Questions about my need to me engine.

[Airshac]

Just getting to know this engine. Coming over from VW buses and aircraft maintenance. The engine seems very easy to work on.
I did a compression check and had 3 cylinders at 70 and one at 65. How is that? I don’t know anything about the history of the engine.

Secondly, I think the thermostat is stuck. I guess by default, if it malfunctions it will stay in the open position. I ran the engine for twenty minutes and water was coming out the exhaust but the water temp gauge never moved. I was concerned to run it longer because I don’t know if there is a way a bad thermostat could cause water to by pass circulating through the engine? Where is a good source for a new thermostat?
Thanks for the help!

[Hawkeye54]

Welcome to the site ! There is a lot of help / expertise on the A4 available here. If you check the 'home page' and the 'online catalog' , a lot of your questions will start to be answered . . . Hope that helps !






Rick

[Surcouf]

Welcome!
Most if not all parts available at our sponsor Moyer marine.
Strongly recommend to get the Manual, a mine of information on maintenance troubleshooting etc..

https://www.moyermarineforum.com/forums/showpost.php?p=121189&postcount=159

you will find a lot of help here!

[ronstory]

Welcome and back to your original questions. Your compression is OK, not great but OK. Also, if the engine hasn't been ran regularly, you will likely see that compression increase a bit with regular use. there are techniques of putting Marvel Mystery Oil in the cylinders after use to let is help clean any deposits on the rings, etc.

How do the spark plugs look? That's a great indication on how the engine is running.

Regarding cooling, are you fresh water or raw water cooled?

[JOHN COOKSON]

I would be sure the temp gauge, wiring and sending unit are working.
Is there a valve on the bypass after the tee fitting between the engine and thermostat housing?

ex TRUE GRIT

[ndutton]

If you're raw water cooled and located anywhere other than the tropics, your engine takes forever to warm up even with a thermostat. When I was raw water cooled I rarely saw temps greater than 120° (late model cooling system, Southern California water and original Holley 3 spring dual action thermostat).

[Airshac]

If you're raw water cooled and located anywhere other than the tropics, your engine takes forever to warm up even with a thermostat. When I was raw water cooled I rarely saw temps greater than 120° (late model cooling system, Southern California water and original Holley 3 spring dual action thermostat).

On the coast of North Carolina sitting at the slip running for that time at about 1500-2000rpm. Next weekend I’m moving the boat about 6 miles, probably motoring most of that so I’ll keep an eye on it. There wouldn’t be away for water to by pass circulating through the engine if the thermostat malfunctioned would there? I don’t think so. It is raw water cooled.

[Airshac]

Welcome and back to your original questions. Your compression is OK, not great but OK. Also, if the engine hasn't been ran regularly, you will likely see that compression increase a bit with regular use. there are techniques of putting Marvel Mystery Oil in the cylinders after use to let is help clean any deposits on the rings, etc.

How do the spark plugs look? That's a great indication on how the engine is running.

Regarding cooling, are you fresh water or raw water cooled?

Raw water cooled and it’s been sitting for almost two months. The plugs had black soot on them but the tips looked to be in good shape.

[ndutton]

There wouldn’t be a way for water to by pass circulating through the engine if the thermostat malfunctioned would there? I don’t think so. It is raw water cooled.

If I understand the question correctly, that's exactly what the bypass does when the thermostat is closed, bypasses the engine and sends water directly to the manifold. Without testing (stove top pan test?) I wouldn't get fixated on a thermostat malfunction. For that matter, John Cookson's thoughts are equally viable, perhaps a gauge/sender/associated wiring problem. It needs to be checked.

Do you have an infrared temperature gun? It could provide a wealth of information. His question about a bypass valve is important too.

Another thought: are you sure it even has a thermostat? Have you removed the stat housing and had a look inside?

[JOHN COOKSON]

. I was concerned to run it longer because I don’t know if there is a way a bad thermostat could cause water to by pass circulating through the engine?

Are you familiar with a two stage thermostat? The original two stage thermostat in the A4 balances water going through the engine and water going around the engine (the "bypass").

As advised, I would hold off on ordering a new thermostat until you confirm (1) you have a thermostat and (2) if you do have a thermostat that it is working incorrectly.

ex TRUE GRIT

[Airshac]

Are you familiar with a two stage thermostat? The original two stage thermostat in the A4 balances water going through the engine and water going around the engine (the "bypass").

As advised, I would hold off on ordering a new thermostat until you confirm (1) you have a thermostat and (2) if you do have a thermostat that it is working incorrectly.

ex TRUE GRIT

Thanks for the input! I need to dig in to it a little deeper but for the time being I’m going to remove the thermostat just so I can move the boat a few miles knowing that water is circulating through the engine. I realize this won’t allow the engine to operate at optimal temperature but it’s better than having no water circulating. Is there a problem with this line of thinking for this engine?

[ndutton]

Removing the thermostat will not force water through the engine, quite the opposite. To achieve your temporary goal you must have a restriction in the bypass hose, typically a valve in the bypass loop that can be closed partially or even completely.

[ronstory]

Removing the thermostat will not force water through the engine, quite the opposite. To achieve your temporary goal you must have a restriction in the bypass hose, typically a valve in the bypass loop that can be closed partially or even completely.

Neil--

That pic is likely the prettiest bypass valve install I've ever seen.

[Airshac]

So this is a picture of my engine. The raw water comes in at the orange handle on the right hand side. What can I check with the engine running to make sure water is circulating through the engine? I verified that water was being pushed by the pump and discharging from both hoses on the left. Water leaves the engine in the black hose on the left goes to the water heater then to the exhaust via the black/green hose
.

[ndutton]

You always have full flow through the manifold regardless of thermostat position, even if you have no thermostat. As I offered earlier, an infrared temp gun measuring head temperatures would be an excellent diagnostic tool. Also, you can guaranty water flowing through the block if you obstruct the bypass hose, thermostat installed or not. If there's any uncertainty, the bypass hose is the one right next to the starter. Even a pair of vice grips will do in a pinch. It's a temporary measure if you need it until you try the many other suggestions that have been posted.

Here is a link to a flow diagram that should help. The late model diagram applies to you.

https://www.moyermarineforum.com/forums/showpost.php?p=23836&postcount=1