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Old 08-30-2020, 07:34 PM   #1
Paul Bennett
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Default Thread - I screwed up

1950 Mercury-shinny new stroker engine - at the bottom of the stock radiator is an drain petcock. As I needi a thermoratic switch to control the new electric fan, I had the radiator shop add a bung to the bottom radiator tank of the same thread as the drain petcock, which they did.

I Amazoned a good looking 170 thermo-switch, learning that 'good looking' isn't a good way to specify threads. I doesn't fit, likely metric.
Can someone tell me what the threads are? Like 3/5NPT or some such so I can reorder a proper switch, i.e. one that actually fits.

Thanks

I'm getting closer to engine swap scheduled for Sept28 - I need to figure out changing the 4bbl Edelbrock carb for throttle linkage to the pass side as its now on the drivers side. Who sells linkages?
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Old 08-30-2020, 08:10 PM   #2
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Default Re: Thread - I screwed up

Is the bottom of the radiator the cool spot or the hot spot. I don't know, but if it's the cool spot aren't you getting the wrong readings for the fan.
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Old 08-30-2020, 08:25 PM   #3
Jack E/NJ
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Default Re: Thread - I screwed up

>>>3/5NPT or some such>>>


No such. Better check with the shop which NPT fitting they installed. Jack E/NJ
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Old 08-30-2020, 09:06 PM   #4
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Default Re: Thread - I screwed up

a thread pitch gauge would be best, they are cheap, you will use it again. if not, grab some stuff and try to thread it in there! most likely 1/8" pipe thread, like a drain petcock, or 1/4 " pipe, like an air tool fitting. just try a few things, with your fingers, no wrench, dont wreck it, and figger out what size you have
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Old 08-30-2020, 09:40 PM   #5
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Default Re: Thread - I screwed up

A suggestion: When you wire up your fan I would recommend that you consider including a toggle switch somewhere in the circuit to activate the fan in the event that the sensor fails. This happened to me on a road trip and I had to jury rig a wire to keep the fan on to get back home.
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Old 08-31-2020, 06:12 AM   #6
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Originally Posted by paul2748 View Post
Is the bottom of the radiator the cool spot or the hot spot. I don't know, but if it's the cool spot aren't you getting the wrong readings for the fan.
At the bottom, the water has already been cooled by making it's pass through the radiator. You need the fan when the water is getting TOO warm, which will be up top where it is exiting the engine, headed toward the radiator at it's warmest temp. You might want to make sure the bung is mounted LOW on the top tank, down close to the core, in case your radiator system likes to keep the water low in the top tank. I think I would also mount it near the RIGHT (Passenger) side inlet, because most flatheads like to run a few degrees warmer on the right side than on the left. But WTH do I know? DD
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Old 08-31-2020, 06:24 AM   #7
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Default Re: Thread - I screwed up

why not use the senser probe that comes with a thermostat then you can dial in the
temp the fan comes on. With the thermo switch your kind of stuck with its setting.
With the probe you stick it right through the radiator fins quick easy. And yes bottom
is cool and the top is hot maybe half way up for the sensor.
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Old 08-31-2020, 08:25 AM   #8
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Quote:
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why not use the senser probe that comes with a thermostat then you can dial in the
temp the fan comes on. With the thermo switch your kind of stuck with its setting.
With the probe you stick it right through the radiator fins quick easy. And yes bottom
is cool and the top is hot maybe half way up for the sensor.
Agree with big job. Figure out your "thread" mystery with a thread gauge...very handy tool to have for lots of reasons, and plug that bung. Then go with the sensor probe stick that can come with the thermo fan kit...eg. Hayden. This gives you the flexibility to place it at the best place in the radiator core.

Also agree with the toggle switch override. Have experienced a couple of thermo switch failures...and mine always failed in the "off" position!
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Old 08-31-2020, 08:48 AM   #9
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Default Re: Thread - I screwed up

Drain petcocks are normally 1/4 npt. Does the drain petcock fit in the new bung?
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Old 08-31-2020, 08:56 AM   #10
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Default Re: Thread - I screwed up

Here's an idea.
https://www.youtube.com/watch?v=NVysqXm81aw

Years ago I installed an electric fan that came with a thermostatic sensor switch that could easily be attached to the radiator and also controlled the temp. at which the fan came on. There was also a manual switch under the dash to override the sensor.

Any reason you can't plug your fitting at the bottom (wrong location) and just install a sensor that mounts on the radiator and can be controlled with a manual switch if desired?

Last edited by 19Fordy; 08-31-2020 at 09:03 AM.
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Old 08-31-2020, 09:03 AM   #11
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Default Re: Thread - I screwed up

mines an early girl with one sender so ran the thermo switch of the other head gauge shows one side and can tell when fans cut in so know what the others doing Thermo switch is a grounding type so just piggy backed a ground wire thru a on/off switch for manual control
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Old 09-07-2020, 03:44 AM   #12
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Drain petcocks are normally 1/4 npt. Does the drain petcock fit in the new bung?
My 1/4 npt sensor came today and fits nice, thanks for helping with the thread numbers.

While I'm in the minority here regarding sensor location, however I'm quite convinced I'm correct. The contra opinions caused me to think about it. Radiator cooling happens from the fan OR from car speed OR both, even depending upon outside air temperature.

The radiator must provide cooling of the water which enters at the top and exits at the bottom. At highway speeds on a cool day moving air provides adequate radiator cooling and the electric fan just isn't needed. Placing the sensor at the outlet of the radiator works properly for that condition. Placing the sensor where water is always hot doesn't cover the high speed cool day situation.

I will report results once I get the car on the road with it's new engine.
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Old 09-07-2020, 03:50 AM   #13
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Default Re: Thread - I screwed up

.

Paul....Is it more important for the fan to cool HOT water, or to cool water that has already been cooled after going through the radiator? Just curious! DD
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Old 09-07-2020, 06:10 AM   #14
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“Placing the sensor where water is always hot doesn't cover the high speed cool day situation.“ If your traveling at road speed on a cool day, the motor won’t get the water hot enough to trigger the fan sensor anyway. But, on a hot day in traffic the sensor will trigger the fan and start cooling the water sooner.......Mark
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Old 09-07-2020, 10:51 AM   #15
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Default Re: Thread - I screwed up

This is from the Speedway site " Make sure the fan switch is mounted in the manifold or radiator tank so that the bulb is submerged in the HOT engine coolant."
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Old 09-09-2020, 09:04 AM   #16
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Default Re: Thread - I screwed up

we seem to be missing something what temp is the sender and what is its range yes normal postition is below the thermostat and setting reflects this around 195 on and 185 off with 175/180 thermostat however if the switch was low enough in temp range it could be set at the rad outlet /waterpump inlet some jap engines do this and it is usualy done where the thermostat is in the lower hose junction [landcruisers come to mind ]
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Old 09-15-2020, 06:19 AM   #17
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.
Paul....Is it more important for the fan to cool HOT water, or to cool water that has already been cooled after going through the radiator? Just curious! DD
Hot water doesn't get cooled by the radiator UNLESS cool air flows through the radiator fins cools the water flowing through the radiator.

What we are discussing is the source of the air flowing through the radiator fins, how to control it when a greater flow of air is needed.

So, Coup,... my answer to your important question: ... it is NOT important to cool water that has already been cooled. But how can that happen that hot water was already cooled? Hot water won't get cooled by the radiator simply because the radiator says "Cool It". If it flows through the radiator without air flow through the radiator fins, hot water entering WILL STAY HOT on exit.

I think the water cooling concept muddles our thinking because the dash temp gauge monitors temperature of water leaving the engine. As well it should. Plus the standard fan is a permanent fixture, always providing air flow.

One must think of the radiator as a device capable of cooling water if and only if, air is made to flow through the fins, either with car speed or a fan. Come to think, perhaps throttle control could be added to a heat sensor. But officer, the car engine was simply cooling itself.
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Old 09-15-2020, 06:37 AM   #18
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Just read an article in current HOT ROD magazine on this topic. Apparently new cars have a temperature sensor at the inlet to the water pump and attempt to maintain 200-220F for best coolant results.

Water pump inlet is the same as lower radiator tank.

Done please...I'm 2 weeks away from engine install in my restomod Merc. That's where my head is at. Restomod is perhaps a mis-lable but the 286 flathead is reputed to be 200 hp. A stroker and pretty.
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Old 09-15-2020, 04:46 PM   #19
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Quote:
Originally Posted by V8COOPMAN View Post
.

Paul....Is it more important for the fan to cool HOT water, or to cool water that has already been cooled after going through the radiator? Just curious! DD
Quote:
Originally Posted by Paul Bennett View Post
Hot water doesn't get cooled by the radiator UNLESS cool air flows through the radiator fins cools the water flowing through the radiator.

What we are discussing is the source of the air flowing through the radiator fins, how to control it when a greater flow of air is needed.

So, Coup,... my answer to your important question: ... it is NOT important to cool water that has already been cooled. But how can that happen that hot water was already cooled? Hot water won't get cooled by the radiator simply because the radiator says "Cool It". If it flows through the radiator without air flow through the radiator fins, hot water entering WILL STAY HOT on exit.

I think the water cooling concept muddles our thinking because the dash temp gauge monitors temperature of water leaving the engine. As well it should. Plus the standard fan is a permanent fixture, always providing air flow.

One must think of the radiator as a device capable of cooling water if and only if, air is made to flow through the fins, either with car speed or a fan. Come to think, perhaps throttle control could be added to a heat sensor. But officer, the car engine was simply cooling itself.
If you want to 'play' with words, that's fine...re-READ my question in post #13. Implication is clearly that FAN is 'cooling' (OPERATING)! My 'meaning' was that it seems to make more sense (to ME) to start the fan running when it senses that the water is WARMEST (at TOP tank), so that when the fan DOES come on, it will begin removing heat from the warmest water as it flows through the radiator. If the warmest water causes the fan to BEGIN operating AFTER it arrives in the bottom tank, that ALREADY-HOT water will have missed the opportunity to be cooled during that pass through the radiator, and will begin it's cooling pass through the engine to become even HOTTER. Fini! DD
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Old 09-15-2020, 07:14 PM   #20
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Originally Posted by V8COOPMAN View Post
it seems to make more sense (to ME) to start the fan running when it senses that the water is WARMEST (at TOP tank), so that when the fan DOES come on, it will begin removing heat from the warmest water as it flows through the radiator. If the warmest water causes the fan to BEGIN operating AFTER it arrives in the bottom tank, that ALREADY-HOT water will have missed the opportunity to be cooled during that pass through the radiator, and will begin it's cooling pass through the engine to become even HOTTER.
After 6 rereads I simply don't understand what you are trying to say. Can you rephrase it all? I'm trying to understand what may be an important concept.


Read this pertinent article in Hot Rod...
https://www.hotrod.com/articles/tech...itch-location/
It would seem that car manufacturers don't agree on location any more than we do. However I seek an understanding.

Last edited by Paul Bennett; 09-15-2020 at 10:18 PM.
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