Does a radiator cooling fan have a thermostat that controls when it comes on?

 

If you are talking about the belt driven fan, the clutch is actually a low-grade form of variable torque convertor, somewhat like the one that transmits the power from your engine to your automatic transmission. The amount of fluid-coupling slippage inside the unit is controlled by a valve, and the valve is, in turn, controlled by a bi-metallic element on the front of the clutch.

When the bimetallic element gets hot, it closes the valve and that diverts more of the fluid from the slip path to the drive path, reducing the inefficiency of the clutch and increasing the fan speed.

 

If its an electric fan, the PCM controls when the fan comes on based upon inputs from the engine coolant temperature sensor and vehicle speed.
When whatever warrants the PCM to want to turn the cooling fan on, the PCM than provides the ground for the fan's relay.

 

It is an electric fan in an 04 V6. I figured something is not telling the fan to kick on. I just wanna be prepared if it's gonna cost me my first born.

 

You can switch out relays with something else and see if that makes it work (or, the thing you switched with not work!).
Otherwise, you can always wire the fan to run whenever the vehicle is on.

 

I switched it out with the engine relay and still same results is why I think it is something not telling it that the vehicle is not moving and it needs the fan to cool. Thanks guys.

 

So, can someone walk me through what needs to be done to bypass the computer and just have the fan running constantly or by a manual switch? It seems like a simple task but I am sure I can find some way to mess it up. Even pictures drawn with crayons would help this Jerry's Kid. I read somewhere that the sensor just provides the ground to the relay that operates the fan. Would I just need to ground the relay?

 

Wiring
This is perhaps the most critical section, and probably the most overlooked and misunderstood. There are many wrong ways to wire an e-fan, and they all are demonstrated during the frequent electric fan discussions on the various forums and mailing lists.

Probably the worst thing that people do is to wire the fan to a switch in the cockpit. This is the Zen concept of your "inner thermostat". Unfortunately, this built in thermostat is unreliable. The idea here is that you watch the temperature gauge, and manually turn the fan on at idle or when the temps begin to climb during low-speed creeping. The flaw in this idea should be obvious. For one thing, people are far from perfect, and can easily forget to engage the fan. In addition, the temperature gauge in the '89+ cars is horrible. By the time it has moved from it's normal (middle) position, the car is already too hot. It is entirely possible to have a defective temperature gauge, and the stock unit is only a relative indication of the true temperature of the car.

The opposite of this is to wire the fan to operate anytime the car is running. It is connected directly to a 12V IGN source, perhaps through a relay. The downfalls of this are threefold. One, you don't need the fan on all time. It is only required when sitting stationary or driving slowly. At cruise, a spinning fan is just an unnecessary load on the electrical system. Which brings us to point number two; the fan loads an already factory-overloaded electrical system. The factory 2nd gen alternator is either rated at 70A ('86-'88) or 90A ('89-'92). These ratings are optimistic, and actual output is somewhat less. Adding a constant 10A draw on this system is quite a bit of stress. Finally, you may actually overcool the car at idle, causing the thermostat to close. Not only does this increase fuel consumption, foul spark plugs and foul the O2 sensor, but it may cause a "heat spike" should you start moving under high load. The engine will heat up in the lag time it takes the thermostat to come open.

Now that we've covered what you shouldn't do, we will explain how to correctly wire your fan.

The most important concepts are: fuse, thermostat, relay. The fuse is perhaps the most important part, as it is all that stands between a wiring problem and electrical meltdown. It is critical that this fuse be located as close to your +12V source as possible, and be rated for "just enough" current to start and run the fan without allowing much overhead. This is one part most commonly missed.

The thermostat is simply the control device. The thermostat in your cooling system controls water flow through the rad depending on engine temperature. The fan thermostat controls the fan, turning it on when needed and off when not. These thermostats are available from most electric fan suppliers, as well as Summit Racing. Searching the Summit online catalogue for "thermostat" will quickly turn up several. The best are all electronic, but the electromechanical work as well. Just be aware that they may stick if they get dirty. As far as I know, all fan thermostats are adjustable, but you might want to verify that the model you are looking at is before you buy. Skipping the thermostat and just using a switch is not recommended, for reasons explained above.

Even though most thermostats have high-current contacts built in, it is important that you use a relay to switch the fan. As mentioned, electric fans pull large startup currents. This causes arcing on the switching contacts, which will wear them out over time. Using a relay means that you will wear the contacts in a cheap relay, and not an expensive thermostat. The relay is also designed for high-current abuse, whereas the thermostat contacts might not be as robust.

 

So, would be better to purchase a new electric fan thermostat sending unit? Or is that not what I am needing? I found it on Summit. I have no clue where it would go either. I really should take it to a shop but I just can't afford it.

 

I'm in the process of changing my belt driven fan to electric fan. I bought the wiring kit from Pep Boys which included all wiring, adjustable thermostat, relay and pretty detailed wiring diagram. I suggest you see if an auto parts store will let you look at the instructions in one of the kits. If it looks doable to you, give it a shot. I'm going to do the installation and wiring of the fan on my Dak myself. I've had pretty good luck with wiring projects so far (well luck, plus a couple of years of electrical engineering ).
Good luck!