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Radiator cap pressure rating???

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  • Patreer
    replied
    Hi All,
    Please let me know if ok.
    Tks

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  • Patreer
    replied
    OK, I have been testing the bird several time now and it's still runiing at 210. Should I worry?

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  • Patreer
    replied
    I just did the test and clearly heard the thermostat pop while opening. I'm now waiting for the coolant to cool down. leaving the cap open.

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  • simplyconnected
    replied
    Did you ever do any canning? Canning produces a vacuum all by itself. Your radiator uses the same technique; first coolant is heated but when it cools down, the air inside contracts into a vacuum (provided your radiator cap has a good seal).

    Cars with radiators LOWER than the engine (like Corvette and Escort) have used this technique for decades. It's important for those cars to have coolant in the aluminum heads at all times or they crack.

    Over a few heat/cool cycles, your heater core should displace the air bubble with coolant. This is evidenced by finding a lower coolant level when the system is cool enough to check. Modern cars use the overflow to pull liquid back into the system. That's why their systems are always 'to the top'. - Dave

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  • Patreer
    replied
    OK Thanks John
    I'll do this and see if it helps.

    Pat

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  • jopizz
    replied
    Changing the heater core should not cause your temps to be higher than before. My thought is that you have air in your system. Make sure you run the car with the radiator cap off and the heater control on hot to bleed any air out. I would not go to a 15 lb cap. The higher pressure will only put stress on your engine and radiator. Stay with 13 lbs. I've used the same oil many times and I haven't noticed higher temperatures.

    John

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  • Patreer
    replied
    Good day from Montreal,

    I had to change my heater core recently and since I noticed the coolant tempature is higher then before (I have a gauge, a 180F thermostat and a 13# radiator cap).
    Temperature used to be at 180F point all the time, but now I see that thermostat opens when engine warms up and after running for 20 minutes or so temperature climbs in the 195-210F range.
    Yesterday we had 75F oustide and my coolant temp was more than 200F.

    Even on the highway it does the same as if themostat was not operating.

    I'm worried about overheating.
    Should I change my radiator cap to a 15#?

    Forgot to mention I switched to Shell Rotella T4, 15W40, if it may have an impact.
    (1960 Tbird, 352)

    Thanks for your help

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  • Guest's Avatar
    Guest replied
    I know the 7lb isn't going to work in the summer. It will start spitin up. but I bought this car on flebay with a stuck motor and everybody gave up on it. From a ford dealer no less. Has 80000 on it and runs FINE. Been sitting since 1977. Took a little playin with it but you wouldn't believe how this car runs and everything works. (no clock). It's a 66. I think my 60 will run it down. But then I have figure out how to stop.

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  • Guest's Avatar
    Guest replied
    Originally posted by bcomo View Post

    I wanted to add something about the purpose of a radiator cap.

    The purpose of a radiator cap is to raise the boiling point of the water/antifreeze mix.
    This is 100% correct. If one is concerned that the correct pressure cap will blow out the cooling system, it is time to perform a little service.

    Additionally, the purpose of 7# caps was in the days of using either water or an alcohol based coolant. On this time period systems, it will not only cause spitting but will ingest air on the intake, creating air pockets and creating even more problems.

    The AC radiator cap being correct for this period is interesting. I always cringed from anything not marked FOMOCO.

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  • YellowRose
    replied
    Radiator cap pressure rating???

    Hi Bart,

    Thanks for posting that information! I have never seen the explanation of the purpose of the radiator cap explained before. That might explain why some Tbirds overheat more easily than other ones during slow moving parades. I have not run Yellow Rose in a parade yet. I just checked my radiator cap to see what it is. I thought it was a 13, but I see it is a 14. Hopefully, with that cap and the metal shroud around the radiator now being in place, I will not have that problem. Sooner or later, I will probably find out. Maybe those who have had the problem, if not using a 15psi cap, should try one...

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  • bcomo
    replied
    I wanted to add something about the purpose of a radiator cap.

    The purpose of a radiator cap is to raise the boiling point of the water/antifreeze mix.

    The normal boiling point of water is 212 degrees Fahrenheit (F).

    Typical engine operating temperature after the themostat opens (with good air flow) is about 200 degrees F.

    You can see that there is only a small difference between the two.

    A radiator cap increases the boiling point of water by raising the atmospheric pressure (pressurizing) the system. When the water gets hot, it expands, but the radiator cap keeps the water pressurized by not allowing it to escape from the system untill it reaches the psi rating of the cap.

    A 15 psi cap will raise the boiling point of the water by about 45 Degrees F. So now the boiling point of the water in the system becomes 212 F + 45 F = 257 F

    So, the lower the psi rating of the cap, the earlier the water will boil, and the engine will overheat at a lower temperature. A lower psi cap will definitely keep the system pressure lower, but in stop and go traffic or high abient temperature, the engine will overheat faster and blow water from the overflow.
    Last edited by bcomo; January 27th, 2009, 10:10 AM.

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  • dgs
    replied
    I had a 6 or 7 lb cap and it wouldn't keep the fluid in. At temp it's just spit it out the overflow. I switched to a 13 lb and mostly cured my problems. Of course, I found a weak lower rad hose, freeze plug and now either a leaky heater core or temp control valve. Oh well.

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  • Guest's Avatar
    Guest replied
    I'm running a 7lb. cap on my 66. Freeze plugs are a little weak and what else I don't know. I'm sure I'll find out soon enough.

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  • trim code 76
    replied
    Thanks guys!! Knew I would get the right answer from you.

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  • FeFranco
    replied
    Originally posted by JohnG View Post
    The lower the pressure the better.... less stress on that cheesy expansion tank on the top! Make an overflow bottle for inside the engine compartment (for non-show times) and catch anything that comes out so you're not dumping toxic stuff into the street.

    john
    Well put and this is what I found out. My expansion tank was leaking at the seam so I brought it to the radiator shop for repairs. The repairman told me that he would recommend a 10lb cap because of the typical temperature fluctuations in the radiator. Mine will easily see 210 on the gauge at a stop light in the summer, but climb back down to 180 when I get moving (i have a gauge). Sure, it will spit it out, but if you have an overflow it will eventually suck it back in. I HAD a 13lb cap.

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