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!

IMHO, you don't have a problem. The various temperature senders and the in-car gauge simply aren't calibrated to the accuracy you expect. There are some pretty wide tolerances in these mass-produced thermocouples. As you've already found, you have no glitches in the wiring nor in the operation of the system as a whole. What you are experiencing is simply the non-linear, inaccurate performance of the sender's output. If it really bothers you, then you really only have two choices: buy a few more senders and swap them out until you find one that outputs the readings you're looking for; or modify the gauge circuit (possibly with a small variable resistor (potentiometer)) to calibrate the gauge to the sender's signal.

Additionally ....the stock fan switch on the Fiero is designed to turn on the fan at 235* (as Blooze says these things aren't exact ...so it seems like the fan switch is operating as designed). There are lower temp fan switches available on Rodney's site (I think it is RodneyDickman.com) that can switch the fan on at 210* instead...they are designed for the 2.8 but I think they are pretty universal and will probably work on the 3.4 (if I have this wrong I'm sure someone will chime in)

Here is what I did: I bought this thermostat and installed it next to the radiator input hose by the healight. Then I just zip tied the sensor to the input hose on the radiator. Wired it into the relay in parallel with the engine temp switch. I just set it to whatever I want the fan to come on at, Works perfect and you can adjust it to your hearts desire. Best of all is that they cost you $11.00 delivered. Larry



Ebay

[This message has been edited by trotterlg (edited 09-30-2013).]

I installed the Rodney fan switch a 190 if memory serves and the fan comes on around 210 on the gauge.

Thanks guys, you've really put me at ease. 235 seemed like an impossibly high temperature for a fan, and the fact it wasn't prompt at 235 was really making me nervous. I do not want to melt this engine... it's a 20k rebuild (per the previous owner, anyway).

I think I will do nothing at the moment since we're heading into Fall & Winter when Sacramento gets chilly, but before next summer rolls around invest in a Derale or Hayden fan controller -



I have the adjustable version of that kit installed on my XR4Ti (because I no longer have a spot for the factory switch) and it's been solid. Derale's sender's are 3/8" NPT, so it should just thread it in where the factory switch is. I'll put some time in trying to find a more appropriate temperature - or I can always fall back to the adjustable one.

Thanks!

the best way to check it is to get a digital meat thermometer and check the obvious spots for the actual heat registered.

The temp gauge sending unit could be a problem, Mine reads about 40* high

Arn

Pull the wire off your fan temp switch and ground it (engine running, or at least key on). If the fan doesn't run, the problem is not the temp switch.

quote Originally posted by TopNotch: Pull the wire off your fan temp switch and ground it (engine running, or at least key on). If the fan doesn't run, the problem is not the temp switch.

4. Verified that when I ground the connector at the fan switch, the cooling fan & blower start

As stated the gauges and what-not are not spot-on. Whereas I had my spider overheat far from home once, I've added a toggle switch to that car and my 2 Fiero's to avert such. I can now flip a switch that will bypass the relay and put + 12 volts directly on the fan. I can be useful in hot weather whereas you drop the engine temp before it gets anywhere near hot. Easy and cheep insurance.

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When I was originally concerned the cooling fan wasn't coming on at all, I was just flipping the AC on to turn on the fan. I just really don't like relying on a manual process to save my engine from melting down.

I did a little looking last night, and found the following info that may be of value to someone:

Wells GM Fan Switches:

SW500 close 220-240 / no open specified = Standard Motor Products TS147 = 3040674 (this is stock)
SW505 close 213-229 / no open specified = Standard Motor Products TS85 = 14043275
SW555 close 210 / open 205 = Standard Motor Products TS136 = 3053190

They're all the same connector, 3/8"-18 NPT threads. They should all slot right into a Fiero. Seems like the full range of OE thermostat-compatible switches. I think I'm going to invest in that SW505/TS85 and see where that gets me. The SW555 part is the expensive Buick GN switch, which seems pretty cool for a more or less stock, street driven car, but I'll fall back to it if necessary.

I use a 180* Derale switch.

Arn

Wow, that's really cold! Much too cold for a stock thermostat, and probably too cold for California in general!

My Corvettes work the same way. They come on at 235*, and kick back off around 215*. I swapped 160* stats into them. Fans almost never came on and temp very seldom went over 180*. I like mine running cooler myself. Ive never had any issues. Heat, defrost all work fine in winter and never noticed any difference in gas mileage (they have digital readouts thats proven pretty accurate).

I have one of those setable fan switches on the SuperBee and Mercedes. Mine are from Flex-a-Lite. There great. In winter i can turn them off, and leave them on full time for parades and such in the summer.

[This message has been edited by rogergarrison (edited 10-03-2013).]