adam c

iTrader: (2)

You are the "King" of cheap..........or at least the Jester.

israel

iTrader: (3)

good discussion guys. thanks to everyone who contributed. my FD will be cooler and happier because of it (some day)

negative

good information

I really hate my fan mod though. I have 2 switches for it, which is really annoying. I really don't know how it works. It's just too much to think about. If my fan mod was just 1 switch that turns it off and on, I'd be happy. Can someone explain to me the basics of this mod.

RonKMiller

Amazing how things run full circle, here's the bottom line:

1. The Cirian mod (in it's time) was useful. Outdated
now, but useful.

2. If you have the ability to control your temps with
the PFC, great.

3. If you want the best solution, the cheapest,
easiest, no brainer - Miata Thermoswitch,
Miata Thermoswitch, Miata Thermoswitch.

It WORKS, period. For $35.00 and a half hour of sweat, it is phenomenal insurance.

Your engine will thank you many years from now for being so thoughtful. So will your bank account.

T88NosRx7

iTrader: (1)

my haltech can control when the fans turn on.

mecman

iTrader: (11)

I did it. Between that and the downpipe my under hood temps are noticably lower. I never hear that boiling coolant sound anymore.

adam c

iTrader: (2)

1. The cirian mod still works great.

2. Most of us don't have a PFC

3. If you really need a no brainer, you are driving the wrong car.

4. I sure didn't expect to see this again.

negative

I just decided to remove the fan mod and get the Power FC datalogit fan mod (or whatever it's called).

honegod

this turns out not to be the case.

nuclear submarines use exactly this system to circulate the cooling water through the reactor.
they no longer USE water pumps to circulate the water, just the temperature /density differential.

as in, with a properly designed system thermal convection will cool a nuclear reactor.

{at least that is what they taught me in Heat Transfer and Fluid Flow class in nuclear power school }

in our cooling system there is only the thermostat that will prevent flow, when the pump is not turning water will flow freely between the vanes on the impeller.

so there WILL be flow from the hot engine to, and through, the cooler radiator when the engine is not running.

running an electric fan after shutdown will absolutely cool the engine down more rapidly.

the guy with the spark plug sensors - do a time/temperature curve on the rate of temperature change after shutdown with and without fan running.
I'll bet a nickel that both curves will look pretty similar for the first couple to few minutes, and then the fan curve will start getting steeper and steeper until it levels off when the thermostat shuts.

CapitanCombo

I tried many times to find that wire to do the mod
but i was unable to find it
maybe our european Fds do no have it!
so i did the relais fan mod
any website to find more infos for the Miata thermoswitch mod?

apex_sideway

RonKMiller ... what year is your seven? Some here on the thread said it didn't work for their year. Just wondering.

DamonB

You are comparing apples to oranges. Nuclear reactors are DESIGNED to work that way.

Cool water being denser will move to the lowest point, right? You know where the lowest point on an FD is? The nearly horizontal radiator. So all your cool water will sit in the radiator and not get to the engine. If the convection flow is so great inside the FD, why do we need a water pump? (and the FD isn't the only car I can think of with a pump; I think approximately all of them have a water pump ( except the Model T as was pointed out at one time, but that isn't apples to apples either. )

Now there is one VERY easy ways to prove that there is no convection coolant flow in the FD. First leave the fans running and watch the temp gauge. Then don't leave the fans running and watch the temp gauge. If convection flow is occuring the temp will drop much quicker with the fans running (it doesn't).

FormerPorscheGuy

I did the Miata thermo switch mod and I have had no ill effects. My fans cycle on and all here in the Houston heat (yes, its still warm here). I did it for piece of mind.

Israel, you still don't have your car up and running yet? Arn't you going on two years of down time?

blueskaterboy

yanni put in the fanmod when he had the car... i turn on the fans when it hits 185 and it keeps it around 170-180...

poss

iTrader: (5)

Fans off=heatsoak=rising temps
Fans on=cooler engine bay/coolant=cooler temps

Makes perfect sense to me

Also, just because the thermostat is in the way on the top side, doesn't mean that coolant doesn't move, or at least transfer heat through the bottom hose.

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DamonB

Coolant cannot move from the radiator to the engine unless the thermostat is open. The system cannot flow to or from anywhere outside the block with the thermostat closed since the coolant cannot circulate. It's like having a hose with it's own ends joined to form a circle. If you had fluid flowing around and around inside this hose and were to pinch the hose shut in one spot on the circle, flow would stop everywhere. As for any convection, yes the cooler denser coolant will try to go to the lowest spot of the system. The lowest spot of the system is the radiator, not the block. After engine shutdown the coolant will remain hot enough to leave the thermostat open, but there will never be coolant move from the radiator ino the engine block since there is no pump to make it do so. Convection can't do it. The cooler, denser coolant will settle to the low point in the system (the radiator) while the hot coolant stays in the higher points (the engine and thermostat housing).

Where's the temp probe for the gauge installed? If it's not in the block or the throttle body coolant line you're not reading engine block temps; any other location is in front of the thermostat.

maxpesce

never mind - my point previously made! Replied w/o reading entire thread.

David Beale

The Canadian cars did not get the coolant module under a warranty program. The dealers want $50 or so for it. My car does not have it. I don't intend to get it. Coolant boiling after shutdown is not "fixed" by this mod. It is a symptom of a "vacuum" leak at a coolant cap. I fixed that problem when I first got my car 5 years ago by replacing both caps and the small hoses that go to and from the AST. I may get the Miata thermoswitch, but here in Canada I haven't noticed any temp. problems. I suspect the European cars are in the same boat as ours.
I suppose not seeing 90 F days have something to do with it ;-).

adam c

iTrader: (2)

Honegod is right. If you drive the FD under water, you don't need a water pump

honegod

sorry, it is more like comparing baking apples to eating apples. in that they both share the same essential nature, with subtle differences that make one more suitable for certain uses than the other.

Quote:

Cool water being denser will move to the lowest point, right? You know where the lowest point on an FD is? The nearly horizontal radiator. So all your cool water will sit in the radiator and not get to the engine.

the bottom of the radiator is pretty much level with the bottom of the engine, yes ?
so any up angle of the radiator will be ABOVE the lowest part of the engine.

that is the working head for the water.

yes, it is not much head. so yes there will not be a LOT of waterflow, but there will be some.

the ONLY way there would be NO waterflow would be for EVERY BIT of the radiator to be BELOW every bit of the engine. this is not the case, yes ?

Quote:

If the convection flow is so great inside the FD, why do we need a water pump? (and the FD isn't the only car I can think of with a pump; I think approximately all of them have a water pump ( except the Model T as was pointed out at one time, but that isn't apples to apples either. )

I think the point of confusion is "so great". the convection flowrate is most likely pitiful when compared to the ammount of heat the running engine produces.

but we are not talking about the running engine, we are talking about a NOT running engine, where all the heat energy that we wish to remove is already present.

a finite quantity.

so the rate of flow through the system is not only removing heat from the whole system but it is DISTRIBUTING that heat energy throughout the engine.
so the hottest areas of the engine will transfer their heat to the cooler areas OF THE ENGINE.

this redistribution of heat energy internally will not show up on a temperature guage unless you are specifically looking for it with sensors placed where the difference will be .

the point is that this increased redistribution of heat will ONLY take place if the water is circulating, and the faster the water moves the quicker the engine temperatures will equalise.

having a fan cooling the radiator will result in some water circulation through the engine.

Quote:

Now there is one VERY easy ways to prove that there is no convection coolant flow in the FD. First leave the fans running and watch the temp gauge. Then don't leave the fans running and watch the temp gauge. If convection flow is occuring the temp will drop much quicker with the fans running (it doesn't).

that experiment is flawed. it assumes that the point where the temperature is measured at will reflect the OVERALL heat energy state of the entire engine and cooling system.

this is unlikely to be the case.

what your guage will read is only the temperature of THAT specific area of the engine.

so the point you measure might well stay at 195° while that bit over there drops from 250° down to 195° ten times as fast

I could devise a series of temperature probes that would give meaningful readings on system temperatures and the rate of energy change in the system, but I would need to get PAID because it would be laborious and somewhat expensive.

Fd3BOOST

iTrader: (7)

I neever bothered because you can just turn on the a/c and it kicks the fans on.
So why bother, its already wired up.

Kento

This thread has been resurrected for the sole purpose of mental masturbation....

RotorMotor

iTrader: (5)

but dont you work the engine even harder if you turn the ac on?

DamonB

You go climb under the car and figure out how much that is. It ain't much.


So you claim that we are unable to measure the coolant temps inside the engine and then along with that supposition decide that convection is happening at a rate that cools the motor even after shutdown? That is absolutely flawed.

honegod

?

the point is that the radiator is NOT lower than the engine, and in fact much of the radiator is ABOVE the lowest part of the engine.

that gives us the heigth difference we need for convection to take place.

not much, ok, but SOME !

and that is the point, that SOME additional cooling will happen through thermal convection.

Quote:

So you claim that we are unable to measure the coolant temps inside the engine

are you one of the folks who feel that when someone points out an error in your understanding that you are being insulted ?

I said we can measure all kinds of temperatures inside our engine, I questioned the RELEVANCE of these particular measurements to the question of whether or not thermal convection was increasing the rate of heat removal from the engine.
and provided an example.

Quote:

and then along with that supposition decide that convection is happening at a rate that cools the motor even after shutdown? That is absolutely flawed.

that thermal convection IS taking place is a simple matter of physics, that it will cool the engine is equally simple physics.
that running a fan to increase the temperature differential between engine and radiator will increase the rate of fluid flow through the system is also simple physics.

the rate at which this cooling is taking place is a whole 'nother thing, requiring several measurements taken at several places to provide the data points with which to fill in the energy transfer curve.
the rough overall shape of which curve I previously estimated.

I have made no claim of mystical knowlege, just the ability to see physics when it happens in front of me.