Guys,

I have an 88 IROC with the TPI 305 and 5-speed, and the car has air-con. I have an aftermarket chip in the computer, but it's not very radical (passes California smog test!). I also have a 180 degree t-stat with a couple holes drilled. Radiator has been recently rodded-out and flushed.

The thing runs fine during normal driving, but if it's a HOT day, and I get stuck in slow traffic, it wants to heat up. Both fan motors are OK, and I've replaced both fan relays. No blown fuses. And mechanic replaced the thermal sensor in the engine.

Before, when it started heating up from no airflow (slow or stopped traffic), once the temp went over about 220, you could hear BOTH electric fans turn on, and it would cool the engine down quickly. This was great.

Then, the thermal sensor in the engine failed and the fans would not turn on at all. I tried to fix it myself (not knowing it was the sensor) by replacing the relays and looking for blown fuses, but no-go. I took it to the shop and the guy there replaced the sensor, and recharged the freon in the air-con, which he said lack of freon would keep one of the fans from coming on.

Now, the primary fan (driver side) only comes on, only when the temp gets well above 220, and if it's a hot day, the single fan is not enough. What can I do to get BOTH fans to turn on when the temp gets too high? The mechanic told me the secondary fan only comes on when the air-con is on. Well, why did BOTH come on before, but not now???

Lastly, both fan relays are over by the battery. One is on the fender, the other on a bracket by the radiator. Which one is for the primary fan? Thanks in advance!

 

If I recall, the primary fan (on my '89) is the one in front, the 2ndry is by the fender. First to see if that's your problem just swap'em ...but, the 2ndry fan only comes on after 240+ degrees (factory sensor). Or with the AC. You can replace the 2ndry fan sensor, which is located in the pass. side head, between #6 and #8 plugs, with a lower setting one from the factory. On my '89, doing this will turn on
BOTH fans at 200, and off at 185, I also run a 170* Tstat.

Hope this helps.

 

Hey Mike, thanks a bunch. You're one of the few who seems to know what the hell is going on with this thing. I hope you don't mind if I ask you a couple more, just so that I fully understand the thing.

1. - I assume the primary fan is controlled only be coolant temp. Where is the sensor for the primary fan? Is it separate from the sensor for the temp gauge? Is the primary fan's turn-on point controlled by the ECM?

2. - Let me verify my understanding that the secondary fan is controlled by the A/C and by coolant temp. When the A/C is on and there is freon pressure, the fan is on, and if the coolant temp goes over a certain point, this fan also turns on? This coolant sensor is the one located between #6 and #8 plugs? (Impossible to get your hands down there because of all the plumbing.)

3. - Over on the passenger side by the battery are the 2 fan relays, with the one on the fender being for the secondary fan.

4. - On the firewall between the master cylinder and the fender are 3 more relays. The odd one is for the fuel pump, the other two are for MAF power and MAF burnoff?

5. - Any idea why this thing eats MAF burnoff relays at the rate of one every 18 months or so?

6. - Does removing the screens from the MAF help performance much?

7. - Where would one go about finding a temp sensor that would turn on the fans at a lower temperature?

8. - Who would you recommend for a t-stat with the lowest flow restriction when full open?

Thanks again!!

 

removing the screens from the MAF sensor does almost nothing, unless you have alot of other mods to free up incoming air.

 

Not a problem.

 

is it the coolent temp sensor or the fan switch that turns on the fan at a lower temp. I thought you get a fan switch to go with a different tstat not a coolent temp sensor.... what s the deal?

 

Mike, thanks again for your valuable help.

Re the MAF burnoff relay, I don't know what the exact failure is. I get a Check Engine light, and the ECM code (36) tells me MAF burnoff failure. I replace the relay and the problem disappears. It's gotten so that I keep a spare relay and proper size nut driver in the glove box. I just chuck the old relay in the trash and forget about it. The relay is only $12, much cheaper than a MAF. Interesting that this same relay model is used for MAF burnoff, MAF power, and both fan relays.

Re MAF prices, I had the local dealer quote me $400, and the local parts shops want about $200. Hummm....I can replace a LOT of relays for the price of one MAF....

Re the secondary temp sensor, I think I want one that turns on at 220, and off at 200, so I can keep my 180 degree tstat. Where I live, we get a bit of snow in the winter and some mornings are a bit below freezing. So I want a warm heater, and I don't want to be changing tstats. Whatever the mechanic put in ther doesn't turn on the fans until the needle is near the top of the temp gauge, and I'm getting scared to death. That engine has never boiled and I've had the car since it was brand-new. I'll be damned if I'm gonna let it boil over now.

Regarding a drilled tstat, sometimes, if it's REAL cold outside, and I'm on a long steep downgrade, using compression braking, the engine will overcool, and the temp goes way down to near 100. Any problem with that?

Thanks again for your help, I really appreciate it. I owe you a beer.

 

Lol, first things first...I have to go to Carson City next weekend...careful about that offer, I only drink the reeeeeaaaallly expensive stuff Naw, wife wouldn't let me drive after a nip, your beer is safe for now.

I'm not sure about the sensor you're looking for that would go in place of the stock one, but there are manufacturers that make adjustable ones, although I don't know the on/off range of them. I think instead of using the stock location in the head, you plumb them in the heater line and you have access to adjust...then splice into the relay wires.

You could also get into PROM burning and change the primary on/off settings as well. See the PROM board on how to get started.

As far as the temp dropping to 100*'s, you may want to verfiry that with a scan tool (see the PROM board again on inexpensive alternatives) if it is going to 100*'s, then you're going to be going into open loop, so milage and performance my suffer a bit until you go back into closed loop (about 103*F), but maybe no difference...on a long downgrade the exhaust has probably cooled the O2 down enough to cause open loop anyway...

I'd check the wiring on the sensors for S's and G's, make sure he has them connected, make sure the relays are getting energized...FYI, when the sensor sees warmer coolant, it's resistance decreases to the point that it becomes a short to ground, which energizes (by grounding) the relay.

ECM does the same thing for the primary fan...it grounds the relay as well.

General:

Yes and no The CTS feeds the temp to the ECM, ECM see's the temp and when the programmed values are reached in the EPROM, the ECM sends a ground state (probably through a quaddriver?) to the primary fan relay, which energizes the primary fan.

This CTS is located in the front of the intake manifold.

The secondary fan relay is energized via the highpressure swith in the A/C, as well as coolant fanswitch, this switch is located in the pass side head, between #6 and #8 spark plugs.

On the driver side head, between #1 and #3 plugs, is the coolant sensor for the gauge.

Does that clear it up? BTW, this is for dualfan cars.