Electric Water Pump questions ...

[A26B]

Originally Posted by RussMcB

Appreciate all the responses.

The main reason I started this thread was because I've read posts suggesting that once the bypass is fully activated, the coolant is going to follow the path of least resistance and therefore not much of it is circulated through the radiator - It's much easier for the water to flow right back into the engine (because the WP is pulling it out, creating lower pressure).

So, while a better radiator and t-stat holes are great improvements, if the above is true, they alone might not solve the issue (under conditions where the bypass is open for extended periods).

Russ,
The bypass is NOT an open or closed only valve ("snap valve"). It is spring loaded and starts to open when the back pressure in the stock radiator reaches a specific point called "crack pressure," i.e. a "throttling" type valve. For conversation sake only, lets assume that point is reached in a stock cooling system at 5500 rpm and the t-body bypass valve spring requires 5psi to move the bypass valve "off-seat".

At this point things begin to happen, 1. back pressure is maintained at 4 psi, which is the amount of pressure required to exert 5 lbs force, the force required to initially lift the bypass valve off seat.

If rpm is constant, a point of equilibrium exists and the bypass valve is allowing some amount of coolant to "bypass". Let's just say the T-Stat bypass aperture is at 10% of full open capacity. Further assuming that the water pump discharge flow rate is 75 gpm and 90% of that flow, 67.5 GPM, is going through the radiator and the balance, 7.5 GPM, is being bypassed

As rpm increases, flow rate increases, back-pressure increases and the t-stat bypass valve responds accordingly and at 6,000 rpm and Pump discharge is at 85 GPM. The additional flow rate is going to generate more back pressure and the bypass will open further, allowing the added volume to bypass. The flow through the radiator will remain relatively constant at pressures great enough to open the bypass valve.

This process continues until the water pump reaches its maximum GPM output which is not linear with RPM, i.e. the pump may reach its maximum flow rate before maximum rpm, depending on several factors.

Please remember that the values I used are for demonstrative purposes only and are not representative of actual or theoretical values.

The cooling system back pressure can be raised by increasing the flow rate through the radiator & thermostat, such as a Ron Davis Racing Radiator and the drilling of holes in the thermostat flange. It should be noted that removing the thermostat entirely may be counter-productive to overall cooling efficiency. There is a balance in the velocity of coolant through the radiator and air quality/velocity, to achieve the best heat exchange.

I agree with you, the fans would be most useful during cool-down at slower speed.