Water flow with bypass system

[GregH]

having the bypass valve and the thermostat removed on the engine. Due to the colder Lake Ontario waters, I haven been setting the bypass a good 80% open.

it has got me wondering how exactly this makes sure the cooling water bypasses the engine block to reduce cooling too much. Without the thermostat inside the housing, the input water has a nice hole to drain down into the block. I assume once that is "filled" more bypass water would flow directly across to the outflow side of the housing. But of course I am just guessing at how the water flows inside there.

Anyone have a better understanding of just how the water flow works with the bypass system and NO thermostat?

[Al Schober]

Greg,
The primary flow of coolant from the pump is into the engine through the cover plate on the starter side of the engine. This coolant circulates around the cylinders then up into the head. It leaves the head through the thermostat (or through the hole where it was) then goes to the manifold. The bypass allows some of the flow from the pump to bypass the engine and go directly to the manifold. There is no flow from the t'stat housing back into the engine.
How much of the coolant goes which way depends on a lot of things. All you can really do is to 'encourage' it to go one way or the other.

[edwardc]

When the bypass valve is fully open, the flow resistance from the input water tee, through the openvalve, to the output side of the thermostat housing is MUCH smaller that the flow resistance through the block. Therefore, most (but not all) of the cooling water goes through the bypass.

[GregH]

that makes sense about the flow resistance and most bypassing the T, but when it reaches the thermostat housing with no thermostat, it's just a wide open dome with a small exit and a larger hole where the thermostat used to be.. why doesn't it take the larger hole and follow gravity.. or maybe it does?

So I am guessing that with the block full and low flow of water through it, fills and meets the faster water from the bypass and this is enough for the current to continue (mostly) straight across to the outflow tube instead of flowing down into the block?

sorry.. this is where my brain goes at times wanting to understand things

[sastanley]

It can't flow back into the block, because the water pump is constantly sending in more supply..It would eventually flood the block's water jacket and head toward the manifold as long as the pump is spinning..which it is as long as the engine is running since the pump is gear driven.

You could maybe put a pressure gauge anywhere along the route to see if you have x.x PSI, which would verify flooded cooling chamber(s).

[JOHN COOKSON]

Close But Not Quite....

that makes sense about the flow resistance and most bypassing the T, but when it reaches the thermostat housing with no thermostat, it's just a wide open dome with a small exit and a larger hole where the thermostat used to be.. why doesn't it take the larger hole and follow gravity.???? or maybe it does?

In a RWC engine:
When the water leaves the pump first thing it sees is the tee in the side plate. No water "bypasses" the tee.
At the tee the water is routed into the engine or around the outside of the engine ie the "bypass". If the water can't go around the engine because the bypass is restricted it is forced to go through the engine. There are two ways that the bypass is restricted: By valve on the bypass hose and by the double action thermostat. A valve is a after market addition by the owner. The double action thermostat rams up into the top of thermostat housing as the engine heats up blocking the flow inlet from the bypass into the top of thermostat housing.
As the engine ages the water passages become restricted thus forcing more cooling water around the bypass the engine will run hotter. There are two ways to deal with this problem: restrict the bypass forcing more water to go through the engine and clean the engine water passages with an acid flush.

ex TRUE GRIT

[ndutton]

I'd like to offer this Greg:

When the original Holley three spring dual action thermostat was no longer available, various efforts were made to regain control of the A4 cooling system. MMI sourced a replacement thermostat that didn't fit so they made it fit with a spacer, Indigo developed their remote thermostat system and perhaps the simplest of all, the bypass valve for at least partial manual control came into existence. It was the only system that worked without a thermostat.

Now MMI has developed their own thermostat (two of them actually) specifically designed and manufactured for the A4 late model cooling system that is a direct replacement (read: no adapters, special housings or spacers required) for the original Holley three spring. The new product restores the cooling system to its original design and intent.

https://moyermarine.com/product/mmi-thermostat-late-model-double-acting/

I get an odd pleasure in spending other people's money so to that end, why would anyone prefer one of the older work-around measures when the real deal is available now? I've had a new MMI thermostat installed for over two years and it has worked perfectly. I still have a bypass valve installed but it remains full open to allow the thermostat to do its thing.

[edwardc]

.. why doesn't it take the larger hole and follow gravity..

Both the block and the bypass hose are full of water and being pressurized by the water pump. The unpressurized outlet from the thermostat housing is the only place the water CAN go. It can't "follow gravity" and flow into the already full block, and it can't flow against the pressure.

[GregH]

ok, I think from my readings on here I may have misunderstood some of the finer points about using a bypass and thermostat use etc.

I have the original 3 spring thermostat and it works fine - opening at 160F (stove top testing). Engine was running between 180 and 200 before I started tinkering with the bypass (removed Tstat) people were talking about. Now with lake Ontario water (now = past season) the temp gauge does not get above 120 (gauge does work tested)

Before tinkering and Tstat removal I did not have the bypass valve installed. So I'm thinking put the Tstat back in and run the engine, get the engine nicely warmed up, and from there if it's back to reading 180-200 again my next step is?



Raw water cooled.

[ndutton]

Engine temperature study

Before tinkering and Tstat removal I did not have the bypass valve installed. So I'm thinking put the Tstat back in and run the engine, get the engine nicely warmed up, and from there if it's back to reading 180-200 again my next step is? Raw water cooled.

Temp gun measurements at nine locations as the engine warms up, before and after an acid flush. It will tell us a lot.

This worksheet is what Don used during the new thermostat prototype field studies a couple of years ago:
A4 Temp Worksheet.pdf

I've included my measurements for RWC, thermostat installed, bypass valve fully open for comparing your numbers:
A4 temp worksheet RWC with Tstat.pdf