Well after nearly 15 years I own a 3rd gen again. My last one was an 84' Z28 I drove into the ground.

The new/ used one is a 91' RS with the 305 and 5-speed. Seems pretty much all original with 139k on the clock. Apart from a replaced clutch (not sure how long ago but it works well enough and doesn't slip) everything looks like it came with the car to include the alernator. Most everything works but I have identified one problem and I have a few other questions. Here goes:

Biggest problem I have is the fan does not come on. While driving the car runs just fine temp wise. However if it sits for more than 5 minutes the temp rises and approaches the red. I think the problem is related to the fan. Can anyone shed any light on this? Do the fans themselves simply go out or is it a relay maybe?

Cigarette lighter does not work. Fuse?

Oil pressure guage is kind of weird. When cold the needle moves around and travels past the 60 psi mark. Eventually it settles down.

Clutch pick up is in the first 1/2 to 1 inch of travel. Is this typical and/ or can it be adjusted?

What kind of MPG can I expect?

Overall what is the opinion of the 305 TBI motor. Mine has 139k. Is it about to blow or do these last to 200k plus with proper care?

Any other info would be appreciated.

Thanks.

 

well about the fan i would check your relays and some of the firebirds and camaros had fuses for the fans maybe all of them did? i know my last one did. id check that maybe give your thermostat a check also.As far as mileage goes i just hit 181,000 and my motor runs strong i would expect yours to go well over 200,000 if it was taken care of. i get about 17-21 in the city and 23-28 on the freeway but it all depends on your gearing ad how you drive

 

Try turning on the AC. When you do the fan should come on too that should help you diagnose it. The LO3 uses a sensor in the head Mine was passenger side rear of the head in between the 6 and 8 cyl. When it went out i just put a adjustable temp prob in my radiator to run the fan. Don't know where ur located but I have a spare LO3 fan if you need I got the dual setup now for my TPI swap.

 

what vette said x2. I still have the adj switch as a back up on my new engine. If the fans don't come on for some reason, this switch will force them on.

 

Check the fan motor first, spin the blades and make sure it spins freely with no roughness, the bearings can go bad and lock it up. I have the same car and have about 200,000 miles and still have the original clutch, so they last if not abused, my clutch starts engaging just off the floor and isn't a sudden thing, yours may not be set up correctly.And I get 21/24 MPG avg., 27+ hwy.

 

Where are my relays and how do I check them? I don't remember where the fuses are and I don't have the manual describing which fuse is which. Is there a link somewhere here with that info?

Thermostat is new based on the new gasket peeking out from beneath the housing.

Thanks for the MPG info.

I'll try the AC trick shortly.

What is an adjustable temp probe and how does one hook it up?

Thanks for the offer.

More info on this Adj switch?

I did check the fan and it spins completely freely. No resistance at all. It just won't come on.


Is there a description somewhere on how to setup the clutch correctly? Mine is a sudden thing and it's hard to get a feel for when it begins engaging.

 

Warmed the car up and turned on the AC. Fan came right on and temps remained in check. So that would rule out a bad fan motor, and fuses and relays am I right. So I'm thinking the problem is related to the sensor somewhere on the passenger side head? Probably not telling the computer the car is hot enough to kick on the fan. BTW what should the 305 run at temp wise and when should the fans kick on?

 

Anyone have anymore information on the sending unit on the passenger side head?

 

not sure about the sending unit but my car always runs from 170-190 temp never had it go past 200

 

If your car is a 90 Firebird with TBI then your gauge is wrong or the car has been modified to run cooler, stock the fan won't come on until somewhere north of 210/220 deg. unless the AC is on.

 

So any ideas or help troubleshooting this fan issue further? I'd rather not have to run the AC to keep the car from overheating.

 

Yes , but you won't like it . That sensor is very difficult to reach and replace . But it is likely the problem . It doesn't cost much , like $10.00 or so but it will make you mad while replacing it . You will need to get to it from underneath your car . On the passenger side . It is above the starter,like a foot above it , and above the knock sensor. It is way up near the spark plugs and there is wires and your dipstick tube brace all making it hard to reach .You'll need a deepwell socket to get it out . Just get the size of the socket from the new one .

Also the fuses are underneath the dash , drivers side , just where your left leg is . Should have a plastic door that you open . Fuses should be labeled in the box .

 

Thanks for the detailed description. I've just spent the last 1/2 hour reading up on the fan switch on the passenger head. Search is a nice feature. Anyway I've deduced that the problem is in fact the fan switch and not the fuse, relay, or fan since it kicks on when I flip the AC to on. Going to source a new fan switch today in a lower temp range (maybe on at around 200, off around 185) and put it on. I have a lift at home so I'm thinking I should be able to pull it off without to much trouble. Famous last words.

 

Someone must have just replaced the thermostat then or something.. i know my v6 i used to own ran at the same temp though

 

The stock switch turns the fan on at 238 degrees F.

The thermostat is supposed to be a 195. If you put in a 200 degree switch, the fan will be on a lot more than it needs to be. If you put in a lower temp thermostat, you'll be altering the conditions the ECM assumes for proper operation.

Unless you test the switch for the temp it closes, you don't know whether or not you've got a problem. Factory dash gages aren't exactly traceable to the National Institute of Standards and Technology (formerly known as the National Bureau of Standards).

 

Ok. Been doing some more research and I have confused myself now. I bought what I believe to be a coolant fan switch for my 305 TBI engine that goes between the #6 and #8 cylinders. I understand this part sends the signal to the fan to come on at a predetermined temp and then turn it off.

As I continue to read up on the 305 though I'm reading that the coolant temp sending unit on the front of the motor on the intake manifold next to the thermostat in fact sends the signal to the fan to kick on and off. Again this is 305 TBI specific.

So can someone please confirm which part/ sensor does what? Do I change what I though was the switch on the passenger side head or do I change the sensor on the intake manifold. I have only one fan on this car.

Sorry for the ongoing drama.

 

i remember that switch broke when i had my other firebird and the fans still came on but the car was VERY hard to start on a cold morning because the switch had broken off of the intake manifold and my car was thinking it was like negative 50 degrees out which made it hard to start in the morning. since my fans still work after it was running
i don't think this would be your problem. just my Opinion though.

 

Well gonna put the fan switch on when I get home tonight. Either the fan starts working or I'll be back with more questions.

 

]
The one on top goes to the computer. It is easy to change . Most likely not your problem though . The one on the drivers side goes to the gauge . The one on the passenger side goes to the fan . Of course it is the hardest to change . I asked a good friend of mine why didn't they just have one unit sending info to all 3 places and he said the TBI computer was too weak for that back then .

 

Cool sounds like I'm back on track. Will update tomorrow or tonight once I have it switched out. Hope it works.

Thanks.

 

And you cig lighter iissue s probably a fuse. If the interior lights and defrost don't work aswell then it is the fuse. If they work then you have to change the cig lighter socket itself.

 

All the interior lights work. The existing lighter looks pretty rusty. I figure I'll just buy a new one from Classic or maybe the dealer and put it in.

 

Well I finally got under the car to take car of the coolant fan switch. Guess what I found. For starters the switch did not have a wire plugged in. The plastic nub on the end of the fan switch had melted on the side facing the exhaust manifold. Connector had been off for awhile. Found the green wire with the connector tucked away by the motor mount and found that the connector was missing. Only the metal crimped on pin that rest of the connector secures to the fan switch was left.

I put that problem aside and focused on replacing the fan switch first. No real problems. Undid the old original switch and after losing half to a full pop cans worth of coolant I got the new sensor started and then torqued down. Next I had to deal with trying to push the exposed pin still attached to the green wire into the new sensor to see if it worked. Plug it in as far as it would go and warmed the car up. Fan never came on. I'm going to assume the switch is good and I just couldn't properly seat the pin/ wire into it to make it ground out when the temps got hot enough.

For the time being I grounded the green wire so the fan runs as soon as the ignition is turned on. Now I need to try and source a new connector that I can splice onto the green wire and hook it up to the new switch. Anyone know if dealers carry replacement connectors or will I have to buy a new wire harness with connectors on both ends?

Basically I'm halfway there guys thanks to your help.

 

Try efi connections ad on this board they have all the connectors you should need 9 or 10 bucks

 

Thanks for the tip!!! Just ordered the exact part I need to permanently fix the fan switch issue for $10 shipped.

 

Keep us posted . I'm curious how this one will turn out . And good luck . Hope the bad connector is the problem .

 

I have a 92 'Maro RS with a 305 TBI and i am at 199xxx miles. it runs great and doesn't drive like it has 199xxx miles. so you won't have a problem with 139xxx, unless it wasn't taken care of before you. but you shouldn't have a problem.

 

My dad reported getting right at 20 MPG with the A/C on when he drove my 305 91 RS from So Cal to Phoenix in August a couple years ago. I always had my foot in the throttle when I drove it so I never got a really good number myself.

Also, my 305 died at about 110,000 miles but it was my fault. Accidentally redlined it on the way back from Vegas with low oil. Up until then it had always run hard and been a blast to drive.

 

For MPGs, i get around 28 hwy with the t-tops off. about 25 city with just the windows open. its a 92 'maro rs 305 tbi, and a 700r4 tranny. i've heard of cars getting as low as 10 (performance cars), and mine was the highest i've heard so far. so you could expect anywhere between 10 and 30 MPGs.

 

Averaged about 27.7 on the freeway the first time I calculated it. Still working on figuring out combined city/ highway driving. Hope the 27+ wasn't a fluke. Pretty good if you ask me for a 17 year old car with a V8.

 

Finally installed the new connector to the sensor and spliced it to the wire harness. Warmed the car up and no go. The coolant fan switch do not trip the fan to come on. The sensor is brand new, the connector is brand new, the fan works when I ground it so........

I remember reading on here that the coolant fan switch grounds itself to the engine block when it trips turning on the fan. One problem with this is fi you use teflon/ plumbers tape to seal the coolant fan switch to the block the switch can't ground out anymore. Anyone know if this is true? Do I simply remove the teflon tape from the threads and re-install the coolant fan switch? I'd rather just do this than assume the switch is bad and buy another one.

 

Man that really sucks that the new sensor didn't do it . I am not sure of the grounding problem you were talking anout . Only other thing I can think of is maybe a fusible link .

 

Here's some ideas you might consider.


https://www.thirdgen.org/cool

 

if you can ground that green wire and the fan turns on then the engine either isnt hot enough or you are not getting a good ground i would take a ohm meter and heat the car up and start checking for resistance from the center connector to the OD of the sensor when that starts to hit 60 ohms on the 10X scale the car is at the right temp plug the green wire back in if the fan doesnt turn on check the OHMS again but instead of to the sensor OD check it to the block make sure it is around 60 OHMS or less and then double check that the pin is seating into the connector properly

 

dont waste your money, they give you a 4th gen one for 20$ and swear up and down it works, ask me how i know good thing i had my dash apart and found that out right in the parking lot. Just go to your auto parts store and buy a generic one, works the same and fits, you just have to modify the harness.

 

I posted the grounding/ tape idea in the cooling section and the consensus is that the tape should not interfere. Got a lot of suggestions on how to trouble shoot the sensor. I'm more inclined to just buy another one though and install it with less or no tape.

Good read. Thanks for the link. Might go one of these routes if I can't get it working like it supposed to. Will definitely go to a lower temp switch after reading that link.

The car is certainly getting hot enough. When I shut down at the last white mark on the dash gauge I can hear the coolant bubbling. I'm convincing myself I have a bad sensor or there is to much interference grounding to the block with the tape.

Thanks for the tip. I'll give the generic lighter a try.

 

Well if anyone is interested the drama continues. Yesterday I switched out a second coolant fan switch.....and nothing changed. Fan still does not come on. I've troubleshot everything in the system and verified they work. Fan, relay, fusable link, wiring, no air in the system...only thing I have not specifically tested individually are the two new switches I have installed in the passenger side head. I don't really think the chances are very high that I have bought two new bad switches. Only odd thing that happened this time is when I started the car afer swapping the new switch in the fan kicked on immediately and ran for about 5 minutes before cutting off and never coming on again. During those five minutes I could here the relay on the firewall going spastic opening/ closing repeatedly. I did spill more coolant this time and may have gotten some on the connector on the switch or in the connector that plugs into the switch. Once it dried if that was the cause of the rapid relay action relay and fan stopped and has been silent since unless I ground it out manually.

So anyone have any new ideas. I've run out except for one. The only other thing that i can think of is that for some reason my fan is tied to the ECU like the two fan systems. Don't know why mine would be controlled this way since I have only one wire running to and from the switch and everything I have read here says that my fan is not ECU controlled.

My next step is to pick up the Hayden switch from Pep Boys today and just bypass the factory switch.

 

you should try replacing the relay $12 napa has them the only thing left it in the system not replaced or known to be working... i would try it before hacking into the harness

 

Relays do work intermittantly sometimes.

My bypass switch was on a single fan and now on a dual and works absolutely perfect.

 

It's usually the fan switch in the pass. side cyl. head that goes bad. The switch in my '86 Bird just went out again. This will be the 4th one I've had to put in my Bird. As far as longevity, the Bird's LG4 305 has 203,865.3 miles on it and still runs strong. It's my other daily driver. I get consistent 18 mpg in the city with this car and 24-25 mpg on the hwy. And thats with a diconnected lock-up switch. My Iroc gets 19-21 mpg in the city and 28-30 mpg on the hwy, and it's got the LB9 TPI 305. It gets better mileage than my wife's Caravan. Both Bird and Iroc have 2.73's in the diff. The 305 is a pretty reliable and robust motor, I've been trying to kill my LG4 now for 8 years. If your looking for a good platform to build on, then go 350. But if your thinking more of just cruising, the 305 is reasonably reliable and economical.

 

Isn't the relay know to be working since I can turn the fan on by turning on the AC or grounding the wire for the coolant fan switch?


Not sure if you read the whole way through this thread but as of yesterday I replaced my 1 month old fan switch with another one and it did not work also. At least it didn't solve my fan problem. I find it very hard to believe that I have installed two bad fan switches back to back.

 

i think the fan will still run with the a/c even if the relay is bad... as i know the fan will run with the A/c even if you dont have the coolant sensor hooked up

 

Well I've verified the fan can be turned on via the A/C if the switch is not hooked up but how do I test the relay?

 

unplug the relay and remove it from the bracket some relays have sight holes that if they are no good melt plastic into the holes inside the connections of the relay

 

I chased this "problem" for several years. The gauge always showed that the car ran cool. Of course, the gauge is calibrated in an odd manner, so it is hard to tell what temp it is reading, unless it is right on one of the marked lines. It never got up to the 220 line, much less toward the redline.

Also, the fan didn't ever seem to run much unless (of course) the AC was on.

My car has been sitting for several years in the garage aging gracefully. This spring I decided to get it back in fighting trim. In any case, I was determined to figure out why it "ran cool" all the time.

First, I pulled the radiator out of the car and cleaned it up. You should see all the stuff that gets caught between it and the AC condensor.

I then did a flush on the coolant and replaced it with water and Water Wetter treatment. I put in a new 195* thermostat and replaced the gauge sending unit on the driver side head.

At this point the gauge started behaving "normally". The car got past the 220 mark. I replaced the Coolant Temperature Sensor on the intake and made up a cable to read the computer. I then got to see what the computer was seeing for temperature (assuming the CTS is reading correctly). Although the CTS and the Fan Control Sensor are seperate, it did give me an idea what temp the car was running at - much better than the funky gauge.

What I learned was the car didn't run cool. In fact, it appeared to be dead on. Cleaning the radiator and flushing the system was good maintenance, but probably didn't affect anything (should have made it run cooler, in fact).

Also, I learned that the cooling system does a pretty good job of keeping the temp in line, even idling in the hot Texas summer. Running down the road seems to force enough air through to keep it in check without calling on the fan very much.

It takes a long time idling for it to get hot enough to trip the fan. The ECM/CTS usually reports around 235* when the fan comes on.

So, to summarize, replace the CTS and make up a cable to read the computer. That will give you a better idea of how hot the temp is rather than relying on the gauge and the sound of the coolant bubbling.

 

Well...I'll pick up a CTS tomorrow and drop it on. Not like it won't take all of 5 minutes to do. While I agree the dash gauge is not very accurate this is the least of my problems resolving why the fan isn't coming on since technically it is not tied to the fan switches operation.

 

I apologize for the long-winded post.

What I meant was that maybe the temp isn't getting hot enough for the fan to kick on.

Seriously, even here in Texas in 100* weather, my car has to idle for a long time to get up to temperature and force the fan on. If I'm running it down the road, the natural airflow keeps the fan from coming on at all.

 

Finally fixed the cooling issue. I posted a new thread with the details and fix:
https://www.thirdgen.org/forums/cool...ml#post3817040

 

Posted on thread above