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I am a newb here. After 40 years of dreaming, I am finally a vintage Mustang owner. I recently purchased a nearly all-stock 66 coupe 289 2bbl C4.

On one of our 1st outings with her, we were stuck in a VERY long line to get into a drive-in theater and I realized the temp gauge was moving up and oil pressure seemed to be falling, when it continued, I pulled out of line and gave up on the movie. Once I was moving again, all was well in short order. When I got home, a little googling told me that I was not alone and this is a pretty common issue for a stock Mustang. I probably wouldn't worry too much about it except that I have plans for a large classic cruise and parade and fear this will be an issue.

The remedies and opinions are plentiful and I am wondering if there are some of you that can help me sort through what is the best course of action to take. I do have an interest in keeping things reasonably original but am open to making changes for functionality/practicality. So here it goes:
  1. New radiator? If so, Aluminum? Brand? How many rows? (it seems that more than 2 rows requires other modifications)
  2. Thermostat? 192, 180 or 160?
  3. New fan? If so, how many blades? Flex Fan?
  4. Fan shroud?
  5. Coolant additives?
  6. "It's a classic and you should be horse-whipped for changing anything!"
Any insight would be appreciated!

Thanks.
 

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#1 only make one change at a time. Otherwise you won’t know what helped & what didn’t.

#2 install an AutoMeter mechanical temperature gauge under dash. The factory gauge and sending unit is not a reliable indication of overheating. Summit has them

#3 get the stock 190 /195 thermostat. Buy a good one, they are inexpensive. Your car was designed to operate at 195 - 220 F. The stock thermostat doesn’t even fully open until 212 F.

#4 before buying any other parts flush the radiator and engine block. Scale and rust buildup will hurt your cooling efficiency.

#5 your car can have a temp of 225-235 F in traffic without hurting anything. Just so the temp comes down to the 220’s and stays there when moving you’ll be OK.

#6 if the above steps prove fruitless and you really are overheating beyond the parameters listed above, then first get a shroud and clutch fan. There are many recent topics on which one to get. Do a search to find out the right parts.

#7 water wetter + distilled water will reduce temperature 10-15 degrees F in most cases vs 50/50 water / antifreeze mix

#8 a FlowKooler water pump has a fantastic impeller that can move the coolant better at rpm’s under 3,000. That can make a huge difference in cooling capacity.

Z
 

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My first step would be to get an aftermarket water temp gauge to plug in temporarily in place of the factory gauge - so you know exactly what temps you are hitting. 210*F is fine, 230*F is not. Hard to say with a factory gauge although it is a bit odd that your oil pressure would also be measurably declining at the same time.

Past that, your next course of action could be just throwing money at it and doing the whole cooling system, or do it step by step and try to identify the source of the problem. If you do the whole system at once, then your best bet will be a 2-core aluminum radiator (I use Northern, but there are many brands and most are great), a 7-blade clutch fan (unfortunately the 7-blade clutch fans are not reproduced, but they pop up on ebay sometimes) with Hayden fan clutch, a stock fan shroud, a 192*F thermostat, and a new water pump from a reputable brand (I had my original water pump rebuilt by a water pump rebuilder guy, as I could not find an aftermarket water pump with good bearings in it to save my life). That combination is what I run in my hopped-up 289 in Texas in summer and it never struggles to stay cool.

However, I would step back and try to be a little strategic about it first. My first step would be to flush out the entire system really well with a "citric flush", which will remove rust scale from the system. There are many threads posted here on techniques to do this. It may be that you just need to blow some rust out of the system. Past that point, I would look to the positioning of the fan next - you should have a fan shroud installed (and if you don't, install it) and it is worth checking to make sure that your fan is sitting the proper distance into the shroud, and also that you have a good-quality fan. Sorting that out is fairly cheap, which is why I would do that next. After that point, I would go for the radiator and test for blockages, damaged fins, etc., and replace or rod out if needed. A brass stock-style 3-row will work just as well as an aluminum 2-row, but IIRC the brass 3-row radiators have gotten expensive recently. Whatever floats your boat in that department.

Likely your thermostat is fine and doesn't need replacement if the car is operating normally at any other speed. Water pumps can and do go bad, but it is fairly uncommon and again something you would have noticed from other symptoms if it was an issue - but if your problem persists it may be worth pulling it to ensure the impeller isn't damaged (rusty or worn) which would impact its ability to move coolant.

That should be enough to get you well on the road to sorting out your issue!
 

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i would add a fan shroud 1st if you don't already have one, cheap and they work.
 

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1966 289 2V Coupe FMX Transmission 9-inch Axle
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Check this thread. It has part numbers from NPD for the fan and thermo clutch. I put the fan and thermo clutch, the shroud, and a 3 row radiator. Get the fan set right within the shroud and get the largest diameter fan that you can and still fit in the shroud. Usually 18" dia. shroud with a 17.25" dia. fan.
 

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Welcome to VMF. Already very good advices posted above. If you want to learn more about how to keep a vintage Mustang cool check out this serie of videos:

Starting from the basics all the way up to the coolant.
 

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Guy in the video above knows something about how engines work, but he is sadly misinformed on how heat transfer works, and he has no idea what the purpose of the thermostat is. It is NOT there to "slow" down your coolant flow so the radiator has more time to remove heat. The reason his car overheated with a 160F T-stat is the same reason it would overheat with any other T-stat: there's something wrong with the cooling system. The thermostat REGULATES engine temperature. Water going faster through the radiator IMPROVES heat transfer, and it also means water is going faster through the engine.

Regardless, use a 190F T-stat. Overheating at idle is usually cured by a better fan, a cleaner/bigger radiator, or a high flow water pump.

Wonder why there aren't more internet "experts" telling people to use a lower flow fan, so the air has more time to transfer heat out of the radiator? Same bogus principle as slowing down water flow so it spends more time in the radiator...SMH

MrFreeze
 
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I am a newb here. After 40 years of dreaming, I am finally a vintage Mustang owner. I recently purchased a nearly all-stock 66 coupe 289 2bbl C4.

On one of our 1st outings with her, we were stuck in a VERY long line to get into a drive-in theater and I realized the temp gauge was moving up and oil pressure seemed to be falling, when it continued, I pulled out of line and gave up on the movie. Once I was moving again, all was well in short order. When I got home, a little googling told me that I was not alone and this is a pretty common issue for a stock Mustang. I probably wouldn't worry too much about it except that I have plans for a large classic cruise and parade and fear this will be an issue.

The remedies and opinions are plentiful and I am wondering if there are some of you that can help me sort through what is the best course of action to take. I do have an interest in keeping things reasonably original but am open to making changes for functionality/practicality. So here it goes:
  1. New radiator? If so, Aluminum? Brand? How many rows? (it seems that more than 2 rows requires other modifications)
  2. Thermostat? 192, 180 or 160?
  3. New fan? If so, how many blades? Flex Fan?
  4. Fan shroud?
  5. Coolant additives?
  6. "It's a classic and you should be horse-whipped for changing anything!"
Any insight would be appreciated!

Thanks.
You want to know something, My car has NEVER had a shroud since the day way back in 1965 when it was born.
Start with a gauge to know the exact temperature it is running at,once you know that then and only then will you know if you have an actual issue . From there do a coolant (citrus) flush . 192/195 thermostat.
Also show us pictures of what you have now before jumping into changing things.
Unless of course you have unlimited money to spend in which case carry on down the path of replacing everything.
Also welcome to VMF and congrats on getting a car,I have had mine nearly 40 yrs.
 

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+ 1 to all the great advice. I'd add a radiator filter to the list. It'll protect the new radiator after the citric acid flushing.
 

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You may not even have a problem. Do #1 and #2 from zray's list before you do anything else and report back.

Also, the oil pressure will drop as the oil warms up and the engine rpm's are down. As soon as the rpm's go up, so does the pressure. If you want to really know what's happening, install a mechanical pressure gauge so you know the actual pressure.
 

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+ 1 to all the great advice. I'd add a radiator filter to the list. It'll protect the new radiator after the citric acid flushing.
The "foot" from an old leg of panty hose makes a good, cheap, disposable cooling system filter....as long as there are no runs or holes. I caution against going through SWMBO's dresser drawers looking for a good pair...
 
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