My car (stock 305 tpi Z28 -87) has problem with overheating.. I checked it yesterday and it seems that the dual fans are not working so good. One of the two fans starts when the engine is allready overheated... shouldn´t both fans start at the same time?

and why doesn´t it start faster, before the car goes to hot?
It practicaly boiled in the expansion tank and just one fan ran for about 20 seconds.. I figured it can´t be the fan relay that is broken... I mean either way it works or it doesn´t.

Another question.. if the car goes real hot should the fans start even if the ignition is off?

Any suggestions guys?

 

i would first find the fan switch which can be located in the radiator of in the intake manifold. It measures the water temp, then turns on the fan, Depending on how much air they move, is how long they stay on. But not 20 sec. Sounds like the sensor or switch, what ever you want to call it, ( usually called temp sensor, or fan switch.) is gumed up with deposits from old age and old collant. Replace sensor. I am not sure completely if both fans come on at the same time or not. BuT I do know that at least one should come on before the car get close to overheating.


I believe that once you turn off the car, that kills the power to the fans. you could also check the fan motor for the other fan to see if it works or not.

 

- Turn on your A/C.... does the 2nd fan come on? On some dual fan setups, the 2nd fan wont come on unless the A/C is on.

Also, main fan will not come on till 230 or so. 230 is not overheating.

 

heres what i know: primary(drivers) fans come on when the temp is around 225 - 230, it is controlled by the computer, the passengers fan(secondary) comes one with the fan switch on the passengers side engine block between the 6 and 8 cyclinders, and is comes on at 240 something. Also the secondary fan will also come on when the a/c is on and bulids pressure and with the right pressure the pressure switch on the compressor or on one of the a/c lines i forget will make the fan come on.

 

Swede, you have two fan relays. If you are cooking in the expansion tank it is too hot. Most likely your primary fan is not coming on. As far as the relays, you had better believe they can be intermittent, as a matter of fact it is the most common problem with these cars. The relays suffered form a design problem which GM never really admitted to. The newer relays are a different internal design and are quite reliable. If the CTS sensor was bad it would throw a SES light and you would get a 14 or 15 trouble code. Get two new relays and then give it a try. I'll bet your problem goes away.

 

Where are the relays located? I found one of them.

 

On most dual fan setups one is located near the radiator below the cap area, on the 89 I have the secondary relay is located on the pass side above the battery.

 

Thanks, I'll check that out.

 

I decided to make a manual switch for my fans... So now I just push the button when It´s gets to hot..work great..I´ll post pics of it later.

 

I had a fan from a thunderbird SC put in my IROC as I was having a similar problem with overheating. I've not had that problem since.