Cooling fan operation, Removing 1 of 2 fans? Options

[94bird]

Are the fans in series in our LT1 engines? Can I remove one of them and still have one working fan? I'm in the middle of doing a few things on the car and the engine isn't running so I'm hoping someone knows before I reinstall everything.

[Jon A]

On your '94 you have one fan that kicks on first and a second that kicks on after that. In '95 or '96 they switched to a dual speed set-up where both fans kick on at the same time at low speed and then they both kick up to high speed when required. This is a much more efficient set-up. With both fans on low speed you're using less power, making less noise and moving a ton more CFM through the radiator than one fan on high speed--you can see why they switched. I've tested it quite a bit--one fan on high just doesn't cool worth a crap, both on low speed do better since you aren't sucking air through the opening for the other. And of course both on high speed flat sucks that radiator cold....

That's why I would worry about you removing one of your fans. If you do that you'll open up that hole even more which will make the other even less effective. I know it's not like you commute in the thing anymore, but if you did you would overheat it if you got stuck in traffic on a really hot day. If you seal up the hole for the fan you removed, you'd probably be OK but then you're really restricting air at high speed and will probably have problems there.

Just removing it you'd probably be OK if you only ran on the track at high speeds but I'd still be worried about getting stuck on a red-flagged track or something causing you to overheat. The best option would be to cut the shroud in half and re-sealing it so the one fan is effective at cooling at least a portion of the radiator well but not blocking the rest at high speed.

I know what you're thinking, those are heavy mothers, aren't they? (IMG:http://www.frrax.com/rrforum/style_emoticons/default/ohmy.gif) But I'll bet you'd have to search high and low to find an aftermarket set-up that moves more air....

[On Edit] Oops. Maybe this was just a simple wiring question...sorry. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/biggrin.gif) Your fans should be wired in parallel...I think. If you have a Helm's they have decent wiring diagrams of them. Mine won't do you any good since it's different. I would assume they are wired in such a manor that if one burns out (or you disconnect it) the other would still be functional. This would be easy to confirm with Tunercat the first time you run it.

This post has been edited by Jon A: May 31 2004, 07:06 AM

[94bird]

I've decided to modify my testing at the track and will instead just remove both fans and the shroud. I wouldn't use that for a race but it should be a good test of whether reducing the air flow restriction behind the radiator helps cooling while on track at speed. If it does help cool the car at speed and under load then I'll likely just get an aftermarket slimline fan that will just help maintain idle temp and mount a switch for it in the car.

My main goal is trying to figure out if having both stock fans running on high helps my cooling or if the air flow I get through the radiator without fans is greater. I have zero problems cooling the car at idle and during dyno runs, but under extended useage I have some real problems.

[rmackintosh]

Mike, I tried removing one fan and both when my car was overheating...neither helped....although that is probably USELESS info, since NOTHING but the new radiator solved THAT problem.

What I did do was have my fans custom programed to come on like Jon said....either both on or not....also played with circumstances as to when they come on. Seems to work OK.

[94bird]

I'm quite surprised that with the BeCool radiator and oil cooler (ran stock radiator and stock oil cooler last year) I'm now running hotter than I did last year. Yeh, I added about 50 RWHP too, which adds temperature, but I suspect something else is wrong. Sounds like your experience would say my experiments won't do me much good and I should just go ahead and pull the engine and rebuild it. While it's out I can look for other problems.

[Jon A]

I wonder if there isn't something else going on as well, Mike. Last week wasn't hot, but it wasn't freezing either--temps were in the mid 60's. In 45 minutes of solid hard running, I couldn't get the temp over 180. And I still have the big AC condencer in front of the radiator. Have you guys who have taken it out really sealed up the air path in front of the radiator? It's pretty good from the factory, but if you just yank the AC I think a bunch of air is going to be spilling around the sides of the radiator.

I've spent a lot of time contemplating the fans as well. I have no doubt that you'll cool better at high speeds with nothing there, but how high does the speed need to be? Are you going to be heating up on the rest of the course? Sort of interesting...those rectangular openings in the shroud that look like they have some purpose--in '93 they had trap-door style valves in them. These would be closed at lower speeds to make the fans more efficient but at higher speeds, when the fans are actually impeding flow, they'd open to let more air through the shroud. I've been thinking of buying one of those and riggin a switch to it just to see when it opens--and if it makes a difference if the fans are on or off. I have to think that at some flow rate, the fans will let more air through just freewheeling than when they are running. But for all I know that flow rate may not be achieved until 150 MPH.

I had mine shut off at 85 MPH last week and it seemed to work just fine. One hard part about this is that they have a minimum running time. Once the low speed fan (or both fans in low speed mode) is activated, it won't shut off for 50 seconds no matter what happens. So, if they click on at more than one place on the course they'll pretty much be on the whole time. I disabled the low-speed circuit for that reason. One thing I found out with the dual-speed set-up--don't try and program out the low speed because they'll never kick on high unless the computer has already turned on the low speed. I pulled a wire in the fusebox to disable the low speed operation even when the computer has commanded it. The high-speeds will run for 30 seconds minimum. So, at my 85 MPH setting I was basically only turning them off for the front and back straights. I figured that was probably a pretty safe bet for my first experiment.

Anyway, I'm not really stressing over it. I just like playing with gadgets. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/wink.gif)

[94bird]

I started looking at my shrouds more over the past day or so since seeing an auction on ebay where the fans/shrouds from a '95 Camaro were for sale. They had no openings in the shrouds like mine has. Now from your comments it appears the '93s had trap doors over the openings in my shrouds. That helps to explain things a little. Don't know why the shrouds would go back to solid in '95 though.

You couldn't get your temps over 180 with the stock radiator and a condenser in the way? Heck, I've been over 210 deg. at every track event over the past 2 years probably at near stock HP in the summer. That's surprising.

BTW, I have foam on the sides of the radiator sealing up the escape paths for air. I think it's sealed up pretty well.

[#07]

Have you guys who have taken it out really sealed up the air path in front of the radiator? It's pretty good from the factory, but if you just yank the AC I think a bunch of air is going to be spilling around the sides of the radiator.

No I havn't,and what you are saying makes perfect sense.I'm gonna look into fixing that.Yep just went out there and a good 1 1/2" veritcle gap on both sides.

Hey Mike if you want to know(case you forgot) for your test which fan is on first its the driverside.I saw today as I was waiting to bring the temp up to bleed out air after the heater core delete.

I was amazed that only one came on "new to me" not used to this w/ the other cars being both come on. I may look for a 96 fan set-up.

Tony

[94bird]

Tony, some foam works great to seal up the gap and it's available cheap at Home Depot. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/smile.gif)

[rmackintosh]

Have you guys who have taken it out really sealed up the air path in front of the radiator?

Yep...about as GOOD AS IT GETS sealed wise.....and I STILL go (IMG:http://www.frrax.com/rrforum/style_emoticons/default/ohmy.gif) when I hear you guys running 30 mins. at 180 degrees!

I am LUCKY with all the NEW STUFF, to see 220 degrees...

Course that is at 95-100 degree weather!

(IMG:http://www.frrax.com/rrforum/style_emoticons/default/unsure.gif)

[Jon A]

Keep in the weather in mind. I did see a bit over 200 last year at PIR when it was around 90 but never approaching 220. That might change if I run on a 100 degree day at my current power level. But yeah, that's why I'm not in a hurry to do many "upgrades" at the moment. If it ain't broke.... (IMG:http://www.frrax.com/rrforum/style_emoticons/default/wink.gif)

I don't think the shrouds ever went solid, Mike. My car has the openings--my PS cooler is mounted in one of them. Are you sure the auction wasn't pawning off parts from a V6 car or something?

You know, come to think of it, it seems those with LT1's having cooling problems are mainly older cars with the old fan set-up. I wonder if it's not just the wiring that's different--maybe the newer fans move more air? How loud are your fans? Just one of mine on high speed sounds like a freaking jet engine under the hood.

[#07]

I was amazed that only one came on "new to me" not used to this w/ the other cars being both come on. I may look for a 96 fan set-up.

I wonder if on the stock 94 fan set-up if you were to add the SLP manual fan switch and run it on high if that would run both the fans.
I also wonder if you were to get a 96 fan set-up put it on the 94 and plugged it in would it preform as it were on a 96.Like Jon has described the 2 at low till a certain temp then 2 high.

[rmackintosh]

I wonder if on the stock 94 fan set-up if you were to add the SLP manual fan switch and run it on high if that would run both the fans.
I also wonder if you were to get a 96 fan set-up put it on the 94 and plugged it in would it preform as it were on a 96.Like Jon has described the 2 at low till a certain temp then 2 high.

I could be wrong on this, but I think this is a PCM programming issue....to make the 94 perform like a 96 that is....

[Jon A]

It's a wiring issue. The 96-up cars are wired differently and have three fan relays in the fusebox. I *think* when the PCM commands Fan #1 the wiring runs both fans in series, and when the PCM commands Fans #1 & #2 they run in parallel.

In any case, I'm running an old OBD1 PCM and it has no idea I have the newer fans but they operate the same as they did with my stock PCM. Changing the fans themselves wouldn't change how they operate since they plug in separately.

However, some initial digging has shown the 96-up cars have a different part number for the fan motors themselves. They *might* be higher power. All I know right now is they are different.

[94bird]

I found a Hayden slimline fan 16" in diameter that flows 1900 cfm (rated at 1600 cfm through a typical radiator as restriction). I haven't measured yet, but I think I could fit 2 of these side by side on the back of the radiator. I have no idea what my stock cooling fan flow rate is though. 1900 cfm sounds like a boat load of cfm, but I haven't taken a look at what our engine at work is using for fans. Time to do some benchmarking.

Anyone know our stock fan flow rates? Any greater for '96 possibly than '94?

[94bird]

I am LUCKY with all the NEW STUFF, to see 220 degrees...

Course that is at 95-100 degree weather!

When I was running 250 deg. in a few laps at Putnam Park it was in the high 80's, maybe low 90's.

[94bird]

I measured the size of my plastic deflector that directs the air from under the car into the radiator. It was 32"x4" in size. However, at least 1" of this vertically is actually behind my front fascia and is thus not in direct contact with the frontal air flow so I redid the area to 32"x3". Here's the calculations I get for air flow that hits this barrier at various speeds.

MPH miles/min ft/min cfm
10 0.17 880 587
20 0.33 1760 1173
30 0.50 2640 1760
40 0.67 3520 2347
50 0.83 4400 2933
60 1.00 5280 3520
70 1.17 6160 4107
80 1.33 7040 4693
90 1.50 7920 5280
100 1.67 8800 5867
110 1.83 9680 6453
120 2.00 10560 7040
130 2.17 11440 7627

I think it's fair to assume barely more than half that actually makes it's way through the radiator given the restriction across it, the sharp bend the air flow has to make to enter the radiator and the fans/shrouds behind it, as well as the restriction under the hood in getting air flow out. If that's the case, 2 of the 16" Hayden fans at 1600 cfm a piece would equal the air flow across the radiator up to about 100 MPH. The stock fan diameters are only about 12" BTW.

I've started asking some friends who work at GM to see if they can find the flow ratings of our stock fans for both '94 and '96 model years. We'll see if I get lucky.

Randy, with your front breather setup, what's your frontal area for the scoop?

[robz71lm7]

On your '94 you have one fan that kicks on first and a second that kicks on after that.  In '95 or '96 they switched to a dual speed set-up where both fans kick on at the same time at low speed and then they both kick up to high speed when required.

Not 100% correct. (Wow, I'm correcting Jon)

This is all taken from my Helm manual and personal experience with my '94.

Early '94's are the way you described-one fan at a time. Later '94's run both fans at two different speeds. The older models run one fan at 12 volts and then turned on the other at 12 volts for high speed operation. The newer ones run the fans in series at low-speed and in parallel at high-speed. IOW, at low speed they each see 6 volts and 12 volts at high speed. My '94 was built in 12/93 and has the newer system. I found this out when wiring my cooling fan switch.

I believe the only difference is the wiring (series vs parallel), but I'd have to check my Helm manual to be sure. It's been a while since I wired up my fan switch.

[94bird]

From Shoebox's site:

There are two versions of the dual fan configuration:


1993-1994 - Primary and Secondary fans that operate at only one speed. When initially commanded on, only the primary fan (driver side) comes on. It operates alone at full speed. If the temp threshold is met for addtional cooling, the secondary fan (passenger side) also is commanded on. At this point, both fans are running at full speed.
These fans use a two relay architecture that can be seen in the fuse/relay panel that is under the hood.


In late 1994 and into 1995, there was a change to low and high speed fans. When initially commanded on, both fans will come on at a low speed. When the high speed temp threshold is met, they both bump up to high speed. A three relay architecture is used for this fan version (seen in the fuse/relay panel). By adding a third relay, low speed can be achieved by running the power to the fans in series. This way, each fan does not get full voltage and runs at a slower speed. High speed happens when the relays switch to provide full voltage to both fans. Low speed is less noisy and should result in greater fan longevity. High speed is not always needed.

==================

Note the comment about 2 vs. 3 relays. Just checked mine and I have 3 relays, so I guess I have the newer setup. I knew I hadn't seen my fans come on individually before.

[ESPCamaro]

What setup did the 93 cars have. I thought that they had a single fan/shroud.

Or some other F-body.


Mike, if you have one of your fans out could you weight it? (IMG:http://www.frrax.com/rrforum/style_emoticons/default/biggrin.gif)


What setup did the V6 cars have? And did the V6's have a smaller radiator? (IMG:http://www.frrax.com/rrforum/style_emoticons/default/biggrin.gif)