Fan-mod pointless? I think not. - RX7Club.com - Mazda RX7 Forum

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Fan-mod pointless? I think not.

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Old 11-05-03, 10:49 PM
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Fan-mod pointless? I think not.

Now previously there have been some arguments that the fan-mod is pointless and only accomplishes blowing hot air around. However, if one puts some thought into it, they will see two things:

1. There has to be areas of low pressure and air-exit points underneath the hood - otherwise radiator and IC airflow would be more crap than it already is.

2. Since hot air rises, it WILL vent outwards with the introduction of newer outside air into the system (the air the fans are sucking in). Cooler air will also further increase the ability of the underhood components to radiate their heat to the atmosphere, whereas hotter stagnant air will most definitely not help.

Some background info: I recently installed a DEFI temp-gauge into my car. However, the probe is not T'd to the coolant system yet - it's actually strapped to the corner of the chassis near the brake booster.

Now even though this is a probe made for measurement of water temps, it WILL provide standard temperatures. Typical driving that promotes ample cooling shows around 75 deg F on the gauge (what the probe is reading from the corner of the engine bay). The second I stop the car and come back 15-20 minutes later, the probe is now sending 130 deg F to the gauge. Regardless of how accurate the actual temperature is, that's a delta of 55 degrees!

Before I tee the probe into my coolant, I'll do the fan-mod and let you guys know the results.
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Old 11-05-03, 11:04 PM
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Nice, good idea. Some good numbers on how "worth it" the fan mod is.

Personally, I have a lower temp thermostat, and my tuner lowered the temps my fans come on at via the Power FC, so my temps should be good . But it'd be nice to have some data anyways.
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Old 11-05-03, 11:32 PM
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Yea, there's been a lot of naysaying about the fan mod in other threads. My 2/100ths of a buck:

The *simple* fact is when the engine is off and the fans are on I can feel cool air go in through the nose and hot air out the (under)sides of the car... so SOMETHING has to be cooling off.

It *may* not cool the block *that* much, but other underhood things (rubber parts) can benefit from this cooling as well.

There's the argument about wearing out the fans, but it's negligable.

The only real downside I see is battery drainage... and everyone trying to cram a miata thermo sensor up your a$$!
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Old 11-05-03, 11:46 PM
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just adding my 2 cents

I don't know if I did the fan mod the way everyone else does, but I wired one of my fans to come on with the ignition. This worked great this summer but as soon as temps got below freezing around here, my car would not warmup to operating temp. So today I unplugged the fan and drove around. It soon came up to normal operating temp and ran fine at 25 degrees. This proves to me how well the fans help cool the car.
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Old 11-05-03, 11:50 PM
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Yea, the miata thermoswitch is all well and good, but that doesn't do anything for when the car is off - which is when the heat-soak starts in the first place.

Most of the "down with the fan-mod, up with the miata switch" crowd seems to be misinterpreting the intent of the fan-mod, which is to reduce the amount of underhood temperatures after shutting down the car and NOT to manually control the fans anytime you want (there's a 2 minute delay anyways).

I'll go ahead and just hook up a crappy switch tonight and test it.
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Old 11-06-03, 03:27 AM
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Just did a couple measurements after driving around for 45 minutes.

I grounded the fan diagnostic plug (single-wire black harness w/ spade connector near ECU) manually. Fan immediately goes to medium while car is running (not 2 minute delay) and after killing the engine and removing the key drops down low speed. Unshort the connection after 30 seconds and the fan runs on low-speed mode for 10 minutes. Initial differences are about a 30 F deg drop in underhood temps (as measured by that tie-wrapped probe in the corner of the engine bay) after 20 minutes.

I'll test it tomorrow too when it's slightly warmer.

One could actually just bypass the entire 10-minute time limit by throwing in a cheap timed relay in the mix instead of relying on the timer inside the diagnostic unit itself.

For instance, wire a factory fog-lamp switch to trigger the relay countdown and set it to 20 minutes. It will then ground the connection to the fan diagnostic plug which will run the fans on medium (and not low which happens when you unground it with a normal fan-mod) for 20 minutes and then the relay will switch to off, turning the fans off.

Since 20 minutes on medium is better than 10 minutes on low, that could be the way to go. Just so long as the battery is not overly drained during that period.
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Old 11-06-03, 03:33 AM
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That being said, a fan-mod should be used in combination with removing as many unnecessary ancillary devices from under the hood and other cooling modifications:

Remove Power Steering pump
Remove Air Conditioning compressor
Remove Airpump (midpipe required)
Miniature battery
TB coolant bypass
Upgraded radiator
Single-turbo (obviously a big one).

In my opinion, the use of that large battery, power steering, and air conditioning equipment were unneeded, especially in the tight engine bay of the FD.
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Old 11-06-03, 07:51 AM
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you could also pop the hood for the last mile or so on the way home, and then leave the hood open in the garage.
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Old 11-06-03, 10:38 AM
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Originally posted by clayne
Yea, the miata thermoswitch is all well and good, but that doesn't do anything for when the car is off - which is when the heat-soak starts in the first place.

Most of the "down with the fan-mod, up with the miata switch" crowd seems to be misinterpreting the intent of the fan-mod, which is to reduce the amount of underhood temperatures after shutting down the car and NOT to manually control the fans anytime you want (there's a 2 minute delay anyways).

I'll go ahead and just hook up a crappy switch tonight and test it.
Well, if you want to use the Miata thermoswitch AND control your fans manually all you have to do is detach the rear window defroster strip plug lead at the hatch and let it dangle.

You can now turn your fans on low (which is probably 75% of the CFM of high) ANY time you want by depressing the rear defroster switch on your console.
You also get a a free "idiot light" display on your dash to remind you that you have the fans (defroster) on and are rapidly draining your battery - and dramatically shortening the life of your VERY expensive alternator - by using it to charge your depleted battery day after day.

When you actually NEED the rear window defroster during colder months - just plug it back in.

As far as I know this only works with the stock ECU.

Consider me part of the "up with the Miata thermoswitch and disconnect your defroster lead as well if you want a no brainer automatic fan mod and manual fan control at the same time" crowd.
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Old 11-06-03, 10:52 AM
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Since I have a turbo timer, what I usually do is shut the car off, turn the timer off, then turn the car back to power (not start the engine), activating the timer, and set it for 10 mins before i walk away. ... it turns the fans on as soon as the temps start to creep (which is soon).

I notice the temp is ALOT cooler when i come back and restart the car.
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Old 11-06-03, 10:52 AM
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Originally posted by clayne
That being said, a fan-mod should be used in combination with removing as many unnecessary ancillary devices from under the hood and other cooling modifications:

Remove Power Steering pump
Remove Air Conditioning compressor
Remove Airpump (midpipe required)
Miniature battery
TB coolant bypass
Upgraded radiator
Single-turbo (obviously a big one).

In my opinion, the use of that large battery, power steering, and air conditioning equipment were unneeded, especially in the tight engine bay of the FD.
Although I really like the Fan Mod, suggesting that everyone make the changes listed above is ridiculous. Many people, like me, appreciate our power steering, and AC. We don't want hassles at smog time, so we keep our air pumps, and twin turbos.

I did upgrade my radiator

Did we need a new thread for this?
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Old 11-06-03, 11:07 AM
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Originally posted by adam c
Although I really like the Fan Mod, suggesting that everyone make the changes listed above is ridiculous. Many people, like me, appreciate our power steering, and AC. We don't want hassles at smog time, so we keep our air pumps, and twin turbos.

I did upgrade my radiator

Did we need a new thread for this?
...and you probably bought a $175.00 unit from Radiator Express.com, didn't you? You cheap bastard....

And yes, of course we need a new thread - for the newbies!
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Old 11-06-03, 11:52 AM
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Originally posted by RonKMiller
...and you probably bought a $175.00 unit from Radiator Express.com, didn't you? You cheap bastard....

And yes, of course we need a new thread - for the newbies!
Although I certainly am a cheap bastard, I bought a NEW fluidyne. Only paid $400 for it though

For $5 I'll tell you where.........
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Old 11-06-03, 10:41 PM
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Add to the list of mods:

1 - Vented Hood
1 - datalogit (or tuner) to turn your fans on at a lower temp
1 - upgraded intercooler
- upgrade to dual oil coolers if you don't have an R-model


...I think of all the items above though, the vented hood is the most likely to affect your heat dissipation since it will naturally exit the engine bay by the path of least resistance, up.

Also, don't overlook the benefit of knowing your coolant/water mixture. I plan to be draining and refilling so that I know for sure what mine is and adding water wetter to the solution as well. I'll be possibly considering auxiliary fans for my IC as well, just to be sure that I've got good airflow through it (but I am a tad concerned about airflow at speed being impeded by the fan...anyone know anything about this?).

Patrick
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Old 11-07-03, 03:24 AM
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Plenty of people run the fans 100% of the time while on the track - no issues with fan blade turbulence.
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Old 11-08-03, 04:25 AM
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I was toying with the idea of making a timer box. Perhaps something that would run the fans on low for a few minutes after activating a channel on the alarm (aftermarket).

Ron, maybe I'm missing something... but are you saying the defroster trick will run the fans AFTER the engine is shut off?
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Old 11-08-03, 09:59 AM
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Originally posted by InsaneGideon
I was toying with the idea of making a timer box. Perhaps something that would run the fans on low for a few minutes after activating a channel on the alarm (aftermarket).

Ron, maybe I'm missing something... but are you saying the defroster trick will run the fans AFTER the engine is shut off?
Nope, key has to be on.
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Old 11-08-03, 10:44 AM
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I think this whole thread is pointless. Turbo timers are goofy.

I think we all agree that we'll just FEEL better about leaving the fans and turbos running so that things cool down but other than adding a couple of minutes of life to the rubber components it does not actually DO anything more than 30 seconds of idle before shutdown.

If everyone were to spend as much time and effort working on keeping their engines cool while RUNNING it would be alot more productive.

When was the last time you:

1) Checked to make sure your radiator's EXTERIOR was
free of what I call "mung": insect parts, dust, plant
parts, sand, bent fins. I'll bet that if you haven't
checked in a few years you would be amazed how
clogged up it is just from everyday driving. Put a
REALLY bright light behind it and start looking - if
you can see through it all. You can try to backwash it
but the only way to make sure it is 100% efficient is
to buy a new one. And please, don't waste your
money on a Fluidyne or Koyo "racing" radiator unless
you ARE racing or running high HP. It's pointless
when for $175.00 you can put in a new, two row
copper and brass unit with METAL end tanks that is
MORE efficient than aluminum. (It does weigh two
pounds more though...)

2) Ditto for your oil cooler(s).

3) Checked/replaced your thermostat with a new OEM
just as preventative maintenance? $8.00.

4) Cleaned the blades on your fans completely?
Clean propellers push a hell of a lot more air
than dirty ones. Even a thin layer of dirt will
lower efficiency dramatically.

5) Did my "hot air out" mod to allow the engine room
to actually suck hot air out and breathe the way the
designer of our car intended without resorting to
ill fitting, heavy, aerodynamics spoiling, ugly and
insanely expensive after market vented hoods?

6) Look at the INSIDE of your coolant hoses to make
sure they are smooth and allowing maximum flow?
As hoses age they fall apart from the INSIDE out,
become very rough and impede flow.

7) Did the Miata thermoswitch mod? Cheap, easy to do
even for the ham fisted, and it works flawlessly to
keep your engine from ever overheating in the first
place without putting ANY additional stress on
your battery, fans or alternator.

8) Took a good look at how much your front mounted
intercooler / aftermarket front end impedes airflow
through the engine room?

These are all "little things" but they add up BIG time to keep everything cool.
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Old 11-08-03, 08:18 PM
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Originally posted by RonKMiller
I think this whole thread is pointless. Turbo timers are goofy.
I dont know if this was in response to something else, but I'm talking about a fan timer. It costs like $5 to make. I can be a cheap bastard too. Maybe I'll whip a few up, 'cause some people need to cool off here. (This isn't directed specifically at you Ron)

I, for one, don't have problems with the engine running too hot (mind you I don't race this car ) and my cooling system components are pretty clean. I, and others, have simply noticed the engine compartment is obviously cooler in many areas after letting the fan mod do it's thing after shutoff. Well, compared to just shutting everything off altogether, fans and all.
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Old 11-09-03, 12:56 AM
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Originally posted by InsaneGideon
.......... I can be a cheap bastard too. ........
Excuse me????

I believe that title is already taken
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