mbfan72

My 87 is co-driven in autocross so it gets a lot of runs. I'd like to cool it off between runs a little quicker. The car came with the heavy duty cooling system but the auxiliary fan has never worked. I'd like to switch it to manual control.

I have the electrical diagnosis manual (but I'm no expert at this) and it appears the auxiliary fan is completely independent of the regular cooling fan, ie it has its own temperature switch and relay and does not feed back to the ECM.

I was thinking of simply placing a switch between the blue wire into the auxiliary fan relay and the red/black wire coming out (once I find out why the fan doesn't run).

Would this cause any issues?

oldalaskaman

no issues, its a pretty common changeover. the temp sender is usually what goes bad. run it thru a relay, I have mine on a switch and also put a resetable 'manual' circut breaker in line . a little overkill, the pusher fan doesnt actually do much , you'ld be better off getting one of the upgrade puller fans that dewitts sells and upgrading to a two row radiator. the dewitts fan is a bit noisy but works well. those two items will pretty much cure your heat issues.

AGENT 86

Yes !! You would be trying to feed a motor from a low amp circuit, with that plan.

Do it it safely and correctly, tap into the dark green/white wire and bring that wire into cabin switch. The other side of switch goes to a ground source.

Now you will be controlling the relay, just like the switch in head does.

LD85

this is a simple straight forward way to achieve your goal!

staugur

I have a manual fan switch kit here I never used. PM me if you would like it-comes with instructions.
Dave.

cuengineer

As Agent 86 says, it is really easy to put a switch in to the green/white wire. Just do a good splice to the wire leaving it connected to everything and bring a wire into the cabin to your toggle switch and then run another wire from the other side of the switch to a good ground (I ran mine to one of the bolts holding the brake master cylinder). Doing this, you are putting a switch to provide a ground for the relay's control circuit, i.e., low power required through the switch. Note that he fan will only work if the car is switched on.

The thing that took the most time for me was to figure out where I wanted to mount the switch. I ended up needing to replace the dash light bulbs about the same time so I ended up putting my fan switch near the instruments by drilling a hole in the dash just above and to the left side of the steering column. Is convenient and not obtrusive. I found a toggle switch that I like the looks of at Radio Shack for less than $5.

c4cruiser

The aux fan doesn't come on until coolant temp hits something like 238 degrees. You can test the fan operation by disconnecting the dk-grn/white wire from the temp switch on the left cylinder head and grounding it when the ignition switch is ON. If it doesn't run, it may simply be a bad temp switch or a bad relay. There is a diagnostic procedure in the FSM Electrical Diagnosis book on page 8A-31-4.

While you can build a circuit to run the aux fan independently, it really doesn't move a lot of air when compared to the main fan. You may want to consider wiring up the main fan to allow it to run with the engine off.

Depending on the amount of time between runs, the aux fan may not drop coolant temps enough to make the effort worthwhile. And you would be only cooling the liquid in the radiator. Once the engine starts and you start moving up in grid, the cooler liquid in the radiator moves into the engine and the hot coolant moves into the radiator. With a co-driver, the engine runs twice as much compared to single driver cars.

One thing you should be doing (even with a fan running) is to open the hood between runs. That helps to allow heat from the engine escape muck quicker. Pushing the car forward in grid can help too.

mbfan72

Thanks for the feedback. I should have seen that the temperature sender was just a switch that closed above a certain temperature completing a circuit.

Can I control the main fan in the same way (it looks like it from the diagram.