eliminating the bypass on FWC

[sastanley]

So, one of the things I did on my A4 was eliminate the bypass when I went to FWC.
For context, my electric circulation pump for the antifreeze had a 3/4" hose output, so I upsized the hole in the side plate to accommodate the larger hose. My thought was the low head pressure on the electric pump was no problem and then when the thermostat got to 160° the t-stat would open up. When the t-stat was closed it would just circulate in the block water jacket waiting for the t-stat to open. I used the original gear driven pump for the raw water. This pic shows the bypass blocked off, and the Thatch mod. I ran this for 7 seasons from 2014 to 2022 before I sold the boat.

[hanleyclifford]

The fact that you ran it successfully for seven seasons is proof enough that it worked. Presumably the thermostat had a small hole to allow a bit of coolant thru to fill the downstream hoses. Apparently there was sufficient coolant in the manifold to stabilize the temperature. The Thatch Modification was therefore essential in your case. It must have been difficult to add coolant engine cold and running, But you made it work - the proof of the pudding. Still, I suspect the method is peculiar to the use of the electric pump.

[hanleyclifford]

Shawn - Does the hot water tank on your new boat have an exchanger built in?

[Dave Neptune]

Any type of centrifugal pump will allow a system like Shawn's to work as it is the same as millions of automobile engines. Getting the engine "burped" just means you need to have the fill point at a high spot or a suction style recovery tank and cap. Easy and almost fool proof.

Anyone ever try to burp some BMW's with all of their air pockets?

Dave Neptune

[joe_db]

Any type of centrifugal pump will allow a system like Shawn's to work as it is the same as millions of automobile engines. Getting the engine "burped" just means you need to have the fill point at a high spot or a suction style recovery tank and cap. Easy and almost fool proof.

Anyone ever try to burp some BMW's with all of their air pockets?

Dave Neptune

Try an MR2 with the engine behind the driver and the radiator in front of the driver.
Also try any car with auto climate control. The hottest they usually can set the heat is 80, so on a hot summer day the heat will never go on and the valves will never open.

[joe_db]

I don't get this layout at all
Is the thermostat in? If so, you are running against a closed thermostat when cold, does it leak enough to supply the exhaust?
When I had my FWC system on with the electric pump, it could just barely keep up on a warm day, the engine was in the 180-200 degree range. The last thing it needed was a thermostat of any kind.

[hanleyclifford]

The problem with deadheading the flow at the thermostat is that it (mostly) stops coolant flow throughout the system. The difference between automotive and the Atomic 4 is that the exhaust is initially cooled in the manifold. The problem is that the manifold thus heats up faster than the rest of the engine. In any case I've always been a "flow" guy - I like that antifreeze to be racing around the system at start up, bypassing ONLY the exchangers. Takes a little longer to heat up but does so more uniformly.

[joe_db]

Nevermind, the raw water is headed to the exhaust.
This still seems like it would make the manifold very hot with no flow.

[hanleyclifford]

Nevermind, the raw water is headed to the exhaust.
This still seems like it would make the manifold very hot with no flow.

In a FWC system the raw water should be in a separate loop - the problem being that it is not affecting the manifold, just the exhaust system downstream of the injection point.

[sastanley]

Any type of centrifugal pump will allow a system like Shawn's to work as it is the same as millions of automobile engines. Getting the engine "burped" just means you need to have the fill point at a high spot or a suction style recovery tank and cap. Easy and almost fool proof.

Anyone ever try to burp some BMW's with all of their air pockets?

Dave Neptune

The heat exchanger tank/cap was the tallest part of the system..just above the manifold/at same height. You could see the coolant whooshing by the HX opening when the pump was running.

Shawn - Does the hot water tank on your new boat have an exchanger built in?

No, I do not think so. I can at least confirm that there is no coolant currently running to it, but I'd have to stick my nose in there to see if it has hose connections. It was installed later I am pretty sure when one of the POs was living on the boat in a marina (and therefore plugged in).

For a while, I ran with no t-stat, but I reinstalled it when I went to a larger HX. The HX in this picture was just a little too small..The next size up Sendure was a multipass unit, another inch in diameter and allowed reinstallation of the thermostat and a more stable temperature.

[hanleyclifford]

I think Shawn got away with his system design for two important reasons. 1) He did the Thatch Modification which ensured that his manifold was always flush with coolant thus modulating the rate of heat increase especially near the exhaust outlet and 2) The differential in temp increase at the sensing point (the thermostat), and the hottest point in the manifold was not enough to cause a problem.

[sastanley]

Oh.. I think I get it now...we are worried that the manifold might have been running hot if the t-stat was closed and antifreeze wasn't circulating. I suspect there was a hole in the tstat..it was whatever the replacement they sold with the adapter before designing a replacement for the Holley 3-spring.

I don't have the data anymore, but I held a temp gun on all the engine parts and don't remember a hot spot, and I do agree the Thatch mod probably helped with better circulation and getting the air up to the manifold and then to the HX for burping purposes.

[joe_db]

The engine definitely has hotter and colder areas:

[sastanley]

Joe, I agree with that 100%, I just did not see any extremes that I recall. Even the 'cheap' Rustoleum spray paint did not get hot enough to flake off the manifold.
These are all just data points to inform other A4 enthusiasts. My solution maybe does not work for everyone.

[joe_db]

I was surprised a bit about the heat difference side to side. The port side of the engine is much hotter than the starboard side. This does explain why all the predictions of doom and gloom for a cold engine do not come true. I have not run a thermostat in ages, my water temps usually are about 120 and rarely past 130.
In theory that should cause a ton of fouling and stuck valves, not to mention badly fouled oil.
In practice the part of the engine where the valves are runs way hotter than the coolant and so does the oil. I need to see if I have a good photo, but the oil is way hotter than the water in my engine. When I changed it last week it seemed like a waste of good oil, it literally looked brand new.