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Discussion Starter · #1 ·
I have a 1966 Mustang with 289 engine with no AC. I recently replaced my water pump as it had a small leak. Ever since my car has been overheating. I then replaced the 180 F T stat. While replacing I noticed that the old thermostat was stuck open so I was happy to have replaced it. It still have over heating problems. I then raised the car on ramps and tried to burp the cooling system. I then took it for another drive. I drove about 20 km and It started to over heat again. I decide to take my car to Jiffy lube so that they could flush out my coolant and pressurize my cooling system. I thought maybe there was air in my system. That didn't work either. I took temperature readings with my laser temperature gun. The rad was hot and gurgling and coolant was coming out of the over flow hose. I don't have a coolant reservoir. Perhaps it was overfilled at Jiffy lube. The temperature readings were... Top hose 200 F, the bottom hose 175 F, Water pump housing 220 f, Thermostat housing 224, engine block close to thermostat sensor 234 F. I took off my upper rad hose to see if I didn't put the thermostat backwards by mistake. It was installed correctly so that isn't my problem unless it's defective. When I leave my car parked over night I do have a small leak. About 1 1/2" round. It's directly under the bottom rad hose. Unfortunately I can't see where it's coming from. Today I will clean up engine bay to remove all the coolant spills in the engine bay just to make sure. I'll also take a closer look for leaks. Any other suggestions?
 

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175* seems hot for the lower radiator hose. Can you feel cold spots on the radiator with your hand, or find them with the temp gun? Cold spots means clogged tubes. How did the coollant and passages look when you pulled the water pump? Good luck
 

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Discussion Starter · #3 ·
The passages looked good. I did things differently today. I didn't drive the car. I just let it run in garage for over 30 minutes. Here's what I did and the temperature measurements I obtained. I turned on the heater and kept car running without radiator cap with a baking thermostat in it. here are the temp readings

-coolant at radiator with baking thermostat 201 F
-top hose 147 F
-bottom hose 118 F
-engine block 178 F
-Thermostat housing 158 F
-Water pump housing 179 F
For the radiator. I took temp measurement on top of rad. Left side closet to top rad hose 203 F, Middle of rad 199 F and right side where radiator cap is 185F.
 

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To recap.
Car was not overheating but had a leak in the water pump.
Replace water pump.
Now have overheating.

What do you think went wrong?
 

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When do you have your "overheating problem"? If you're tooling down the highway is it running hot, when stopped, idling is it running hot or all the time? Did you move the distributor at all when you replaced the WP? Did you unhook the vacuum advance hose and not reconnect it?
 

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Be more specific on the replacement parts. What water pump did you install? What coolant? Same as before? Ratio?
What thermostat? Btw, it is good practice to test the thermostat before installing. Just throw them in a pot with water and heat it up on the stove. Check if it opens and closes as expected. Drilling a small hole at the 12 o’clock position helps getting air out. Some thermostat have this already.

Since your car is fine at idle it points into the direction of a flow issue and since you just replaced the pump this would be my candidate.


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A similar thing happened to me with my '69 Cougar many years ago. When I replaced the water pump, I flushed the cooling system. This dislodged of bunch of gunk which clogged the radiator and caused the engine to run hot and eventually overheat. I had to have the radiator taken apart for a "rod out" get out all the gunk. This may have happed to your radiator during the water pump replacement.
 

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Discussion Starter · #8 ·
When do you have your "overheating problem"? If you're tooling down the highway is it running hot, when stopped, idling is it running hot or all the time? Did you move the distributor at all when you replaced the WP? Did you unhook the vacuum advance hose and not reconnect it?
The problem just started so I haven't done much testing. It seams like it's overheating when driving. Today it didn't overheat at idle when parked in my garage. Two days ago, I drove 21 km "17 minutes" 80% of that was Hwy. I drove to Jiffy lube to have coolant flushed. When I got to city driving it was getting hot. I only drove about 3 km in town, It was still climbing and gauge needle was touching the "P" on my dash. When driving back home after coolant flush, it looked like it was running cool. Then the last 4 km it ran hot again. This morning I just ran it in my garage for half an hour or so and it didn't overheat. My temp measurement are in my previous post. First post shows high temp when driving and post #3 show temp readings which seams to be normal when it was tested in my garage. Perhaps with the rad cap off some air came out. I haven't drove it today because of rain. I'll take it out for another test drive tomorrow but not confident it is fixed. The vacuum advance hose is connected to the front of carburetor. There's just a rubber hose. No electrical wires are connected to canister. I'm assuming that's normal?
 

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Discussion Starter · #9 ·
To recap.
Car was not overheating but had a leak in the water pump.
Replace water pump.
Now have overheating.

What do you think went wrong?
Yes I replaced the water pump. It wasn't overheating with the old water pump. I then replaced thermostat. The old T stat was stuck open.
 

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Discussion Starter · #10 ·
A similar thing happened to me with my '69 Cougar many years ago. When I replaced the water pump, I flushed the cooling system. This dislodged of bunch of gunk which clogged the radiator and caused the engine to run hot and eventually overheat. I had to have the radiator taken apart for a "rod out" get out all the gunk. This may have happed to your radiator during the water pump replacement.
Thanks for the advice.
 

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Discussion Starter · #11 ·
Be more specific on the replacement parts. What water pump did you install? What coolant? Same as before? Ratio?
What thermostat? Btw, it is good practice to test the thermostat before installing. Just throw them in a pot with water and heat it up on the stove. Check if it opens and closes as expected. Drilling a small hole at the 12 o’clock position helps getting air out. Some thermostat have this already.

Since your car is fine at idle it points into the direction of a flow issue and since you just replaced the pump this would be my candidate.


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Thank you for the advice
 

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Discussion Starter · #13 ·
I ran my car with rad cap off for 1/2 an hour to see if that would get air out of my cooling system. I took it out twice with no overheating issues. Thanks you to everyone for the help.
 

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On a side note. I took a seminar on doing IR scanning on electrical equipment. Two things to know. First you're not reading at the red dot but rather a whole field. It's cone shaped and the surface field becomes larger as the distance increases so there is a possibility you may be reading something else. The other item. Not all surfaces reflect the same way. Different colors and textures reflect differently. You can have two surfaces the exact same temperature but the IR gun will read them at different temperatures. The best thing to do if possible is to carry some electrical tape, put a piece on what you want to read and compare. This way you'll be reading off the same color and texture. I know you can't do this all the time but when you can, it helps.

I feel however what you were reading with temperatures is fairly accurate and not the problem. I'm going to say it's the pump itself. If it's a rebuilt stock or a new stock replacement I'll bet it's just a cheap inefficient impeller. A one size fits all. I'd suggest buying a good quality pump such as something on the line of a Edelbrock if it's a driver and not a judged show car. I bought a PRW knock off of a Edelbrock by accident. While I was furious I was the victim of a bate and switch, it was all my fault. Anyway I own it now and it actually works quite well. My car always runs cool, meaning it never overheats even with less then ideal fan set up.
 

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Discussion Starter · #15 ·
Thanks Tom. try the tape and take a reading a close range. I'm also using my dash gauge and temp is showing normal readings. Should I be worried about my gauge? My can isn't a daily driver. I bought my water pump from a local supplier. I have no idea what brand it is. I should of got a edelbrock pump but didn't know any better at the time. I will definitely consider switching.
 

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Thanks Tom. try the tape and take a reading a close range. I'm also using my dash gauge and temp is showing normal readings. Should I be worried about my gauge? My can isn't a daily driver. I bought my water pump from a local supplier. I have no idea what brand it is. I should of got a edelbrock pump but didn't know any better at the time. I will definitely consider switching.
The tape trick and IR stuff was more of a general comment and tip not that you did something wrong at all. But yeah, these cars are no longer people's common everyday vehicle. I think a lot of stock replacement parts for our Mustangs are more as a place holder rather then a serious service type part. At least with aftermarket performance parts, they're made to work and solve a problem. Unfortunately at a cost.
 

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I tried a Edelbrock pump, and went back to a flowkooler pump on mine.
 
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