboxer

I don't know about the best way but a straightforward way is to wire a switched jumper across the radiator thermostat bringing the wires back into the cockpit and a little hidden switch - use household two core cable and spades with a spade splitter on each thermostat terminal so it is completely non-invasive/reversible - bring the cable round the engine bay and find a grometted entry to the cockpit to slip the wire thro - find somewhere to locate a switch or just use an inline mains light switch shorted accessibly dangling down

This is a good idea, and better than wiring into the power side of the circuit. In the latter case you'd have to find a switch (to put in series w/ the fan) with an adequate current rating, or install a properly sized relay (to handle the fan current) which would be controlled by a small switch in the cockpit. Neither approach is as elegant as jumpering the thermostat as greyboxer proposes.

[Matto]

Your 400i uses the same radiator switch as my 308 QV. FYI...if you're sure that your switch is good, you can install one that will close at a lower temperature. The VW switch is a perfect fit. Be sure that you install a new crush washer as well. This option will be a lot cleaner than any new circuit or toggle switch....and will take you a h*** of a lot less time....and no new holes in your car

RADIATOR COOLING FAN SWITCH 2 POLE
VW PN# 82395948182 180F
VW PN# 82395948172 160F

Cheers,

-Matt

[Robz328]

I will be posting soon as RobzWorkz #7b soon enough...

Two weeks ago, I just had another incident where my fan didn't turn on at a reasonable temperture (first event was with OEM 328 failing stuff 3 years ago...the "implied" cause of RobzWorkz #1); this one with an aftermarket switch circuit); engine got hotter than I wanted it to. Glad to say that only a small amount of coolant was lost.

I decided this wasn't ****ing happening again, so I devised a manual override switch and added an engine bay fan as well (I'll give Tommy Cosgrove props for this idea). I also used a simple aftermarket thermal relay switch (my aftermarket curcuit had "adjustability" and it adjusted itself to very hot indeed..."get the **** out!" was my assessment).

The circuit is close to OEM and should work on a 2-fan setup (the thermal switch had two lines to support 2-fan arrangement).

The manual override will allow me to prevent overheating in the future.

I call it my SuperCool Circuit (TM) (trademarked for fun, especially when in italicized Ariel Black font).

Details to come...

[Mitch Alsup]

If you just want the fans to run, but not full blast, you can put a 1 ohm resistor (20 Watts) in the auxilliary switch circuit.

You can also use a 3 position switch {normal, slow, blast} to operate the fan over the thermostatic control. So for operssive Florida (Texas, Arizona) heat, set the fan for slow (unless you are driving the snot out of the car.)

[f355spider]

Originally Posted by Matto

Your 400i uses the same radiator switch as my 308 QV. FYI...if you're sure that your switch is good, you can install one that will close at a lower temperature. The VW switch is a perfect fit. Be sure that you install a new crush washer as well. This option will be a lot cleaner than any new circuit or toggle switch....and will take you a h*** of a lot less time....and no new holes in your car

RADIATOR COOLING FAN SWITCH 2 POLE
VW PN# 82395948182 180F
VW PN# 82395948172 160F

Cheers,

-Matt

That is probably the simplest solution. But I have to admit I never had a problem with either my 78 308GTS or my 87 308GTS in 90+ degree temps with either car. The only time I did with my 328, it was found my radiator was partially clogged and needed to be cut open and rodded out, where they run brushes through all the tubes to clean out the debris. After that it worked perfectly.

I guess my point is all these various "work arounds" may not be necessary if your radiator is in tip top condition and the fans operate as intended.

[mikeyr]

I plan on doing a fan switch on my 360. The day I purchased my 360 it overheated on me because it was low on coolant and the rather poor design of the 360 fan system is that if you are low on coolant the switches don't turn the fans on just when you need them the most. On my old FIAT I had wired the fans to a switch on the dashboard, when I was stuck in traffic on hot days I could turn the fans on before they came on automatically and keep cooler. I don't want to bypass the automatic part, just be able to turn them on.

Glad I am not the only one thinking about it, I assumed I could run a wire to the cockpit to a switch and off both sides of the sending unit. Just want to turn on one fan, no need to turn on both.

[jacques]

You guys are great. Everything in my system is fucntioning well, as designed. I just prefer to get a "head-start" on the radiator switch, so that the fans don't have to play "catch-up" to the normaly swicthed on H2o temp...Also, I regularly use my thermo- laser gun to check all poeratining temps aroud the car, just to keep our friendly Vega gauges honest. I also plan to install a proper fuse in the line. The elegently simple brdige between the fan switch contacts is the option here,for me, since our older cars are somewhat electronically more basic. Simple is basically more elegant here.(Think of Elke Sommer juxtapposed to Jen Lo)...thank you all. Jacques.

[netman]

Watch how you do this. I did this once as a kid and my fan would run on with the key out of the ignition. My second attempt was even worse. I connected the power from the ignition module to the fan. The fan acted like a generator and keep the car running. Third time was the charm. Used the broken rear defroster circuit to energize the fan at will. High school. No money but plenty of time and a know it all attitude.

[Robz328]

Originally Posted by netman

Watch how you do this. I did this once as a kid and my fan would run on with the key out of the ignition. My second attempt was even worse. I connected the power from the ignition module to the fan. The fan acted like a generator and keep the car running. Third time was the charm. Used the broken rear defroster circuit to energize the fan at will. High school. No money but plenty of time and a know it all attitude.

Pretty interesting...the fan/battery keeping the car running...you need ignition in place (as you said) to do something like that.

I made sure my circuit worked even if ignition was off and key removed.

I figured a cooled-off engine is way more valuable that a drained battery.

BTW, I usually pull the manual battery cable disconnect anyway.

Most cars today have fans that run w/o keys in the ignition.

[FasterIsBetter]

In my admittedly limited and non-expert experience and opinion, running the fans after shut-down, especially in a rear engine/front radiator car, is worthless. But even in a front engine car, once you shut down, the coolant stops circulating, and the "heat sink" in the engine will not be effected by running the fans. Unless the coolant is circulating, keeping air running through the radiator does nothing to reduce temps inside the engine.

Now, when out driving, assuming your thermo-switch is working properly, the fans should come on by themselves when needed. When driving more than 25 or 30 mph, the airflow through the radiator from the movement of the car should be more than sufficient to cool the radiator, and at higher speeds, the fans are unnecessary. There should be enough air to keep the engine at proper temps. When idling or in traffic, the big problem is not the fans, it's the water pump. At idle, the pump is not moving enough coolant fast enough to keep the engine at normal operating temperature. Effectively, you have to increase the idle rpms to the point where the water pump is moving the coolant through the radiator. Step on the gas pedal a bit and see if the temp comes down; you'd be surprised.

If the fans are not coming on and the engine is overheating, the problem is the thermo-switch or related relay. Change them if they are not working right. If the fans are coming on and the engine is overheating, you have other problems. And if it is running hot while driving at highway speeds, the issue is not the fans, it's probably the radiator, water pump impeller, thermostat or other problem in the cooling system.

[It's Ross]

The simplist solution would be a toggle wired in parallel with the temp switch. No need for additional relays, etc.

[ago car nut]

My TR fans shut off when you turn the ignition off, always maintains a normal temp.


Ago

[BigTex]

Originally Posted by jacques

My car is a 1980 400i with three fans in the system. I would very much like to override the thermal fan switch during oppressive
Florida summer conditions. Any and all help is greatly appreciated.Thanks. Jacques.

You put a paper clip jumper in the the jack for the thermo switch.

They will run all the time as long as the ignition is "on".

[Robz328]

Originally Posted by FasterIsBetter

In my admittedly limited and non-expert experience and opinion, running the fans after shut-down, especially in a rear engine/front radiator car, is worthless. But even in a front engine car, once you shut down, the coolant stops circulating, and the "heat sink" in the engine will not be effected by running the fans. Unless the coolant is circulating, keeping air running through the radiator does nothing to reduce temps inside the engine.

(the rest of your post seems right on, although it would seem your idle may be low or wp belt slackened if you need to rev to get cooler from idle without vehicle motion; if charge light comes off, idle should be at a good point...just a guess).

I'll grant you that the cooling configuration in this car (in fact, for almost all cars) will allow no significant natural circulation flow after the engine is off; this means that, apart from the residual flow which dissipates very quickly, no mass flow rate is happening after engine shut down. However, even if the thermostat is closed, there is quite a significant amount of heat transfer throughout the system; this is due to the heat capacity of the coolant and the lower temps outside the engine.

Try this exeriment on a 3x8: idle the car in stop and level (hand brake on, not in gear, of course-like I should be one to say)) and run enough to get the fans going. Continue to idle until the fans go off (assuming you are in an environment where the temp difference will support it...sometimes it seems forever before the fans trip off while idling; could also be too strong an idle seed, generating too much heat to drop temps...you can temorarily reduce idle speed...generally not necessary if set correctly). When fans go off, immediately turn off the engine and place ignition switch back to on (keep lights, etc. off to save battery). The fans should trip on after enough heat has wicked from the system into the radiator. They should run and turn off again, having removed residual heat a little fater than in an ambient condition.

This was for a nominal 3x8, where ignition-off keeps fans off.

Also, it's much better to continue to idle until the fans trip off, especially after some spirited driving (see Owner's Manual p.33 for '89 328US). This is to remove engine heat through the radiator.

Now, walk around the parking lot on a hot day, at a mall or somewhere, and listen for the fans running on cars of which the owners have obviously left and (supposedly) taken their keys with them...residual heat being removed by design with igntion-off conditions.

[mikeyr]

a few here have said you don't need to bypass the fans, in my 360 the fans work fine and the car does not overheat BUT when I come home for work, I have to drive about 1 mile in stop/go traffic. By the time I get to the last stoplight, the fans are on and cooling the car just like they are supposed to. I end up in my driveway 2-3 days of the week with the fans running, sometimes I let the car idle until the fans go off, other times I just shut off the car.

If I had a remote switch I could turn on the fans before they needed to come on and I think that would prevent the car from getting hot enough to turn the fans on, it worked on my FIAT when I would hit traffic I would turn the fans on and it would never get hot enough for them to come on automatically.

That is why i think its a good idea, its not that the system does not work as intended.

[jacques]

Running the parallel wiring to the radiator/ fan switch terminals using two "piggy-back" connectors, thus no need for any splicing..the switch, of course, is the bridge/jumper.

[blkprlz]

Originally Posted by jacques

Running the parallel wiring to the radiator/ fan switch terminals using two "piggy-back" connectors, thus no need for any splicing..the switch, of course, is the bridge/jumper.

I would add one caution here. As additional wire is run, voltage drop increases as well. We find that our power windows suffer from voltage drop because of the length of run & its wire gauge.
That VW switch is the best alternative, I think.

[FasterIsBetter]

Originally Posted by blkprlz

I would add one caution here. As additional wire is run, voltage drop increases as well. We find that our power windows suffer from voltage drop because of the length of run & its wire gauge.
That VW switch is the best alternative, I think.

Bruce,

On most cars, the voltage to run the fans does not go through the thermo-switch. That switch only triggers a relay, and the fans voltage goes through the relay. Adding a remote switch won't change that, it is only used to trigger the relay. I'm pretty sure the same is true on these cars.