So I thought the 1985 had a two speed fan and we are unsure if the dash temperature gauge is the problem or some unknown ground for the circuit. I can let this car idle for 30 minutes The fan never comes on gauge seems to operate normally rising from room temp to hanging mostly at 220 but going beyond to the 230or so after awhile no fan. If I turn on the A/C fan comes in as expected. We went looking for a resistor up front but found none. We knew the temp switch needed replacement ordered the single speed kit from Rodney Dickman for 195 thermostat
If with the car at 220 I ground the wire going to the switch bingo the fan comes on.
Only 84 Fiero w/ AC have 2 speed rad fan. Engine at 220-230°F is not an "over heat" condition and why GM used 235° engine switch. AC turn on rad fan is for added air flow because AC Condenser heats air above ambient and could make problems for engine cooling. See my Cave, Rad Fan
Quickly climbs at Idle may not just no air flow. Change T-stat to Stant SuperStat. That works a little different to normal even often tho looks same to you. See my Cave, Thermostat
Check for crush pipes etc in rest of section.
May still have block rad tubes and worse from weak/no "antifreeze" in 30+ years. You might see block rad tubes but often need to empty, pull left hose, a try to snake a bore scope to at bottom of tank and tubes. Right Tank often looks perfect w/ same problem.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Suspect we have a failing temp gauge. The radiator core is flowing, system has pressure car does not boil over. That fan never comes on though, sounds like this motor is just happy running at a warmer temps. I'll leave it alone for the time being and move on to the next issue.
We do have some kind of issue in this circuit fan never comes on will overheat eventually.
My infrared thermometer indicated top of head gauge sender read 266, thermostat flange at the head read about the same fan switch was tougher to hit but was 255. No fan. If I ground the wire going to the fan switch in the head fan comes on if we turn on the A/C fan comes on.
We jumped across the connector at the fan relay upfront the red to black fan comes on. Replaced the fan relay no change.
Back to the engine fan switch connected meter positive to the switch negative to the strut mount stud. Run the engine up to 240 ish meter goes from open to about 7 ohms resistance so I’m guessing the switch is good
This seems like an issue on the ground side of the circuit control.
We Teflon taped the switch threads on the fan switch is there any chance that could foul the ground enough.
I’m confident the ECM is good.
Someone has spliced in a wire in the ECM harness I’ll guess it was from a fuel pump issue but who’s to say I’ll try and post a picture.
Suggestions appreciated.
[This message has been edited by mkoski (edited 09-19-2020).]
The fan switch activates the fan relay, by providing a ground for the relay coil. And the switch grounds through the threads on the outside (to the intake manifold). So yeah, Teflon tape can mess with that. Also, make sure the engine-to-chassis ground strap is intact. The ground path of that circuit goes through the engine to the ground strap, then through the chassis to the battery.
Also, 7 Ohms resistance on the ground circuit is too much. Ideally, it would be less than 1 Ohm. If you remove the Teflon tape and use paste instead, that should help.
Thanks for the reply, The fact that I can ground the green/white (I think), wire going to the fan switch in the head and the fan turns on, makes me think all the wiring between the switch and the fan motor is good. Bad switch right? I ordered a new factory switch and installed it without any Teflon tape same problem as with the Dickman part after awhile temp gauge pegs idiot on dash illuminates overheat, overflow tank starts to make noise. Ground that wire, fan comes on motor is back to a happy 220 or so in short order. Now I'm under the impression that the ECM takes information from the temp sensor in the thermostat neck in order to manage fuel trims etc. it does not really care a whole lot about what the fan switch is doing at least in the 1985 model and thus I'm not worried about a damaged driver in the ECM.
The guy I bought this car from boasted a bit at the time that his kid drove it all the way through high school and "dad" had mostly kept it going with junkyard parts. So really I doubt this fan was working when I dragged the car home. I have an occasional code 35 but that's it and even the 35 has started to disappear on its own.
I am concerned though that I may have an assortment of components that don't belong together. In the engine compartment I have two wire connector red in color. unused a green/blk maybe and a green one of the wires is keyed power and guess what if I ground it with the ignition on yep, the fan comes on. these are not added wires they go into the factory harness.
You are correct about the temperature sensor for the ECM. It is completely separate from the fan switch. And the fan switch does not interface with the ECM.
They didn't start doing ECM fan control until the '87 model year.
Sounds like the previous owner did some wiring hackery. Can you take a photo of that 2-wire connector?
Sure, here you go see what you think I guess next step is to open up the loom it’s in and look for spliced wires. Still though if I ground the wires at the switch connector fan comes on. ,
If with the car at 220 I ground the wire going to the switch bingo the fan comes on.
Just to clarify this statement from the first post... The coolant temperature should make absolutely no difference. At any temperature, grounding the wire that goes to the fan switch should turn the rad fan on.
It's not making much sense that two different fan switches are not turning on the fan, if indeed the coolant is reaching the required temperature. It would help to know what temperature your coolant actually is. I don't suppose your have a scanner (or appropriate cable/WinALDL) to use with this car?
Correct, if I ground the wire the fan comes on regardless of coolant temperature.
Actual coolant temperature at a given moment during testing: I can only estimate based on the dash gauge that clearly is wrong but does operate, My infrared thermometer which provide me with more of an estimate based on my experience with infrared. However the dash idiot light will come on signaling over temp that one I trust.
Regret I do not have the connector reader that you referenced. I did consider ordering it but it comes with a CD. I no longer have anything with a CD drive.
It strongly points to a bad switch in the head or the switch is not submersed in coolant since when I ground the wire the fan turns on. The AC belt is gone the compressor is there, the P.O. indicated when I bought the car that it used to work but he thought the evaporator had a leak I think he gave me a used evaporator with a collection of other parts. I have not checked the wiring over to the compressor because like grounding the wire if I turn on the AC at the dash the fan comes on.
Yesterday I ordered AutoMeter Cobalt Digital Series Gauge 6937 and a Standard Motor Products TS85 Temp Sender/Sensor which I think will fit in the switch position and will activate at a much lower threshold. I know it may foul the spirit of the ECM engineers that put the parameters into the system but I can order another factory switch once I confirm that is the issue.
Did you have any guess about what that red connector was for ?
That red connector doesn't look familiar. But then again, I haven't touched an Iron Duke engine in years. Maybe it goes to the A/C compressor? The compressor should have a fan switch on it, also. And it grounds out the green/white wire, just like the fan switch on the intake manifold. But the fan switch on the compressor is pressure based (refrigerant pressure) rather than temperature based.
I think Duke Engine harness are All make for 2 speed rad fad but red connector goes nowhere on 85-88. GM made Thousands of Wiring Harness parts and many have "extra" plugs that go nowhere unless you have X option. Why? Because easier and cheaper for them to ignore some wires vs. make more PN w/ exact wiring.
Even PN to inventory can easily cost 10's of Thousands of $. Example: GM already made several "Cross cabin" harness for Door Options and 2 min 84 front harness and 1 and 2 speed fans and each one causes cost for GM to design, make, storage at many stages, inventory them too, and more handling on the factory floor. While many use JIT to make a car now to not inventory and store parts car's factory, most parts are still in inventory somewhere because many made X part in batches and go on to make Y for some other thing. Someone is paying for that and you pay in the end.
Red connector and whatever wire isn't mention in any book showing 1 speed fan... Maybe 85-86 just wired to same 1 speed wire and relay and turn on if shorted to ground. 87-88 has fan control under ECM that will turn on rad fan at 2 temps. Maybe even so, red con is wired as backup or just made engine wires before ECM type/programing was selected.
I agree with ogre that red connector was full of old oil and fine debris. May well have never been connected to anything on this unit, but it is certainly part of the fan circuit, ground the Green/white and the fan comes alive. Now the other green or maybe it has a white stripe too I can’t tell also turns on the fan when grounded. So under Ogre’s conclusion that must mean these two greens are tied together in the loom and the guy on the line just connected the one called for in the build sheet attached to the sub assembly. Or left over 1984 inventory.
I’m confident this engine has never been out, it belongs to this chassis.
An air pocket, yep a real possibility. Or I have gotten two faulty switches that’s about all that is left.
The overflow tank holds the level seems right I’ve run this through half a dozen thermal cycles taken it for a ride at various highway speeds. Still though could be a pocket that comes around the corner and stalls.
The overflow tank holds the level seems right I’ve run this through half a dozen thermal cycles taken it for a ride at various highway speeds.
Not quite sure what you mean by "holds the level", as the overflow tank level should go up every time the engine reaches operating temperature, and then go down again when the engine cools off.
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Originally posted by mkoski:
An air pocket, yep a real possibility. Or I have gotten two faulty switches that’s about all that is left.
If one of them is a Dickman supplied 210° on and 200° off fan switch, it would be easy enough to check with a continuity tester while in a pot of hot water on the stove.
[This message has been edited by Patrick (edited 09-23-2020).]
Sounds like you've ruled out just about everything. In a previous post, you mentioned the fan switch changing from open circuit to ~7 Ohms when the engine gets hot, so that switch is good. Also, the fan and relay are good because you can activate them by jumping to ground.
The only thing I can think of is the ground path from the fan switch to the battery. Just out of curiosity, have you tested the resistance from the body of the fan switch (i.e. the part where you put a wrench) to the intake manifold right next to the switch? The resistance through such a short distance should be a fraction of an Ohm. If it's more, then maybe the threads in the engine need to be cleaned out, as well.
If one of them is a Dickman supplied 210° on and 200° off fan switch, it would be easy enough to check with a continuity tester while in a pot of hot water on the stove.
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