Hey guys,
I've got an 87 Trans Am, 305 carb engine (LG4), auto trans, single radiator fan. I've read the stickys and did a search in this section. The info was very helpful.
My problem is that the fan won't kick in without the AC on. The engine overheats while idleing without the AC. With the AC on, the fan runs, engine stays cool. So, the fan relay, AC circuit and the fan motor are working. The problem seems to be the fan coolant switch (not the temp sending unit, it's on the thermostat housing with a yellow wire). So, I thought I would replace the switch. Problem is, I can't find it. I read in one of the posts that the switch was on the right side head. I've been all over it and can't find the switch. I know the wires going to it are supposed to be dark green and black, but I just can't seem to locate it.
Anybody have any suggestions where GM hid the fan coolant switch on a 305?
Any help or ideas will be greatly appreciated.
Thanks

Here's a picture of the Jet- Fan switch on my "91" LO3 camaro. It's on the passenger side head between the #6 and #8 spark plugs.

The fan switch has 1 wire going to it that gets grounded to the block when the coolant reaches 200* which completes the circuit and turns the fan on.

I'm also havin the same problem locating the fan switch. The pic you posted thats from underneath the car right?

Yes, the picture was taken from underneath on the passenger side.

GKK,
Great info! The picture is a big help. I really appreciate you taking the time to do that. I think I can find it now.

Actually, I did find a single wire laying loose in that area with a broken connector. That must be it. I'm probably going to order a lower temp switch with a new connector.

Thanks again for the info.

I apologize for bringing up such an old post, but my question is directly related to the image and information provided.

I just got a hypertech radiator fan switch for my LG4 T/A. In order to actually replace it, do I need to go at it from beneath the car? Do I have to remove the exhaust manifolds? I was going to deal with it when I put headers on, but if this is something I can do simply by going at it from below, I will do it today.

How did everyone else change theirs? Thanks

Alrighty, I met success by going at it from under the car. Removing 3 wires, 2 orange and one giant black one that bolted to... the starter? Anyway, after 80lbs of kitty litter for the "little bit of coolant" that "might" drip out, two eye wash bottles and a few words that cannot be repeated the fan switch is replaced and running fine.

Glad you got it changed out. I did mine when the motor was swapped.

Something else I found out. There's a bypass on the electric fan circuit that turns on the fan anytime the AC is on.

SO I just bought a 87 TA wityh the LG4. Same exact problem described in the first post. My car has headers so I can more easily see the switch, but its broken off. I found a single wire near by that has the plug on its end broken off. Can anyone tell me what color the wire is?


Thanks for any help, Kevin.

should be green with a white stripe

I've got a 160tstat and the lower temp fan switch. The motor never seems to get to 160 according to the temp gauge. Is this a problem? The fan doesn't turn off. I don't have any problem with this, but is it not a good thing that it doesn't get to 160 or 180? Did I go overboard with keeping it cool? My goal is to get jet hot coated shorty headers and with the engine bay cooler, run an open element air cleaner.

Am I keeping the engine too cool?

I would haft to say that is a bit cold, you should probally have it run at 180. what fan switch did you get?

I got the hypertech 4026 fan switch. that is also 160* Since they are somewhat expensive and a PITA to change, would just going with a higher thermostat be an alternative option? I still have some misconceptions about how the cooling system works. I thought with a 160*t-stat and 160* fan switch, it would operate around 160 or a tad bit warmer. However, it never seems to make it up to 160.

What temp should i run at and can i get it to run at that temp?

Probally whats happening is once it hits 160 the an turns on and doesnt allow it to get any hotter. If you only change the fan switch it would still cause your fan to always come on early, It would probally be better t do the fan switch over the t stat, but i woud still bump the t stat up to a 180

so fan switch comes on at 160*, t-stat opens at 160*. If I get a 180* t-stat, then the coolant won't cycle through the radiator until it gets to 180, then it will cool down to hopefully 160ish?
Should I have gone with the hypertech 180* fan switch as well?

What is the difference between 160* and 180* in terms of operating performance?

Correct, its like once the coolant starts to cycle the fan comes on too nd doesnt allow it to fully warm up. If the engine doesnt get warm enough the oil will be really thick. If you are wanting to just change One of the things the better thing to do would be the fan switch, coolant cycles at 160 then a higher fan switch kicks on at 180. I personally am in the process of doing a 180 t stat and then a 200 or so fan switch. If you change the just the thermostat to 180, the fan will be on once your engine gets to 160 and possbily prevent coolant from ever even cycling


At 160 I wouldnt think the engine isnt warmed up enough and the oil doesnt combust and would make your engine run as it does when the cars warming up becasue it doesnt fully warm up, so it kind of sticks in that mode. 180 just seems like the best choice.

very much for the help. I'm sorry I hijacked this thread, but it was all relevant to what I had done.

I guess I'll see if anyone wants to trade or has the 180 for sale. Which fan switch are you using? The hypertech one? They are around $50.

I was tired of it always running at 220* when cruising through town or stop and go of car shows/cruises. I guess I went a little overboard. Thanks again for the help.

Ive got the stocker right now, but im fixing to change it soon, Im doing the thermostat tommarow and see if it fixes my problem, I beleive mine quit opening because my fans comming on, had coolant flushed but still overheating as long as I run below 220 I will be happy, but if It doesnt I plan on getting the hypertech one that comes on at 200 and off at 185, or maybe the jet one, the are like $5 difference in cost.

I just used this thread to find that sensor. Even in searching this thread didn't pop up- IMO it is sticky material.

i have a 350 goodwrench that has a single wire electric fan switch drivers side of the block. the car was original 86' carbed 305 but with this new motor its doesnt have a thermostat temp sensor. how would i rig one up so my coolant temp gauge works? as far as i can see there isnt a wire in the harness for it, or it is already being used for the fan switch. i could put the temperature sensor in the manifold beside the waterneck but what wire from the harness to use??????

Dumb question, but R U sure the fan switch is on the dr side? Never seen that before on a sbc.

If motor isn't original, sure there isn't just an idiot light sensor in your dr side head..........and that's why your gauge isn't working?

Just a thought.

hey ....I just did my a/c removal and i Have the hypertech 160* t-stat and fan switch.

My car runs Under 160* now. I was IMpressed but NOW should i be concerned? I also have a little bit of lucas oil cycling threw the engine till the next oil change..... And also it is on average 30 to 40 degrees( 4 the next 5 months) here and we are up 4500ft.

i thought the cooler your car runs the longer it will last? Kinda like a hyundai(lol) with its cold stock plugs and dual fans.

is the wire yellow for your temperature sensor for the gauge? a picture would help Im trying to find it so i can get my gauge working again thanks

i have a semi built tbi SBC motor and my switch is on the passenger side kinda near some spark plugs......i will see if i can get a digital cam to help out.