Hi everyone,

I looked around everywhere and couldn't find a strait answer to my issue so i'm hoping someone can help me out.

So a couple of days ago I got my 91 z28 running. It has the 5.7L TPI if this helps, now its having overheating problems (maybe). About a year ago I remember and old mechanic (I don't use anymore lol) tell me that there was a piece of plastic hanging down and he removed it and said it serves no purpose and that I don't need it. Then the high temps started happening to the point where the car reached 250 and I wanted to pull over and let it cool because in my mind the car was overheating. I brought it to my mechanic where he told me what he could do was wire a toggle switch to my dash so I can turn the fan down this would bring the temp to 210 (Still hot in my opinion) but once I got to highway speeds it would climb quickly. Also if I turned off the car and went to start it the next morning it wouldn't want to idle i'd have to hold the gas until it warmed up.

Anyways this is where I'm at, I want to undo the switch and redo the stock wiring. I found out today that apparently I never really had an overheating problem, these cars are just normal at 220 lol Also I did look under the car and saw that there is no air dam.. guessing that was the "thing I didn't need" that they removed so a new one is on the way.



As you can see the black and pink wire was cut and rerouted to the switch that's on my dash. This feeds the 12 volts to the fan. It looks like this was the only thing that was altered... Couldn't I just reconnect this connection and see if the ECM turns this fan on once it gets to 220?



I have a stock dual fan setup. the fan closest to my camera, the one on the right, is controlled by the switch on my dash. I have no idea what controls the one on the left... I've only ever seen it on once and it was when the car was hot, like around 250. but I never saw it on again.

 

250 isn't dangerous with cast iron heads. Around 240 degrees is the optimal temperature for combustion in cast iron heads. So, 250 is high, but not point of concern. I would wire that relay up correctly, and make sure your cooling system is in good order.

 

Yeah i'm gonna start fixing up the damaged aux cooling fan circuit and see how that goes.

The cooling fan on the left in that pic I found out today it the one that's controlled by the ECM so I tested it by letting the engine run and it got up to 250 then the cooling fan kicked in and cooled it to about 220 and it shut off. So I drove it around and it never went above 250. Even with the missing Air Dam (Still ordering it though lol)

So about that aux circuit (the one where the relay is all the way to the right in the pic of relays) if I test that with a multi meter there is 12 volts at the striped black and pink wire, (the one that's cut) at any time like when car is off, engine is cool like below 100F. Now, if I go to were the fan switch is located in the pass side cyl and I take that wire and ground it to the engine, I hear the relay click and the voltage drops to 1.0 volts. I think the relay is bad because of that but shouldn't also be reversed? Like if i'm grounding that wire.. shouldn't it turn the fan on not off? How do I reverse that?

 

I wouldn't be surprised if it's wired like that because the relay went bad and the PO decided to just "rewire" it instead of plugging in a new relay.

 

So replace the relay and try to connect the fan back up as well as the fan switch and see what happens? No need to reverse the way the relay works? It just seems backwards to me.

 

You don't ground the wire out of the passenger cylinder head. You put positive power to it and the fan should come on.

 

You have to have the airdam intact on these cars, at highway speeds it pushes air up to radiator. They will run alot warmer or even hot at highway speeds without it.

 

Or you'll fry the relay