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I named my baby OJ.
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Discussion Starter · #1 ·
I posted previously that my radiator was bubbling....
well I realized that this tends to happen when I'm driving slowly up a dirt road, which happens fairly frequently over here on the Oregon coast.
Not much airflow getting through the radiator, and the fan is NOT coming on.
In fact I've never heard the fan come on.
Normal driving at highway speeds, no bubbling! I do have a new rad cap arriving today I think as well.

So, how can I test the fan, and the corresponding thermostat that controls it?
Please note I am not talking about the thermostat that controls the flow of coolant, thank you.
 

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The PCM turns the fan on (or tries to) when the engine coolant temp sensor (located on the pipe line leaving the thermostat housing, pretty much obscured by the large rubber air inlet duct) thinks the coolant is above about 210 degrees. That sensor has two contacts to its connector,and if you pull that connector off of the sensor, with the engine running, the can should turn on. But there are 3 other relays involved. The relay inside the fuse/relay box close to the driver's side strut tower has the relay which is sup;posed to supply 12 volts to one side of both fan relays (these are hidden behind the air filter housing inside the fender. One of them gets one side of its coil connnected to ground, for the low speed fan to come, the other relay gets one side of its coil connected to ground to cause the high speed fan to come on. Each of these relays may have some melted contacts or melted connectors to them.
A good test of the fan is to pull the connector apart, and connect 12 volts directly across two of the wires, and across the other two wires, thus testing for both low speed fan and high speed fan motor operation The fans themselves do quit working after enough years - bad bearing, bad motor coil, etc.
With a 99 I believe, the fan should run very briefly at the time of first turning on the ignition. You may need to have the hood open to hear it or feel the air flowing. This would only be for a few seconds.
 

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I don't know if it's the same with third generation cars, but on the second gen you can test the fan by having the ignition on, engine not running (or running, it'll just stop) and then removing the fuel injection relay under the hood. The fan should then run regardless of engine temperature.
 

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Unplug the silver connector on the thermostat housing and the fan should come on

The fan should also come on with ac but will not come on until coolant reaches 220 or so
 

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I named my baby OJ.
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134 Posts
Discussion Starter · #5 ·
Hey Thanks guys! I'll let you know what happens.
Great info!! (y)
 

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I named my baby OJ.
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134 Posts
Discussion Starter · #6 · (Edited)
So, 1st off fan IS working, so that's good news.
Comes on at start up as someone mentioned.
AC was on too, so not sure if that has something to do with it.
Had to order the rad cap, genuine Motorcraft. Installed.
Not completely certain but haven't noticed any bubbling lately.
Keeping an eye out. Knock on wood!
Thanks for the help!
 
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Glad that you are having some success with the car, and thanks for letting us know.

If the a.c. is working and you have it on with the engine idling, the fan should be running; either immediately after you turn the a.c. on, or soon thereafter, since the coolant will get hot pretty soon.

It is possible to buy a small coolant tester, which you use by sucking coolant into the tester with its rubber 'bulb', and it will tell you either the percentage of antifreeze in the system, or the boiling temperature / freezing temperature of the coolant. Doing an ebay search for the terms "antifreeze tester" will show you what they look like. Should be done when the coolant is not hot, at least not scalding hot.
 

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I named my baby OJ.
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Discussion Starter · #8 ·
Well I just changed it recently, so
I think I'm good. 50/50
 
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