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Thread: Alternative Coolant Bottle Caps

  1. #1
    Senior Member Trstno1's Avatar
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    Alternative Coolant Bottle Caps

    I have read that the Delorean has a 15 PSI coolant system. With that being said, the coolant bottle has a 15 PSI cap on it. I have been looking into getting one of those Mr. Gasket Thermocaps to show the coolant temp more easily. Unfortunately it looks like they don't offer a 15 psi one. They have a 13 PSI cap and a 16 PSI cap. Would either of those work? Or is there a different brand that is available that has a temp gauge on it that is rated for a 15 PSI coolant system?

    thermo cap.jpg
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  2. #2
    '82 T3 Turbo FABombjoy's Avatar
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    FWIW I just reassembled my coolant system and pressure tested it to 16.5PSI

    I'll be running a 16PSI cap since a quality new 15PSI cap is too elusive to find. IMHO If 1 PSI breaks your coolant system it was already on the verge of failure.

    I'm skeptical that the thermocap will work correctly connected to a header bottle and not directly to a radiator. Since the cap isn't touching coolant it will only tell you the temp of the vapor at the top of the bottle.
    Luke S :: 10270 :: 1982 Grey 5-Speed :: Single T3 .60/.48 Watercooled :: Borla Exhaust :: MSD Ignition :: MS3X EFI :: DevilsOwn Methanol Injection

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    Senior Member Jonathan's Avatar
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    It isn't so much what your coolant system piping can withstand as why that original number was chosen in the first place. Automotive cooling systems were allowed to go no higher than 15 psi to avoid being classified as a pressure vessel, i.e. boiler. If the "vessel" pressures go above 15 psi (14.7 psi really which is equivalent to 1 bar or 1 atmosphere) than they would be subjected to all the same design codes and certifications and inspections as regular boilers. No automotive company wanted that, so all the cooling systems stopped at 15 psi. This is a 100 year old philosophy.

    Another aspect of that max pressure (which when your system gets to 15 psi, it will relieve itself out that reservoir cap and not risk over pressurizing itself) is that it also translates to a certain temperature your coolant can get to, and subsequently the engine itself. Pure water will boil at 212 deg F (or 100 deg C). When you raise the pressure though, it boils at a higher temperature. Not that our temperature gauges are terribly accurate, but this is why you will see the engine/coolant temperature get to say 220 deg F. It is still a liquid at that temperature because of the higher pressure. If you suddenly have a loss of pressure, like the cap relieving or a hose split, what you end up seeing is your coolant immediately flashing to steam. Why? Because 220 deg F coolant won't stay as a liquid at atmospheric pressure. As soon as you lose system pressure, all that 220 deg F coolant will begin to boil until the overall temperature comes back down to something less than the atmospheric boiling point (212 deg F).

    I don't know what implications would come from using a 16 psi relief setting versus a 15 psi one. I'll bet the guys selling the caps can't tell you either (or care). I would tend to stay with a 15 psi cap as was intended.
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    Senior Member Bitsyncmaster's Avatar
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    I run a 13 PSI cap. The only reason for pressure is to bring the boiling temp up. At 12 PSI water boils at 242 deg. F, at 16 PSI it boils at 252 deg. F. So not much difference with most any cap.
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  5. #5
    Senior Member Domi's Avatar
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    I have the 16PSI version ( bought at Summit) on my car and it works fine

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    Senior Member DMCVegas's Avatar
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    But how accurate would that cap really be? The existing temperature gauge gets it's reading from a probe mounted directly in the cylinder head for a current, accurate temperature. But with the design of the coolant bottle, this unit would not only be in an isolated location, but would also be bathed in coolant that has already been chilled from the heater core circuit, as well as the core itself.
    Robert

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    Senior Member Chris 16409's Avatar
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    Chris Miles

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  8. #8
    Senior Member Trstno1's Avatar
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    Quote Originally Posted by Domi View Post
    I have the 16PSI version ( bought at Summit) on my car and it works fine
    do you find the temp info to be good or is it really off?
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  9. #9
    Senior Member Domi's Avatar
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    I found it accurate to the sensor.

  10. #10
    EFI Squirted DARCOM's Avatar
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    I personally run a lower psi thermostat as a car gets older. After all the cycles of getting hot and cold and metals expand and contracting. Pressure in the cooling system will weep water past some gaskets and over time this will cause pitting and other leaks. less pressure on a older system to me is best to save my head gaskets. I also have a overflow tank so the coolant does not drip on the street.

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