Hi guys, my name's Sunny. I have a '87 Fiero GT. I bought it about a year ago and only recently got it running right-ish (after buying a ton of parts lol). This was/is a project car, I don't think I'll ever get it fully finished as I am in no way a professional mechanic. I've been using this forum quite a lot to help me get it going. Either way it's been a ton of fun getting to where it is now.
Onto the problem. The temp gauge reads about 60+ degrees higher than the actual temperature. I have no idea why. I bought a new sensor (the old one was partially melted) and it's still reading off. I only believe it reads higher because I used a laser thermometer on the coolant hoses, they say it's 160°F. Gauge says it's 240°F. Not sure if it's relevant but I checked the actual sensor itself and it reads 280°F. I bought a new water pump and radiator, also checked the lines underneath the car for any kinks, used a chemical cleaner and "burped" it when I put in new coolant. So I know it can't actually be getting that hot, right?
Is it the gauge? The sensor getting too hot from the heat inside the engine compartment and giving a false reading? Something wired wrong? Or something else entirely that I completely missed? I've been messing with it for awhile and I'm completely stumped. Appreciate you reading this, thanks!
Exactly where you measure and how can and often will affect whatever reading you get.
IOW gauge is likely reading near actual temp in that location.
Even if you get a ECM Scanner, that sensor number may not be a match for gauge sender even if very close to each other.
That's assume gauge and all wiring is 100% and rarely true even 1 year old cars w/ same or similar gauge setup. Meaning gauges often lie for many reasons and Iffy wire to sender is only tip of that 'berg.
Try Measure w/ IR pointed to base of T-stat house. Should be closer to engine temp. Hoses are insulation and input output or both coolant flows ≠ to engine temp and you often get bogus data measuring at any hose.
------------------ 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)
Hey man thanks for replying! I had no idea about the hoses, I thought I was clever but I won't be trying that anymore haha!
So I measured the temp at the thermostat housing it was reading at 120°F when the gauge was 210°F. I mean I shouldn't expect it to be accurate to the exact degree, but should it really be that much of a difference? If not is there a guide or something I can go through to make sure it reads closer to the real temp?
EDIT: Saw somewhere online there was an auxiliary engine fan, would it help if I found one if it even exists?
[This message has been edited by Sunny (edited 08-01-2022).]
85-87 V6 Aux fan runs same way as rad fan. That what 2 tubes from trunk is for. See my Cave, Rad Fan
Gauge or ECM data reads 210 to 230°F is Not "overheating" and normal. 240 is getting uncomfortably hot but not overheating either no matter what hype here and elsewhere... See rest of cooling section in cave and get Stant Superstant and both caps. Even if If current caps are good and right rad cap because caps are stant caps are hard to get in a hurry in many places.
WHERE on T-stat house can change reading... Upper section toward cap can read coolant after passes thru the T-stat or even see close T-stat and "freezing" temp in winter if engine hasn't started to warm up and open the T-stat. At bottom where bolts to engine can read at or near engine temp.
I forgot to note that I have the fan set to turn on with the key, so it's always on. A/C doesn't work so I don't see a need to wait for the engine to heat up enough to turn it on at the original programmed temperature. I couldn't get a thermostat to fit so I don't have one haha. Would getting one actually help? I figured that if it was always open it would stay as cool as possible. But if you think I should get one I'll go order it.
I went ahead and got those caps you were talking about. Wasn't too much and they're handy.
I did the laser thing on the bolt for the thermostat housing after hitting the highway for about 45 minutes. Was going about 70mph. It read 155°F but the gauge was way past 260°F. It didn't make any weird sounds or smell like anything was burning so I guess it wasn't overheating?
I tried to find that scan tool but all I found was painter's tools. Do you have a link to one handy?
Do you think getting the temperature inside the engine bay would help get a better reading?
Also I ground the sensor to the bolt for the ignition coil. I'm not entirely sure if it matters but I figured it should mention it. When I got the car that wire wasn't connected anywhere so I just guessed haha.
[This message has been edited by Sunny (edited 08-03-2022).]
From your picture, it appears that the temp sensor is one for the ECU, not for the HOT lamp and the gage.
The sensor will not work for the gage.
The black wire should be disconnected, as it is providing a path to ground to whatever the other wire is hooked too.
The correct sensor in that location should have a rectangular socket that is missing part of the side, and the plug should be rectangular with a tang. Wires should be green and green with a yellow stripe.
I see the two properly colored wires, so it is just a matter of getting the proper sending unit and matching plug and wiring it in.
Oh man I just went the parts store and asked for a temperature sensor. I didn't think I'd get a wrong part lol
Yeah I had to use another wire because when I used the green and green/yellow the gauge would max out even though it hadn't even started.
I'll go check the fiero store to see if they have it. If not what is the sensor called exactly? Just so when I go to look it up I don't end up with the wrong one again lol
Yes above is "new style" ECM sensor and not light/gauge sender. New plug is much better @ keeping water out. Plus/Worse contented that way may have fried the part. Put the tip in water w/ thermometer and check chart See my Cave, Sensors Quick Ref
TFW parts are gauge/light sender. pins go to resistor or switch and ground thru case.
Put away the ray-guns and use one of these as a test tool. It's new and direct and doesn't need to send the results thru an engine wire harness that may be iffy. I keep one on the shelf. Prices and quality vary. Stay away from ones with just 3 colors on the scale and no temp numbers whatsoever.
------------------ "Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut
[This message has been edited by Spoon (edited 08-05-2022).]
To answer your question, where is the one you have now supposed to go. It is the ECM temp sensor - Listed at the Coolant Temperature Sensor in this pic. It only goes to the ECM and has nothing to do with the gauge. And as stated before, the sensor is not electrically the same as the temperature gauge sender.
Hey so I finally got enough money for all the parts y'all said to get and it works! Sorry it took forever to get the parts, test them and let y'all know how it went but that's life, right?
Got one of those mechanical sensors you were talking about, Spoon. It read the same as the gauge in the dash so it's all good!
