TGGodfrey

This is not a typical my fans wont come one thread so please read carefully. Was a mechanic years ago, just looking for another view on this, perhaps I am missing something obvious or makign thsi too complicated clouding my vision..

1997 Z28 Been sitting for good 7 years, just never did anything with it. Motor has 45k on it. New Waterpump, All new hoses. Burping it yesterday, everything went well, outstanding heat ect. Few bubbles came out of the fill funnel as expected. Just as I was about to call it quits and put the rad cap back on, decided to wait and verify the fans kick on.

No fans and it started overheating. Shut everything down, after the overflowing and boiling quit, washed it down. Started testing fan circuits.

Fan Circuit: All wiring tested to be free of shorts and continuity as expected. All relays tested for operation and contact making ability. I also went as far as to actualt the fans from the C100 connector green and blue wires. It was then that it dawned me that the Snap On scanner has functionaity testing for the fans.....that was a nice hour wasted.

With the Scanner (mt2500), I am able to turn the fans on and off both hi/lo.

In an attemt to prove the coolant switch bad, pulled the pigtail off the pump and jumpered it, Scanner ready 303*F as it should. With KOEO no fans, KOER no fans. Even using a 150 ohm resistor the PCM sees 222* F and still no fans like that either.

Turned the A/C on to defeat the CLT Sensor, NO FANS.

Now with the scanner able to turn the fans on through the PCM, we know the transistors in the PCM are good. That leads me to believe the progamming has somehow failed.


Any other ideas?

I dont recall the LT1 requiring pressure in the cooling system to operate properly like some others so the fact I had a fill funnel in the radiator when the initial problem occured shouldnt be an issue. That still doesnt alter the fact I cant get the ECU to turn on the fans by tricking it into beleiving the engine is hot. In 20 years of automotive I have seen the programming of 1 ECU get scrambled, that was aftermarket ECU and it wouldnt even run.

Tonight I am going to put a new coolant switch in the waterpump since the one in there now is the original, and after it overflowed I am going to install a new Thermostat just to make sure the one in there didnt get damaged.

shoebox

222° is not enough to turn on the fans. 226° is. Often, when a cooling system is refilled, air is not fully purged from the system. What happens is the temp sensor in the head (the one for the gauge) will get some steam pockets passing by and skyrocket the temp reading (when the engine is not actually that hot).

Did you possibly get the remote reservoir and steam line hoses swapped at the radiator? Also, after re-reading what you wrote, did you leave the cap off the radiator? If so, coolant is going to gush out after the thermostat opens. The cap must be on.

I would make sure the system is properly bled and then watch the temp on the scanner until it gets over 226° (to give time for the PCM to react) and see what happens. Your other tests indicates all the fan system circuitry is ok. Chances are, you have no trouble at all.

4th Gen LT1 F-body Tech Articles

TGGodfrey

Thats interesting. I dont remember the LT1 being required to be pressurized to operate, saw it more in the 4 cylinder cars. Perhaps that is my problem and it does explain just about everything.

I was in the shops when these cars were new and I think i only fushed mine a few times in its life. Other than failed opti's we didnt see many of them come in. I dont recall any oddities when burping lt1's but ****, its been 20 years and I dont work on them much on the side due to time constraints with work and other hobbies. Usually I just watch the air pockets come out of the steam pipe and once its a steady stream, cap it off, fill the overflow and let it do its job. This time I just wanted to let fans kick on and it bit me in the ***. Honestly I cant even remember waiting till the fans kicked on (unless it was fan issue) in the past. Considering the coolant has to flow uphill the get to the thermostat it makes sense.

Steam and Overflow cant really be swapped on the 97. Two different sized hoses but regardless I know I didnt. Mistake like that is obvious (to me anyway).

You could hear steam pockets when it overheated so I am going to swap out the thermostat. I have seen to many fail to trust it. Sensors are all the factory originals. Since the coolant is drained at this point its just a bit of insurance for the long run.

I am not sure why the fans wont come on with the a/c on. The compressor clutch is locking in so the compressor is active. The only thing I can think is the car is not at operating temp and that may be one of the permissives.

Shoebox, Thanks for the second look. I do appreciate it.

RamAir95TA

I know you keep saying "burping" so I'll assume that means "bleeding." Are you using the two bleeder screws as mentioned in Rob's cooling system guide?

shoebox

Regardless, you'd be surprised how many people manage to swap the hoses.

Fan operation with a/c on is a function of pressures in the system, so that may be playing a part in that scenario.

What I was saying about having the cap on was that it will overflow from the neck if not capped after filled and thermostat open.

TGGodfrey

Ramair....I did not use Rob's guide but yes of course I used the bleeding screws to remove air from the heater hose and intake rad hose. Burping and bleeding 2 different things. Bleeding is using the bleed screws built into the system. Burping is running the motor with the radiator open (cap off with or without a fill funnel). When I say fill funnel I am referring to the funnels that will attach to a radiator and not leak. Funnel accounts for the raise and lower of coolant level as air works its way out of the system. Bleeder screws are great but there are always small air pockets left in the heads when the system is drained. (I am sure you already know this).

I burped the system the same way I did yesterday. Only I used my scanner as a temp gauge rather than the car instruments. at 195* the thermostat opens and the coolant level raises as air works its way out and coolant expands. When I got all the air out I let it cool and capped it up. Let the car warm up and sure enough fans kicked on at 228* (prolly a delay from 226 or just a percent error on the sensor). My fans I cant hear, I was able to tell based on system voltage fluctuation as they started up and the coolant temp dropping.


So what happened yesterday? I am willing to bet the block didnt have a 50/50 mix so when i added a gallon of 50/50 the mixture wasnt where it needed to be. With the radiator cap off the coolant began to boil, I estimate 240*f but there is no way of telling for sure. At atmospheric pressure the boiling point is lower than it would be under 16psi of pressure.

I ended up with 50/50 gallon of coolant begause I didnt pay close attention to what I picked up at the parts store and ended up with 50/50. Foolish mistake, I paid for water!.

My A/C pressure is prolly low due to our 12* temps here in IL right now. If the PCM is programmed to turn on the fans for A/C based on pressure of the system then that explains that. Most all the info I found on the internet (I never took classes or earned an A/C cert) claimed the fans will come on anytime the ac is turned on. I thought it was unusual but stranger things happen.

Now I get the pleasure of changing the coolant level sensor. That managed to take a poop during this ordeal.

Injuneer

Stock t'stat should start to open at 180*F.