Just remember your geometry, gentlemen. Any increase in diameter increases flow by a factor of 4, as in area of the circle.

 

Yep, a lot of early cars only had 1/2 heater hoses and worked fine.

 

Is that what the ratio is? That's good math to have for the future.

Hey... Happy birthday Dave. Somehow I missed that until just as I was running out the door last night.

 

Thanks, Bugout!

If you make the bypass hole 1/2" you will rob all the flow thru the filter. I wouldn't make the bypass hole larger than 1/4". Remember pressure is controlled by the rad cap and the pump just provides flow. In other words, you can have zero flow and still only have 18 psi pressure, until the coolant gets hot enough to produce steam. Steam expands exponentially and pressure increases rapidly. That's why air pockets are so dangerous. They create places for steam pockets to form.

Lets just assume for the sake of discussion that the flow rate thru the filter and 1/4" bypass hole are the same. As the filter picks up debris, the flow rate decreases and the velocity of the flow thru the bypass hole increases. Pressure will remain the same. Also remember that the water pump is a submerged centrifugal pump and doesn't add pressure, it only provides flow.

Until the thermostat opens, 99.9% of the water pump flow goes thru the heater core. After it opens, very little flow goes thru it. It still gets system pressure. A good thermostat acts like a throttle valve controlling system temperature, opening and closing gradually.

 

OK I need to find out if I have confused myself on this. I was under the impression he had installed the filter inline to or from the heater core. Is there a bypass port in that housing? If so I agree this doesn't need to be very big. I thought we were talking about the normal line passages through the filter needing to be larger for more flow through the heater core?

Have I mixed myself up here??? lol

 

He drilled a 3/16" bypass hole on the filter housing.

Sorry, but I just woke up after trying it catch some sleep for work tonight and my mind isn't quite clear yet. It's been a while since I've done any hydraulics work, but the flow is controlled by the smallest orifice in the system, that being the inside of the barb connectors for the hoses, forgetting about the filter and the bypass hole. There will be a slight pressure drop after any orifice that restricts flow, but it's negligible compared to flow drop.

Most of my work was with positive displacement pumps and pressure control valves. Working with a centrifugal pump is another ball game because pressure is only created by heat expansion and controlled by the vent cap. It's a closed system, not an open system like a well pump filling a vented tank. Centrifugal pumps don't build much of a pressure head because they have too much internal clearance. They are designed only to create flow. Most well pumps aren't true centrifugal anyway, but are high flow turbine pumps that need to be submerged. In a cooling system, the only reason for pressure is to control the boiling point.

I get very wordy when trying to explain because that's the way my mind works, like thinking out loud.

Basically what I'm saying is the flow will be divided between the filter and the bypass hole. Too big a hole will negate the filter.

 

No you are good about how you worded it...and I understood having done a lot of hydraulic system work myself. Where I goofed myself up is I did not realize he had implemented a bypass aside from the positive flow ports through the housing and filter. If this is the case my advice to drill this bigger is absolutely wrong. I thought the main porting through the housing and filter was going to be restricted to that small hole (as many are on big rigs) which would be a disadvantage in this case and needed to be bigger for more overall flow through the core.

 

Please nobody butcher me for resurrecting this thread. OP did you ever cut your coolant filter open to find out how it looked? if no response I will start my own thread on this