Ok, before describing problem and checks, I have searched many threads and have tried various fixes and no luck yet, and yes i am a novice...so

1985 z-51, apparently no aux fan that i can tell...Cooling fan will not come on, have let heat up to near 250 and still no fan, cooling system itself seems to be fine as when I drive at highway speeds car cools down to mid 170's...I turn key and air conditioner switch and no fan, I connected terminal B of relay switch located at MC to battery and fan does comes on so I replaced relay ($10) at that location, still no fix, yes I checked fuse, I then went to sensor on passenger side of block by dip stick, it is plugged in, I removed it and with AC on tries to ground it and no fan (dont know if fan is suppossed to come on or not)...I am at wits end...any advice and ideas welcome...

thanks

 

Have you got power on the supply wire to the relay? (big red )
May have blown the fusible link on that wire

Jumper red to terminal B and see if fan runs

 

Thanks for the reply, fan did not come on when jumping B to relay power line, is the fusible link in line right below relay connecter, if so, how easy to replace?...or our the fusible links the two wires with small foam looking cyclinders near the firewall? thanks again

 

Here is a picture for what you are working on. It doesn't get any simpler than this which is nice on some of the 80s stuff. You can see where the voltage comes in from the feeds and what to ground to active the relay.

This is not out of an FSM but should be enough information to get you there.

 

Possibly, link is a black plastic cylinder on the wire

IIRC on the early cars
the heavy red power feeds are connected to the starter Pos terminal and the fusible links are at that end.

 

OK, thanks, so I assume I have to cut out both sections of wires with black cyclinders (cyclinders do not appear to come apart) and replace (splice in) with like (assume local O Reily's would carry)?...also, this just recently started occuring, but as I certainly have come to find out with these cars, nothing last forever....also pcolt94, thank you for the diagram

 

Don't replace a fusible link until you know it's bad. It's a lot of trouble and may not solve your problem.

Since you have an '85 and I have an '86, the following may not be 100% accurate. That said...

The auxiliary fan is located in front of the radiator. If you have one, you can see it by looking under the nose of the car at the radiator (actually the A/C condenser in front of the radiator).

The coolant temperature sender in the passenger side head is for the water temperature display in the instrument cluster. Try disconnecting it and see if the instrument panel display changes.

Maybe the '85 is different, but on my '86 the fan is controlled by the ECM. It uses the coolant temperature sensor on the front of the intake manifold (under the throttle body) to determine when to turn on the fan. If that sensor is bad your car will run really badly, so it would be obvious if something is wrong with it.

On my '86 the auxiliary fan is controlled by a temperature sensor in the driver's side head between spark plugs #1 & #3. If the above diagram is accurate for your car, it could be there.

On my car, jumping ALDL terminals A & B will cause the main fan to come on, but not the auxiliary fan. The ALDL connector is just above your right knee when you're sitting in the driver's seat. There may or may not be a cover on it that just pulls off. Terminals A & B are in the upper right corner. The traditional way of jumping them is to use a small paper clip bent into a U shape. With ignition on and engine not running you can also see the error codes stored in the ECM with this method. Here's a drawing of the ALDL connector:

 

I'm sure that Cliff's information is accurate and he indicated it was for an 86. The drawing and information I posted was for model years 84-85.

 

this is correct you may not even have a problem. The data from the sensor in the front side of the intake is what the ECM uses to open/close the main fan's relay circuit. The sensor in the passenger head just changes resistances to the cluster - that's it nothing more. It is not uncommon to have slight differences in readings between these 2 sensors. Use a real time scanner/software to "see" what the intake sensor (CTS) is showing when the ECM turns "on" the main fan. Compare CTS temp to the temp on the cluster to see what's what. Be aware that poor conductivity in the sensor(s) connectors or even oil soaked sensors connectors/terminals can change/mess with the resistances of a sensor(s) and give a incorrect reading.

 

Cliff, when I jumped terminal A and B under dash with ignition turned, no fan...also, after I did this and turned on the key the car ran terrible and was smoking, does this jumping of the terminals cause the car to flood?

 

Sorry guys you are both only partially correct.
'85 ONLY ( where is CFI-EFI when you need him ) had the 86 style ECM control of the fans with the 82 -84 style mechanical switch as a back up.
A one year only setup never repeated

 

Which puts you back to original diagnosis of no power at fan relay.

If as you say you
jumpered the incoming red relay supply wire direct to the relay outgoing fan wire and nothing happened ;
then you have NO power supply to relay; PERIOD.

To prove a point,
temporarily run a fused wire from batt Pos+ terminal to the relay as a replacement for that red wire and see if fan runs as it should when up to temp or A/c turned on.

 

OK then, I saw a cross over in my information so here is the other piece. Is one of them correct now?
Are we getting closer

 

In re-reading the original post, I see a Z51 mentioned. On my '86 the auxiliary fan is part of the Z51 package, so your car may have one. That would be the left side of the diagram above.

 

Guys, I appreciate the help, but whenever I jumped terminals A and B under dash it cycled something near my intake, now car wont even stay cranked and idles real rough with my foot on the gas and is real smokey with an aweful smell, it ran like a champ before, just overheated when in traffic at idle, now I cannot even drive it, w.t.h, I hope somebody can help me here, this has gone from a simple electrical issue to something else, anybody have any ideas or suggestions on what happened?

 

Make sure you don't have terminals A & B connected together.

Also try to re-set the ECM. Remove a battery cable for a minute and then reconnect. I might clear the problem if the software is locked somehow.

I don't beleive when you should be running the engine when connecting A & B, but ONLY have the ingition turned to ON.

I will let the experts 80 guys confirm this.

 

yea, I did connect A and B together, but engine was not on, just ignition...I will try to reset via disconnecting battery

 

a sure way to tell if you have the aux fan, get on your knees at the front of your car, look up in that big hole, if you see a fan , you have one, if you dont see a fan , you dont have one.

 

Here is another thread that may have some '85 fan/relay locations/ RPO code info: http://forums.corvetteforum.com/c4-g...1985-fans.html

Like rodj says it does appear that there is not + 12 volts available to the fan relay(s) or your fan motor itself has a problem.

If you only jumpered the terminals mentioned in this thread your electrical issues should not have been compounded.

 

Nope.
As stated 85 only main fan is a one off ( a combination of ECM control and temp switch)

But as stated,
one could also have the B4P aux fan ( which OP has confirmed he doesn't have ) independently operated from a different temp switch