Hi guys!
There is a problem with my 91 Trans AM, about several months can't resolve it.
So I have TPI on my 305ci LB9 engine with two fans, but 2nd doesn't starts.
When temperature rize up to 240F/115C, only 1-st fan (black/red wire) starting.
Also it's starts when I connect with paper clip A+B ports at diagnostic can.
2nd fan I can start only when I connect pigtail connector to ground or shortcut relay (black/pink wire).
all parts are new, caps, sender, sensor, switch, thermostat, rediator, waterpump and hoses.

what did I miss?

gauge STANDARD MOTOR PRODUCTS TS76
switch ACDELCO D1852B
sensor STANDARD MOTOR PRODUCTS TX3
thermo STANT 13356

 

Check your radiator cap for pressure. Mine was also over heating. bought a new 4 core rad. and a cap at the same time. cap was 16 lb. Installed the cap, on the old rad. and now takes a long time to get to temp. and now I have a new rad. I don't need.

Good luck.

 

Can't believe how many people are having temperature issues these days...

You're saying the primary fan doesn't come on until 115C. That's about in line with the factory calibration which calls for the fan to turn on 108C. Can chalk up the delta to some amount of variation in accuracy between the temperature gauge vs the coolant sensor. So nothing wrong there IMO. Ignore the Fan2 temps... the ECM is capable of controlling the secondary fan, but GM didn't wire the system that way on the Camaros/Firebirds; only the Corvettes.




The secondary fan is not controlled by the ECM. It's controlled by a separate temperature switch which activates at 114C. If your gauge is off by ~7C, that would mean the gauge would hit ~121C before the secondary fan turns on.

So the reality is what you're seeing as "high temperature" is actually how it came from the factory and is actually running how GM designed it.

If you want the car to run cooler, I'd recommend getting a 180 thermostat and then getting someone to burn a chip with a lower on temperature for the primary fan. Then get an aftermarket fan switch with a lower on-temperature.

For reference, here's the circuit for how the fans are controlled... Though don't become confused about the secondary fan connection to the ECM. That wire only reports the secondary fan status to the ECM. Secondary fan control is actually on pin GF8.

 

Thank you for your reply, I think there is no problem with cap. High temp was before changing to new original one.

 

Thank you for your detailed reply!
Actually this is my second config of sender, switch and thermostat. I changed them all twice))
So I believe gauge show actual info.
I can't understand why switch 108C doesn't turn on the second fan.
I wanted to configure all, like from factory with out any additional switches, relay etc.
By the way, I think my A/C compressor empty, could it cause on that issue?)
When I turn A/C on with Hi and Max, second fan doesn't starts and only warm wind.

 

The fans on these cars don't do much. They're only going to come on while the car is sitting at a stop. 99% of the cooling comes from the air dam under the front of the car, forcing air up and through the radiator. With it's location on the car, and proximity to the ground multiplied by the idiot factor, the air dams tend to get ripped off and then you get "My car overheats, help!" threads.

 

If you have not refrigerant in the system, the A/C compressor won't turn on. Open the hood, turn on the A/C with the engine running and see if the clutch engages.

 

Already done it, no any moves with clutch. A know tha there should be pressure for starting it. But I don't know can it be a reason of fan failure.

 

An empty A/C system has nothing to do with your "overheating". The secondary fan temperature switch will still turn the secondary fan on.

I put the word overheating in quotes because everything you're telling me in terms of operating temps so far doesn't suggest there's actually a problem.

But If you're trying to say that the secondary fan doesn't come on at all ever, except

This tells me ground coming off the fan itself is good.

You might have a bad secondary fan relay. Test => Turn the key on and ground the gray wire coming off the fan relay (terminal F). If the fan turns on, your relay is bad (assuming the new switch you installed is good).

Another test would be to swap the primary and secondary relays. If the primary fan then doesn't turn on when the engine gets up to temperature, then the relay is bad.

I'm skeptical the battery (orange) and keyed ignition (brown) inputs to the relay are bad since if those connections were bad, the primary wouldn't turn on either since primary and secondary fans share those.

 

When I connect gray wire to ground, fan starting up. I thought it was a test for correct wiring.
And relays I changed with each other.

 

Have you let the temperature get up get up to ~120 on the gauge? If that switch is the factory replacement then that's likely what the gauge will read before that fan turns on based on what you're telling me.

 

For now, this is MAX temperature. On this point 1st fan starts and temperature falls down for two sections then rising up again.

 

Well, you've proven the 2nd fan works by manually activating the relay. That essentially eliminates everything in green below as a possible fault.

Last thing to try is take the connector off the temperature switch and ground the connector. That'll prove out the part in yellow.

If the 2nd fan turns on, then that only leaves your gauge and the temperature switch itself as the problem. Either the gauge is not reading the correct temperature or the activation temperature of the switch is not correct.

 

Is the air dam just 1 piece that is in the center of the car or is there suppose to be side pieces with it also

 

Depends on the car. What do you have?

 

it is likely that the primary fan is providing enough cooling so that the secondary fan switch never meets its set point.

why not disconnect the primary fan and run it hot enough to see if it engages the secondary?

as long as it's not boiling over it is not overheating. just let it idle with the primary disconnected while observing.

the dash temp gage is NOT a good indicator of actual operating temperatures. don't assume it is a true measure of the state of nature at the sensor. use an infrared themometer if you want to get a better indication of the operating temp.