Help fan wont go on replace the sensor
 

help i jus replaced the sensor the fan goes when i turn the ac on the fan comes on but it wont go on when it almost at 240 i need to fix this fast could i have a bad relay

Re: Help fan wont go on replace the sensor
 

You could. Check the relay by grounding the wire that goes to the fan switch you just replaced - if the fan comes on when that wire is grounded, either you got a bad fan switch, or your gauge is off (which is very likely). Cars don't 'overheat' until they actually boil over - if it's not boiling over, then it's not overheating. These factory gauges are for looks, not very accurate.

Re: Help fan wont go on replace the sensor
 

well i grounded that wire and it goes on but isn't it kinda rare that its the new switch oh and the engine did boil over with new sensor in

Re: Help fan wont go on replace the sensor
 

Stock TBI fan switch, on, 238F.

Re: Help fan wont go on replace the sensor
 

It's not a bad relay if the fan comes on with A/C on. It's either a defective new switch (unlikely) or a bad connector or wire for the switch. Inaccurate guage is a given.

Re: Help fan wont go on replace the sensor
 

I hate the factory fan switch setup - I never get them to work for more than a month - I even tried a $90 aftermarket switch that only worked for 45 days.

I spent my next $90 on a Flex-a-lite fan controller and never looked back - I highly recommend leaving that bad fan switch in the head as a plug (only thing it's good for), and getting an aftermarket seperate fan controller, and be done with it.

Re: Help fan wont go on replace the sensor
 

well that single wire that goes to the sensor i tested that by grounding it put a algator clip on the little prong in the plug and the fan kicked on so i dont think it could be that and what do you mean by Inacruate gauge is given
also deadbird my fan always use to kick on as soon as the gauge hit 220 and the temp when right down

Re: Help fan wont go on replace the sensor
 

I assumed you had a TBI since the majority of the v8 RS's were.
Regardless of what your gauge showed, the factory fan switch (for any model with a fan switch) turn on temperature was 238°.

If you have a TPI and dual fans, the ecm will turn the primary on at 220º, the secondary turns on with A/C or, the 238° fan switch.

Autozone p/n sw505 is a 215° fan switch. A TBI fan is temperature controlled only by the fan switch. Turning the HVAC controls to A/C should also turn the fan on by grounding the relay just as the fan switch does.

Re: Help fan wont go on replace the sensor
 

yup its a tbi 305

Re: Help fan wont go on replace the sensor
 

but im confused now cause the jus replace the new switch with another new switch and the engine boiled over so even if my gauge is wrong the fan still didn't not go on with either switch but the wire that goes to the switch i grounded it and the fan went on so there isn't a break im lost

Re: Help fan wont go on replace the sensor
 

If the engine "boiled over", replace the radiator cap, and make sure you have about a 60/40 mix of water/AF in there. That mix at 16 psi (what a NON-DEFECTIVE rad cap holds) doesn't boil until about 265°.

The factory setup is designed to turn the fan on at around 235°. Works great. The switches don't go bad much; I've had the same one in my car, I think, since I've had it (well over 25 years now) in several different motors. At least, I don't recall ever buying one, for sure not in the last 15 or so. Just make sure you get it tight enough into the head that it makes good contact with the head metal; about 5 wraps of Teflon tape and torque it to about 25 ft-lbs and you should be good to go.

Re: Help fan wont go on replace the sensor
 

The fan switch should be (fairly) accurate. Your gauge could read 260° and the engine is only 230°. The fan switch still has 8° until turn on.

That's why I stated the lower temperature fan switch.

edit: I also agree with sofa. I tend to replace my radiator caps ever other year. 1) to assure it doesn't leak (gasket) and 2) so it keeps the pressure held in the cooling system.

Re: Help fan wont go on replace the sensor
 

but why all of a sudden would not come on and why would the radiator cap affect the fan not coming on cause if it boiled over it must have been pretty hot

Re: Help fan wont go on replace the sensor
 

Because the switch isn't getting to 238°.
'In a closed heated system, the higher the pressure that can be maintained, the higher the liquid temperature can be without boiling.'

Re: Help fan wont go on replace the sensor
 

ok now is there any other thing you think of that could cause this cause i want to check every thing and also if i get a new cap my fan will go on at 220 like it use to ?

Re: Help fan wont go on replace the sensor
 

Dude just ground the switch and have it run when the ignition is on. So much easier but it will cut down fan motor life

Re: Help fan wont go on replace the sensor
 

no disrespect but i want to fix whats wrong not a simple good enough fix

Re: Help fan wont go on replace the sensor
 

None taken, In my climate during the summer my fan needs to be on all the time anyway because of the 120+ degree weather so I had the fan wired as I stated then in the winter I would undo that and let the switch control it. Then like a year ago the switch went out so instead of changing the switch I just ran all new independent power/ground wiring and threw a toggle switch in there, I had to do this anyway because I had a main power wire in the cars harness burn up while i was driving. So i redid the harness and added the independent fan wiring to supply the extra power the new fan needed. Now in the winter I control the fan and during the summer I just leave the switch on(wont run unless ignition is on). Works for me. I prefer it.

Re: Help fan wont go on replace the sensor
 

I am actually having the SAME exact problem currently, 92' Camaro RS 305 v8 TBI. Me and my pops have been trying to fix this issue and have not found a solution. We replaced the Fan Switch twice now and all 3 switches haven't made it turn the fan on. Usually before once the gauge read around 240 it would kick on for me, now it doesn't work at all. Checked the wire by grounding it and it comes on, so the sensor has to be working, the wiring is fine. Is there any other ideas as to what could be the problem?

The only solution so far has been to keep the fan on at all times, but I want this to be working like it's supposed to as I'm sure the OP wants as well.

Re: Help fan wont go on replace the sensor
 

sucks my only option is for me to turn th ac on to cool down i really need some ones help on fixin this

Re: Help fan wont go on replace the sensor
 

If the sensor isn't making good contact with the casting, it won't work. GOtta make sure it's in there tight enough.

Everybody seems to think their car can't possibly work at 230° or more; after all, "water boils at 212°. WRONG. That's a GROSS over-simplification. The truth is, PURE water, at SEAL LEVEL PRESSURE, boils at 212°. But anti-freeze raises the boiling point just like it lowers the freezing point, so a 60/40 mix boils at about 240 - 245° at SEA LEVEL PRESSURE; and pressure ALSO raises the BP, so that same mix boils at around 265° at 16 psi, i.e. where a FUNCTIONAL rad cap keeps it.

I have NEVER EVER EVER, not is ANY kind of car, had to hack on the cooling system to get it to work right. THose engineers at the factory are pretty smart: they got it to work right. If it's not broke somehow, it'll work right again. Instead of looking for ever more ways to hack it when a previous hack didn't do any good, find what's broke, and fix it.;)

Re: Help fan wont go on replace the sensor
 

i understand that whole concept but i don't get how my fan went from kicking on as soon as the gauge hit 220 to not working and with a new fan switch it still didn't come and the needle was jus about to hit the red line and thats when i killed it

Re: Help fan wont go on replace the sensor
 

I understand all that, I know what therookie is talking about because im having the same problem. If we leave the car running without turning the fan on manually, the car WILL overheat, as in everything starts to boil and it WILL redline, mine has already redlined twice, once before i caught in time and the other i didn't notice till I smelt coolant and the junk was exploding out of the reservoir.

Re: Help fan wont go on replace the sensor
 

Ardanza that is exactly whats happening

Re: Help fan wont go on replace the sensor
 

Okay so the only thing I have been told that could be the reason is that when you buy the new fan sensor, you know that white tape that's around it? try taking it off and than put the part back on, that's what someone told me earlier today that could be the problem. Haven't tested this out yet and won't be able to til sunday, but if you try it let me know and see if that works.

Re: Help fan wont go on replace the sensor
 

Another option for sealing the threads without the tape is liquid teflon thread sealant. Try the sensor from Autozone that deadbird recommended. That will turn your fan on at 215. that may have been in the car before. That's why the new sensor doesn't work the same way.

Re: Help fan wont go on replace the sensor
 

Replace the fan relay.

Gages are not as bad as people think, and your gage appears to be fine; the temps you are(and were) seeing, verify this. And fan switches rarely go bad; your original one was probably fine, and your new one apparently is too. And I doubt the problem is debris-related, as with a gradual build-up of debris in front of the radiator, you'd have probably seen a gradual increase in running temps over time, not a sudden increase like you've had; a sudden increase would probably mean a large piece of debris just got in there, which you'd have probably noticed at the time.

However, it is possible your relay could be bad. Grounding the wire for the fan switch can still make the fan turn-on even if the relay is bad. And fan function during AC operation is controlled by the AC pressure switch, which can also still work even if the relay is bad. But the thing that won't work if the relay is bad, is the primary operation of the fan. And primary operation is apparently the problem here, a fact you stated, which is not only relevant, but it's the key:

That's where it should be turning-on, even with a single fan set-up. The fan switch is merely a back-up feature. And for something as critical as fan operation, which is electrical-only, GM knew it was absolutely essential to have a simple mechanical back-up plan in-case primary operation failed. And we apparently have that very situation here: the fan used to turn-on at 220-ish, but now it's not, so the engine is heating-up to 240-ish, where the fan switch turns-on the fan to try to cool-down an already very hot engine.

New relays are inexpensive, so get one and see what happens. If it works, it'll be the best money you've spent, and your car will be back to "normal."

Re: Help fan wont go on replace the sensor
 

Well the thing is it's not turning on at all, either at 220 or 240 (and I apologize, i just realized I did type 240 before and I meant to say 220, it always turned on around 220 not 240, typo on my part). And I believe the rookie is having the same issue as me. I'll try to replace the relay and see if that helps at all as well.

Re: Help fan wont go on replace the sensor
 

TBI motors were solely dependent on the fan switch for temperature control. The fan switch is 238°. The HVAC controls, for TBI, directly ground the fan relay to turn the fan on.

220° is an ECM controlled fan temperature. Any and all fan switches were 238°

Rookie stated this is the motor we are talking about.

Please find any ECM control in the attached factory diagram and tell me the fan switch turn on temperature....

Re: Help fan wont go on replace the sensor
 

I never said the fan switch turned-on the fan before 238, not even that it should.

In fact, I never even addressed the fan switch as the problem, because the problem, for both rookie and Ardanza, isn't with the fan switch. Their fan switches are working fine. But all the responses keep addressing the fan switch(and other oddities), rather than addressing the real problem.

The real problem is that their respective fans are no longer turning-on at the primary temp of 220, and that's what I was addressing. And that, as you've just confirmed, is the responsibility of the ECM, not the fan switch. That's why I quoted rookie in my post, because he specifically said his fan used to turn-on at 220, but that's no longer happening. And Ardanza is also saying the same thing about his fan.

Regarding HVAC controls, they work with in conjunction with the relay, the AC pressure switch and the fan switch. But that also has nothing to do with the fan's primary on-temp, and I never said it did.

Re: Help fan wont go on replace the sensor
 

The point is, that one the TBI single fan system, there is no ECM fan control. This is obvious in the factory diagram. The only way to lower fan on temp is to use a lower temp switch. The factory temp gauges are notoriously inaccurate. Mine used to read very low, now while the fan continues to come on at it 180 programmed temp, the gauge reads 240. The relays in both these cases are obviously fine as the fans on both cars come on with the primary circuit closed.

Re: Help fan wont go on replace the sensor
 

well i installed a new idler arm and while i was down the i poped the sensor out again cleaned it up and even took a wire brush to the block clean as best i could and still nothing i re grounded that wire to double check and it still kicked on also i noticed on my radiator about have way down on the side were the rad cap is there was a flat prong coming of it but i did see any wires near it now im now sure if this a new radiator from the PO ill try and take pic when i get home

Re: Help fan wont go on replace the sensor
 

I understand your point, doc, but there are two guys in this thread whose situations suggest otherwise. Even my own experience with a past TBI car suggests otherwise(though I never had any problems with mine).

The original poster, the rookie24, stated twice, once in post #7 and again in post #15, that his fan used to turn-on at 220, but it doesn't anymore, now only turning-on at 240. And Ardanza has come-in and said the same thing about his. And the fan on my own past TBI car always turned-on around 220(and I never used the AC, so that has nothing to do with it). My fan never went to 240-ish before it turned-on. If that had happened, I'd have freaked-out lol, so it's not something I'd have ever forgotten.

Regarding the gages, of course gage problems can occur, but bad gages are not the norm. Yet that suggestion is tossed around so heavily here on TGO that it makes people think they're all faulty. But they just are not.

So given what the rookie24 and Ardanza saw and said is true about their fans consistently turning-on around 220 instead of 240, but suddenly changing to not turning-on until 240, then I doubt their gages have been fooling them all this time, so something besides the 240 fan switch has apparently been controlling the fan's primary function, consistently turning it on around 220. And the only thing it could be is the ECM, just like it does with single-fan TPI cars.

Re: Help fan wont go on replace the sensor
 

la my fan wont turn on at all

Re: Help fan wont go on replace the sensor
 

it wont go unless ac is on or i ground that wire that goes to the sensor

Re: Help fan wont go on replace the sensor
 

Ya our fans won't turn on at all unless we turn on the AC, than the fan turns on. When we ground the wire thats to the fan switch sensor, it turns the fan on. The Fan switch sensor is in working condition, tested in boiling water, but it still won't turn on the fan for some reason. Our gauges are working properly as well. What we were stating is that before our cars started to overheating, the fan used to turn on around 220, but currently it will not turn on automatically anymore. That's what we are currently trying to solve.

Haven't been able to get around to messing with the fan relay, would you happen to know where the fan relay is located?

Re: Help fan wont go on replace the sensor
 

Dude.... well said! That should be posted at the top of the forum in reference to all vehicle systems!!

Re: Help fan wont go on replace the sensor
 

There is no ecm fan control for tbi.

Re: Help fan wont go on replace the sensor
 

.

Re: Help fan wont go on replace the sensor
 

That's a low coolant level switch. Only the digi-dash cars had a light for that, iirc. Replacement radiators have them regardless.

Re: Help fan wont go on replace the sensor
 

Did you test continuity through the switch after it 'clicked' closed ?

Re: Help fan wont go on replace the sensor
 

Yep sure did, had it rigged up to turn a light bulb on. even after taking it out of the water it kept it on for quite some time.

Re: Help fan wont go on replace the sensor
 

You've confirmed it does indeed close as should. Did you have have thermometer in the water to confirm temp ?

If boiling temp is true to the fan switch turn on then, that leaves two issues.
1. The fan switch is not grounding to the block or,
2. The internal (engine) coolant temp is not reaching the confirmed 238°f turn on temp to switch to ground.

If the car (engine) boils over before 238°, which is confirmed in a controlled condition of boiling water (for the fan switch to turn on), it could be due to the aforementioned weak radiator cap or, poor coolant ratio/age.

Re: Help fan wont go on replace the sensor
 

Any updates ? Open ended threads help no one.

Re: Help fan wont go on replace the sensor
 

Sorry mothers day weekend, was traveling.

Haven't been able to get around to it yet, but yes, i did have a thermometer in it, but i didn't pay attention to it, cuz as soon as bubbles started to show up the sensor started working.

The car starts boiling at 260~ roughly, gauge is definitely working fine. So I have been able to try the fan relay or try and reground the switch to the block. As soon as I'm able to I'll post on here

Re: Help fan wont go on replace the sensor
 

You can easily test continuity from switch to block by shorting the fan switch connector to the outside of the fan switch. It should turn on if the switch and the block are providing a path to ground.

Always start testing by shorting this lead to ground then working backwards.

When you say you were 'down there' and cleaned the threads on the 'block' I'm concerned that maybe you were futzing with something else? The fan switch should be up top on the pass side cylinder head.

Re: Help fan wont go on replace the sensor
 

Okay so situation update.

I replaced the fan switch with one that was 100% working and took off the tape just to make sure it was grounded. Fan still doesn't turn on.

I replaced the Fan Relay. Fan Still doesn't turn on.

I replaced the Coolant Temp Sensor. Fan Still doesn't turn on.

To clear up all the earlier confusion, the OP and me both have a 305 TBI and our fans will not turn on when it reaches ANY temperature that should trigger it. If we do not turn on the fan manually via air conditioning, the car WILL overheat and start to boil over.

Are there any other ideas?

Re: Help fan wont go on replace the sensor
 

Pressure test your cooling system. If it's leaking somewhere it will boil over before it reaches the 'on' temp for the switch.

Before replacing all of that stuff, did you verify the components had failed by testing as outlined above? What happened when you grounded the switch lead that is connected to the fan switch between the number 6 and 8 spark plugs? You may have needed a small screwdriver or other conductor to fit into the switch housing when you grounded it.

Re: Help fan wont go on replace the sensor
 

Hey guys,

I'm having the same issue with my 92 RS. My fan won't turn on unless I ground the connector on the fan switch (which is in between the 6th and 8th sparkplug, passenger side), and it will turn on when I put the AC on. My fan switch looks like its been changed before (everything else has surface rust on it, and the switch doesnt). Yes, I have a 305 TBI. Let me know your solution. I kind of want to keep this car all-original..But I might have to buy a fan controller now.

Re: Help fan wont go on replace the sensor
 

yeah,

this just started happening to my 92 305 TBI firebird. curious to know if there has been any resolutions... i have all the same symptoms, fan will not go on at any temperature.

at first i suspected a bad ground or worn wiring because when i started having this problem i swear i could jiggle the wiring harness and the fan would start to creep slowly to a start and i would usually be able to make it home. buuuuut yesterday it stopped working all together, despite my jiggling/plugging and unplugging of the same electrical connectors.

and then i found this thread.. when i turn on my A/C the fan fires right up, with no hesistation. even made it to the beach roundtrip with the guage hovering below the halfway mark.

before i go out and buy a new switch, i'm going to test it and then have a serious look at the dark green and white wire from the switch to wherever it goes. after looking at the diagram deadbird posted (thanks a bunch btw) i realize that everything else in the circuit seems to be working swell.

i'm also not really interested in adding a redundant fan controller. let you know what i find out, subscribed.