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Old 09-11-2008, 09:25 PM
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Fans stay on too long!!

Hey guys. Here's the situation. I've got a brand new HUGE aluminum radiator to go along with my freshly built 383 sbc and the dual 12" flex-a-lite fan package with the adjustable thermastatic control for cooling. I am using a stock GM water pump with this set up as well. Anyways to get to the bottom of things I am having cooling issues. The temp sensor is threaded into one of my aluminum AFR heads. I have adjusted the fans to come on at about 215 degrees because my thermo is a 195 degree and I have been told to set my fans to come on at approximately 20 degrees above the thermo since they shut off at 15 degrees lower temp then they turn on at. Anyways I'll fire it up and let the engine stay on the fast idle cam (2000rpm) to warm it up. I'll watch the temp gauge climb all the way up to around 215-220 then boom the fans come on. The problem is they will NEVER shut off as long as the engine is running and don't drop the temp much at all. The lowest the temp gauge will go is maybe 205 then back up and down meanwhile the fans are going at full bore. I know the water jackets of the block are completely brown with rust (as they are for any cast iron engine that has had a drop of coolant in it). I don't think this should be a problem though since I have such a big radiator (biggest aluminum one jegs makes) and dual 12 inch electric fans Not once will my fans turn off and the thermostat will never close either because it is a 195 degree. I am wondering if this is normal because this is all happening while the car is not moving. Maybe if the car were moving the extra air going through the rad would have a huge effect?? To make matters worst when I go to shut off the car the fans will stay on then cycle off then back on for about 10 minutes or so, needless to say my battery dies. I'll go back out a few hours later and it will hardly have enough juice in it to start her back up (brand new 800CCA battery as well). I am gettign really annoyed with this and cant seem to understand what I need to do to fix this problem. I am using 50/50 water/antifreeze mix with no additives/ Should I change the size of my water pump pulley to a smaller one so the pump turns more rpm's this pumps more water. Also is there anyway I could use a 12 volt capaciter inline with the electric fans so that my battery doesn't get drained everytime I shut the engine down?? Has this ever been attempted or done?? Anyways thanks in advance for any help with these questions.

Keith

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Old 09-11-2008, 09:49 PM
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< Shakin head.
Anyways. Think about this a minute, if the fans are wired not to shut down when the iginition is off then it`s not wired right. Also in your post you said the magic words "NOT MOVING" If the vehicle is not moving what other airflow does it have? only the fans are cooling it at a dead stop, and since your running a 195 degree t stat then they won`t shut off until the engine is below that tempature. When you shut the engine down the coolant temp will rise because the coolant is no longer flowing. it`s the same as a pot on a stove. but since all engines work this way it`s not hurting anything.
Airflow is what cools it when the car is moving, nothing is cooling it other than the fans when it`s at a stop. I would go to a 180 degree t stat. I would drill one small 1/16 hole in it to assure it can burp itself.
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Old 09-11-2008, 09:50 PM
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Fans

I am no real mechanic but I know what I think.
I think the temp range is too high why 195*?
The 205 to 215 temp range is far too close to disaster for my nerves.
I live in NC, and being stuck in traffic on a 99* day down at the beach takes all the cooling leeway I can get.
maybe strokers have to run that hot, and I just don't know it.
I just put elec fans in my 65 c10, and the instructions gave me the choice of going direct to the battery, with a manual switch if I wanted but recommended that I go thru the relay, to the ign. switch so the fans will shut off when I shut the truck off and NOT drain the battery.
If you go direct to the battery the fans will not shut off until the thermastat tells it it's cooled off.
If the motor is shut off the best the fans can do is cool off the water sitting right in front of the fans because there is NO WATER circulating anywhere.
If you shut it down at 215*, there is ALWAYS temp surge, because of the no circulation thing.
So I recommend you put it on the ign. switch.
Also....with my engine..it sits WAY back, and I have a short pump.
I have the fan on one spacer, as well as the elec fan.
It seems to be working without a shroud, but I have read in several blogs where running a shroud and proper fan spacing, even with electric fans is pretty critical to good cooling. I seems like without a shroud the elec fan only cools a smaller area of the radiator. The object is to draw air thru as much of the radiator surface as you can and not just in the spots where the fan is. That is what the shroud does. I thought it was just safety stuff that took up too much space...LOL
My Son's VW Jetta has an EXTRA smaller electric water pump that circulates the water thru the engine and the radiator even after the engine is shut down...these run till it cools off. It works really well. That heat surge is murder on the aluminum engines I guess.
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Old 09-11-2008, 11:55 PM
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I too think you should drop to a 180 t-stat. I'm running the dual 12" Flex a Lites as well and I've got them set to come on at 205 and shut off at 190. They work very well, even when the truck is not moving. Very reliable.

I do use a different style fan controller though. The one I use has a probe that slides between the fins of the radiator.

http://store.summitracing.com/partde...5&autoview=sku
I know it looks cheesy but I've had very good luck with it.
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Old 09-11-2008, 11:57 PM
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If you want to keep it wired the way you have it with cooling after shut down. You need to use the probe type thermo sensor that goes in the radiator fins for the fans. It takes a long time for the engine to cool without water circulating thru it. And drop the engine thermostat down to 180-185deg or so.

Blazin we must have been typing at the same time. LOL!
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Old 09-12-2008, 12:00 AM
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Thanks for the replies, but let me clear one thing up with you guys. The INSTRUCTION manual that came with my electric fans SAYS "Hook red and black wires DIRECTLY to battery and NOT through ignition so the fans can remain on after engine is shut off." I thought it was a little weird too because i suspected it would drain the battery, I guess I sha'll switch down to a 180 degree thermo and run my fans through an ignition relay. Thanks again.
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Old 09-12-2008, 12:03 AM
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I am using that exact same probe kit, I have the exact same flex-a-lite fans as well, they came together and the probe is in the fins near the inlet of the radiator.
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Old 09-12-2008, 05:56 AM
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I am sure you have heard the fans on newer cars running after the engine is off and OEM didn't worry about battery drain......there is nothing wrong with 205 or even 210...personally I think people run their engines too cool....... most power will be made with a warmer engine
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Old 09-13-2008, 12:34 PM
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You need to wire your fans through a keyed relay, not directly through the key itself. Hot wired directly as you state, does not make sense. Doesn't matter who recommeded it.
YES, I have seen those stickers under hoods that state, "Caution, fan may start at any time even if the key is off."

If you want the fan to run 10 minutes after turning the engine off, the 80s Chrysler cars, Omni/Horizon/K cars had a 10 minute fan relay.
Chrysler had a bulletin back then to disconnect the timed relay because people were annoyed about the fan running. Battery power was not compromised, and the fan ran to prevent hot start vapor lock problems on those carbed cars.

I use 195* thermostats in 96% of everything I build that is to be driven on the street. 195 is OK if you have a proper cooling system. Under ideal circumstances the engine should never run hotter than 10* more than the thermostat rating.

Your biggest problem seems to be that your fans are of insufficient airflow capacity for your cooling system. You should also determine if your fans are sucking hot engine compartment air back into the front of the radiator.

IMO electric fans are an ego thing sort of like having chrome rocker covers. Unless you get a fan that pulls extremely high amps, you probably won't cool a high power engine with electric fans. Some of these new cars pull 60 amps. Too many people want to run electric pumps and underdriven pulleys to save horse power and then throw a humongous radiator in there to try to cool the car... wrong set up.


Not being able to see your set up
, I can only suggest that your water pump be overdriven, AND if possible, go to a factory type engine driven thermostatic fan clutch type fan with proper shrouding.

An OVERDRIVEN water pump is MANDATORY with a big radiator.
High coolant SPEED causes turbulence within the tubes reducing or eliminating laminar flow therefore increaseing heat transfer.
It is also possible that a high flow water pump might be necessary with a humongous radiator.

An old wives' tale says that if a radiator is too big it won't cool. Possible if the flow goes laminar. But generally speaking, a boat won't overheat if the lake is too big.
An old wives' tale also states that if the coolant goes through the radiator too fast it won't cool because it doesn't have time to transfer heat, so slow it down. When you slow it down, it also slows down inside the engine and therefore gains more heat.

The overall problem is coolant exposed to the air, and AIRFLOW.

I have never built a car with a cooling problem. period.
JMO, CSE for several years.

Last edited by ScoTFrenzel; 09-13-2008 at 12:43 PM.
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Old 09-13-2008, 02:12 PM
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I did the electric fan thing one time years ago, and then went back to the stock clutch fan set up, the electric was too much hassle even so I did cobble up most of the parts from a junked buick park avanue. Clutch fans when in good working condition do the job just fine. I can see the fans being wired to the battery so they stay on if your running a electric water pump on a drag car and you can leave the 2 on between races to cool the engine, we used to do that. But on a street car it`s not called for or needed.
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Old 09-13-2008, 05:56 PM
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I agree with the others that suggested the probe be installed at the radiator. If the probe is at the head, the fans will never shut down when running and take a long time after shut down if wired separate of the ignition.
I too would run a 180 stat with the fans set to come on at 190.
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Old 09-13-2008, 06:44 PM
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It is possible that your switch is set just a little bit too low and they are trying to cool the engine below that of the thermostat. A friend of mine, who has yet another identical setup, tinkered with his switch setting after I had set. Not long after that he started complaining that once his fans came on they never shut off. He had the switch set too low.

How about your sensor bulb tube? There aren't any kinks in it are there? It is also possible your switch isn't working correctly.

Don't be discouraged, once those fans are setup properly they work great and are very reliable. I've had mine on for five years without any issues. They should be more than adequate for the cooling needs of a street driven small block, even those in the 400+ hp range. They are hooked directly to the battery with a fuse and they will come on once or twice after the engine is shut off, especially in hot weather. I don't worry about it and I've never had a dead battery from it.
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Old 09-14-2008, 12:19 PM
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Quote:
Originally Posted by sexypizzaman
Hey guys. Here's the situation.

Anyways to get to the bottom of things I am having cooling issues.

The problem is they will NEVER shut off as long as the engine is running and don't drop the temp much at all.

Keith
As pointed out there are several perceived problems with your set up.

The main fact that you state is that your fans "don't drop the temp much at all"...... is a good indicator that your airflow is poor, either too small fans or hot air being recirculated.
Everything else is MOOT if the sucker won't cool anyway, isn't it?
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