Since I bought this '87 GT (3.4pr swap) nearly a year ago I've been unable to get the cooling fan to operate at what I think is a normal temperature. I am hoping someone can suggest something I have overlooked, so here's what I've done/verified:
1. Replaced everything. New gauge sender, FI ECU sender, fan switch, thermostat
2. Drained and refilled the cooling system
3. Thoroughly checked grounds. Everything in the car works great, charging works perfectly - I really have little reason to doubt the electrical system
4. Verified that when I ground the connector at the fan switch, the cooling fan & blower start
5. Verified the relay (by the headlight) is in good shape and switches properly
6. Turning the AC on turns the fan & blower on every time without fail, so I am sure the fan & relay are both good
7. The initial cause for alarm is that the gauge reads about 250 degrees (!!!) before the fan starts, but....
8. So.... I bought an ALDL cable and Tuner Pro to verify the gauge - it's very high at low temps (it reads ~220 when the ECU shows ~195), but loses ground as the engine heats up (when it reads ~245, the ECU shows ~240).
9. I have no reason to doubt the cooling system. It takes a good long time to get hot (traffic, or a really long stop light in high ambient temps), and seconds after the fan starts engine temps drop rapidly. In my testing tonight, I waited until 240 degrees (as shown by Tuner Pro), let the fan come on, and it was down to 210 degrees in a matter of minutes. I am sure there is excellent circulation, as cooling at the radiator is reflected at the engine quickly. The heater works great, too. As long as the car is moving at more than 25mph (and well past 80mph
) the engine temp stays between 190 degrees an 200 degrees (as shown by Tuner Pro) without fail. Everything about the cooling system behaves - except the fan.
10. Once the fan turns on at 240 degrees (as shown by Tuner Pro), it shuts off again at about 215 degrees (as shown by Tuner Pro)
I just don't know what else to even look at. The only thing I've got left is that there is a 5 degree temperature skew between the FI ECU and the fan switch, AND that this particular fan switch is optimistic when it opens. I'm under the impression it's supposed to close at 235 degrees (Tuner Pro says that happens at 240 degrees) and open at 205 degrees (Tuner Pro says that happens at 215 degrees). Am I being paranoid and does this all sound ok? Or, is this an actual problem and what have I overlooked?
Thanks for any tips!