[DeTomaso] Fwd: Radiator Caps

Wed Sep 18 11:33:04 EDT 2013

Just found this at Stewart gauges website.

Michael

*Tech Tip #2 - Radiator Caps

Radiator Caps*
In a cooling system, a higher pressure equates to a higher boiling point
for the coolant. Higher coolant pressures also transfer heat from the
cylinder heads more efficiently. We recommend using a radiator cap with the
highest pressure rating that the radiator is designed to accept. In
general, performance radiators will accept 22-24 PSI, and professional
racing radiators will accept a 29-31 PSI.

The coolant will typically only build to 16-18 PSI, due to expansion up to
200°F. However, if the engine does overheat due to external factors, the
pressure inside the cooling system could reach as high as 28 PSI. Once the
radiator cap has opened and vented coolant, the engine will not cool down
until it has been turned off. The radiator cap is basically a "safety
valve", so always use the highest pressure radiator cap that the radiator
will tolerate. If you are unsure of the pressure rating for your radiator,
check with the manufacturer for the maximum recommended operating pressure.

*Radiator Cap Location
*The radiator cap should always be located at the highest point of the
cooling system, and on the low pressure side (after the radiator
core).Cross flow radiators mounted higher than the engine are ideal because
the cap is on the tank that is connected to the water pump inlet. This
configuration offers 3 advantages:

  1.The cap is at the highest point of the system, allowing any air to
migrate to the area just below the cap. In the event the cap vents due to
excessive pressure, the air will escape first. 2. This area has the lowest
velocity within the system, allowing air to separate from coolant even at
high engine RPM. 3. The cap is located on the low pressure (suction) side
of the system, so it is unaffected by the pressure generated by the water
pump.
For cooling systems NOT using a cross flow radiator, mounted higher than
the engine, you must use a surge tank. A surge tank is typically a 1 quart
tank mounted at the highest point of the system, with the radiator cap on
top. The bottom of the tank is connected to the inlet side of the water
pump with a 1/2" or 3/4" line. A 1/4" to 3/8" "bleed" line from the side of
the surge tank is connected to the highest point of the low pressure side
of the radiator. The bleed line allows some circulation through the tank
while the engine is running. The surge tank is also large enough to allow
the air to separate as the coolant flows through it. Air in the system will
then migrate to the area just below the radiator cap, again so that it will
forced out first if system pressure exceeds the radiator cap's rating.

In street car applications, an upright radiator (top and bottom tanks, with
the cap on the top tank) represents a compromise that will work, as long as
the car is not operated at sustained high RPM, like those seen in racing.

*Any aftermarket thermostat housing that mounts the radiator cap directly
above the thermostat location, or that mount the radiator cap in the top
coolant hose, are NOT recommended. Both of those housing styles are poorly
designed, and will push coolant out of the cap at high RPM.
*

On Wed, Sep 18, 2013 at 11:28 AM, michael at michaelshortt.com <
michaelsavga at gmail.com> wrote:

> Every pound of pressure raises the boiling point of water 3 degrees. if
> your system is designed for 10 psi and the cap is capable of holding that
> you have increased the boiling point 30 degrees.
>
> So a 16 psi cap could stand a temp of  260 degrees, whereas 22 psi could
> handle up to  278 degrees.
>
> I guess none of us want temps anywhere near 260 anyway, so perhaps the
> lower rated cap is sufficient.
>
> The next point then becomes, if the cap fails to release the pressure,
> then something else might, like a hose, gasket, etc.
>
> Michael
>
>
> On Wed, Sep 18, 2013 at 11:20 AM, Larry Finch <fresnofinches at aol.com>wrote:
>
>> Overflow is zero pressure cap.
>>
>> But why so high - 22PSI - on the surge tank cap?
>>
>> Larry
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> --
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>
> Michael L. Shortt
> Savannah, Georgia
> www.michaelshortt.com
> michael at michaelshortt.com
> 912-232-9390
>
>
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-- 

Michael L. Shortt
Savannah, Georgia
www.michaelshortt.com
michael at michaelshortt.com
912-232-9390

This email is protected by the Electronic Communications Privacy
Act, 18 U.S.C. Sec. 2510-2521, is confidential and may be legally
privileged.  If you are not the intended recipient, you are hereby notified
that any retention, dissemination, distribution or copying of this
communication is strictly prohibited.  Please reply to the sender that you
have received this message in error, then delete it.  Thank you

-- 

Michael L. Shortt
Savannah, Georgia
www.michaelshortt.com
michael at michaelshortt.com
912-232-9390

This email is protected by the Electronic Communications Privacy
Act, 18 U.S.C. Sec. 2510-2521, is confidential and may be legally
privileged.  If you are not the intended recipient, you are hereby notified
that any retention, dissemination, distribution or copying of this
communication is strictly prohibited.  Please reply to the sender that you
have received this message in error, then delete it.  Thank you