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1966 Mustang A-Code Coup, 289 V8 Automatic transmission
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Discussion Starter · #1 ·
Hey all - My 15 year old son and I are working through the mechanics of my his first car, and I am looking for advice on the cooling system.

First:
1966 Coup, A-code, 289 4bbl with AC and power steering. The fan is a six blade, belt driven, 17" diameter, and it sits about 3" away from the 2-row original-looking radiator core.

We live in Phoenix, and since it is currently winter, it is 72 degrees and sunny. We picked up the car about a month ago. It had been sitting in a warehouse in CA for 40 years. Nonetheless, it runs and drives, but we are working through some of the bugs that need to be worked out. The one we are currently working on is that it is overheating. We so far have replaced the temp sending unit (it was completely dead), flushed the block and radiator, installed a 180 deg thermostat (it was missing), replaced the radiator cap (13lb), and replaced the supply, return, and bypass hoses. We spent considerable time trying to make sure we purged the air out of the system after the flush, but I will be honest, I am only about 80% sure we got it all.

When we start the car from cold, it will run and idle for about 15 minutes before the temp gauge goes to about center. As I watch with the radiator cap off, I can see some flowing coolant after a while, but then there is an event point where it just guysers out of the cap. Probably 4-6" of fountain coming out of the fill hole. If I leave the cap on, the gauge will float up to about 80% to H, and then start coming back down to about 60%, then swing up to 85%, back to 65%... it kind of ratchets its way up to the top end of the gauge and then I shut it down. At that point, coolant is streaming out of the pressure relief hose.

A couple of things I figured out by reading through many of the posts... first - it does not have a fan shroud, and that appears to be a pretty big deal. So I went ahead and ordered one that is close to stock.

Second - I learned that taking temps with the ol' IR gun could prove handy, so we will be doing that part tomorrow. I plan to take reads at the thermostat housing, supply hose and return hose. I am hoping to figure out whether or not the radiator is actually removing any heat. Then I will do it again with the fan shroud on to see if I have any improvement. I will also use this data to see if the sending unit/gauge is reading correctly.

So here are my questions:
1) is it normal to get a guyser out of the radiator?
2) Are there any other points that I should be reading temperature?
3) I am pretty suspicious of the radiator being plugged up after sitting for 40 years, so assuming I need to replace it, should I go with a 2, 3, or 4 row? Does anyone have a specific recommendation for a Phoenix based car?
4) Knowing it will be blazing hot in a few months, and the car has Air Conditioning, should I plan to install an electric fan?

Thanks in advance for your insight!
 

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07 Mustang GT
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Idle speed maybe too high causing your geyser when the thermostat opens. If you're running a flex fan, it should be 1" from the radiator, or centered 1/2 in 1/2 out of the shroud. I would put an under dash mechanical temp gauge on it to see what your actual temps are.
 

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First thing I would do is ditch the old radiator and go aluminum. This single change fixed all my overheating issues. I added a flex fan without a shroud. All my troubles are behind me now.
 

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1966 Mustang A-Code Coup, 289 V8 Automatic transmission
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Discussion Starter · #4 ·
Ok - the aluminum radiator is a likely next step, but I want to diagnose a bit before I go down that path. How do I know if I have a flex fan? The idle sounds pretty normal… any chance it could be a plugged radiator?
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Firstly, don't go throwing money at what you think might be the problem.
Water coming out of the radiator without the cap on will almost always happen.
Get the IR gun and take temps before the thermostat, after the thermostat and top and bottom radiator hoses. If they fall within specs then you have a faulty temp sender on top of your intake manifold.
The fan is too far away from the back of the radiator, it needs to be no more than 1 inch away.

If temps are still too high, flush the radiator and even look at power flushing the engine block.

Start simple, it will be a process of elimination.
 

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1966 Mustang A-Code Coup, 289 V8 Automatic transmission
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Discussion Starter · #7 ·
OK - We took some temps this afternoon that I would like to share with you all... @Tony 64 Unfortunately I did not read your post closely enough, and only took readings after the thermostat, at the top hose, and at the bottom hose. But I think I have some good data to share and I am interested to hear what you all think.

The top section corelates the gauge readings with the temperature on the outlet side of the thermostat. The next section shows readings each minute for 17 minutes at the thermostat, the top hose, and the bottom hose.

The final section shows the temperature 1 miute after we shut off the engine.

Here is the interesting thing... The data shown here indicates that the coolant never got over 166 degrees, even though the gauge was at 100%. But after we shut off the engine, I pulled the air filter off and took a reading right at the sending unit and it was 220 degrees. then about a minute later, and after a little gurgling sound, I shot the thermostat outlet and upper hose again and they were way hotter. Thermostat housing was 220 degrees, and the top hose was 190. Bottom hose was still about 146. I am thinking stuck thermostat, but I am interested th hear anyone else's thoughts.

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1967 Mercury Cougar XR7
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I think your temp sender is a new one, and most of them are garbage. They do not read accurately, because nothing inside them works right. If you could find an original, it'd probably work great, and your mystery 'overheating' problem will be gone. =)

The temps you recorded all look just fine to me.
 

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OK - We took some temps this afternoon that I would like to share with you all... @Tony 64 Unfortunately I did not read your post closely enough, and only took readings after the thermostat, at the top hose, and at the bottom hose. But I think I have some good data to share and I am interested to hear what you all think.

The top section corelates the gauge readings with the temperature on the outlet side of the thermostat. The next section shows readings each minute for 17 minutes at the thermostat, the top hose, and the bottom hose.

The final section shows the temperature 1 miute after we shut off the engine.

Here is the interesting thing... The data shown here indicates that the coolant never got over 166 degrees, even though the gauge was at 100%. But after we shut off the engine, I pulled the air filter off and took a reading right at the sending unit and it was 220 degrees. then about a minute later, and after a little gurgling sound, I shot the thermostat outlet and upper hose again and they were way hotter. Thermostat housing was 220 degrees, and the top hose was 190. Bottom hose was still about 146. I am thinking stuck thermostat, but I am interested th hear anyone else's thoughts.

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Nice data!

180 degree is when the thermostat starts to open. It is the minimum operating temperature, not the maximum. Ideal running temperature is 200F. 210 is not overheating. 220F may not be either.

There needs to be head space in the top radiator tank (vertical flow type) when filled cold to allow for expansion. It's a significant volume, more than a pint but less than a quart. What I do is fill the upper tank over half way, install the cap, run the car down the road until it gets to normal operating temperature and let it spit out the excess. Then after it's cool, note the level in the tank. As long as all the passages at the bottom of the tank are covered, all is good.

Horizontal flow radiators use a surge tank positioned above the radiator. Similar deal- very little coolant in them when cold.

I recommend a multi-day chemical flush. Several off-the-shelf chemicals have instructions on their containers. You're flushing both the radiator and the engine.

Use distilled water and 50% anti-freeze.

No need for an aluminum, multi-row radiator on a stock motor. I run a big block 390, high compression, with its original two-row brass.

There is a chance you will still have problems sitting in summer traffic. If so, best to go with an electric cooling fan. That requires an oversized alternator and upgrades to the original wiring, so you're looking at a $500 or more bill if you do the work yourself.
 

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1966 Mustang A-Code Coup, 289 V8 Automatic transmission
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Discussion Starter · #11 ·
Hmmm… so you guys are thinking I may not have an overheating problem at all? Ok - but before I hang my hat on that I want to do the data check again. This time I want to read temp upstream and downstream of the thermostat to see if it is actually opening.

when I put the thermostat in, should the spring side be toward the engine, or toward the radiator?
 

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07 Mustang GT
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Hmmm… so you guys are thinking I may not have an overheating problem at all? Ok - but before I hang my hat on that I want to do the data check again. This time I want to read temp upstream and downstream of the thermostat to see if it is actually opening.

when I put the thermostat in, should the spring side be toward the engine, or toward the radiator?
There is a flow arrow on the thermostat.
 

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1966 Mustang A-Code Coup, 289 V8 Automatic transmission
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Discussion Starter · #13 ·
@07redstang - I did not find an arrow on the one I installed... I checked throoughly because I remember that from my high school days! But I think it is right - I put it spring side into the block. I just wanted to make sure.
 

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The spring side is where the brass module is, so that side faces the hot coolant in the block. Otherwise it would take longer to open.

Best thermostat to get is a Stant SuperStat.
 

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Hey all - My 15 year old son and I are working through the mechanics of my his first car, and I am looking for advice on the cooling system.
Just invest in a new alu radiator, either OEM style or 1 row larger. Then you might want to replace the WP. You can get a hi flow version for that engine. Electric fan isn't necessary, a good flex fan will work just fine. If the mustang is an automatic I would get the radiator without the tranny cooler instead id recommend installing a separate trans cooler. Keep the radiator for engine cooling only. Just my thoughts.
 
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