I did wonder about the cavitation and if any signs of damage were being noticed on the impeller or surrounding parts. Thought that might be more of an issue when the thermostat is closed, if the bye pass was restricted. Interesting point made, increasing cap pressure reduces cavitation. That makes sense when I think about it.

As pointed out no restriction in the radiator is unrealistic but getting that as low as possible is still the best first option (but unfortunately also by far the most expensive) through more cores and also that equates to more surface area to dissipate heat. Aluminium radiators dissipate much more heat than copper and brass but wouldn't have longevity or original appearance, none that I've seen anyway. When slow moving or stationary, getting as much air through the radiator as possible is probably the most important factor.

I suspect the pressure changes from the pump with the engine revs increased might be substantial for a bottom hose to flatten if the wire is not installed, as it is also having to overcome the internal pressure created from the heated coolant. It has been decades since I've seen a bottom hose flatten like that and I cannot recall if the engine was at full temp or not.

One thing that I have never seen properly addressed is the cavitation that is likely to occur in the Y block/Tbird stock pump. The pump has radial vanes which means that the cross sectional area of the flow paths in the rotor are increasing from the center where the water enters the to the rim. Water being non compressible means that there must be leakage around the vanes as the water slows down relative to the rotor. OR there must be some cavitation in the pump. A really well designed industrial centrifugal pump has a more or less constant flow area from the center to the rim of the impeller. Such an impeller will look like some turbo wheels.

The normal recommendation for T birds is to put a smaller pulley on the pump thus speeding it up. This might be OK for a car used in Parades but is going to make any cavitation issues worse at highway speeds or racing. It will make the fan move more air through the rad at slow speeds which is probably its main benefit. The vanes added to the back of the T bird pump rotor will also tend to cavitate badly. Actually slowing the pump down might help more at highway speeds. One thing that you can do to decrease cavitation is to increase the water pressure in the system so a 13 psi rad cap is a good thing in a cooling system in good shape. Plugging the bypass also works for me. But trying to keep temp low as a goal in and of itself as opposed to getting cooling adequate to the needs of the engine just clouds the issue.

Doug T

The Highlands, Louisville, Ky.

Granted that there is a pressure differential present with a cars water pump but it pales in comparison to the pressure generated by the heated expansion of the coolant. In a perfect world where there is no restriction, there will be no pressure if taking temperature out of the equation. I’ll add that part of that pressure differential is generated by the difference in temperatures at the top and bottom of the radiator so separating the effect of each could be measured by simply measuring the pressure differential on both a non-running and running engine.

Lorena, Texas (South of Waco)

The pump must create some pressure in the top tank and reduce pressure in the bottom tank otherwise the water wouldn't circulate. Most cars will have a wire coil in the bottom hose to counter the pressure change when engine revs increase, to stop it being flattened as the pressure becomes less than atmosphere. As the pressure drops at the bottom a corresponding increase must occur at the top in a closed system. The change in pressures are from the pump impeller driving the water up, and on the other side the resistance of the radiator cores (the inability for the water to flow through the cores fast enough to balance the pressure).

To force more water through the radiator the pressure must then be increased in the top tank. The two examples given are, increase pump speed and restricting the bye pass. As it was mentioned by pegleg, the heat from the motor increases pressure in the system. As the revs increase also the pump speed increases and so the pressure in the top tank increases, this combined with the existing pressure from the heated engine will eventually overcome the spring pressure of the cap if it becomes high enough. I have seen this occurring when an engine has been driven only at low revs it will maintain a higher water level in the top tank than if it is driven using higher revs but still maintaining normal running temperatures.

When I got my green outfit, the first thing I did was drive it down from Sedona on 107 degree day - staring at the temp gauge with bag of ice on my head. Fortunately - it never boiled over (that should have told me something....). When it cooled off, I pulled the cap and added water. Not the right move, very next drive - it spit it out.

Experienced local bird owner told me to drive it 'till it hit a "normal hot" temp not boiling - then check the water height in the tank cold and afterward, use that for my fill mark. The explanation being that the "overflow" was the surplus tank capacity. Desert drivers are greedy for water capacity so I added an overflow tank. And a steel six blade fan.....

I found a recommendation here to use a "high flow" thermostat - removed mine and found it to be about the size needed for a lawn mower. If you haven't been to the CASCO site and seen their water flow test - do so. Found that a high flow, big block Chrysler thermostat would work nicely in the Ford housing - NAPA #6 will too - and the "normal hot" gauge temperature dropped a bit.

Next I found out about the bypass hose and what its function was - and quickly realized that a considerable amount of water passing through that port was not going through the radiator. When your thermostat is wide open and you still need more cooling - its a function of how much hot water can go through the radiator. It will plainly accept more than it was getting - reducing the movement through the bypass instantly changed the temp gauge again.

Next trick is looking for a smaller pulley - raising the pump RPM relative to the engine RPM. Several methods are available - I used one from a 302 - Concours, sells one - its easy to get a +10% improvement. I've also put a Hayden fan clutch on it - and a rigid seven blade aluminum fan. All of the improvements I put on were reasonably priced - and mechanical - even though an electric booster fan was tempting.

 
 Steve Metzger       Tucson, Arizona

If you don't have a recovery tank you must allow some room in the radiator for expansion; i.e, don't fill the radiator all the way up to the bottom of the filler neck. Without a recovery tank any excess is blown out the overflow tube until the coolant finds it's proper level.

To add to what Steve said, The pump does not increase system pressure, heat does. The pump circulates water, period.

Frank/Rebop

Bristol, In ( by Elkhart) 

OK, I hear you. From the comments made there are no mechanical ill effects from the modification. I did have thoughts of it bursting solder joints or ballooning the top tank. In saying that I still get blow bye when the revs come up, and my cap is good. My car has the standard overflow, so maybe it would not be noticeable if it had an overflow tank that then would allow it to be drawn back. I have noticed that since I let the level drop below half way on the top tank it doesn't seem to be an issue and the coolant level has stabilized. I don't know if any mods have been made to the pump area to increase pressure as I have not worked on it, and it is as I bought the car.

3/8 is correct.I was thinking heater hose ID.

  

I believe you want a 3/8" pipe plug?

"The Master Cylinder"

Enjoying life at the beach in SOCAL