Coolant flow path

[zachmac]

Searched but couldn't find it: does anyone have, or have you seen a diagram of, the coolant flow through the engine? Also, is the inlet to the water pump (where the hose attaches) the inlet or outlet (is it where water flows in or out)? I assume the former as it seems to lead to the eye of the pump.

Here's where I am going with this: if someone for whatever reason runs without a heater core (or has it bypassed) why not block off the heater tube flange and inlet to the head which would be exactly the same no flow through that path that having the heater temperature control valve closed creates. Clearly that path is not essential to normal engine cooling as again any time the heater control valve is fully closed there is no flow there.

By blocking it off, as opposed to what I've most commonly seen, a direct connection of the heater tube to the head inlet; wouldn't you increase the flow from the pump that goes through the radiator? Seems like any time that circuit is open (open heater valve or bypassed with tube direct to head) you are always circulating some part of the pump flow without it passing through the radiator; a good way to get heat to the heater core but not optimal for engine cooling.

[bradartigue]

However the core itself is a radiator; the fluid exiting the core is cooler than the fluid going in.

IIRC the pump runs in the same direction as the drive belt.

[vandor]

The water pumps pulls the water in from the lower radiator hose. Not ideal for the engine, but this way the natural flow of water (hot water goes up, cool water goes down) helps the water pump. Ideally, and on some newer engines, the cooled coolant enters the head first, as it's a lot hotter than the engine block.

[4uall]

This might help https://www.youtube.com/watch?v=m5Xnrfjc9qU

Google is your friend

[zachmac]

Thank you all for your replies. I think most all of my questions got answered. I appreciate the video but I already understood the external flow paths. I was just trying to confirm (you all did that) that the internal flow path is from the thermostat, into the pump, into the block and then back through the head to the tee. As Csaba points out, not ideal, but it is what it is.

Brad,

Of course the heater core is itself a fluid to air heat exchanger, but my real question was IF it is bypassed as many are, doesn't it make sense to block off rather than short circuit (head to return pipe path) that flow path as you now have some part of the pump flow bypassing any heat exchanger? With everything stock it is a moot point as you are either rejecting the heat in that circuit to the heater core (heater control valve open) or there is no flow there (heater control valve closed). But again, for all those owners who have bypassed a leaky or non-existent core, doesn't it make sense to block that path off? As a side benefit you could use the head connection as strictly a high point vent.

All just silly hypothetical on my point as I have a perfectly good heater core I'll be reinstalling today along with the rest of the cooling system; just thinking out loud.

[bradartigue]

No idea, I would imagine not as there isn't a significant amount of flow through the pipe and hose. However if it means anything the rally (not csa i mean the cars they actually raced) cars had it blocked and had no pipe under the exhaust.

At least the two I saw years ago

[zachmac]

No idea, I would imagine not as there isn't a significant amount of flow through the pipe and hose. However if it means anything the rally (not csa i mean the cars they actually raced) cars had it blocked and had no pipe under the exhaust.

At least the two I saw years ago

Makes sense as any high performance car (racer) doesn't care about a heater and is producing more heat from the heat source than stock so they would want to maximize cooling. Just seems like a simple "fix" for anyone running without a heater core.

Csaba,

The engineer in me can't resist commenting that the pump drawing from the lower hose has zero impact on the system flow in a properly vented, full, closed loop system PROVIDED the pressure drop from the bottom of the radiator to the eye of the pump doesn't cause a loss of net positive suction head such that the pump cavitates.

As the general energy equation taught us, the net change in Kinetic and Potential energy from any point in a closed loop back to the same point has to be zero. That just leave heat in (the engine), heat out (the radiator), work in (the pump), no work out, and then changes in flow energy and internal energy. If we design a system where the heat in = the heat out (the desired situation here if we want stable temperatures) then the pump just has to create a high enough differential pressure to overcome the head loss (conversion of Pv energy to friction, i.e. internal energy) to keep the fluid flowing at some steady rate. Pumps basically do just that, create a set differential pressure (at a given speed).

The problem with taking suction from a lower point is then one of the associated drop in pressure with the increased PE from the bottom of the radiator to the eye of the pump. This means the pressure of the fluid entering the pump is lower than it would be if the water never got that low. All of this results in some supply pressure at the pump eye that is lower than it otherwise would be, as well as THROUGHOUT the system (pump provides a set delta P). Again, not an issue UNLESS the pressure at the eye of the pump drops below the saturation pressure (pressure at which the current temperature will cause the liquid to vaporize). This is why it's so important to make sure you have a good radiator cap that maintains system pressure; the first place it will boil is at the lowest pressure point in the system, the pump inlet. This rapidly exacerbates the issue as now a fluid that is already too hot for the pressure it's at stops flowing and gets a lot hotter.

There, that is surely more than anyone ever wanted to hear on the topic.

BTW, as I was installing the heater core and radiator back into the car just now it occurred to me that this post might seem like I was trying to "look smart" or imply some how that Csaba and other don't already have this knowledge (and lots more). Just wanted to edit to say not the case at all, I'm just an insufferable engine-nerd.

[KevAndAndi]

http://www.fiatspider.com/f15/viewtopic ... 15#p125549

Here's a post that contained links to coolant flow diagrams created by a forum member. My work computer won't let me view Google docs, so I can't tell from here whether or not the links still work.

[zachmac]

http://www.fiatspider.com/f15/viewtopic ... 15#p125549

Here's a post that contained links to coolant flow diagrams created by a forum member. My work computer won't let me view Google docs, so I can't tell from here whether or not the links still work.

The links work and those are excellent reference diagrams, thanks!

[joelittel]

Every time I read "my work computer won't let me...." in a fs.com post I have to laugh a little bit.

It's funny to me that so many of us sneak a peak at the forum while we're at work, on our lunch breaks of course.

[vandor]

> my real question was IF it is bypassed as many are, doesn't it make sense to block off rather than short circuit (head to return pipe path)

No. The coolant wants to take the path of least resistence inside the engine and flow from the WP to the outlet as soon as possible, ie. by cylinder #1. To counteract this the head gasked only has small holes toward cylinder #1 and #2, and larger holes toward the back. Still, the rear cylinders in most engines run hotter than the front ones. Providing and extra flow path toward the rear of the engine helps even out the temperature among cylinders.

[vandor]

> The engineer in me can't resist commenting that the pump drawing from the lower hose has zero impact on the system flow in a properly vented, full,

Yes, correct. The reason I said it is not ideal was that cool coolant should ideally enter the head first, as the head needs to dissipate more heat than the block.

Of course the reason for the coolant flow is that originally cars did not have water pumps, coolant circulated by thermosyihon, where hot water in the engine rises and cooled water in the radiator falls. It made sense that when manufacturers first started to install water pumps they were designed to help the natural thermosiphon flow. In engines designed in the last 60-70 years waterpumps create way more flow than thermosiphon ever could, but only more recently did engineers realize that it's more efficient to run the coolant the other direction.