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Old 06-11-2019, 05:01 AM
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Cooling question

Now that the heat is on here in Florida the AC is running regularly. Temp is good when at 45mph & above, 180 stat, it runs just above that.
In stop & go traffic it runs up to 200-205, not a problem but it gets a bit warmer when stopped/parked.
Currently the fan controller is powered with ignition on. My thought is to switch the power to constant 12V on so the fan runs until the controller shuts it off.
Theory being the hot water will circulate back through the radiator until the thermostat closes and the fan sensor reaches it shut off temp.
Yes?
No?

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Old 06-11-2019, 06:35 AM
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You don't have a problem, don't try to make one! What I mean is maybe the fans will run the battery down...did on my '35 Ford pickup several times. I think there would be minimal water movement with the pump not running. Cool water in the radiator would not go to the block and push hot water into the radiator the way I see it. You may also find that while driving in stop and go traffic the water coming out of the bottom of the radiator is about 150 degrees.
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Old 06-11-2019, 06:40 AM
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Quote:
Originally Posted by Bob37pont View Post
Now that the heat is on here in Florida the AC is running regularly. Temp is good when at 45mph & above, 180 stat, it runs just above that.
In stop & go traffic it runs up to 200-205, not a problem but it gets a bit warmer when stopped/parked.
Currently the fan controller is powered with ignition on. My thought is to switch the power to constant 12V on so the fan runs until the controller shuts it off.
Theory being the hot water will circulate back through the radiator until the thermostat closes and the fan sensor reaches it shut off temp.
Yes?
No?

I had a big argument with someone on that subject. I drilled a few 1/8" holes in the t-stat and would put an electric fan on my bumper to cool it down before going into the garage. Even after the stat closed, it still circulated the coolant by convection currents to cool the whole engine many times faster than just letting it sit with the hood open.
I was told everything you can imagine, this one guy thought it was the dumbest thing he ever heard. One other guy said on his one old tractor the radiator is up high and it has no water pump, so it may work.

Now for the bad part of the story, after installing aluminum heads, it stopped working!!! The ONLY thing different is the heads. It cools the radiator and that's it! So I suggest try putting an electric fan on the front to see if it works for you before re-wiring. I know a lot of modern cars the fan can and will turn on and off after the ignition is off. Whether the coolant circulates or not, IDK? (by modern I was thinking of the first time I heard a fan run with the engine off. I was about 15 and the car was a brand new VW Rabbit Diesel, around 1977?) I guess that's not modern is it?
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Old 06-11-2019, 07:11 AM
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It sounds like your car is running well. I agree with 39, you are asking for dead batteries if you switch it. Most fans pull at least 20 amps, if they run for five minutes that is equivalent power to cranking the engine for almost half a minute.
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Old 06-11-2019, 08:50 AM
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Thanks guys!
Cold water sinks, hot water rises. Thoughts on this came from different "modern" cars having the fan run after shut down.
As long as the T-stat is open water should circulate through the radiator, and the fan controller temp will shut the fan off before the T-stat closes
I'm gonna use a jumper (or just leave the key on) and run some tests when I get home from a run. That way I'll see if and how long it may take to cool, and also moniter the battery drain.
At least the controlled environment won't leave me stranded!
I'll report back with my findings.
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Old 06-11-2019, 09:12 AM
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What you see is normal. Yes if you continue to fan cool the radiator some convection will occur but that happens naturally anyway at shut down as the radiator has a lot of surface area so the coolant in it will surrender its heat pretty quickly. That will at least in theory result in some amount of convective flow dictated by the rate of cooling, the amount of open flow area somewhere between the open thermostat and if closed any vent holes in the thermostat. The flow is probably not continous there is probably a dulition location where the colder coolant is rewarmed by the hotter and for a while reduction if not stagnation of the flow probably occurs. I haven't modeled this but what is known about thermal flows makes this logical.

The important thing is to keep surfaces inside the cooling jackets wet, this requires keeping coolant under the boiling temp of the coolant mixture. Contemporary systems with water and glycol mixes use system pressure to force this outcome. So keeping up on system tightness is of paramount importance.

Bogie
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Old 06-12-2019, 01:27 PM
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If it's not overheating while running, leave it alone. You won't accomplish a thing running your fan while the engine is stopped, except drain the battery as mentioned earlier.

How many millions of cars with mechanical fans ever had a problem because water heated up after the engine shut off that wasn't caused by the owner?

I'd say put a bigger fan on to knock the idle temps down, but you said your not having any trouble, so leave it be and work on something more important.
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Old 06-15-2019, 12:54 PM
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So I went ahead and proved the consensus theory today. Got home from a morning/lunch run withthe AC on, temp in the 195-200 range. shut down & left the key onto run the fan. After 20 minutes there was no appreciable change in the displayed temp.
You guys were right, don't fix it if it aint broke!
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Old 06-16-2019, 07:12 AM
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Don't completely pass off the whole idea of it not working on any vehicle, there are plenty of late model cars that cycle the fan on and off after the ignition is off.


And what I said about mine, it really did work! But something with the convection currents got messed up when I put on aluminum heads? I'll bet if I put a very small water pump in the bypass hose it would work again. It's just nice pulling the car into the garage with slightly undersized A/C when the engine temp is down to 110 rather than 210.
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Old 06-16-2019, 09:57 AM
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I have been fighting engine temperature control since I bought a new 1969 Pontiac Firebird 400.

I broke the original 3.36 rear end and the Pontiac 50,000 mile drive line warranty replaced it with a 4.33 rear ratio, at my request. The Dallas Zone Office knew I was drag racing the Firebird but replaced the rear end anyway. After I had the 4.33 installed, I could not drive at sustained Highway speeds without the engine overheating. I had to borrow a friends trailer when I participated in drag racing events. It had a stock Pontiac Firebird HD radiator with three tube core and was the best you could get without chopping up the radiator shrouds and mounts for a special aftermarket radiator with oversize tanks with a 4-tube in-line core. The aftermarket staggered core 4-tube radiators are no better than a stock three tube radiator.

The 4.33 rear ratio was not designed to be used in a 1967-1970 Firebird for anything but drag racing.

I have a 4.11 positraction in my 1962 Bel Air and the OE radiator leaks from the top tank when I shut the engine off. I must replace the radiator this summer with a new one from Show Cars in New Ulm MN. I hear they are good radiators and fit correctly without any butchering of the sheet metal.

Last edited by MouseFink; 06-16-2019 at 10:07 AM.
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Old 06-16-2019, 11:14 AM
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Quote:
Originally Posted by 55 Tony View Post
Don't completely pass off the whole idea of it not working on any vehicle, there are plenty of late model cars that cycle the fan on and off after the ignition is off.


And what I said about mine, it really did work! But something with the convection currents got messed up when I put on aluminum heads? I'll bet if I put a very small water pump in the bypass hose it would work again. It's just nice pulling the car into the garage with slightly undersized A/C when the engine temp is down to 110 rather than 210.
The aluminum heads would change the heat budget by passing heat faster than iron. Between them moving heat at a faster rate the coolant inside the jackets would start looking closer to the radiator's heat loss rate which would rduce if not nearly eliminate the thermal differences that cause convective flow. The aluminum heads and intake mght ven reach a point of heat loss to where the thermostat closes or approaches closed so convective flow is way reduced if not stopped.

So what you observed makes sense.

Bogie
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Old 06-16-2019, 11:49 AM
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Originally Posted by MouseFink View Post
I have been fighting engine temperature control since I bought a new 1969 Pontiac Firebird 400.

I broke the original 3.36 rear end and the Pontiac 50,000 mile drive line warranty replaced it with a 4.33 rear ratio, at my request. The Dallas Zone Office knew I was drag racing the Firebird but replaced the rear end anyway. After I had the 4.33 installed, I could not drive at sustained Highway speeds without the engine overheating. I had to borrow a friends trailer when I participated in drag racing events. It had a stock Pontiac Firebird HD radiator with three tube core and was the best you could get without chopping up the radiator shrouds and mounts for a special aftermarket radiator with oversize tanks with a 4-tube in-line core. The aftermarket staggered core 4-tube radiators are no better than a stock three tube radiator.

The 4.33 rear ratio was not designed to be used in a 1967-1970 Firebird for anything but drag racing.

I have a 4.11 positraction in my 1962 Bel Air and the OE radiator leaks from the top tank when I shut the engine off. I must replace the radiator this summer with a new one from Show Cars in New Ulm MN. I hear they are good radiators and fit correctly without any butchering of the sheet metal.
I expect with 4.33 gears you got into the range common to long circle tracks where sustained high RPMs with a stock cooling pump causes it to cavitate the coolant with the result of less liquid being circulated so you get high speed heating. The three common approaches to this have been to reduce the size of the impeller blades or remove some entirely; change the pulley ratios to slow the pump down; use a more carefully crafted aftermarket pump, or some combination of these things.

I have to admit that I find it odd that very little information is published on this subject, like high speed engine cooling is a secret. Which it might be! I've found for high speed circile tracks there is a thin line being walked between engine cooling needs and minimizing aerodynamic drag. To say the point is to minimize the amount of air passing through coolers as this increases overall vehicle drag which the body guys are working hard to minimize while the engine guys working on making more power which requires more cooling. To some extent the engine and driveline guys can use more exotic materials that just can be run hotter, but rules constraints play hard here let alone the state of art of current materials. Hence my attraction to Southern style "run what you brung" racing. While it could put lesser financial participants in the stands rather than on the track, freedom, as we all know, fosters innovation which pushes the technical dung ball faster ahead than living in an imposed state of engineering stasis.

I find a lot of these technical rules frustrating, the association mantra from places like USAC and NASCAR is about keeping this top level of racing affordable to level the technical competition. I mean, bite me, this is a game played between huge corporations, univeristies, and uber wealthy billionaires; "affordability" is hardly a concern at this level.



Bogie
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Old 06-16-2019, 01:42 PM
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With the 4.33 gears, the clutch fan and the air flow through the radiator on my 1969 Firebird could not cool the engine at sustained 4,500 RPM in 4th gear. Those parts were not designed by GM to use on a engine at 4,500 RPM and 55 MPH. If I went on a short trip I had to drive at at a sustained speed of no more than 40 MPH or the engine would over heat.

I drove 300 miles to participate in the 1967 AHRA Spring Nationals in Odessa Texas. I was in my 1959 Impala with a 327 CI / 365 HP long block, 3-2 bbl, 4-speed, double hump heads, and 4.56 rear gears.

I had no heating problem if my sustained speed remained below 50 MPH on the highway with only bursts of speed passing other cars up to 100 MPH. I won my class in AHRA F1-E/HR at that race with 13.47 ET with no overheating in 90 degree spring weather.

There were only eight contestants in F1-E/HR class. In the class eliminations, I raced against the Ray Capps “Head Hunter” Dodge Charger funny car from Mesquite Texas. It was among the first mid-engine all fiberglass funny cars. The 1967 AHRA Spring Nationals was the third race for the “Head Hunter” funny car.

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Old 06-16-2019, 03:06 PM
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The coolant will not flow by convection in an old style system as it will in a new cross flow system if there is an upper coolant tank and the coolant level is below the upper hose inlet. For the hot coolant to rise and enter the radiator there can not be any air to block the convection process.

I don't know this applies to your coolant system but it is a thought.

John
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Old 07-14-2019, 06:07 AM
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Update: Cool as a cucumber! :)

I did some research in the file of receipts I got from the P.O. and found the electric fan used was installed way before the AC was added. Numbers showed it was a 15" fan rated at 1100 cfm.
Worked fine with no AC running.
But inspite of the above recommendations/info, "I" was still not happy with the increased temps from the AC.
Sometimes it isn't 'really' broke, but just needs a bit of tweaking!
So... I installed a 16" fan from Flex-a-Lite rated at 2500 cfm. Temp now holds steady at 180* under all conditions.
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