Hi-

I've got a '84 Trans Am with the stock electric fan.

A few months ago my heater core developed a leak- as a temporary fix I bypassed the core by looping a length of heater hose to the heater inlet/outlet nipples on the engine (which is factory stock, btw).

While temperature-wise it seemed to run fine for a while until the other day when after a 10 minute drive I noticed that the electric fan had kicked in. While normally I wouldn't be concerned, two things occured to me:

1) The outside temperature was < 55 degrees,

2) The temperature gauge was reading less than 200 degrees. The fan normally kicks in around 220.

While trying to explain this to myself, the only answer I can come up with is that my heater core 'fix' isn't allowing coolant to circulate very well in the passenger side head (I had noticed that the hose is kinked slightly, which could be restricting flow), where the electric fan control switch is located. However I'm not familiar with how the cooling jacket is set up for a 305, so I wanted to ask if this might explain what I'm seeing here.

Ideas? Or if I'm barking up the wrong tree, where else can I check to find the cause of this?

Thanks!

 

Your heater core bypass won't cause that. Three things I can think of quickly

1. Relay stuck closed
2. Cooling switch shorted
3. A/C switch shorted (if you have it)

Did it kick off, or stay running until you shut it down? Have you drove it since, what has it done?

 

Ah, ok. I didn't think it would be the cause but it was the last time I did anything to the car that would even remotely account for that problem. BTW the car does have factory A/C.

No, I haven't driven it since but I need to to see if I can get it to act up again. When it first did it I don't recall the fan cycling off until I shut down the engine. In a day or so when I can find some time I'll drive the car around the block to see if I can get it to do it again, and I'll post a update on what I find out.

Thanks for replying, btw!

 

Update- while I didn't take it around the block I started the car up a bit ago and just let it warm up to see what it'd do.

After about 10 minutes of running, and at around 150 degrees the fan kicked in for about 5-10 seconds then kicked off. A few minutes later it ran again for another 5-10 seconds then kicked off. I let it warm up to around 190-200 but it didn't try to cycle again during that time. I did check to make sure the A/C was off (in fact I had set the lever to the off position) and when it cycled for the first time I ran the lever over to heat and back to off again to make sure it wasn't making bad contact, but the fan was unaffected.

So I don't think the A/C control is the cause of this- either I've got a flakey relay or the temp sensor is going out on me - and I'm leaning towards the sensor right now...

 

I wouldnt be worried. The stock temp gauges (all the stock gauges for that matter) are absolute garbage. If you had access to a Tech1 and a DVOM, youd see how inaccurate they really are...tach included.

 

dave,
did you ever figure out the problem?
mike

 

Not absolutely but after that last test I'm 90% sure it's the sensor switch. I'm running the one out of a Buick GN that I got at the dealer about 2-3 years ago. Can't believe it's already going out :P

When I get a chance (weather permitting) I'd like to disconnect the sensor and watch the temp gauge again to see if it kicks on before it hits 190*. If it doesn't then the sensor's at fault- but if it does then I'll be taking a look at the relay....