Cascade Crew

popballz · Posted: Thu Nov 18, 2010 2:37 pm Post subject: what temp/sensor triggers fan?

I have the two fan setup on my 87 tip 305. It could be wired like an 88 though because it was made late in the year and that's how my throttle cable was.

So one fan comes on at 235*, I assume the other fan should come on before that?

Both fans work, both relays work. I found the wire that should be grounding which goes to a sensor near the bottom between #6 and #8 cylinder.
I assume this sensor is not working but I don't know when it should be clicking on.
I also can't see the actual sensor from the top and have not gone underneeth so do you know what this sensor is? White wire with a black or darkblue wire.

The fan turns on when I ground the wire going to this sensor, so I know everything else is working.

MrMike98 · Member Joined: 18 May 2010 Posts: 231 Location: Bremerton

On my 90' i have the one fan (com controlled)to come on at ~ 190 and u are correct the second fan is controoled by that temp switch (and AC)mine is ~220.
u can get different temps. try summit etc. a bitch to change...
good luck
Mike

popballz · Posted: Thu Nov 18, 2010 3:54 pm Post subject:

Twilightoptics · Posted: Thu Nov 18, 2010 5:30 pm Post subject:

My TPI had one controlled by the ECM and one controlled by the A/C.

TBI and pre '87 cars with single fans it's controlled by a fan switch (temp sensor in the head.)

MrMike98 · Member Joined: 18 May 2010 Posts: 231 Location: Bremerton

I'm saying i programmed my (730 ECM tpi speed density)chip for a 190 fan turn on temp. u can make it anything u want.
i have a 180 t stat, so i tuned things accordingly..and all seems to work, as engine temp never exceeds 190...

mike

aaron_sK · Posted: Thu Nov 18, 2010 8:31 pm Post subject:

My guess would be a failed CTS. The ECM controls the primary fan based off of what it thinks is the actual coolant temp. When the sensor fails the ECM thinks the engine is always cold, so it runs rich, and the fan never comes on.

If you can datalog, you should be able to check for this easily.

RSFreak · Posted: Thu Nov 18, 2010 9:31 pm Post subject:

On my 2.8, there is a CTS (small one) on the intake manifold by the water neck and a second one on the front on the intake manifold (large one). Which of these controls my fan?

aaron_sK · Posted: Thu Nov 18, 2010 9:35 pm Post subject:

One of those triggers the seventh injector. The CTS that the ECM pulls off of has a typical 2-wire GM weatherpack plug, the auxiliary injector sensor has a wire clip-style plug that looks like an injector connector. The sensors are not interchangeable.

iansane · Posted: Thu Nov 18, 2010 9:37 pm Post subject:

Dumb question but the knock and fan switch wires weren't swapped were they?

BluFbdy · Posted: Thu Nov 18, 2010 10:52 pm Post subject:

if someone did that id have to punch them in the face. lol theyre pretty easy to tell apart, im pretty sure the one in the head controls the fan, i gave up chasing this gremlin and just wired my single fan to a switch with a relay, you can also get a rad fin insert that will kick the fans on and off according to your temp range you set, you can get them at westbay for around 30$ i believe

aaron_sK · Posted: Fri Nov 19, 2010 6:19 am Post subject:

*two cents*

Manual fan switch is a horrible idea. The one time you forget about it, and you'll be buying a new rad, or rebuilding your engine.

As has already been well established on here, Summit sells cheap (under $20) temp sending units that screw into any NPT port on the head or intake. Several guys (myself included) have used them with great success.

White / drk blue sounds like the knock sensor, actually. I seem to remember the line for the auxiliary/aircon fan being a single green wire. It's been awhile since I had a factory dual fan harness in front of me though.

iansane · Posted: Fri Nov 19, 2010 10:19 am Post subject:

Twilightoptics · Posted: Fri Nov 19, 2010 10:27 am Post subject:

BluFbdy · Posted: Fri Nov 19, 2010 3:40 pm Post subject:

I don't have it now, I used it when I was in az and with it being so hot, I just had it running at all times, I yanked the relay when I got here, I just flip it to max ac for the heat now lol stays steady at 180

91camaro_rs · Posted: Fri Nov 19, 2010 4:15 pm Post subject:

i like my setup...comes on automatically at 200* and have a manual switch inside as well

IROCDave · Posted: Fri Nov 19, 2010 6:43 pm Post subject:

I have a dual fan settup on my 87 IROC. The temp sender on the drivers side head is for the temp gauge. The sender on the passenger head is for the computer / fans IIRC. The knock sensor is in the block, below the temp sensor on the passenger side. There is another temp sensor in the intake near the thermostat housing ( front of the manifold?) that is for the 9th injector. My memory is a little foggy, been 10+ years since the stock intake was on my car but I think this is correct info.

The 2nd fan only kicks in if the AC is on our the temp gets over 225 F. You should be able to get by with the just one fan in the PNW, unless you have major mods and or there is something wrong with the cooling system.

BTW, the passenger side temp sensor will be a PITA to change, especially if you havent cracke the stock exhaust manifold bolts in a while. Even if you have, I think the manifold / header has to be taken off to access the sensor.

aaron_sK · Posted: Fri Nov 19, 2010 9:01 pm Post subject:

Al Hasse · Posted: Fri Nov 19, 2010 9:31 pm Post subject:

I replaced my fan switch a year or so ago. No problems with the headers for clearance. Only problem might be if coolant isn't drained first, it will drain through the switch hole when it's removed.

aaron_sK · Posted: Fri Nov 19, 2010 9:33 pm Post subject:

Al Hasse · Posted: Fri Nov 19, 2010 9:40 pm Post subject:

Been there. Had the thing ready to go in as soon as the old one came out, I slipped with the new one before getting the threads lined up enough to thread it in. Coolant everywhere.