A4 Exhaust Raw Water - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Gas > Atomic 4
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Old 11-09-2009
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Question A4 Exhaust Raw Water

No water is coming out of the exhaust on my 1973 A4.

It has run very well for years until now.

I checked the following:

The engine starts up and runs beautifully.

All hoses have been disconnected and observed to have good water flow all the way to the muffler.

At the muffler good, hot, pressurized exhaust comes out.

At the water inlet into the muffler I noticed that with the raw water cooling line disconnected exhaust comes out at a pretty good pressure.
This seems wrong but I don't know.

The engine runs fine but the temperature shoots right up over 200 at idle within just a few minutes.

In summary it looks like I have good cooling water flow all the way through the engine but somehow it is blocked at the muffler and doesn't come out.

What do you guys think?
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Old 11-09-2009
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Disconnect the muffler, and go from there........i2f
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Old 11-10-2009
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The exaust has been done 100 different ways BUT at some point the water gets injected into a pipe to cool the hot gas before the water lift muffler and this can get all kind of rusty and block the flow

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Old 11-10-2009
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The mixing elbow itself could be sufficiently corroded to block the flow at that point, or as Tommays points out the injection nozzle could be the culprit.
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Old 11-10-2009
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Are you sure you don't have blockage in the engine cooling passages? The raw water cooled A4s are noted for that problem. If so, you will need to back flush or acid flush the engine.
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Thinking about your problem If your sure you have WATER FLOW then i would check the thermostat as i just changed one that was stuck CLOSED

It allowed full water flow through the bypass and into the exhaust manifold BUT NO flow through the block which is were the temperature sender is so it got HOT

I cant really see how exhaust could flow through a water lift muffler and NOT water so you need to take a picture as there again no standard install

And one final thought the exaust manifold is the final place ALL water has to flow through and it could be blocked
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Last edited by tommays; 11-11-2009 at 07:54 AM.
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Old 11-11-2009
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The A4 is a thermostat BYPASS engine .... meaning if the thermostat is CLOSED (bypassing the flow 'around' the engine) ... the entire flow of water is bypassing the block. When the thermostat is OPEN, water enters the engine block. (corrected/edited)

A more common water ***blockage*** problem in the A4 is the Universal Cast Iron Exhaust manifold ---- slab rust !!!!!!!! Huge 'platelettes' of rust break loose from the internal water passages of the exh. manifold casting and thus block the water outlet. (Sometimes these 'slabs' will temporarily shut of the flow and when the engine is stopped, they fall back to the bottom of the inside of the manifold ..... waiting to later block the flow at the most inopportune time. Easy way to check: remove rubber inlet hose and see if there is flow (3 gallons per minute at ~1500 rpm), then reconnect the inlet and disconnect the outlet. If no flow at the outlet, remove the exhaust manifold and turn it upside down .... and use a stiff wire and insert in both the inlet and outlet and BREAK up all the 'slabs', then shake the manifold until they ALL come out .... there will be some slabs that have 'cemented' themselves to the bottom of the manifold. DO NOT use ACID to clean out the manifold (or engine).
BTW - take a dental pick or other 'probe' and count how many treads are left in the engine casting (manifold bolt holes) when you remove the manifold and its bolts. If you can count 4-5 threads remaining, then the A4 still has enough 'meat'; 3-4 or less threads remaining .... you will soon need a new engine.

For more precision to validate that the manifold doesnt have pin holes (communicating water to the 'gas side' and into the cylinders), seal either the inlet or outlet, apply a 'nipple' to the other and with a gage and hand pump (*with gage and gas-tight shut off valve) inflate the manifold with at least 10-15 psi of air pressure, and shut off the valve. Watch the gage to 'hold' pressure - shows that the manifold is still 'intact' internally.

Never ever ever, drain the cooling water from an A4 and store it 'dry' as this will accelerate the formation of 'slab rust'. Always 'store' or lay-up the engine with fresh water + antifreeze with **RUST INHIBITOR**, never 'dry'.

Other: The A4 usually never wears out!!!! it usually rusts away on the 'inside'. The best way to prevent internal destructive red ('ferric') rust is to 'run hell out the engine' and be sure that the engine/manifold gets HOT regularly. The HOT temperature will 'convert' red (ferric) rust to black/blue (ferrous) rust - which is 'protective' to cast iron (the US Navy 'never' shuts down its cast iron engine systems for this very reason). When being made in a foundry, etc., cast iron when it cools down in it mold when made, stratifies - like an onion with many 'layers'. The formation of red rust between these stratification layers generates huge pressure and breaks the layers apart (slab rust), keeping the protective (ferrous) black rust intact will prevent such destruction - by use of rust inhibitors or keeping the engine HOT. If you want your A4 to 'last', run the hell out of it.

Last edited by RichH; 11-11-2009 at 01:05 PM.
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Rich

The A4 is a thermostat BYPASS engine .... meaning if the thermostat is CLOSED (bypassing the flow 'around' the engine) ... the entire flow of water is THROUGH the block. When the thermostat is OPEN, water BYPASSES the engine block.


You have that backwards NO water can flow through the block were in enters through the tee on the water jacket plate When the thermostat is closed other than a small amount through the air bleed hole in the thermostat

It ALLWAYS goes through the bypass to cool the exaust manifold
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Last edited by tommays; 11-11-2009 at 12:37 PM.
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Quote:
Originally Posted by tommays View Post
Rich

The A4 is a thermostat BYPASS engine .... meaning if the thermostat is CLOSED (bypassing the flow 'around' the engine) ... the entire flow of water is THROUGH the block. When the thermostat is OPEN, water BYPASSES the engine block.


You have that backwards NO water can flow through the block were in enters through the tee on the water jacket plate When the thermostat is closed other than a small amount through the air bleed hole in the thermostat

It ALLWAYS goes through the bypass to cool the exaust manifold
Yup you're right. .... must have been momentary 'dain bramage'. I corrected the previous post.
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I agree with "Faster" that happened to me.
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