running bad/over heating

[Josh]

Help! My a4 is running verry rough, it will not idle and it is overheating. I need some advice. I have rebuilt the fuel pump and carburator so i think that it hase something to do with the overheating. It has overheated three times such that the paint on the head has blistered up.

Thanks

[Don Moyer]

Josh,

Whether or not the rough running is connected to the overheating, you'll have to take care of the overheating first. Here is a guide to "overheating basics" to get you started:

Check first to see if you have a normal flow of cooling water coming out of the exhaust. A normal flow of engine cooling water will usually be sufficient to build up a head within the water lift muffler at idle to overpower the exhaust pressure, and result in a "batching" of the water out of the exhaust every second or so.

If you do not have a normal flow of water through the exhaust system and out the back of the boat, your water pump could be too weak to provide sufficient water flow, or you could have a restriction in a location that can limit the total flow of water. Examples of these restrictions include a blocked raw water through-hull, a piece of broken impeller in the elbow on the outlet of the water pump, a clogged manifold, a blockage in the inlet fitting to the exhaust system, etc.

If, on the other hand, you experience overheating while observing a normal flow of water out of the exhaust, you will have to look for a restriction that is preventing water from entering the block and preferentially moving through the by-pass hose instead. Examples of such a restriction are a blockage within the "T" fitting, blockage in the diverter cap inside the center of the water jacket side plate or a thermostat that is stuck in the closed position.

You can troubleshoot the extent of a blockage in this location, as well as getting some short term relief, by clamping the bypass loop partially closed with a pair of pliers or a small "C" clamp.

NOTE: The bypass loop is the hose between the "T" fitting in the center of the water jacket side plate and the inlet to the thermostat housing. The short hose on top of the head between the thermostat housing and the manifold is not part of the by-pass loop.

If the flow of cooling water out of the exhaust reduces significantly as you clamp off the by-pass hose, the restriction would be quite serious and will probably require removal of the water jacket side plate and/or or the thermostat for further inspection, cleaning or replacement.

Don

[Fred]

Don,

I cannot tell you how much I appreciate your forum and your advice; it has been an incredible resource.

I have a 1973 C&C 27 and have had great luck with my Atomic 4 until just prior to haulout in October. While I was motoring to the crane, the engine was running rough and I had steam drifting off of the heat wrap (older asbestos I think) on the hot section of the exhaust.

Started up this spring, just fine on the hard but had the same rough ride and steam heading back to the mooring.

Water is coming out of the transom, along with a hint of a whitish fluid. The engine runs fine at idle, but as soon as I start to power up, it starts to hesitate and run rough.

I've adjusted the carb. main idle screw, with little change, so I'm looking at the back end now.

The engine temperature is consistant at 140 degrees, this engine has always run at about 140.

The configuration of the exhaust to the waterlift muffler (the original) is a short piece of exhaust hose; I was going to start there to see if it may be blocked. I was also going to pull the exhaust tubing past the muffler to see if it may have collapsed.

The oil is not milky, so, knock on cast iron, I don't think any water has penetrated the oil.

I was not planning on pulling the exhaust system at this stage, but taking it a step at a time, I'm petrified that I may break off one of the bolts. Any suggestions on all of the above???

Fred

[Fred]

I removed the exhaust hose from the waterlift muffler, only to discover that the metal exhaust split at the water entry point, solving the moisture and steam on the outside of the hot section of the exhaust question.

Do you happen to have a pdf file of the exhaust design, as you do for the Catalina, for a C&C 27 Mk II? That would be a great help.

I'm on my way to the boat, to start apply liquid wrench and MMO to the bolts that hold the exhaust to the exhaust manifold in an attempt to start the removal process.

Any other suggestions?

Fred

[Don Moyer]

Fred,

Here's a link (http://www.moyermarine.com/reference/exhaustsystem.pdf) to the exhaust system sketch.

Don

[Fred]

Thanks, this helps.

Fred