Help! Aux Fan Not Working

[woodpuppy]

I love this site, it's been a big help to me.

First post by a new member.

I just purchased a 1986 Corvette with 75K miles on her. Unfortunatley even with the low miles she is still in rough shape. The previous owners were not kind to her.

I've been working my way through her; first to get everything working as it should, so that I can then start upgrading and improving things.

The area where I am stuck now is the aux fan in front of the radiator does not run.

If I put power directly to the fan it runs. I've changed out the relays. Jumped the relay connection A to E and the fan runs. Jumped the diagnostic terminals A to B and then grounded relay connection terminal C (or was the E again) and the fan runs. With the ingnition on or off I get the correct voltage reading at relay connector terminal E.

I'm using an old Chiltons Manual to help guide me through the trouble shooting and in one of the steps it talks about checking out the fuseible link. The problem is there are about 6 fuseible links that terminate behind that battery on the same connection post. How do you tell which one goes with the aux fan?

The Chiltons Manual also mentions that th eproblem could be in the Ignition System or the ECM.

Help please.

Thanks,

Jeff

 

[Hib Halverson]

I love this site, it's been a big help to me.

First post by a new member.

I just purchased a 1986 Corvette with 75K miles on her. Unfortunatley even with the low miles she is still in rough shape. The previous owners were not kind to her.

I've been working my way through her; first to get everything working as it should, so that I can then start upgrading and improving things.

The area where I am stuck now is the aux fan in front of the radiator does not run.

If I put power directly to the fan it runs. I've changed out the relays. Jumped the relay connection A to E and the fan runs. Jumped the diagnostic terminals A to B and then grounded relay connection terminal C (or was the E again) and the fan runs. With the ingnition on or off I get the correct voltage reading at relay connector terminal E.

I'm using an old Chiltons Manual to help guide me through the trouble shooting and in one of the steps it talks about checking out the fuseible link. The problem is there are about 6 fuseible links that terminate behind that battery on the same connection post. How do you tell which one goes with the aux fan?

The Chiltons Manual also mentions that th eproblem could be in the Ignition System or the ECM.

Help please.

Thanks,

Jeff

1) Use the Chilton to line your cat box.
2) Buy the factory service manual then troubleshoot the fans with the information in the book.
3) I'm on a road trip right now without access to my 86 FSM. As I recall the aux fan works off a simple temperature switch and the main cooling fan is controled by the ECM. It could be that the temp switch is not working.
4) As I recall the aux fan only comes on when the coolant temp gets pretty high. Has the coolant temp been higher than the aux. fan's "on" temp?

 

[woodpuppy]

Thanks for the quick reply.

The main fan appears to be operating normally, on @ 234 degrees and off @ 205.

It is my novice understanding that the aux fan should be running either sooner or at the same time as the main fan. I could be totally wrong, but that is what I am basing my concern on that it is not working.

You could be correct and the engine hasn't gotten hot enough yet for it to come on.

I've also read on several post and other sites that the aux fan should come on as soon as you turn on the A/C and stay on as long as you are under 40MPH.

Again a novice at this and trying to get the straight scoop on how it's supposed to work and how to verify that it's working and if it's not working how to isolate the problem area so it can be corrected.

Any idea what the temp specs are for the main and aux fan for coming on and shutting off?

Thanks for the info and help.

 

[Vettefan87]

To my knowledge the small aux fan does NOT turn on while the main cooling fan is on. I don't think it turns on until higher temps then 240. My 87 has never seen temps high enough for it to come on, since I have changed the temps my main cooling fan comes on. Hope this helps. My 87 FSM is outside in the garage I can try to look tomorrow and see if it has any other information in it.

 

[woodpuppy]

VetteFan87,

Thank you for the info. It would be much appreciated if you could verify and let me know at your liesure.

If that turns out to be the case then I'll need to (re)review the the threads about how to get the temps down and all the different options discussed.

My first take is that installing a switch to the aux fan so I can turn it on and off at will is the way to go to help keep engine temps down.

Seems there are too many confilicting opinions on changing thermostats to 160 or 180 degrees and/or the various coolant fan temp kits from the aftermarket places as to what works and don't.

Oh what to do, what to do, hmmmmm?

 

[ken mohr]

The aux or pusser fan does turn on at a higher temp. The pusher is controled by the temp switch and not the computer. I changed the temp switch in the driver side head (between 1 & 2 to a camaro switch a tfs4 or fs4. Turns on 210* off 200*. If you are over heating, clean out in front of radiator. I got a hell of a mess out of there. Now as long as the car is moving it never gets over 192*.

 

[vetteoz]

Or you can wire Aux fan with main fan so both run at once.
Both relays are turned on by grounding ; the main is grounded by the ECM and the aux by the switch in head.
Splice the aux fan relay control wire to the main fan control wire and remove connector from head switch.

 

[woodpuppy]

Ken,

Thanks for the info.

 

[woodpuppy]

Vetteoz,

Thanks for the info.

 

[Baldie88]

Woodpuppy, for what it's worth I've been in the same situation. I hated to see those temperatures climb, especially with the digital readout. I did put in a switch that turned on the fans earlier just like you mentioned. But with a 195* thermostat the front one essentially ran all the time.

However I attended a seminar by Gordon Killebrew and he said our C4s are meant to run hotter. So I switched back to the regular switch and I have no overheating problems. I'll admit that when I do a parade during the 4th of July my temps get up to 227* but then the regular fan kicks in and drops it right back down to 195*. I've never had the front fan kick on yet. I did clean between the radiator and condenser and you would be amazed to see what's in there so I would recommend that.

No disrespect to those who run cooler thermostats. I've just learned to live with the factory settings.

Ron
"Baldie88"

 

[woodpuppy]

Ron,

That's the big debate, both internally with myself and it appears on this web site and others; change things to run cooler or just live with it.

Richard Newton author of "101 Projects for your Corvette 1984-1996" also states that changing things will not get you any more HP only a cooler running engine that may not operate as designed by GM for peak performance.

Sounds like today's project will be to clean out in front of the radiator.

Thanks,

Jeff

 

[Vettefan87]

I changed my Tstat to a 160, and have my fans set on at 180 off at 165, and with bolt ons and free mods I ran 13.9@101mph. with a 2.3 60 foot. So I am not sure if you actually see a gain in performance or not. No disrespect to all the others that definitely know more then I do, I just hated to see coolant temps at 230.

 

[woodpuppy]

VetteFan87,

Thanks for the reply. How did you change your temp on/off settings? One of the kits from the usual aftermarket Corvette places?

I cleaned out in front of the radiator, flushed the cooling system, and put in new coolant yesterday and it ran hotter than before while sitting in traffic. If I am moving there is no problem temps usually stay under 205 degrees, but as soon as I have to stop at a long light or in traffic the temps start to climb quickly. It's nerve wracking to me to see my temps get up to 235 degrees (or higher) before my fan kicks on.

I've been debating about staying stock and running it the way GM designed it or making changes to get it to run cooler. Not really interested if it increaeses performance or HP, I just want it to run cooler. Doesn't seem like there is a large margin of error if it starts to overheat before damage is done.

I was taking the approach of staying stock and just making sure everything was in correct working order and let the temps be what GM designed, but after doing the work yesterday and seeing the temps remain "too" high for my liking I think it's time to try something else.

I think I'll change the fan switch for the aux fan to a cooler one first and see how that goes. If it's still running hotter than I like I'll then go for one of the kits that allows the primary to come on at a lower temp.

Still trying to figure out how the kits work since the ECM controls the primary fan on/off temp settings. It is my understanding that you can change the primary temp sensor, but regardless of what the sensors parmeters are the ECM will still control the on/off settings for the fan.

I have a lot to learn!

Regards,

Jeff

 

[woodpuppy]

What bolt ons and free mods are you using?

 

[Vettefan87]

I had a chip burned with a moates adapter, but I have been having problems with that so I went back to my Hypertech that I bought years ago.

As far as my mods descreened MAF, TB coolant bypass, I bumped my timing up to 12 degrees advanced, Ported plenum, and minor porting on the intake manifold.

I also have TPIS coated headers, Vortex Ram Air, 1.6 Rolling rockers, and I also installed underdrive pulleys. The pulleys I installed after I ran the car so I am not sure how much they helped, but it feels like it.

Did you check for air pockets after you flushed the coolant?

 

[Paul Higg]

Clean out your radiator, by that I mean remove it, straighten out any bent fins, then use a bottle of water wetter, perhaps replace the engine coolant temp sensor as everything rides on that. Do a COMPLETE drain and flush.

 

[woodpuppy]

Paul,

I've done all those steps except replacing the coolant temp sensor (I have one on order from MAM) but I'll put it in as soon as I get it.

Thanks for the reply.

 

[Paul Higg]

You're welcome.

Good luck and let us know how you make out. We all like to learn from others.

 

[woodpuppy]

Update

Here are the steps I have taken so far. Now I am in an evaluation mode.

1. Flushed cooling system. No real improvement seen, actually a little worse.

2. Cleaned out between the radiator and condesor. Slight improvement seen.

3. Replaced stock aux fan temp switch with a 200/185 temp switch (part# 609-106) from MAM. Aux fan would not run. I knew the fan was good, but even with the lower temp switch installed the fan still would not come on.

4. Pulled all of the fuses and replaced them with new ones. Aux fan started coming on @ 200 degrees.

5. I've only driven it this was for 1 day and the temps (ambient) were also cooler, but the digital readout never got above 200 degrees while sitting in traffic and were usually around 185-195 while moving.
6. Now I am just going to run this way for a while and see how things go.

Thanks to all who offered advice and help.

I think I can now move on to my next issue on my punch list.

 

[Paul Higg]

COOL! Pun intended!