overflow resivoir question

bumpskier45

Registered User
My overflow resivoir has a leak in it and when I went to the dealer to get another one they said my car called for one with a sensor,well mine doesn't have one on it,however right next to it near the mass air flow sensor is a plug so I will assume im supposed to have one,my car is a 93 sc 5 speed btw.
does this sensor that is supposed to be on there have any bearing on when the fan motor comes on? because I have replaced the fan motor,the ircm with a known working one from bill at sc perfomance,and still no low speed.
Allow me to make sure I am on the same page as everyone else,I know the stock gauge is not all that accurate I have been told,so when my car gets to the letter M in the word NORM on the gauge that is when the fan is kicking on im assuming that is high speed? lots of questions I know but I just want my car to run as cool as possible,when that fan finally does come in the gauge drops fast but the fan only stays on for like 30 seconds then right back off and the whole loop starts again,thanks for any more advice you all can give me.
 
The sensor they're talking about is the low coolant sensor, and it'd be nice to have.

If you have the VMM, you'll have the light for it. If you don't, it doesn't matter, it's wired to the VMM.

As to the fans - yah, it's hard to tell without some way of monitoring what the ECU sees.

What you're hearing MAY be the low speed fan coming on at "M", not the high speed. It's hard to tell from this side.

One way to test - pull the ECT cable and see how the fan sounds. That should kick on the high speed fan.

If the low speed STILL doesn't work, it may be the IRCM acting up.

RwP
 
overflow tank

The overflow tank has a sensor that tells you when coolant is low via the maintenance monitor. the one that is in the car now most likely has been replaced with one from a regular tbird. I'm sure you can find a good used one for your car here. As for the temp, can you see the leak in the tank? or is your coolant disappearing after driving the car? If you can't see it leaking and you have to keep adding coolant then you could have a blown head gasket the engine is ingesting it. The fan comes on at low speed when the a/c is off and high speed when the a/c is on. There is a temp sensor on the #1 bank r/h side at the front behind the a/c compressor next the oil fill that tells the eec to turn the fan on, you can change it if it is old I would. You can also get a chip or a QH and a 180 t/stat to cool it down I think the fan doesn't come on till the temp hits like 230 or something, to hot for my taste. with the chip or QH you can change the temps the fan will come on at and shut off. The QH is the way to go if you plan doing any future mods to the car it allows you to tune and data log in real time, lot's of folks here are using it.
 
no i never have to refill the radiator,as the coolant comes and goes out there it leaks out the side of it where there is a crack.If high speed motor only comes on if you use the a/c then yes the low speed is working,but dam it waits a long time to come on,way to hot for my taste,I suppose the next step then is a tune for the eec,everything else seems to be working fine I just don't like the temp the low speed comes on at.
 
I would then recommend, before you do anything else, obtaining and installing a QuarterHorse from Moates, so you can monitor the ECU reading of the temperature, and see when it DOES turn on.

It could simply be that the temp gauge is reading high.

RwP
 
I as of yet don't know what the temp is that the car turns on at but it is up there pretty high,also if the fan comes on while im idling the car does something peculiar,the needle spikes up about a quater of an inch then as the fan stays on it brings it down to the R in the word NORM on he gauge,even though the gauge says the temp is pretty high im not so sure it is because the car's timing is not being retarded and I have tons of power out of the supercharger which doesn't happen if the car is to hot,thoughts?
 
Again, see my note about the QuarterHorse from Moates.

With Binary Editor, it will also allow you to diddle with the fan-on temps.

As to how the gauge reads - there's TSBs on both reading exceptionally low (due to a bad crimp) and exceptionally high (due to errors in manufacture, i.e., that same bad crimp). I'd try a new gauge sending unit FIRST. Or if you're really concerned about it, a real temp gauge.

RwP
 
I would then recommend, before you do anything else, obtaining and installing a QuarterHorse from Moates, so you can monitor the ECU reading of the temperature, and see when it DOES turn on.

It could simply be that the temp gauge is reading high.

RwP

That may be a fairly drastic step to take at this point. (Although I do enjoy my QH!)

Before doing that, I would suggest checking the sensor itself. You can do it with:
Long push pins with the plastic balls on the end (qty. 2)
Alligator clips (4)
A length of speaker wire or lamp cord (8 feet or so?)
Electrical tape
Multimeter

1. Backprobe the ECT sensor connector with the long straight pins. Make sure the metal parts of the pins don't touch each other.
2. Run the speaker wire from the area of the ECT sensor to the corner of the hood seal, then behind the fender and through the door opening into the car.
3. Alligator clip the speaker wire to the pins. Insulate with electrical tape if needed to make sure the pins and clips don't touch.
4. Alligator clip your multimeter probes to the speaker wire inside the car. Again, insulate if needed.

Now you can run the car (and even drive around) and see what voltages the sensor is putting out.

Compare those to this graph:
http://www.oldfuelinjection.com/?p=28

And that will tell you what temperature the car is really running at.

Now,there is a chance that the EEC is not receiving the temperature signal correctly. The QH would eliminate that possibility, as it allows you to see all the EEC's internal readings in real time. But I don't know if you need that just yet.
 
Last edited:
I suppose I should have mentioned that in my post,I replaced the ect with a new one and also the one for the gauge as well,oddly enough once the temp started to climb it actually got well past the M in NORM on the gauge before the fan came on,as the fan came on the needle spiked about a quater of an inch up even further,then slowly came down, the fan shut off when the gauge got just below the R in NORM.Im thinking I am going to get what you guys say will read the computer at this point.
 
I suppose I should have mentioned that in my post,I replaced the ect with a new one and also the one for the gauge as well,oddly enough once the temp started to climb it actually got well past the M in NORM on the gauge before the fan came on,as the fan came on the needle spiked about a quater of an inch up even further,then slowly came down, the fan shut off when the gauge got just below the R in NORM.Im thinking I am going to get what you guys say will read the computer at this point.

Aha, that does make a failure of the ECT sensor less likely. You know, you could also bench test the old one if you still have it. Put the tip in boiling water, then read the resistance of the sensor. The chart for ohms is on that same page I linked to.

The behavior of your temperature gauge has me a little bit worried. You may have air bubbles in the cooling system. That could be innocuous, or it could mean a blown head gasket.

If you are willing to pull out the computer and crack it open to install a QH, then you might as well just check an EEC pinout and backprobe the ECT sensor wires right at the EEC plug. You can see if there is a problem with the signal right there, and you won't have to spend money that you might need soon, if there is a different problem. You can also open the EEC and check for bad capacitors or circuit traces, if the backprobing doesn't reveal anything. You still might want the QH, but I am just saying I wouldn't rely on it to fix this problem.
 
Oh, the QH wouldn't FIX the problem, but it sure would help make a diagnosis much easier!

*mutters about OBD1 brain dead monitors*

RwP
 
when i swapped out the upper and lower radiator hoses and filled the radiator back up,I did have air bubbles at that point,but that was obvious due to the heater not working and the gauges large tempature fluctuation,I suppose its possible I still may have more,not really sure how to remove them completely though.As to head gasket,I just changed the oil and I saw no sighn of water in the oil,I use a full synthetic the car has had that for over 10 years. last test drive I raved the crap out of her right up to the 5k rpm mark....had power all day long,surely it couldn't do that with a blown headgasket?
 
lets say for a moment there is still air in the system,how would I go about purging that from the system? only reason I say that is when I drove it to this morning the temp had a fair amout of fluctuation,normally it stays dead solid on the N in the word NORM while its on the freeway,but not this time it wavered as high as the R then back down again.
 
Back
Top