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Discussion Starter · #1 ·
So I notice my car overheats while driving... The weather is getting a bit hot and the car takes around 5 to 10 minutes to start overheating while driving open roads.

Before I try anything I want to hear your opinion as I have 0 experience with this cars.
The car is an 1966 with 289 3 speed auto, in theory (sellers word) it has a new thermostat and the water pump was changed not long ago. The fan looks new and has a shroud

I don't see any leaks on the ground, only something below the thermostat but nothing big.

Of course when it overheated it did spit some coolant
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The radiator looks like a cooper one, maybe original but I can see some type corrosion inside I think
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Is there a troubleshooting I should follow?

Thanks in advance
 

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1967 Mercury Cougar XR7
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There are a few things to look at, whenever it comes to cooling!

1) Was the cooling system clear full of fluid to begin with? With the original radiator, every inch of fins counts. Make sure it's all the way to the neck. It will probably burp a little out when it warms up, but that's just the way it is if you don't have a reservoir (and they didn't come with one from the factory.) Adding a catch can will reduce how often you have to check and see if your coolant is full, but it's not a big deal.

2) Is your timing set right? Too much timing will create higher-than-normal combustion temps, and can cause this. Oddly, running too retarded can also cause overheating, because of all the still-burning fuel going down your exhaust manifolds, and because your engine will be less efficient, requiring you to burn a lot more air and fuel to move down the road.

3) I can see that you have a shroud, but what kind of fan are you running? If it's a flex fan, those things do a lousy job. They are supposed to flatten out and conserve power at high RPMs. However, due to poor design, they mostly just make noise, thrash the air around, and steal power at all RPMs while doing a worse job than most stock fixed-blade fans. Doesn't sound true, but it really is.

4) How old is your radiator cap? Each pound of pressure in your cooling system will allow the temp to go higher without boiling. When they're old, sometimes they just won't hold any pressure at all, and your car will boil over at fairly low temps. This is a super cheap and easy fix, many times

5) Are your radiator hoses in good shape? It's common for the lower one to get so soft it collapses when you rev the engine. It goes without saying that this is detrimental to engine cooling.

and 6) Yep, could need to be flushed. Don't bother with a chemical flush at your local lube shop. Take it to a nearby actual radiator guy. They can hot tank your radiator, flush your block, and make sure it's going to be a lot more efficient.

A couple of other things to think about:

Don't put in a lower temp thermostat. Thermostats don't change the total amount of maximum cooling - they just determine what the max temp SHOULD be. It's your radiator and water pump that do all the work. If it's overheating significantly, whether your thermostat opens at 190 or 90 makes no difference except for how soon coolant starts to flow easily through the radiator. A low-temp thermostat will not let your oil get hot enough to boil away contaminants in the oil when weather gets cooler, and will cause sludge, rust, and bad things to happen in your engine.

If you added air conditioning, you may be overwhelming the factory radiator. Stock, the AC cars had a bigger radiator to begin with.

Depending on where you live, and the overall health of your old radiator, you might need a new one. The factory 18" radiator does pretty good, actually, and I drove mine (3 core brass) all over California in 117 degree heat. If yours needs to be replaced, I would recommend a factory 3 core. If you need to, you could go with an aluminum 2 core. As the tubes are wider on aluminum radiators, going to 3 core often introduces fitment problems. As air passes through so much surface area, it heats up to the point where the extra-thick radiators (4 core brass or 3 core aluminum) typically get very little benefit from the extra tubes. It's also harder for your fan to force air through them, which can cause problems while idling.

The very best radiator for these cars is probably the '69-70 24" big-block radiator, shroud, and thermo clutch fan, but as yours is an early Mustang, fitment would not be a simple matter! Hopefully you can just make your original one work fine.

Best wishes!
 

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07 Mustang GT
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Is it overheating or is the radiator puking coolant out the overflow because you overfilled it? There needs to be some head space in the radiator to allow for expansion of fluids. If its filled all the way to the top of the neck the coolant will muscle its way past the radiator cap and on to the ground like your picture shows.
 

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My original gauge on my 66' GT 289 4v Auto said it was running hot but I installed a autometer copper tube type water
temp gauge and it said it really wasn't as hot as the original gauge did.

Things I did trying to help;

What 07Redstang says was true for me as well, I had too much fluid in the radiator, it would always puke when parked then
it'd get too low on fluid and run hotter. I Prob need to install a catch can but hadn't done that yet.
So don't fill the radiator all the way to the top, keep it close to the cooling tubes that
you see in the fill hole for expansion room when hot.
I even tried that water wetter stuff but not sure it did anything.

I bumped to a 16lb rad cap (this helped)

Timing can cause issues, i've never really found a happy timing spot on my engine, I believe
it is around 12 to 14degrees advanced (I think im on 14deg right now) but i've tried more and less,
i'm thinking 12deg advance is where mine is happy. Planning on revisiting that soon.
(got a 268 comp cam, autolite 4v, Edelbrock aluminum intake, pertronix ignitor 2, hipo cast iron exhaust manifolds)
as I was trying to go back like a K engine but have since made some repairs/tweaks).

It's possible the auto trans fluid "could" be increasing your heat too, I've mulled adding
a extra cooler for the trans fluid to take the heat off the engine. Check the level and color and make sure the trans isn't overheating the radiator fluid.

Fixed a major vac leak on my hose to the transmission and the carb to intake (this helped make the engine run better big time).

I know if I run mine on the hiway at 70+ too long the heat increases to 212 -230 range and
takes a bit of running at 45mph to cool down. It can run funny at idle and doesn't like to restart easily when that hot.

I also think I replaced my stock rad with a new same type (2 core) should have went with
a desert cooler 4core but didnt at the time. In after thought I'm planning on going new
rad 3 or 4 core with electric fans but aint got there yet.

I've got the stock fan + fan shroud (the shroud helped) and I tried a aluminum flex fan with no results (but that was pre-shroud install).

Funny thing I just went thru all of this crap on my dad's 51' Ford Flathead V8 pickup last few weekends,
I had to solder/repair the radiator, installed new hoses & pipes, installed a fan shroud (never had one)
and it runs good without the electric fan now but I re-installed it for those "drive thru overheat situations".
I'ts got 2- 160' thermostats and it's been running around 180-190' on a pretty hot last weekend with no problems,
even left idling at less than 1000rpm it didnt creep like it did without the shroud.
(with no shroud it was 210-220+) So the shrouds defiantly help.

Hope any of this may help in your quest for coolness!

T
 

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1967 Mercury Cougar XR7
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Flex fans are the worst. Don't use one if you have a choice. Not only do they steal more power than most fixed-blade fans, but over time, the flexing of the metal fins causes fatigue. Shedding one of your fan blades when you're at high RPMs going down the road won't do your engine's waterpump any favors. The vibration is impressive, and so is the damage that flying guillotine will do to whatever it hits.

They are one of those innovations that "seemed like a good idea at the time..." right along with fix-a-flat, radiator stop-leak, and head gasket in a can.

You can use one, and it might sort of work, but it'll cause you trouble. Just get something better.
 

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There is nothing wrong with a quality flex fan and they do not rob as much power as you think. I've been using them for 50 years with no issues.
 

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There is nothing wrong with a quality flex fan and they do not rob as much power as you think. I've been using them for 50 years with no issues.
Having seen at least a dozen back-to-back dyno runs that showed less power, and probably 6 flex fan failures during the years, all I can say is that my experience doesn't match yours on this one, Redstang!

I very much respect your opinions and advice, so don't take this to mean that I'm 'calling you out' over a dumb fan. :geek:

It's worth noting, they don't usually fail right away. Most of them take a while for the flexing of the fins to cause metal fatigue.
 

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Discussion Starter · #8 ·
Thank you guys for those complete replies, I really appreciate you taking time to help a newb to these cars...

I am pretty sure it's overheating, not only the gauge went to H I could hear the pressure on the radiator after I turn it off but I am no expert.
Here's a photo of my fan
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and a photo of my radiator cap:
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I went to check the ignition timing and it's poiting to 12º degrees if I am not mistaken.

By the way I went to the garage that fixes the cars of the company I work for and told the chief mechanic that I bought a 66 Mustang and to my surprise they did rebuild an engine for classic mustang 2 years ago (this rare cause it's in France)
I told him about overheating and he said "I bet 100 it's the radiator fault, I recommend replacing it with a modern aluminum one"

Is there a way to install a sensor to read the actual temperature in numbers of the engine?
 

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Thank you guys for those complete replies, I really appreciate you taking time to help a newb to these cars...

I am pretty sure it's overheating, not only the gauge went to H I could hear the pressure on the radiator after I turn it off but I am no expert.
Here's a photo of my fan
View attachment 780935
and a photo of my radiator cap:
View attachment 780936

I went to check the ignition timing and it's poiting to 12º degrees if I am not mistaken.

By the way I went to the garage that fixes the cars of the company I work for and told the chief mechanic that I bought a 66 Mustang and to my surprise they did rebuild an engine for classic mustang 2 years ago (this rare cause it's in France)
I told him about overheating and he said "I bet 100 it's the radiator fault, I recommend replacing it with a modern aluminum one"

Is there a way to install a sensor to read the actual temperature in numbers of the engine?
There are a lot of infrared thermometers that you can just point at things, and it will tell you the temperature.

The neck of the intake is a good place to check, because that should be the hottest water returning to the radiator. If it's reading significantly over 212 F, that's probably too warm. Under pressure, it can go a bit higher before boiling, but 220-230 and that's going to cause trouble. The thermostat should be open at 190, so it shouldn't be too much higher than that ideally.

IMHO, don't go with an aluminum radiator. The brass ones last longer, and do as well or better. A good three core brass radiator is the way to go. You can't just "look" at a radiator cap to see if it's right. Your shroud looks good, but that fan is not the best. Flex fans don't move air as well as the factory ones, and a good clutch fan will not only do a better job, but rob a lot less horsepower too.

Is your distributor set up with vacuum advance?
 

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The brass radiator on my TBird is the original and it works fine.

Looking at the first picture in the OP, that fluid looks very green. It should be at least 50% water. Water conducts heat better than antifreeze. You can buy a simple tester for a few bucks, or francs.

Second as was mentioned the radiator needs headspace. Again referring to the first picture the fluid looks high.

If these fixes don't work than I suggest draining and flushing with a good multi-day cleaner. These work while running the engine 100-200 miles to dissolve all the junk in the radiator and engine block. Let cool, drain, fill with clear water, run till hot, let cool, drain, repeat until the water comes out clear. It may take 5 or more cycles.
 

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A radiator doesnt "need" headspace, but it'll make it, if there's not enough. You can fill it to the top, and it will just burp out the 'extra' - though with pets around that can be bad. Better to be 'too full' than not full enough when it comes to cooling!
 

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Discussion Starter · #12 ·
So, I have been busy with other stuff and I finally got to work on this issue.
What I did:

Flushed the radiator 3 times, everytime I fill it with distilled water. The coolant always came green, no sign of rust or contamination. However some small particles came out so I am going to install a coolant filter.

I got a great deal on the Aluminum 3 core rad with electric fan, shroud and cables. However I need to buy a new fan because the one that came with is to fat and doest fit the car (see photo).

I am going to change all hoses, belt, thermostat housing and I also plan on cleaning the water pump and paint it.

Questions:

1- The thermostat looks new (seller was not lying) but it says 160F, isn't that to low to open? The fan switch is set to 185F

2- Do you guys know a good eletric fan I should buy? What type of CFM value should I look for?

3- I also bought a catch can, do I need to change the radiator cap for that?

Any other information will be useful, thank you
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192 is stock, and works much better. 160 will not let your oil get to proper temp, and will allow water and other contaminants in the crankcase to stay there, rust, corrode, and make mayonnaise of your oil.

My favorite fan setup is probably a thermal clutch and fixed blade fan (not flex) with a good shroud. There are a lot of good factory fans available in junkyards, but finding one that's the right size is key. Additionally, the stock alternator in one of these Mustangs is not going to keep up very well, as all of the 'good ones' draw a lot of amps! If you upgrade the alternator, then you have another quandry: stock V-belts don't have enough grip to keep a higher amp alternator from squealing. If you plan to go EFI, then it makes good sense to do all of this and convert to serpentine, but this 'simple' change kind of snowballs, as you can see.

Virtually all modern caps will be able to use a catch can, so that's no problem. If it has the little silver tab in the middle like this pic, you're good:
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That's the part that allows it to suck the coolant back in through the overflow hose.
 

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You said you flushed the radiator 3 times, Is this because it was clogged with scale and rust?
If you are getting particles in the coolant then I highly recommend that you powerflush the block before you go driving it with new parts.
 

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Discussion Starter · #15 ·
You said you flushed the radiator 3 times, Is this because it was clogged with scale and rust?
If you are getting particles in the coolant then I highly recommend that you powerflush the block before you go driving it with new parts.
I flushed because the coolant was a very strong green, I was afraid the mixture wasn't that good.
Yes, I'll power flush ther block now with hot water with hopes of cleaning everything.

Virtually all modern caps will be able to use a catch can, so that's no problem. If it has the little silver tab in the middle like this pic, you're good:
That's the part that allows it to suck the coolant back in through the overflow hose.
What about the numbers on the cap? The new radiator the cap says 0.9
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I am going to change more than the thermostat. The 2 hoses from the radiator are probably 20 years old and I also find the lower hose did not had a spring that it should have.

I decided to remove the water pump to clean it and paint it... I was only able to remove the bypass hose the other 2 were completely stuck... The one that goes to the heater core even broke as I pulled.
Once I got the pump out of the engine... Oh my god, there was even a rock forming up in one the connections to the engine.

And look at the state of the water pump interior walls....
Wood Automotive tire Tree Trunk Circle
I guess somebody used tap water before.... disgusting. I guess I also have to buy a new water pump and since I have to replace the heater hose, i'll change the heater core as well.

What a snow ball.
 

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Holy cow. That's pretty nasty! I don't even know what the .9 means. .9 bar? Never seen a cap like that one. But nonetheless, if you take it off and look at the underside, you will be able to tell if it can siphon coolant back into the system or not. The "Old style" caps just have one big spring and a stopper that lets steam blow off when pressure is too high. Newer ones have a secondary feature there in the middle that can be sucked inward.

Hang in there, X_Splinter!
 

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If your radiator hose looks like that then get ready for what is about to come out of your block when you power flush it.
No need for hot water, just a good sized compressor and a garden hose. Make sure that you disconnect all hoses including the heater hoses.
Power flush through as many different holes as you can so all the flakes won't get caught when the water goes in one direction.
 
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