kthxbai

iTrader: (5)

I wanted to try and get some other opinions on what could be going on with my cooling fans...

Two weeks ago I was driving the car and I barely noticed the temp gage skyrocketing in time to pull over and spray coolant all over the place and overheat like crazy. After cooling down and re-filling I realized that my fans were not coming on (dual electric LT1 stock fans). I also noticed that the fan relay socket was melted slightly.

This past weekend I replaced the wiring down near the fans and the connectors that plug into the fans (previously my wiring had not been weatherproof as I had forgone the proper connectors. Some of the terminals had burning evident, however both fans still work with power.

I replaced the relay, checked that my power and ground wires were properly connected and healthy, and tested everything out. No luck.

The PCM would not ground the relay no matter what temp the sensor provided (checked that PCM is getting good temp data with laptop), with the temp sensor unplugged, with the ALDL pins jumped, etc.

(for reference, i have both fans on one relay set to come on at around 200 F off of the low temp pin A11 red pcm connector)

So thinking I was clever I reflashed my PCM to control the fans from pin A12, the secondary fan pin for high temp/speed. Now, the fans come on with ignition power, AKA the PCM is constantly grounding that pin.


My best guess is that during whatever current/voltage event melted my relay socket, I managed to fry the circuit in my PCM that handles pins A11 and A12, and they are now permanently open (A11) and grounded (A12).

Any other ideas? As it sits now my fans run as soon as the key is turned, which beats no fans, but still isn't ideal. I am considering installing a manual switch to control the relay.

~Steven

Joe Tag

iTrader: (4)

You need a relay for each fan that's obviously too much draw for just one. Trigger the relays with the coolant temp switch and take the computer out of the loop. Two wire CTS, ground one pin and the other goes to signal both relays. Not as high tech, but neither am I. My single works flawlessly this way.

kthxbai

iTrader: (5)

well its a 30 amp relay, so I think it can handle it. I am running 12 ga wire from the battery to the relay, and from the relay to the fans where it splits to each fan down to 16 ga.

I drove it as was for 4 years without issue, so I am inclined to believe it was a short circuit that actually caused the damage.

Thanks for the idea about wiring directly from the temp sensor- this is the sensor in the water pump that provides the pcm signal? at what temp will it actually trigger a relay?

Pocket

iTrader: (24)

Oem fans have about a 30A turn on draw each, so two fans on one relay is pushing your luck

The two wire CTS will come on with ign and run continuously, it is not designed to trigger fan relays. It is resistance based, so using it to ground a relay will only vary how much voltage must pass through the electromagnetic coil to engage the relay. Some relays trigger at next to no voltage so continuous operation will result

A much better option is a thermal switch from a TBI car. It's a single wire and can be purchased in many turn on temps to suit your needs

Joe Tag

iTrader: (4)

Been running it this way for 15 years, telling people to do it for a few and now you tell me. Going to have to go out and test it now.

kthxbai

iTrader: (5)

Jon, do you know the threads on the water pump sensor off hand? I am not with the car until this weekend.

I am thinking to buy a universal 200 degree on 185 degree off temp switch and replace the water pump sensor. Does the PCM need the temp for anything else?

I would imagine the water pump sensor is 3/8" NPT? If anyone can confirm it would be appreciated.

~Steven

Pocket

iTrader: (24)

CTS sensors vary resistance based on temperature, from something low (often 40ish ohms) to very high (million plus ohms). If and only if your relay coil engages at the exact voltage that the switch reaches xx temp will this trick work. More likely the relay will push voltage through the sensor regardless of temp and resistance because there is a connection still, albeit a crappy one

With thermal switches easily attainable, this trick is useless

I don't recall the thread size off hand, but I'd assume is npt. Do NOT swap the CTS for a thermal switch in the WP. The PCM still needs a CTS input. A better solution is to use the plugged hole in the pass cyl head between the 6&8 exh ports like any SBC

kthxbai

iTrader: (5)

Thanks as always. When I am working on the car this weekend I will take a look and make a plan.

Another question- what is the wire gauge on the stock LT1 fan connectors? I bought new airtex pieces and they have either 16 or 18 ga. , certainly not 12 or 14. Is that how the factory wired them?

I was thinking today about re-wiring completely with two relays, a DPDT dash switch, and 12 ga. wires everywhere, but my connectors arent even 12 ga.

~Steven

Pocket

iTrader: (24)

You need 12ga on the fan connectors to carry that load

Cut some out of a JY car, all gm fans use the same connector

If you're running both fans off one switch, then stick to a standard rocker, not a dual pole. Your setup engages both at the same time. If you were using both PCM terminals or two thermal switches at different temps to engage the fans independently, then using a dual pole switch to override automatic function is a good idea. That way they remain independent and automatic when the switch is off and engage together when on

kthxbai

iTrader: (5)

Looks like I need to find some 12 ga. connectors.. [edit: just ordered some from EFI connection that are 12 ga. https://www.eficonnection.com/eficon...spx?ItemId=552]

And yes, I was thinking dual pole if I re-wired with two relays on both PCM pins. If I keep them both on one relay I will use a single pole, but it is looking more and more like I need to scrap the old wiring completely and start fresh. If the PCM fan control is in fact toasted (which I am fairly certain of at this point) then I will just run two relays off of the same signal and same single pole dash switch, but at least it will provide each fan its own power.