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Discussion Starter · #1 ·
Hello everyone. I'm new here and hope I'll be accepted since I don't own a Mustang. I own a '65 Shelby Cobra replica that has a first gen Coyote engine in it. I'm performing a coolant change. The type of radiator that's in this car does not have a top fill feature. Coolant is filled via an expansion tank that sits in front of the motor. I drained my radiator and filled with water to run through the system to flush the old coolant out. I then drained the radiator again and filled with Motorcraft yellow 50/50 pre-mix. I'm now being told that this type of engine holds a lot of coolant in the block, etc. When I ran straight water through the system, and evacuated it, I was probably only draining the radiator leaving straight water in the motor. My fill with 50/50 pre-mix is probably further diluted now. I was told I need to drain the block. I found what I believe is the block's coolant drain plug. It sits on the driver's side up by the oil filter housing. It's a recessed hex fitting that sits flush with the block. I can't find one on the passenger side so I assume there's only one. My question is will draining from that port remove enough coolant from the motor to get me back to the correct mix when I add new coolant again? People have mentioned that I can take it to a Ford dealer to have them evacuate the entire system with the equipment they use. I'm hesitant since this is a show quality car that doesn't leave my sight. No disrespect to dealers. It's also an open top car. It has no roof. If I make a service appointment and it happens to rain that day I can't bring it. I don't want to do that to a dealer either because I don't want them to lose an appointment slot. Time is money. I could also use some help with burping the cooling system. I'm attaching a picture of the expansion tank to illustrate how the plumbing is lower than the high point of the plumbing on the engine itself. Air won't travel south so burping via the tank may not be an option.

Any insight is appreciated. Thanks.

780226
 

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Easy. Drain the radiator. Remove the lower radiator hose from the radiator side and aim it in a bucket. Start the engine and let it run for a few seconds. Coolant/water will come out of that hose. Do this with a cold engine of course.
That being said you don’t have to be right on the money as far as being 50/50 goes. I’ve ran a couple gallons of distilled water topped off with water straight from the hose and a 16oz bottle of rust inhibitor during the summer, and when I drained it to use coolant for the winter the water came out clean. That’s no where near 50/50. For what it’s worth, water cools “better” than coolant. Honesty I can’t think of a time to where I’ve had enough 50/50 coolant on hand to where I didn’t need to top it off with the hose.... Yes gentlemen, the garden hose. :eek:
Also, if the motor is ran often enough and long enough you won’t have worry about corrosion.
I used the blue one with water and it worked. I don’t own any gauges and I’ve yet to have one rust out on me.
Cooling System Additives - Turbo and High-Tech Performance Magazine
 

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Discussion Starter · #5 ·
Interesting. Good info guys. I have a question about the radiator hose method. Obviously the lower side of the radiator is the cool side. That gets drawn up into the engine via the water pump. That would make that path a one way street I assume. How will coolant back flow out the hose when the pump is trying to draw it in? Also, since engine will be cool, will coolant leave the block with the thermostat closed?
 

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Interesting. Good info guys. I have a question about the radiator hose method. Obviously the lower side of the radiator is the cool side. That gets drawn up into the engine via the water pump. That would make that path a one way street I assume. How will coolant back flow out the hose when the pump is trying to draw it in? Also, since engine will be cool, will coolant leave the block with the thermostat closed?
Yeah, I'm a dummy. It's been awhile since I did it & I might had been drinking.. But yeah, how I did it was I drained the radiator and added water and "radiator flush." once it was warm enough for the T-stat to open (upper rad hose was warm) I pulled the lower hose and let it drain out. I filled the rad with water and repeated until it came out clear when draining. So yeah, the rad needs to be full and the water warm when the lower hose is removed.
 

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Discussion Starter · #7 ·
Makes sense. What I'm thinking now is this. Since my system is over diluted now I can drain the radiator and expansion tank and fill with proper 50/50. I can then disconnect the radiator return hose and point it into a bucket. I then start the engine and wait for thermostat to open and the motor will only be sucking in the proper mixed coolant to evacuate the over diluted coolant from the block. I'll obviously have to keep topping the coolant off to keep things circulating. Any risk to this method assuming I religiously watch the temp gauge? I'm wondering how much the block holds so I don't over flush and waste money on coolant.
 

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Man.. I think you’re overthinking it brother. How dilute does it look? Surely it’s not crystal clear. I’m assuming this isn’t ever going to be in a sub zero temp, so the water freezing wouldn’t be an issue. Get a bottle of Redline’s Water Wetter, or something similar and pour it in. Those additives have anti corrosion additives and “lube” for the pump seals. If you wanted to I guess you could get one of those testers to see what the ratio is. drain it and add 100% coolant until it was at the desired ratio. But surely it’s not 90% water right now. Even if it was, the 10% wouldn’t make it rust like it came off of the Titanic.
 
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