I love a good debate, so here it goes.
1. People would look like idiots if they have to pop open their hood every time they park the car and stand next to it for 5-10 minuts twiddling their thumbs.
2. When the engine first stops, the thermostat will remain open (that's why the coolant temperature increases after shutdown, if you have a coolant sensor in the t-stat housing where the hot coolant exits the engine you'll know what I'm talking about). During that time if the fans are on the coolant in the radiator will be cooled very quickly and change density, the hot coolant fron the engine will flow toward the colder, denser coolant until the temp drops sufficiently to close the t-stat.
3. If you are only stopping for a few minuts (which is a lot of times). Wouldn't you prefer to crank up your car knowing you have sub 180F coolant being pumped into the engine instead of the 210-220 after heat soaking?

 

Answers:


well put!!


Trexthe3rd, I like a good debate too. I agree with #1 & #3. Re #2: The coolant in the engine increases in temperature because it stops circulating, and the engine is hotter than the coolant. It doesn't have anything to do with the thermostat. In addition, I wouldn't call it "flow" of coolant when the water pump is stopped. The is a very slight expansion and contraction, due to temp changes, but it isnt much.

 

I tend to prefer the Miata Theroswitch, 1 you don't have to hack up the interior. 2. you don't have to mess with a lot of wiring just plug and play.

 

Guys, make this your NUMBER ONE priority.

The mod is SO SIMPLE that you'll kick yourself that you haven't done it before.

And it works. Big time.

 

This sounds rather, um, Creative.

It don't work like that. Coolant will expand when it's hot and contract as it cools, but it's not going to circulate inside the system on it's own accord between the hotter and cooler portions.

 

Well, I'll just have to throw in my .02: Can't believe I waited this long....

1. For you guys that are REALLY lazy and cheap (like me) you can disconnect the rear hatch glass heating element in about - oh - two seconds. The connector is located in the upper right corner. It will just dangle there. You can now turn the fans on low at ANY time (which is probably 75% of the cfm of high) buy simply pressing the switch on the center console that turns on the heating element. I don't know exactly why it works but it does.

Badabing - instant fan mod with a stock switch - and you have the added benefit of having the idiot light illuminate on the dashboard to let you know it's turned on.

What about the loss of the heating element? In cool weather - when you need it, and don't need the fan mod - I just snap it back on.

2. Running the fans after you have stopped the engine does N-O-T-H-I-N-G to cool off the engine. It may make you FEEL like it's doing something but it ain't - all you are doing is blowing hot air around under the hood and cooling off the water in the radiator a little. How do I know? I have Rotor Head Temperature leads installed UNDER the leading spark plugs and no matter if you open the hood, run the fans, whatever - the temperature of the heads s l o w l y drops off. It takes a long time for metal to give up heat due to thermal mass. I guess you could throw some ice water on it....


All you are doing by running your fans after parking is wearing them (and your battery) faster. If we had electric water pumps it would be a different story.

3. I also have the Miata thermoswitch mod since I don't want to worry about constantly watching gauges when I drive. I guess if you like to **** around with stuff while you are driving and pretend that you are managing this sophisticated and exotic rotary beast - that will grenade if the temperature peaks even slightly -it is great fun.

I prefer to keep my eyes on all the freakin' left turning soccer moms that have inserted their heads up their anuses while driving. But that's another story.

 

I did not say the coolant is going to circulate by it self. I think people have a misunderstanding of the term "flow". Fluids by nature will "flow" given a temperature gradient. Take a large glass beaker fill it with water and some small plastic beads and watch what happens to the beads when the water is heated.
Now granted, there isn't a lot of dynamic coolant movement, but it will bring the coolant outside the block down to normal operating temperature or lower.

During normal operation of the car, the cooling system achieves a state of thermal equalibrium (~190-210) when everything is working properly. When the coolant reachs that operating temperature the engine internals are at a happy spot. Would you like to circulated 220 coolant through your engine? But that is exactly what you are doing when you first startup the car after a short stop. Anyone with a temperature tap in the t-stat housing can confirm this. When the car is started after a short stop, the coolant temp is sitting at 220 or above depending on how hard you were running before the stop. And it will take about a minute for the coolant temperature to drop back down to the 190 range, maybe I'm **** about my car, but that's a minute too long for me.

While I agree with Ron on the fact that the block will not see a significant temperature drop, but like I said, I can get into my car any time, whether it's a 5 min stop or 15 min stop and crank up the car and see my temp sitting at 180 or below everytime, and know that I have cool coolant goint to the engine. And because I have a temperature controlled fan mod, I don't have to sit there and wait to turn the switch on and off.

If you feel comfortable seeing 220+ on your temp gauge at startup after short stops then all the power to you.

 

Personally it's being a bit **** to worry about the motor temps after shutdown. BTW, my motor temp does not rise to 220 F after shutdown. It's only peaked to 212 F (100 C).

 

I guess I misunderstood:



My guess is the beads rise to the top indicating "flow" as you call it? This experiment is an open system and is not representative of what happens in your closed, pressurized cooling system. The beads "flow" to the top as the density changes and they float to the top. In a pressurzied and enclosed system they would merely form into the high areas (which the t-stat housing happens to be) but they are not going to migrate from the block, through the t-stat, down the lower radiator hose, through the radiator and back into the block.

Yep. There's not.

I typically see about 200-210. Even 220 isn't anything to worry about, that's only 30 degrees hotter than the thermostat and as you already mentioned will drop immediately once the car is started.

I have a stock motor and radiator. I never see temps that high at startup, even WITH heatsoak.

 

Question...

Are you saying that replacing the stock sensor with the Miata unit will cause the fans to operate exactly as they do in stock trim - except that they will come on at 205 degrees instead of 217?

If that is the case, then I see no need to install a switch that I have to remember to turn on.

BTW, I assume that the fam nod does not cause the high speed fan to become manual only operation? I wouldn't like that at all.

I also wonder why grounding the black wire will cause the fan to start "after 30 seconds". What else is happening during that delay.

All things being equal - I think I will install the Miata solution.

 

Yes. The slower speeds work as always but high speed will now trigger at 205 with the Miata part. Absolutely nothing else changes.

 

That's you

Where'd you come across that one? You holding out on us? I am going to go try it.

 

that rear defroster trick, isn't it the same as the parking light trick? but don't think it works on all FDs (not on my 94).

all this talk finally got me around to setting my pfc to kick in the fan earlier now (92 C).

guess it's just added insurance.

 

So when you shut off the car after running it, what is that jacuzzi sound you hear under the hood?

 

i don't hear anything after i shut off my car....

 

Well, like most stuff I stole it from someone else so I cannot take credit for being innovative, just observant.

Actually I should have used the word "thrifty" instead of "cheap"...and yes, I ALWAYS hold my cards pretty close to the chest. Preferably HERS!

 

You need to adjust the jets to allow less air into the jacuzzi intake. You may need to back wash the filter and adjust the PH. Also the blinker fluid can be a factor if its the wrong weight.

(that's the sound of coolant boiling, and it is NOT good)

 

Yeah, I need a new radiator. Stock one is not cutting it...

 

Sorry Ron, gotta cover up my RonKMiller shrine on this one. I'll use an old grease stained sheet........seems appropriate.

Running the fans for 10 minutes after shutdown will cool the engine more quickly. It will significantly reduce the temps around the engine, while it is cooling. It acts to reduce "heat soak" for the whole engine compartment. I believe the more significant benefit is reducing the baking of everything around the engine.

Interesting point about the rear defroster switch. It even comes with it's own dummy light. I need one of those too!

Adam

 

Localized boiling.

 

If it works as Ron says it isn't the same. The parking light trick will turn the fans on at a lower coolant temp but the defog trick will turn the fans on low regardless of coolant temp.

 

"From their experience or from the recorded experience of others, men learn only what their passions and their metaphysical prejudices allow them to learn."

I gotta agree with Damon - you STILL don't get it!

A grease stained sheet! I have been disgraced! - at least cover me up with a shop towel...

 

We idiots think alike. However I am just cheap; not lazy

 

From Steve Cirian's website:

Date: Thu, 30 Jul 1998 10:06:04 -0700
From: "Kinports, Robert" (RBK1@pge.com)

As promised, last weekend I used thermal strips to test the underhood temps after shutdown, but with the fans running for 10 minutes on low (Fan Mod). The previous weekend I conducted a similar test, but without running the fans after shutdown. The difference in temps were were amazing! Those who flamed away at this idea when it was discussed on the list a month or so ago can now put your tails between your legs.

For both tests thermal strips spanning 140degf to 310degf were placed in the following locations:

1) On the inside of the ABS shield
2) On the top of the strut tower bar
3) On the stock plastic IC intake pipe
4) On the stock plastic IC outlet pipe

Temps/results were as follows:

WITHOUT FAN MOD
1) 180degf
2) 180degf
3) 190degf (registered 180degf before turning the car off)
4) 180degf


WITH FAN MOD
1) Did not register (less than 140degf)
2) 150degf (registered 140degf before turning the car off)
3) Did not register (less than 140degf)
4) Did not register (less than 140degf)

Both tests (with & without the fan mod) were conducted after driving the car on the freeway for 20-30 miles with some periods of light boost, and an ambient outside temp of around 80degf. The car was idled for 1 min before being turned off & was allowed to sit for at least an hour afterwards. The test with the fan mod was done with the switch turned off after 30 seconds thereby switching the fans to low speed.

The thermal strips were added prior to the 20-30 mile trip, but were checked after shutting the car off (before heat soak) for a baseline. Only IC intake tube registered on both tests (all others were less than 140degf before heat soak).

An interesting note is that the IC intake temp strip increased by 10degf on each test after shutting the car off, even with the fan mod. The explanation I came up with for this is that some residual heat from the turbos rose to the highest point in the system, which is the IC intake pipe.

After reviewing the above data I can't imagine why anyone wouldn't do this mod. It only costs about $50 to complete using a stock fog light switch & takes less than an hour to do. The cost can be cut to $5 using an aftermarket switch.

"In a debate among true gentlemen, both sides may learn something"

 

HAHA! Good quote!

OK, I'll concede that you are probably going to see an increase in life span of the miscellaneous underhood components of - oh - maybe a few minutes additional - over the life of the vehicle by lowering the temperature more quickly than if it gradually decreased. But now we are truly splitting hairs. (of which I wish a had a few more left to split!)

The important part - and the expensive part - is the engine. My spark plug mounted leads are calibrated and read out on instruments that are guaranteed to be accurate within plus or minus 3 degrees.

And my ghetto "unplug the rear window defroster" fan mod is still cheapest: $0.00

"Facts do not cease to exist because they are ignored"

Take that sheet off my head NOW damnit!