So I bought this semi beat up 94 trans am for the wife, and now we decided it is not worth it to fix it up just gonna go buy an ls1 ram air.

Anyhow, the last owner of the car kept overheating it. He believes he blew the head gasket, but knows nothing about cars. I finally got around to checking it out, and the fans do not come on at all. The a/c isn't charged so I can't check the 2nd fan. It works when you jump it, the relay is ok, and so is the fuse. I installed a new temp sensor in the water pump, and a new 180 thermostat. My scan tool shows the computer knows how hot it is getting, but refuses to turn the fans on or cannot turn the fans on due to a wiring problem. It had a stored code 77 fan #1 problem in the diagnostic history codes. There is no water in the oil, no oil in the water. If it is blown it is burning water in the combustion chamber, but I have yet to prove it is losing water that way. It runs and drives ok, but it does run a little hot like as high as 207 or so according to the computer, and 220-230 on the dash with the fans jumped on.

So I am like now. I have checked some of the other threads on this but it doesn't seem to offer me enough info.

Thanks!

 

207F on the computer is not that hot, if it's accurate. The PCM turns fan on at like 225F, so no fan at 207F (PCM) is normal. Dash gage might read high, or new PCM sensor is a bit low. Does it show any signs of overheating like coolant boiling, or gurgling sounds after shut-off? You can idle or drive to above 225 to see if the fans do come on. No problem, but make sure your rad cap is good first. Just shut down by 230F or so, or of course if you smell coolant, so you don't get it too hot. Don't push it much beyond 230 or it might boil after you shut off.

A cooling system pressure test can help detect a failed head gasket. Pressurize, then check for coolant in the cylinders. Or apply compressed air to the cylinders (like a leakdown test) and check for bubbles in the cooling system.

 

pcm readings go above 215 F and no fans, still sets a code 77 fan 1 fault, but yet the fan works when you jump it on the panel box under the hood. I know the heater core is also plugged up so I am going to do the hose thing and clean it out. I went ahead and put a new radiator cap and a new temp sensor for the dash in, but it still reads very hot on the dash, which may be a product of air in the system. Autozone no longer carries the "block tester" to check the cooling system anymore. I can't find any obvious problems in the wiring either. I may have to put an external control on the fan if nothing else.

 

Again, you gotta get to PCM to read 225+ for the fans to come on.

Another thing that MIGHT be an issue is the water pump drive. When mine failed, it would spin the pump too slowly, especially at higher RPMS initially. As it got worse, the pumping at idle dropped off to nothing. With poor coolant flow the temp in the head runs high compared to that read by the PCM. Failure on my car was that the splines wore off the pump drive shaft in the motor, on the w/p drive gear assembly. I diagnosed it by running the motor without the stat, and saw NO flow in the radiator with the cap off. Thus, no pumping. Also, I was able to reach into the pump through the stat hole, and spin the pump impeller back and forth (engine OFF!), indicating it was not solidly connected to the drive. If you try that be CAREFUL, I sliced my finger on the sharp casting edge by the impeller.

You used an LT1-style thermostat, right? You might try pulling the stat and checking for flow in the radiator.

 

Ok-fan works at 225 shuts off at 215 according to my scan tool. However, the guages are reading 250 and 230 respective to the numbers that the PCM has. I think you may be right about the water pump, it isn't the fans after all. I just changed the oil, not a drop of water in it, I am suspecting we may have a bad water pump and no blown head gasket at all.

 

Before you tear everything apart I'd get a infrared temp scanner and check temps in various places. You could also try installing a mechanical temp gauge temporaly for testing. You could just have a bad temp gauge.

 

It has new sensors on both the water pump and heads, I think it is actually getting that warm inside of the motor quite possibly. I have only seen water pumps fail and pee out though, although the lt1 pump is a weird one.

 

So what's the problem?

225 is correct for fan on. Also when the fan comes on, the temperature goes down. So how could you have a pump problem. If coolant weren't circulating correctly, this would not occur as precisely as it does. The only problem I've seen consistantly on these pumps is bearing failures. But the pump still functions. Your 77 is probably a connection problem.

Now your gage on the other hand which has almost no calibration appears to have a gage problem. As apposed to the sensor since you already changed it.

There are a couple of things you could do. Leave it alone and get rid of the car.

Get a Jet fan switch that screws in the block and turns the fan on around 180 degrees. $69.00

 

Fans work as they should, I have determined. I got the jet fan switch and installed it, (of course cutting up my arms in the process) water pump pcm temps are in the 205 degree range when driving and the guage still shows 210-225 ish at max. No oil in water, no water in oil, no white smoke coming out the exhaust, and no water disappearing as in being vaporized in the combustion chamber due to a problem. Radiator is clear of debris in and out, new sensors and thermostat. I am down to the water pump being the problem, or as you state the gauge is just way off. I am going to pull the front cover off the pump and see how tight the impeller is.

 

Sounds like you have no actual symptoms of overheating. Speedy is right, if the pump was not spinning the car would not recover with the fans on. If you can drive the car more than about 3-4 minutes without spewing coolant the pump is ok. I think you got lucky and the gage is just reading high. If you can do an extended drive without boiling I wouldn't bother checking the pump. Just learn where the gage is relative to the PCM temp, and watch it for any change.

You never said why the previous owner thought it was overheating. Maybe just the high gage, and no overboil?

 

Yeah it definately does not boil over, and I checked the pump and it appears to be ok from the front, so I will just put it back together and sell it "as is where is" noting that it reads high on the guage cluster for some reason. I am only going to ask 3000 for it so it shouldn't be too big of a problem.

 

i am going through this same thing right now right to the T. How did you fix this its driving me nut. Jeff

 

i also have a very similar problem

i only notice a problem at idle, the temp will climb up to the red on the gage with no #1 fan on, and as soon as i turn the ac on the temp comes back down