I have an 87 Camaro SC with the LG4 305 4bbl. It's a Canadian export so there is no computer. The problem is that the radiator won't cut in. I have tried grounding the fan switch connector to the block and the the fan turns on. Whenever the air conditioning is on, the fan is on. I just finished replacing the fan switch itself, and the fan still won't come on when it hits the temperature of the fan switch (108C or 226F). Without the air conditioning on, the car just keeps heating up and the fan will not turn on. I have no idea what else to do. Any suggestions at all would help.

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1987 Camaro Sport Coupe
305ci 4bbl (LG4)
3.23 Gears
THM 700-R4 Automatic Transmission
All Stock

 

87CC,

Did you ground the fan temperature switch wire right at the sensor body? It's possible that whatever sealant you used to install the sensor is insulating the sensor body from engine ground. If you cannot meter a good ground at the sensor body or grounding the control wire to the sensor body does not operate the fan relay, you may have to tightent the sensor more until you cut through the thread sealant and establish a ground path. Check this with an ohmmeter or the sensor wire grounding trick.

If you have a good ground at the sensor body, you might have a bad or incorrect sensor installed. Since most domestic '87s had the analog sensor instead of the hard contact thermal switch, the parts counter may have given you the wrong replacement sensor.

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

I'm pretty sure that the fan temperature switch is grounded right at the sensor body. The only sealant I used on the sensor body is some teflon seal tape on the threads. How would I tell the difference between an analog sensor and the hard contact thermal switch (the new sensor looks exactly like the old one that we took out of the engine)?? How could I use an ohmmeter to check the ground path??

 

CC,

Connect the ohmmeter to the sensor body and engine ground (or battery negative) and test resistance on the Rx1 scale. You should get less than 0.2 ohms.

A thermal switch should have hard contacts that are either opened (infinite resistance) or closed (zero ohms). An analog temperature sensor will have a variable resistance depending on temperature that conforms to the following table:



If you have an analog sensor instaled, the resistance of the sensor would have to drop to around 15 ohms before the relay might energize - or at about 270°F / 132°C.

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Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

So for my car, which type of sensor should I have?? I don't if this will help at all, but the part number on the sensor they sold me is 3040674. Also, for the analog sensor, how would that work properly if it doesn't cut in until 270F/132C, wouldn't that be well over the temperature that the car can handle??

 

CC,

O.K. - Just for you since you're one of the good guys (a Canuck) and just this once...

ECM/PCM 101

The typical ECM uses inputs from various sensors, act on them based on the programming, and operates outputs accordingly. Most of the sensors are analog output. The ECM uses this varying (analog) signal to determine the operating parameter of the particular sensor.

For example, the MAF outputs a 0-5VDC signal. This means nothing to the ECM until it is scaled to indicate that 0VDC = no intake air flow and 5.0VDC = 255 grams/second of intake flow. The ECM uses this information to trim the fuel injectors' output rates.

The coolant temperature and intake air temperature sensors are similar. The sensor varies its resistance from 40,000 to 0 ohms. The ECM applies a 5.0VDC reference signal to the sensor and the resulting voltage (based on the resistance to ground) is scaled as outlined in the above table so the ECM understands the temperature at the sensor. EFI engines (with an ECM) use this information to operate various engine controls - and the cooling fan.

While the ECM controls the fan operation on EFI cars, your control scheme is much less complicated. Your sensor directly operates the fan relay, much like the secondary cooling fan on EFI cars with a dual fan installation. Therefore, until the resistance of an analog sensor is low enough to act like a closed switch contact (about 15 ohms) the relay will not operate. On the other side of the coin, since teh current required to hold the relay closed is much lower than the current required to pull it closed, the fan relay will likely stay on until the analog sensor resistance increases to around 200 ohms, or 205°f / 95°C.

If you get any resistance except a zero or infinite resistance on the sensor, you probably have the wrong one. The 3040674 is listed as a "switch" instead of a "sensor", and the correct sensor for an EFI car is P/N 10045782. I would suspect it is the correct one and you have a grounding issue with the PTFE tape acting as an insulator.

------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

I just checked the resistance between the sensor body and the battery negative and there is no resistance (it reads 0.00 ohms) so I'm guessing that means that the sensor is the right one. Is there anything else I should check??

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1987 Camaro Sport Coupe
305ci 4bbl (LG4)
3.23 Gears
THM 700-R4 Automatic Transmission
All Stock

 

Please help me!! I really need to get this problem fixed.

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1987 Camaro Sport Coupe
305ci 4bbl (LG4)
3.23 Gears
THM 700-R4 Automatic Transmission
All Stock

 

I would be glad to help but hold on, do you have 2 fans or 1 on this car???? if you have 2 fans then there is 2 sensors,,,,,,,,,,, one is a sensor that the computer sees to opperate the second fan and the first fan is opperated WITH a fan switch. FAN SWITCH means that when 226F or so is reached the SWITCH CLOSES the RELAY #1 will close and FAN #1 will run, the second sensor is a resister which the guy above is talking about,,,, when 235F or so is sensed by the ECM, the computer CLOSES RELAY #2 for FAN #2 and the fan #2 cuts in. So make sure you have replaced both sensors with the right sensor one needs to be a SWITCH and the other needs to be a Termistor.

 

First, this is only a 1 fan cooling system. Next, I just discovered some new information. The fan does come on to cool down the engine, but only at a very high temp (~123*C) and it only stays on for about 15-25 seconds (only enough to drop the temp about 5C). Before I had the heads redone (due to a blown head gasket and overheating) the cooling fan would kick in at about 106C and cool the car to about 90C. Is there a reason why the cooling fan isn't cutting the same as it used to??

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1987 Camaro Sport Coupe
305ci 4bbl (LG4)
3.23 Gears
THM 700-R4 Automatic Transmission
All Stock

 

Do you have one relay or 2 relays to this fan, I think you have two, if the A/C is on and the fan cuts in OK then check the RELAY that is connected to the FAN switch, if the FAN Is coming on at a later temp then what it's set for, then go to HYPERTECH FAN SWITCH, out of summit catolog. You can get one that will cut the fan in at 180F and shut off at 200F, make sure you change your thermistat too. Is this car carb. or EFI???

 

There are 2 relays for this fan and both of them have been checked and are working. I don't think that going to a Hypertech Fan Switch will change anything because I have already tried 3 different switches and they all do the same thing and cut in too late and cut out too early. BTW my car is the LG4 305 4-bbl carb.

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1987 Camaro Sport Coupe
305ci 4bbl (LG4)
3.23 Gears
THM 700-R4 Automatic Transmission
All Stock

 

Well 87CamaroChris Hypertech switchs ARE NOT OEM replacements, they are aftermarket custom made switchs for this type of application, here is a link to the HYPER TECH and if you look through the ARCIVES at this site you will find an article on this topic, GET HYP - 4028 part, it cost $50 bucks with shipping but it's worth it.

http://store.summitracing.com/defaul...rchType%3DBoth

 

Make sure you are using a 180F or 195F degree thermostat so that when the fan cuts in at 200F that the thermostat is already open alowing water to get to the radiator and this switch will not turn off till water temp. is below 180F which it will never reach because the engine will produce more heat never getting to 180 so the fan will always be running just what you want.

Here is a post about the product:
http://64.4.20.250/cgi-bin/linkrd?_l...fUltimate%2ecg i

 

What I'm trying to figure out is why the fan switch worked the way it's supposed before, but now it isn't. The fan switch that I have in my car now (the original 106C/222F GM fan switch) isn't working the way that it used to and the replacements that I got (a Standard Auto Parts and an AC Delco 108C/226F) are doing the same thing as the original fan switch. I've seen those Hypertech fan switches, but I'm not sure how it would help my situation. The Hypertech fan switch is supposed to cut in at a cooler temperature, but if the one that I have in there right now isn't working and none of the replacements that I got are working properly, then I'm not sure it would be a good idea to try a Hypertech fan switch just yet. BTW I am using a 160F thermostat right now.

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1987 Camaro Sport Coupe
305ci 4bbl (LG4)
3.23 Gears
THM 700-R4 Automatic Transmission
All Stock