91 Formula 305 TBI overheating issue help

[chris67rs]

hello all, I have been a "lurker" for a while, I have posted only a few times, and you all seem to be very helpfull,

I am having a problem i am stumped with,

My 91 Formula 305 TBI (vinE) has a new engine, new waterpump , new radiator, new intake/thermostat (160 deg.) new plugs/wires/cap/rotor yadda yadda yadda,

It overheats ALL the time. If I turn the AC on , it forces the fan to come on and help, however it still overheats. the fan was totally shot today and it boiled over, I replaced the fan with a 16" hayden electric (about the same size as the stock 17" ) mounted it in the same location, and plugged it into the factory harness, and it still overheats.. there is no sensor on the Radiator that tells it to turn on , its done by the temperature sending units to the ECM , (all sending units are new, there are no pipe thread tape on any of them)

I dont have a clue, I thought that the ECM would turn the fans on when the vehical temp started to rise , however thats a no go . Does anyone have any insight to what the heck is wrong.. I checked everything and the flow is really good, I'm just stumped... Someone told me it could be timing, but timing seems to be fine..

[jbkilla213]

I dont know that I can help you but for when u do get it fixed or just for now too keep the engine a little cooler if you have a tear cowl hood remove the back so it is open and on my car it dropped engine temps like 20 to 40 degrees because it lets all that hot trapped air out sorry i cant really help you out with your problem but hopefully that will help you out for a little.

[MrDude_1]

Originally posted by chris67rs
hello all, I have been a "lurker" for a while, I have posted only a few times, and you all seem to be very helpfull,

I am having a problem i am stumped with,

My 91 Formula 305 TBI (vinE) has a new engine, new waterpump , new radiator, new intake/thermostat (160 deg.) new plugs/wires/cap/rotor yadda yadda yadda,

It overheats ALL the time. If I turn the AC on , it forces the fan to come on and help, however it still overheats. the fan was totally shot today and it boiled over, I replaced the fan with a 16" hayden electric (about the same size as the stock 17" ) mounted it in the same location, and plugged it into the factory harness, and it still overheats.. there is no sensor on the Radiator that tells it to turn on , its done by the temperature sending units to the ECM , (all sending units are new, there are no pipe thread tape on any of them)

I dont have a clue, I thought that the ECM would turn the fans on when the vehical temp started to rise , however thats a no go . Does anyone have any insight to what the heck is wrong.. I checked everything and the flow is really good, I'm just stumped... Someone told me it could be timing, but timing seems to be fine..





your base timing is not set right.... its advanced too far... adjust your timing and not only will it run cooler, but you should pick up a few ponys.

you need to disconnect the computer to set the base timing. look in a service manual, or if you dont have a timing light, get someone that does to do it. good luck. :wavey:

[chris67rs]

I have the manual for the car, it does not reference disconnecting the computer, can I simply unplug somthing under the hood to set the base timing without the stupid knock sensor trying to readjust for my adjustments

[MrDude_1]

yanked from
http://www.thirdgen.org/newdesign/faq/thirdgen.shtml
Q: Why can't I seem to get a proper timing reading?

A: The computer is programmed to automatically advance the timing. You need to disconnect the brown/black striped wire next to the heater box/fan housing and then you can get a real reading. This wire is up along the firewall on the passenger side and usually is right over top of the blower motor. There will be a plug sticking out of the wiring harness loom to allow you to easily disconnect/reconnect it. Otherwise it will seem like it's advanced a great deal. Always remember to reconnect the wire when you have set the static timing!


Q: I have a carburated engine and don't have a wire to disconnect..how do I adjust the timing?

A: You must disconnect the vacuum advance line on the distributor (and plug the hose) to adjust the timing. With this hose disconnected, set the base timing to the factory spec (usually 6 degrees advanced). Remember to reconnect the vaccum hose when you are finished!

[chris67rs]

Thanks I will give it a go. you have REALLY helped me alot and I greatly appreciate it.

[XLR8TORZ28]

One question is " are you losing water".... It may sound weird but a bad radiator cap will cause overheating. When the spring gets worn out it gets weak and releases water at low pressure and then wont suck it back in from the overflow tank.... You might also want to check and see if you are getting good circulation.... with the car cold, start it up without the radiator cap on then go watch to see when the thermostat opens.... you'll know because the water will start flowing real good from the return hose at the top of the radiator....

[Corey]

I get the impression that the fan is also not coming on when it should right? The ecm is supposed to control the fans but the temp sender on the passenger side of the engine (and the one in the a/c line) will override it so I would just make sure that is wired up correctly and not even worry about what the ecm thinks.

:cool:

[MrDude_1]

Originally posted by Corey
I get the impression that the fan is also not coming on when it should right? The ecm is supposed to control the fans but the temp sender on the passenger side of the engine (and the one in the a/c line) will override it so I would just make sure that is wired up correctly and not even worry about what the ecm thinks.

:cool:


im thinking thats not the prob, since with the ac on, it forces the fans on, yet hes still running too hot

Originally posted by XLR8TORZ28
One question is " are you losing water".... It may sound weird but a bad radiator cap will cause overheating. When the spring gets worn out it gets weak and releases water at low pressure and then wont suck it back in from the overflow tank.... You might also want to check and see if you are getting good circulation.... with the car cold, start it up without the radiator cap on then go watch to see when the thermostat opens.... you'll know because the water will start flowing real good from the return hose at the top of the radiator....


you're right... i had just assumed he used a new cap when he got the new radiator and everything else :doh:



try a new radiator cap too.. should be like $3

[chris67rs]

Update:

reinstalled a new 180 thermostat (stock is like a 195)

I set the base timing with a inductive timing light with that single wire unplugged , the one near the AC box on the pass side, it was under the big silver tank looking thing, anywho I unplugged the wire, set the base timing and the car ran fine, looked inside to check the rpm's and they were right around 850 area, the SES light came on since the wire was unplugged, I turned it off, repluged the wire in and the light went out on the next start, the car kinda ran a little rough, but then seemed to clear up when the temp came up, the radiator cap was installed new when the radiator was installed new, so I replaced it anyways with a new cap from AutoZone, I left the cap off so I could watch the thing flow when the thermostat opened,

About 6 minutes later it opened, blew some water through the coils inside which I could watch, and the hose that comes from the heater control valve was also flowing fine. the car cycled through the radiator water just fine. the Fan kicks on (since I replaced the busted wire on passenger side head temp sending unit) at around 215 degrees, with cap off I could see the water flowing and a little steam coming from it, still at 220 and holding.

5 minutes later, check temp and it is at 240 going into redline. I get the hose ready, 3 minutes later, AC is off, Fan is flowing bigtime, radiator is VERY hot, car goes all the way to the right on the temp gauge and boiles water out not alot, but still its Very hot. then it continues to boil over. I cool it off with the hose and it cools down fine. engine still runs great.

I decide to look at the paperwork for my engine. turns out its a 305 that is punched .040 over, would this have anything to do with it,??? I am going to pull the radiator out and have it recored with fresh tubing, and a 4 core style.. maybe this will help with the extra capacity... ?

[jwgarvey]

chris67rs,

Do you have a code 32 (malfunctioning EGR system)? If so, make sure you clear up this problem first. The EGR system, in addition to reducing emissions, will assist with cooling your car.

John
90' 305 tbi

[jwgarvey]

chris67rs,

Also, there is a great article posted at www.ThirdGen.org entitled

GM F-Body Electric Coolant Fan
Specifications and Modifications

By William Weissman (tplsz87@cs.com)

I have read all the article on possible causes to engine overheat too!

jwgarvey@yahoo.com

90' RS 305 TBI

[chris67rs]

well its been fixed, it was not the egr, but the MAP sensor, it was bad causing a low manifold pressure, which messed up the timing, which caused the overheating, the 11.00 part caused me a headache. but all fixed.

[jwgarvey]

Chris67rs

Congrats on finding it!

John

[Stealth89]

Also one other really easy thing to check, make sure your fan is blowing in the right direction, It needs to pull air away from the rad towards the engine. If its wired wrong, it would push heat from the engine towards the rad. Check that