I am having overheating problems on an ’87 Fiero SE 4 cylinder. I understand that the 87-88 years are different. I first flushed the radiator, and also replaced the radiator cap (non-vented), thermostat housing cap, thermostat itself, and coolant line plugs (I did drain from the plugs after the radiator, getting out as much as possible).
The fan does come on with the AC. I understand that verifies the relay and fan motor. From what I have read in archives, the suspect is then the fan switch, but 87-88 Fieros apparently do not have them, and the ECM controls this.
However, idling or running the engine, the fan does not seem to kick in at all, no matter how hot it gets (the temp gauge moves past the middle, then jumps toward the red line, so I turn it off). I can run it by turning on the AC (in fact I have no choice).
While the engine was running, I felt the radiator (warm), and the hose (very hot, with surging inside). I really think the water pump is okay. There is no leakage under it.
Another odd thing that I have noticed is that the amount of coolant seems abnormally low. By this I mean, I drained just over 2 gallons (that’s 8 U.S. quarts, or 7.6 litres for those of us here in Canada) when I did the flush. At first I thought I’d just lost a lot of coolant when it boiled over. The gasket on the old thermostat cap was quite old and cracked, so I also wondered if it had somehow been evaporating from there. But I could only put back in the same amount. If even the 4 cylinder is supposed to take a total of 3.5 gallons (14 quarts or 13.25 litres), that’s considerably more. Should I really be able to pour in 3 ½ milk jugs’ worth? Because I only got out, and put in, a little over 2.
The only place any old coolant could be left would be the motor, as I didn’t bother with that drain plug per Ogre’s Cave recommendation. I don’t know how much might be in there.
Any thoughts as to what might cause the fan not to run, or the seemingly small amount of coolant with no leaks, and an apparently good pump? I have gone through the archives on radiator fans (21 pages), but find little regarding 87-88 4 cylinders and their ECM temp sensors.
I am on West coast Pacific time, and so may not respond right away, depending on where you are.
Thanks very much,
Wayne
[This message has been edited by waynrayn (edited 08-01-2018).]
It's true that the 87 Duke does not have a fan switch, but the Coolant Temp Sensor provides temperature information to the ECM. It could be bad, or you could have no flow in the system. You may end up removing the coolant pump to examine the impeller. The fact that it does not leak does not tell you anything. Look for damage to a coolant tube.
ECM "reads" ECT and controls 2 fan outputs but only Fan1 is used. You need ECM scan tool to see what ECT says to ECM and when ECM commands Fan1 is on or not. And have a meter/light on the Fan1 output pin (other probe is +12v) 220°F is Normal. If you see more from scan tool and Fan1 isn't on then something is wrong.
Is possible ECM ECT etc is "bad" but Likely still have coolant problems not fan problems.
Don't trust dash gauge temp as they often lie. Anything in my cave including heater loop can force high heat or boil over. Boil over and ECT read under ~250-260°F then have cooling problems, engine problems, or sensor/wiring is bad. Example: Engine w/ crack head or head gasket can "boil" in seconds after start the car. Is not Heat but Cylinder Pressure causing fake boil over.
Engine cold And Tstat Out, Caps On, overflow tube is pinch... (Rad cap w/o tube pinch can let tank coolant even air in as pump sucks for this test. Pinch to seal not damage it. Cap can let air in if tube leaks too.) Start to car and wait 30sec to 2 minutes and very carefully try to loosen/open Tstat cover. If pump works can try to push coolant out. If Coolant pipes and rad is good may not push a lot of if any coolant out the cap but you see the flow. Do Not hit the gas w/ cap loose/off. This will soak everything. System Flow will lag the Pump RPM and you have coolant flood trying to keep up when cap is loose/off.
Every Water Pump I've seen for this engine is all metal but can be plugged w/ crap cause low flow. Pulling just to check is a huge pain so do that as last resort. I would get a new pump, pump back to engine block gasket (This gasket in Not included w/ new pump) and pulley tools before pulling it.
If fill as directed in my cave... "Empty" the system ignoring engine. (You Can't empty the Engine or Rad completely.) flush or whatever fill 2 gal of straight coolant NOT 50/50 mix. Fill rest w/ water.
Might be a little "rich" but is ok. You can run up to 70% coolant w/ most brands.
If you did that then coolant tester should tell you have 265°F/129°C to 276°F/136°C hot protection. (-34°F / -37°C to -84°F / -64°C freeze protection) If you boil over again... Then use 50/50 mix to refill.
------------------ 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)
Thanks for your responses. I can give some additional information now. When I run the car with the air conditioning on, there is no problem whatsoever. The temp gauge stays well within normal, rock solid, no problem at all driving for an hour.
When I got back into my garage, I kept the car running, opened the front hood- the radiator fan was spinning- and then turned off the air conditioning. The fan slowed down and stopped immediately, although the car was running and hot.
Does this narrow down the problem to, say, the ECT? (I think this is the same as Gall757 calling it the Coolant Temp Sensor.) Is this cheap/easy to replace? The ECT/ECM is not something that I have worked with or tested before. Ogre: Could you please explain more about testing the Fan1 output pin, like where it's located?
Yes, it's all the same sensor. Easy to replace, and not cheap but not that expensive. Fieros like to run hot, so verify the actual temp before replacing stuff.
Rock Auto calls it the Temperature Sender.
[This message has been edited by Gall757 (edited 08-01-2018).]
Thanks very much, I'm getting the idea that testing of the temp sensor and its connection to the ECM is the next step. I'm assuming that the "Fan output pin" would be part of the ECM?
Any suggestions as to a good (retro?) scanner for a Fiero ECM? Or is a current one fine?
Will report back...
Thx,
~W~
[This message has been edited by waynrayn (edited 08-02-2018).]
Any suggestions as to a good (retro?) scanner for a Fiero ECM? Or is a current one fine?
My preference is to get the appropriate cable to connect to a laptop, and use software such as WinALDL.
Of all the Fieros I've had, my least favorite engine was the 4-banger in the '87. IMO, the '84-'86 duke is simpler, and the '85-'88 V6 is vastly superior.
The '87 (and '88) dukes had a bit more power (supposedly) than the earlier years, but I felt they were more trouble than they were worth. I hated their DIS ignition. There was so much ignition timing advance at an idle (which couldn't be adjusted) that I always had a helluva time getting that car to pass AirCare.
I'm working with the coolant temperature sensor, which seems obvious. I've checked voltage through the harness (5.2v), and also continuity, which beeps fine. The sensor itself looks questionable- the protective rubber head fell off, exposing the prongs- so I decided to replace it, and removed it. I bench tested it, doesn't seem overly abnormal, but it's cheap enough to replace.
I'm wondering if there is a torque spec for replacing this anywhere? Or is it necessary?
