Iroc Overheating Badly

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

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

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.

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).

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?

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

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

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

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

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

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

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.

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

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.

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.

Ok, I will try and check it out with a scan tool, but I do know that if I don't get it shut off and the temp gauge shows it going into the red zone, the radiator will boil over into the expansion tank. This is why I think the whole temp gauge and sending unit is accurate. But I will try and get to this this weekend to have the scanner put on it. There is a local performance shop which can help me with that.

I am seriously thinking about trying this new fan switch though. Here is a link for you all to check out: www.jetchip.com At this site they have additional performance stuff, but also the fan switch which will turn the fans on at 195 and turn them off at 185. This isn't an add-on switch, it's a replacement for the stock GM one.

Sorry about the confusion about which switch replaced. The coolant temperature sensor is the one by the water inlet on the front of the car. That one has been replaced and is new.

In summation, I honestly don't think the gauges are wrong, but that they may be more accurate than originally thought. Since these fan switches were designed to keep the engine running hotter, it makes sense to me that this is the issue. The switch is actually a thermistor and that could be failing thus causing the fans to kick on later than they should.

I honestly appreciate everyone's input here and will keep on posting with what I find. I surely hope this is it, but if not, I'll keep on looking. I have found some fairly creative ideas at www.thirdgen.org about wiring in your own switch to turn your fans on and off, but I just don't think it should have to be that way.

Let me know what you all think please!!

Thanks,

Pat

Sorry guys, forgot to mention that all of the air dams are in place.

Thanks,

Pat

I hear ya about the temp, I don't like it either. My issue, the ECM controls mine through input of the CTS, no fan switch on a '85. So I have to put in a complete stand alone system to run the fan.

Latest Findings...

After reading all about this fan switch and looking at electrical diagrams, I was convinced this was the culprit. That is until I crawled under the car and looked between cylinders 6 & 8 only to find that I didn't have a fan switch there, only a plug. So that shot that idea to pieces.

After more review, and reading more postings, it appears that most people are adding a separate toggle switch to turn their fans on and off when they want to, like in stop and go traffic. It just seems to me that this should not have to be done, that there is just something that was bad in the design, or a setting in the computer set to high, etc.

I still believe that for those of you who have a fan switch between cylinders 6 & 8, that my previous thought-about solution will/may work for you. Here is my other solution which should work for everyone who does not have a fan switch in addition to the coolant temperature sensor.

What I did was pick up a 1K ohm pots (potentiometer) at Radio Shack. I removed some of the insulation from both wires of the coolant temperature sensor (black and yellow wire) and soldered on the potentiometer. There are 3 legs on the pots. The middle leg should be soldered to the black wire and then either of the outside legs will be soldered to the yellow wire. Then turn the pots in the opposite direction of the yellow wire until it stops. I should interrupt here and state that I also picked up an infrared thermometer so I could take temp readings of various parts of the car (engine block, radiator hoses, etc) to help me in deciding at what temp the fans should come on. Once determined, start turning the pots until the fans come on. This will take some minor adjustments, but when the fans cycle on and off like how you want, shut your car off. Then unsolder the pots and take an ohm reading between the two legs of the pots that were soldered. Then head back to RadioShack and pick up a 1/4 watt resistor that is as close to that ohm reading as possible. Don't go lower, get the next one higher.

To date, this has been working just fine. What it's doing is tricking the computer into thinking it's hotter than it is and it is turning on the fans appropriately, only at a lower temperature. This can be done because the computer is reading voltage from the coolant temp. sensor rather than the actual temperature.

If anyone else cares to try this, let me know and I can send you the RadioShack part #'s that I picked up. Oh and total cost was less than $5, with the only exception being the infrared thermometer which was close to $40.

Thanks to all who have replied and checked this link. I think these forums are great and I know they've helped me a lot along the way.

Thanks for all the advice and help!!

Pat

that plug between 6 & 8 IS the switch, you hafta unscrew it from the block and put a new one in its place. It's not actually a switch that you can turn on and off by hand, it operates as a switch.

Right, but in my vehicle, I don't even have the wiring for that switch. My car is an 86 IROC with an 87 350 in it. Since I didn't have the wiring to begin with, I needed a different option.

Thanks,

Pat

Also, I should clarify that by "plug" I mean it doesn't have a connector or anything which can be hooked to it. The face of this plug takes a hex wrench to unscrew it. It is actually a plug and by removing it you can put in this fan switch. I'm calling it a switch as that is the part name. It is actually just like another coolant temperature sensor, except it only has a single wire, so in essence it would work like the temperature sender.

Thanks,

Pat

One last comment on the solution I implemented. After re-reading the solution, I noticed I left out something. I stated to go pickup a 1/4 watt resistor that was as close to the ohm reading of the pots as possible. I forgot to mention to solder it in place where the pots was on the black and yellow wire. You should then tape up the areas where the insulation had been removed.

Sorry, didn't mean to leave that out.

Thanks,

Pat

i see what you mean now, looks like this is out of my league then.