Iroc Overheating Badly

[pr1689]

We have an 86 IROC Z28 camaro. The guy we bought it from put a 350 ored 40 over in it, with TPI. The car has the MSD add-on ignition, the 700r4 tranny with shift kit. It also has the performance chip in it.

The system is holding coolant and it's not leaking. The temperature will rise quickly and runs above 240 and will continue to rise. The only way I can keep it cool is to put the heat on and put the fan on max. Doing this puts the temp between 220 and 240, but obviously this isn't right. It also appears that the dual fans are not coming on properly. From reading the previous posts, I now know that one will come on with the a/c, but when I switch on the a/c, the fan doesn't come immediately on.

To my knowledge, here is what has been replaced:
Radiator (a year ago)
Thermostat (6 months ago)
Coolant temperature switch
All radiator hoses

I'm really at a loss as to what to do. When the fan does come on, it does cool the car down, but it doesn't seem to come on when it should. I have seen the temp approaching the red zone (right at the beginning of the red zone) and the fan is not running.

Does anyone have any suggestions? I would really love to get this fixed.

Thanks,

Pat

[J.Cutta]

You said it had a peformance chip but most chips come with a stat. Make sure the chip is with the right thermostat. Or the chip just might be bogus..Thats my guess

[Genopsyde]

first check the fan motor, I do this by unplugging the harness from the motor, then jumping a wire directly from the + battery terminal to the + terminal on the motor. If it come on, then your motor is good and you can eliminate that. also take note of how fast it spins and make sure any body parts are out of the way of the fan blades. if it spins kinda slow, then the motor is pretty much shot.

you said that the coolant temp sensor is new, so i can skip that step.

next is to test the fan relay that's located on the driver side firewall next to the fuel pump relay. How to properly test it i don't know, someone else can chime in with that info.

as for the secondary fan, you said it kicks on, so the motor and relay to that one are obviously ok. and as far as I know the secondary fan won't kick on right when you turn the a/c on anyway, it comes on once the system reaches a certain temperature.

[instantkevin]

you can't easily test a relay... just by a new one, they are relatively cheap from auto parts stores. this might be the problem.

pull the thermostat out and check to make sure it is not stuck at a partially closed position. while you have it out, put it in boiling water to make sure it opens all the way. it should open before the water is boiling.

a thermostat can get stuck no matter how new/old it is (unless it's the fail-safe brand).

[supervisor1886]

a thermo can crap out at any time, even a new one (relace it anyway with a 160 one)
Blown intake gasket maybe?
Too much antifreezethe
the spoiler fell off?
Signes of running very lean?
bad timing?
Head gasket going and you somehow dont notice it?

Also the temp should not go up that high and you normally should not rely on those fans. I think that if there is no coolant loss or pressure than there is a clog somewhere, try chemical flashing. If this doesnt help. Than maybe high-flow pump replacement?

[pr1689]

I wanted to thank everyone who has responded here. These are all great suggestions and I will look into each and every one of these. Thank you all for your replies and I will repost here with my findings. It will more than likely be this weekend before I am able to repost because of Thanksgiving!

Again thank you everyone and I will be in touch!

Pat

[Genopsyde]

sweet, i hope my suggestions are right, helps my ego.

[pr1689]

Ok, well here are my findings so far. I did go ahead and replace the temperature sending switch, the coolant temperature switch, and the fan relay. What I am finding is that the fans will consistently kick on when the temperature reaches the bottom edge of the red zone, approximately 250 degrees. They will stay on until the temp is reduced to slightly below 220 degrees.

I have not replaced the thermostat yet, although I have picked up a 160 degree thermostat. It really appears that the whatever is activating the fans, has the setting set much higher. I know that it does have a performance chip installed, and I believe someone had mentioned that maybe the chip was bogus. If I'm not mistaken, don't the performance chips let the temperature run hotter before turning on the fans? Should they do that?

What I am considering is putting the stock chip back in and see if that makes any difference as to when the fans are turned on and off.

What do you all think? Any other suggestions?

Thanks,

Pat Rogers

[Genopsyde]

yea, swap the chips and see what happens, then let us know.

[92zcamaroperson]

what do you think the possibilities are of the temp guage being messed up?

[pr1689]

I'm not sure about the temp gauge being messed up. I know if the temperature reaches to the beginning of the red-zone and I shut the car off, it doesn't like to start immediately, like the battery is dead, but if it cools for about 15 minutes, she starts right up. I'm kinda leaning to the temp gauge working correctly. But then again, stranger things could happen!!

I got to thinking again, (yes, dangerous thing!), that if I put in the old chip which was for a 305, that it may cause the car to run really bad since it has an '87 350 in it instead of the '86 305. I'm not sure, but obviously I need to do more research all around. I am going to pull the chip and see if there is any way to find info about it.

Thanks again for all your inputs and thoughts. I will keep reposting here with my findings!!

Thanks again,

Pat

[Morley]

If the fans are switching on and off, then I suspect that your temp gauge is reading incorrectly.
Get a scanner hooked to the ALDL and see what the ECM's temp reading is and compare that to your gauge. I'd bet the gauge is reading high.
Do not run the 86 305 chip, the 305's had 19# injectors and the 350's had 22#...if you use the 305 chip the ECM will think it has 19# injectors when it realy has 22# and will severely over fuel the engine (run pig rich) and can harm the engine.

[pr1689]

Ok, here are some updated findings.

The temperature gauge is working properly as is the temperature sending switch/sensor.

After more research, I've found that in addition to the coolant temperature sensor, the fan relay, and the temperature sending switch/sensor, that there is also a radiator fan switch, whis is also a thermistor. According to what all I've read, these come from the factory set to come on at high temps, like around 240 or so. It is located under the manifold, on the passenger side, between cylinders 6 & 8. This really sounds like this is the biggest culprit here to me. There are aftermarket ones that have a lower switch on & off temperature, rather than the stock GM ones.

Has anyone looked into this or have any additional info on this? I really don't want to hook up a separate switch to turn the fans on when I want to, etc.

I think I am going to try this and see what I find. I'll keep reposting and let you all know what I find.

Thanks,

Pat

[wrightz28]

One thing I didn't see anybody else mention and rule one with a overheating 3rd gen, air dam, in place, all of it?

My '85 reads the same way, one time the guage will read 240 fan on, off at 220. Then the next the gauge will read near red, then on, 220 off. these gauges are not the greatest..

As suggested, hook a scan tool up and see what the ECM sees for a temp, also, if you can get your hand on a infra red thermometer just to verify from all angles what temp it really is running at.

[Genopsyde]

when you originally said that the coolant temp sensor was new, that switch you are talking about that's under the manifold is what I thought you were referring to. That's what I had to replace when my car started to overheat for the first time.