How many CFMs needed from electric fan??

[Tony D]

BTW, what exactly is my 'priorities of importance'? That you have sufficient flow (CFM/GPM) through the radiator? If you are disputing that, indeed we truly disagree!

[bjhines]

Experiments which proved that the 'coverage' as a portion of radiator covered is basically irrelevant---it's the CFM that counts! A 12" 5500CFM fan will work just as well as a 16" 5500CFM fan. Packaging a tight engine bay will benefit from the easier placement of a single 12" as it can 'move' quite a bit on the radiator. Split the difference and get a pair of 2500 10" fans, it's all good. None of them 'needs' a shroud, it might boost effectiveness, but I haven't personally had an issue where I needed a shroud to have the engine operate in the proper temperature ranges I desired (following the CFM guidelines I gave above!)Main point being (and my duct tape example was designed to have someone check their own example) is that the radiator needs very little actual airflow AREA to accomplish what it needs to do. Unfortunately it was not checked. Don't know why.

 

As to switch requirements, I like the Hayden or other 'adjustable' electronic controllers where I can adjust a trimpot to get actual fan on/off temperatures to work where I want them. Were I more ambitious (and if JeffP had more time) I would de-pot their black box and make a multiple circuit to control multiple fans from several different temperature ranges.Right now, I run a single 10" (around 2500CFM) which has a second 10" cycle on if the temperature goes much above 180. First fan is on at 175, second at around 180. On colder days (below 40F) I only run one 10" fan. In July driving in Phoenix in 120F heat, if I am below 25mph one fan is on, and when I come to a dead stop in traffic, the second fan cycles on/off on a 180on 170off cycle. First fan comes on at 175 and shuts off at 165. Thermostat is 160. In temperatures below zero, I can have issues getting to operating temperature and kick myself for forgetting to install the 180F thermostat before going to the cold places...but that hasn't happened in a while.

 

 

Well... I just don't understand this logic. Poor shrouding just means hot water goes straight through and into the outlet tank. If the radiator is too big then get a smaller one.

Why would you "de-pot" a fan controller? when you can make a new one "un-potted". Why did you choose the temp ranges you did. I would never intentionally use a 160f thermostat, where did you get that? I am pretty sure that a proper radiator and a proper fan would allow a much higher operating temp thermostat. If your engine can't reach operating temps in cold weather then you have a MAJOR cooling system flaw.

Edited December 24, 2010 by bjhines

[Tony D]

In Turn:

"Well... I just don't understand this logic. Poor shrouding just means hot water goes straight through and into the outlet tank."

And as long as the bottom tank's temperature is of adequate 'coolness' so that the temperature rise of the engine does not result in a runaway situation, then it's acceptable. Split a hair if you like, but it IS possible that a fan operating in one portion of the radiator will cool the liquid below a point needed for that point---if hot water bypasses it...so what? The end result in the tank for pumping into the engine is what matters. One could say it's all that matters!

 

"If the radiator is too big then get a smaller one."

I have to be honest, I don't know where this is coming from, I am dealing with a stock radiator. FYI: Some Racing Classes do not let you 'downsize' the radiator for the aerodynamic advantages it provides... But again the OP was asking about a STOCK setup. Plenty of room for a couple of smaller fans, or a big single. Pushers or pullers. Whatever floats your boat. Whatever is chosen, it has to have adequate CFM or the car will overheat. I make no more contention than this simple point. That there are other tangential benefits to using my suggestion just happen to be coincidental. If I don't need a shroud, so what? I'm bypassing hot water to the bottom tank? So what? Does it affect the car in any way? No, not in any practical way---and I doubt it will in his application, either! Theory is nice, but we live in the real, practical world.

 

"Why would you "de-pot" a fan controller? when you can make a new one "un-potted"."

Ever reverse engineer something you liked which worked well? On the controller I'm using, they're potted. To see what 'guts' are used, do you have a better idea than de-potting? Crystal Ball Maybe? Of do you have an already drawn schematic with parts list for a circa 1990 Hayden Dual Fan Controller? If so, give it up. Otherwise, to replicate it, it's reverse engineering, and that means getting that black crap off the components and circuit board.

 

"Why did you choose the temp ranges you did."

Running around in 120F heat tends to reveal things guys back east will never understand. Apparently you are case-in-point. The thermal stresses encountered in a typical summer day of 85F here where I live won't be encountered anywhere east of the Mississippi. Not even close. It's got more thermal stress on the car at that temperature than over 110F in Iowa, Georgia, or North Carolina. There's a reason all the OEMs take their cars and run them in a circuit through the SoCal Desert for hot weather testing. My back yard...

 

"I would never intentionally use a 160f thermostat, where did you get that?"

Uh, BJ, that would be Nissan Motor Corporation, Global Headquarters 1-1, Takashima 1-chome, Nishi-ku, Yokohama-shi, Kanagawa 220-8686, Japan. Look it up. "Thermostat, Tropical, 72C" It's used in HIGH AMBIENT TEMPERATURE AREAS (not North Carolina which would use a higher temperature "Temperate" thermostat of 82 or if up north in Michigan the "Frigid" Thermostat of 85C Rating. It's all in the parts books. All OEM. All engineered for THIS application. (Since you put so much stock in that...)

 

"I am pretty sure that a proper radiator and a proper fan would allow a much higher operatning temp thermostat."

Take it up with the Engineers at Nissan. 'Proper' and what is in the car may not be the same thing. As I recall the OP revolved around a STOCK car (more or less) using STOCK components. Such was my recommendation. I will note the acknowledged issues of stagnant flow in the Nissan L-6 which contributes to it's poor cooling performance when stressed. Nissan made a 72C thermostat for a reason, you know! Now, if you can tell my why the whole of the Nissan Engineering Department is wrongheaded in their specification of three separate and distinct thermostat ranges depending on climate and driving conditions, I'm all ears for that one. School me and the dopes at Nissan! You're 'pretty sure'---but what do you really know for a fact?

 

"If your engine can't reach operating temps in cold weather then you have a MAJOR cooling system flaw."

Er, yeah, it's called optimization for 120F Ambient with a 160F Thermal Layer through the radiator, and then trying to operate the same system at 25F. All those big rigs on the road with the big grey zippered covers running down the road in February with the radiator blocked (like a Y2K Chevy Diesel Van where you need to cover the radiator to get decent heater operation because it runs so cold...) They all have a 'major flaw' called 'excess capacity'---this allows them to run fouled, in extreme hot environments, etc... If you live in Malaysia and it's always 32C outside, then maybe you can do one thing all the time. If you live where there is a temperature swing of over 100F it might call for some different setups at different times of the year. I'll go so far as to admit I left out 'at idle' when referring to lower temperatures. At idle I'll stick around 150 to 155 F. I won't get hotter than that until I put a load on the engine. And that goes for if the car has a 185, 170 or 160F thermostat in it. It's simply a matter of BTU rejection with the pump turning at idle and available thermal mass on a below 40F day...

 

For christs sake, the guy asked what CFM fan he needed, and you want to pick flyshit out of the pepper with boxing gloves! If the theoretical argument stimulates you this much, have at it, but from a practical standpoint what I said WORKS and WORKS WELL IN VERY DEMANDING CONDITIONS. Make the wrong (undersized) suggestion CFM-Wise, and you will end up overheating. Tell me it's not so.

 

You can rail all you want about SUPERFLOUS MINUTAE, but the point remains the guy asked what CFM he needed, and not if he needed a shroud or not. Or how he should redesign his coolant system to outsmart the Nissan Engineers.

Edited December 24, 2010 by Tony D

[bjhines]

Tony,

 

You CANNOT justify letting hotwater bypass the cooled area of the radiator. A good fan shroud is important. Datsun even improved the shroud on later S30 models. If you have some proof otherwise then pony it up boy.

 

Tony once argued that a CAST IRON MANIFOLD is LIGHTER than a tubular header. When I weighed each he claimed that all scales were all inaccuarate. This is heading down the same path. I grow sick of your poor judgement. I have more important and more interesting poionts to discuss.

[Tony D]

I'm not justifying it, I'm just saying the amount you are fretting over isn't significant: if the lower tank is 100F, WHO CARES HOW MUCH BYPASSES?

 

That's like fretting over every virgin not having an ideal first sex encounter. No matter how hard you try, it just ain't happening!

 

A shroud will only make "All the water" marginally cool---ending in the same result. Please think of this logically and not emotionally.

 

You will recall in the cast iron manifold debate, my scales said differently and that the tubular header I had WAS indeed heavier than the cast iron manifold! You're right, this is heading down that same path: someone asked a question and you aren't answering it, you're just harping on minutae that is immaterial.

 

If the BOTTOM TANK TEMPERATURE is 100F on a 12" 5500CFM fan and no shroud...

And the BOTTOM TANK TEMPERATURE is 100F on a 16" 4000CFM fan WITH a shroud...

 

I guess your contention is that 'The 16" Fan with a Shroud is BEST' for the application then?

 

Tsk Tsk Tsk...

 

All I have ever said is that the 12" fan WORKS, provides the SAME RESULT, and therefore IS TOTALLY ACCEPTABLE.

 

If you want to be pedantic and INSIST that someone put a fan shroud on it to boost ALREADY ACCEPTABLE EFFICIENCY...well, go for it. I see it as foolish adding of components after the goal has been reached.

 

The first S30's had a shroud, they ALSO had a radiator with marginal heat rejection. They ALSO had the shroud DELETED and functioned JUST FINE in a MAJORITY of the market. Before you invoke history, please recall it all...

[bjhines]

If you need a cooling fan AT ALL, This means that you need to move more air through the radiator than will flow without assistance. A fan shroud is just as important as high CFM flow. Every moden car has a good shroud. thousands of factory designs back up the importance of a proper fan shroud. Your insistance that it is a waste of time flys in the face of millions of dollars of REAL DESIGN by professionals with the equipment to determine what works. If you are OVER-COOLING the water(requiring a hot bypass) then you need better FAN CONTROL(I have more experience than anyone else in this discussion on this part). Allowing hot water to bypass the exchange in the radiator is piss poor design. WE are talking about IMPROVING the antique system. I will insist that a shroud is equally important to CFM flow.

 

I was the person in this discussion who stated wattage requirements and the need for a good shroud. If you can pump enough air with a 2" impeller then you will definitely need a shroud to spread out the flow.

 

BTW

I had great first time sex. The older girl next door was truly freaky and FUN!!!! She was also the best looking minx I have ever gotten my paws on since. Good memories... hmmmm.......where is that yearbook?...

Edited December 24, 2010 by bjhines

[bjhines]

If you achieve enough cooling fan flow to allow some hot water to bypass the exchange(lack of shroud) then you are overcooling the part of the water that did exchange heat. This is wasting power by running the fan at a higher wattage than is required. It puts excess load on the alternator, It may discharge the battery if the alternator is not producing enough power at idle to keep up with fan demands.

[Tony D]

"A fan shroud is just as important as high CFM flow. Every moden car has a good shroud. "

 

This isn't a modern car is it? This is a car that was designed with a shroud, and marketed without it. One which had a 160F thermostat avaialble for it.

 

As much as you want to insist that you MUST use a shroud, common sense says 'no, you don't unless your flow is marginal.'

 

And now we have come full circle. If you have enough flow, you won't NEED a shroud. All the new cars come with ABS and Airbags as well, do I NEED those ALSO?

 

If you want to engineer down to the nth degree and have ONLY that which you NEED...then when you go outside the parameters of design you're screwed and overheat!

 

The radiator on a stock Z is oversized. There is excess capacity. If you three or four core it then there is MASSIVE overcapacity on the heat rejection side of the equation. Sure, then lets undersize the fan, put a shroud on it to boost transfer efficiency....and as long as it never gets hot outside you're cool.

 

I wonder why the Taurus Fan used two speeds...

[datsun280zx]

Ok ok guys no need to argue lol anyways i got it kinda mounted and im leaving it shroudless for now. I just got a question thought. What rating thermostat should i use? im not sure what rating is in there now. Thanks again for all the help guys

[hoov100]

Ok ok guys no need to argue lol anyways i got it kinda mounted and im leaving it shroudless for now. I just got a question thought. What rating thermostat should i use? im not sure what rating is in there now. Thanks again for all the help guys

 

160*

 

As for the needing an entire shroud debate, I do agree with the point Bjhines is trying to make, but it's just useless nitpicking of the cooling system. Regardless if half the radiator has a shroud, or if the entire radiator has a shroud, all of those little tubes all end up going to the same place and out the same hose. so what if a small amount of radiator surface area isn't covered by a shroud, as long as the fan pulls enough air to lower the coolant temp enough so that when it mixes with the rest of the coolant the temp doesn't rise a consider amount and still in the nominal range, then there isn't a problem.

 

You can nit pick it all you want, but if it's not going to show any real world noticeable effects, then it's useless to argue them. If it works, it works. Who cares how it's done.

[Two80z4me]

It would be wise of those who read to listen to 99% of TonyD's advice.

 

With that out of the way, I have a single 16" 2000cfm fan with a semi-shroud on it and it works fine on my semi built p79 L28.

It has seen gridlock Seattle weather at 100 degrees and it never exceeded 185degree engine temperatures. (yes that is a wee bit high, but no where close to the proclaimed danger zone).

Toodles,

Sean.

[Tony D]

One of the things revealed in dyno testing within the past month was the real effect of looping the coolant hose when the heater core is bypassed. With a 160F thermostat, the CHT was over 220F with a thermostat out water temp of 170 at 3000rpms and 25 hp of load. It got worse as the rpms went up.

 

And this was a 20 degree DROP from an unmodified head and block (cooling water tapped over #5 for individual return like on the cooling thread), and mods to the block for higher flow.

 

That means with the same head/block combo unmodified for supplementary flow, and running a 160F thermostat, that area of the head running at 65mph on a typical Z would be nearer 240F.

 

And it's linear. Run a 170, it's 250. Run a 180, it's 260. Run a 190, it's 270. Better run 50/50 antifreeze/boil if you insist on running a 190 or 180 thermostat. You will drop 50 degrees off that running no looped hose, but that's still damn hot at the back of the block!