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Discussion Starter #1
I'm seriously considering pulling the trigger soon on an AC kit for my 65 289. Before I do that I want to make sure my Mustang will be able to keep cool in traffic during the summer. So far I've done the following:

New Radiator (American Eagle 2 row aluminum)
Fan shroud
6 Blade fan
new water pump and hoses.

My main concern is the stock temp gauge, its all over the place and doesnt give me an accurate read. As of now the car runs great and coolant never spills out, but I would love to add an aftermarket mechanical gauge for better piece of mind. The issue I'm running into is I don't have an extra water jacket to add a second gauge. I've looked into the Thermostat housing with an inlet but have been told it does not give an accurate reading. I've also tried replacing the stock sender with a motorcraft unit but the reading is still way too high to be correct. Lastly every aftermarket gauge I've looked at has a sender that is too big to fit in the stock location and hits the distributor....

I was thinking of perhaps plugging the heater outlet on the water pump, then removing the 90 degree fitting where the heater hose goes on the intake manifold and placing an aftermarket gauge there. I could then run the aftermarket gauge along with the stock and see what the temp actually is compared to what the stock gauge is reading. Does this sound like something that could work?
 

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If you want to install an aftermarket gauge, you can use the thermostat housing with the port in it. But first you will need to drill a 1/8" hole in the thermostat flange so that a small amount of coolant can bypass the thermostat. There are also thermostats available with the hole already drilled. The temp sender in the thermostat housing will actually give you a very good indication of how hot the engine is. However, it may not by quite as quick as if the sender were located in the regular position, the small hole will allow the heated coolant to reach the sender a little quicker but will not affect cooling. I usually use the thermostat port for a sender for an electric fan, but it will also work for the temp gauge.

Most water pumps use pressed in bungs for the heater connection. If you remove the bung there is nothing to thread in a fitting to, unless you tap the hole using a pipe thread tap. The exception to this is the Edelbrock Victor water pump which uses threaded bungs to attach the heater hose. There may be others but I know for sure the Victor water pumps do this. The only problem is the Edel Victor pumps are expensive, over $200 @ Summit.
 

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Move the original sender to the Thermostat housing and the Autometer sender to the stock location. Since the stock sender isn't exactly precise it matters little. I did something similar on my 82, moving the stock sender to a jacket access bung on the rear of my manifold. The reading changed a bit from the stock location but the Autometer sender had to have priority. I hate dead gauges so I'm happy the stock gauge is still getting a signal but I only ever look at the Autometer. In my 65 I replaced the whole gauge cluster and I run at a constant 180 with AC on. I also went with a 6 blade fan and your setup sound similar.
 
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Shoot the radiator, top and bottom. That will show you inlet temps and exit temps.
 

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1966 Mustang Fastback
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You can just shoot intake behind the thermostat near where the temp sender is installed. This usually provides better surface for the IR gun and there won't be air in that location like at the top of the radiator. IR guns return more accurate results if you shoot against a flat, rough surface.
 

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Don't point the ir gun at shiny bare aluminum surfaces. It will give a bogus reading. It is calibrated to work on rough or painted surfaces. Upper radiator hose can give a good reading. Also the area that the gun takes an average reading over varies with how far away you take the reading. The area is waaaay bigger than the laser spot.
 

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67 coupe, 69 Sportsroof, 86 hatchback
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Little impractical to use while driving on the freeway I would think.
 

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My gauge works, but I use my IR gun to establish actual temps with what the gauge is displaying. On my gauge right in the middle is 175-180. With A/C on the gauge moves up slighty and IR gun reading is 185-190.

I starting using it after I installed my new C4 to check the temp on the oil pan.
 

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That was my thought as well, whatever the temp is while idling in the driveway isn't going to mean much when he's driving and the A/C is running.
Well, obviously. But he HAS a temp gauge, what he needs to know is what's the proper indication when operating normally. Unless the thermostat is faulty, it will operate at a steady reading, he just needs to be sure what "normal" looks like.
 

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200* is 200* whether the car is sitting still or going down the freeway at 70 mph. What's the difference?
 

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Discussion Starter #15
Thanks for all the replies and advice. I think having an IR gun and monitoring the temps that way is a great idea and I'll probably get one down the road. For now though I'm going to try ToddMcF2002's idea and see what my temp's look like with that.

Also, I was looking around autometer's website and saw this:
FITTING, ADAPTER, RADIATOR HOSE, 1" TO 1.25", 1/8" NPTF FEMALE, ALUMINUM

Maybe this could also be an option to adding a second gauge?
 

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Thanks for all the replies and advice. I think having an IR gun and monitoring the temps that way is a great idea and I'll probably get one down the road. For now though I'm going to try ToddMcF2002's idea and see what my temp's look like with that.

Also, I was looking around autometer's website and saw this:
FITTING, ADAPTER, RADIATOR HOSE, 1" TO 1.25", 1/8" NPTF FEMALE, ALUMINUM

Maybe this could also be an option to adding a second gauge?
That's an expensive way to add a second sending unit. Isn't there some place on the intake manifold to drill and tap another hole for a second sending unit? Post a photo of the forward part of the manifold.
 

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67 coupe, 69 Sportsroof, 86 hatchback
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200* is 200* whether the car is sitting still or going down the freeway at 70 mph. What's the difference?
Pretty big difference. Does the car run hot only at freeway speeds? That indicates a water flow issue or something like the lower radiator hose collapsing. Runs hot only in stop and go traffic? Then likely inadequate fan/air flow issues. Examples of conditions where being able to tell that your car's temperature is spiking only under certain conditions can point you towards the cause. Basically exactly why you want to have a temperature gauge versus a warning light to start with.
 

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Discussion Starter #19
This weekend I was able to install an auto meter temp gauge and finally see what temperatures I'm running. While I was initially happy with the readings they began to rise steadily while just sitting in the drive way idling. After about 30 minutes the temp reached about 210 and the car began to idle choppy struggling to stay on. I revved it a few times and the temp dropped a bit but soon began to rise again. It was late in the evening and not hot at all. I then took the car out for a spin and after a few minutes the temp dropped to about 150-160. It pretty much stayed in that range the whole time I was driving and performed great. When I got home I let it sit in park and after 30 minutes the same thing happened again.

As first mentioned, I want to install AC on the car but with these symptoms it doesn't seem it will be worthwhile especially in summer traffic which will have me idling for at least an hour or more. Im a little at a loss on what to check or do next as Ive already replaced the essentials...

180 Thermostat
2 Row 1 inch Aluminum Radiator (American Eagle)
16 lb radiator Cap
New Water Pump
New Scott Drake Silicon Hoses
6 Blade Fan
Fan Shroud
 

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I know you installed a new W/P, but you may need one that is designed for high flow. They have a slightly different pump impeller design that will move much more water than the stock design pump.

You can also block off any unused holes in the rad support, and insure that the air is not trying to bypass the radiator by flowing over the top of it. The incoming air will take the path of least resistance, and that is usually not through the radiator core. You might turn up your idle a little also to get the water flowing.
 
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