I designed and built this today because it helps cool the car a little bit when you stop. The water in the radiator is still hot and this helps cool it, then it recirculates through the motor a little more by convection, you feel the bottom radiator hose get cold within a minute.

Well it works so hopefully it will help others and here goes with an explanation.



(you can skip this bit if you dont want a technical explanation of how the circuit works)

When the engine is turned on, we get 12v on the ignition wire, this immediately charges up C1 via D1 and switches on T1, pulling its collector to ground. This pulls the the base of T2 down to ground, therefore keeping it turned off.

T2 and T3 are a darlington pair, you can replace both transistors if you wish with a single darlington transistor, I didn't have one available today so I used two. The darlington pair are simply for higher gain. Could even replace them with an N-type FET if you wish.

When you switch the ignition off, the power is immediately removed from T1 and it switches off, the charge from C1 switches on T2 which switches on T3, effectively shorting it collector to emitter which triggers the fan relay.

The residual charge in the capacitor keeps T2 switched on for around a minute and a half, could be more or less depending on the hFE of the particular transistor you get, the tolerance usually varies wildly from 100 to 400.

When the charge runs out from the capacitor, T2 and T3 switch off. This open circuits the collector to emitter of T3 and the fan relay switches off.

If you build the circuit and it doesn't keep the fan on long enough, increase the size of C1 or R1. Dont exceed about 470uF for C1 because it could blow the diode due to the inrush current and about 120Kohm for R1 since it may not have sufficient current to switch on T2. You can add a 50Kohm potentiometer in series with R1 if you want it to be adjustable (less for winter, more for summer).





Remove the airbox from the taxi and unscrew the fan relay assembly.

Wire 2 (red/green stripe - ignition 12v) needs to be cut and the relay side of the wire needs to be joined to wire 5 (thick yellow - constant 12v).

Join the loom side of wire 2 to the ignition 12v input of the circuit.

Splice the fan relay wire 3 into wire 1 (blue/white stripe - EECV thermofan trigger).

Connect the ground wire underneath the earth screw 6.

Mount electronics unit somewhere.

Reassemble and job done.

Good luck!

Well done ..

Now, give me that skyline fan for the front of mine

Hi Bozz
Are you going to sell these?
Station-rat

Probably not, thats why I posted it here to share with others so they dont have to pay more than $5 for such a product....

Why would you want to cool the motor down faster when its off? You could possibly do it damage, crack/warp head etc....

Id much rather that circuit to trigger a water pump inline with the heater hose or something, to circulate the water through the engine for a few minutes after switching it off....

Good idea bozz for sure but ...
this is good too

what voxace said is valid

IE put both together and buya davies craig electric water pump and that circut together and you an eveffective way off coolign the car down on hot day after shutdown

Explain for people like me that may not understand how cooling the water in the radiator can damage the motor or crack/warp the head.



You'll find that if you read my initial post, it states the water will flow through on its own via convection. If you dont believe me, drive your car hard, immediately stop the motor and feel the bottom radiator hose. Apply 12v to the fans for 90 seconds. Then put your hand on the return water hose from the radiator and tell me whether its still hot or whether it is now cool.

Furthermore, other testing I did confirms what I'm saying.

Right after stopping your motor, measure the water temperature using a multimeter on the ohms scale using the engines water temperature sender. You'll find after 3 mins it warms up a fair bit. Lower reading = higher temperature.

Now run the motor again, stop it and keep the fans running for 90 seconds.

Check temperature again. Tell me how much difference there is after 3 mins.

bozz
we are not saying it is a bad idea, just that it be more effective if you could pump the water around
the convention idea has merits but no were near as good as a pump
basicall liek i said combine the 2 ideas and it be awesome

From what I can see, there are basically two things going on here.

Number 1)
Theres worries that cooling down the motor too fast will cause it to damage itself. While the motor is running, the water is circulating, and therefore the water removes the heat. When its stopped, theres still a lot of heat in the engine, so that when the water pump stops pumping it reheats the water hotter than it should. By removing the heat from the water, it should stop any damamge. In things like truck engines, they have a turbo timer, which is used to prolong the life of the turbo, but also to keep the water circulating through the engine.

Number 2)
The belief that cooling the radiator will cause it to convect. When the motor is turned off, it cools down. Even quicker with the thermos left on. However, once it reaches a certain temperature, the thermostat closes, and the water can no longer flow. It will still have an effect, but not as great as first thought. If only we could have an electronically controlled thermostat

I dont think anyone would be doing any damage in trying, but its benefits may be somewhat limited. However, in between the time the motor is off and the thermostat closes, it could be of fairly good use. Might eve be worth a try for those with thermos

Andrew, it works in my car at least, if others wish to try it, it will cost a few dollars and provide *some* limited benefit. At least cool air circulates and reduces a small amount of radiant heat from the exhaust as well.

It will be of little significance on days below about 20 degrees.

On the hot days it will certainly prolong the life of many components and the heat soak in the cylinder head will be measurably reduced, as the thermostat will open further when you switch a motor off. Once a little water has flowed, the heat will be more effectively managed (read: slightly cooler head).

I agree with the EWP idea would provide far superior cooling to this simple solution but an EWP kit will cost a lot more than a pot of VB.

Disco Frank:

I didn't mean to imply you were having a go at the idea and I apologise if it sounded that way, my only concern is the suggestion running something like this could harm the motor. Somebody please explain how or correct the original post to remove the (what I believe to be) misinformation.

Cheers

Question, isn't one of the reasons why the taxi engines last so long is because they are often warm and not doing cold starts? I've heard that it is cold starts that engines hate... So if your cooling down your engine, what gain are you getting?

Yeah youre right there. But its the starting of the motor itself that is where the wear is, not the fact that its cold. If you turn your car off after getting to work, it will cool donw before you drive it next anyway. Every time a motor is started, it needs to do things like get oil pressure up, and this is where the problems occur. Without oil pressure, things wear much quicker.

I get that, but I know my EF will hold heat in the engine bay for quite some time. I can come home after school and before I get to my house I travel down a highway at 100 just cruising (so the cars running coldish), if I come back 4 hours later the engines still warm and the oil levels still fairly up. - which would mean that the cars fairly protected next time I start it.
But if your cooling the engine down every time you turn it off, it means that every time you start your car it's going to be a cold start with the oil pressure right down and what not.

No it wont. The water temperature will warm up a few degrees or more depending on how hard you were driving it right before turning it off because the combustion chamber is a certain distance away from the water jackets, and the metal on the CC side is hotter than the metal on the water side. Same deal with the piston and valves, they're hotter than the water.

Now you stop the motor and this heat gets absorbed, thats why engines rise in temperature right after you switch them off. This solution merely serves to slightly alleviate this specific problem.