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  #1   IP: 71.172.171.68
Old 05-21-2007, 11:20 PM
ChickenEye ChickenEye is offline
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Strange Water Flow Problem - SOLVED

I have a '77 Pearson 30 with the original Atomic 4 engine, raw water cooled. The exhaust system was replaced from the manifold out to the outlet at the rear of the boat three years ago.

During my pre-launch engine test, I ran into a problem I can not figure out. The A 4 started easily and ran well (and continues to do both). When the boat is on the hard, I use a 5 Gal pail and draw water from the pail through a hose and T-fitting. I noticed the engine was not drawing water quite as well as it normally does, although there was definitely water flow from the exhaust, along with some steam. As soon as the engine came up to operating temperature, water flow stopped, but the steam continued. Then, very shortly after, hot, cruddy water began flowing back into the pail from the engine. I shut the engine down and took note of the temperature gauge, which showed about 185 degrees, which is a good bit hotter than normal.

It had been a few years since the water pump impeller has been changed, so I did that (the old one was in good shape with no missing vanes) along with the shaft seals and pump gaskets. After that fun job was done, I removed the bypass hose from the outlet of the thermostat housing and got good water flow on starting the engine, so I reconnected it and got the same result: OK water flow, no water flow, then a backup of water into the pail. At this point I removed the thermostat and made another attempt with the same result. I have attempted an acid flush of the engine according to the recommendation posted here but there has been no change. Weak flow when cold, reduced flow as the engine warms, then the backward flow past the operating water pump. Through all this, the motor runs smoothly and sounds perfectly normal.

I also notice, after the engine has been shut off, water boiling up into the hose where water exits the manifold.

Any ideas or help would be greatly appreciated.

Last edited by ChickenEye; 05-24-2007 at 11:00 PM.
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  #2   IP: 74.40.167.110
Old 05-22-2007, 09:27 AM
JimG JimG is offline
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Sounds like your manifold is nearly clogged or maybe the injection point after the hot section. It's open enough to let a little water through, but once the manifold reaches boiling, steam drives the water back out the water pump.

I'd suggest disconnecting the water hose from the aft end of the manifold and checking the flow - good flow points to the mixing tee, bad flow points to the manifold. I'd pray for the mixing tee!

Seems like a pretty diabolical balance!
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  #3   IP: 38.118.52.41
Old 05-22-2007, 10:13 AM
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I find the clear relationship between temperature and water flow stoppage particularly challenging.

Water flow stoppage occurring at higher temperature is somewhat typical of a blockage within the exhaust system, most likely a breakdown of the inner layer of the rubber exhaust hose several feet after the water lift muffler. However, with your exhaust system having just been replaced three years ago, we'll have to rule out exhaust issues.

The only other mechanism I can think of that would explain the onset of the problem occurring with elevated temperature is the action of the thermostat, but you report the problem remaining after the thermostat is removed.

Looking past the temperature/flow stoppage relationship, the stoppage of total flow can only be explained by a blockage from the outlet of the thermostat housing to the point where the water enters the exhaust system, meaning within the manifold itself or within the fitting where the water enters the exhaust system.

Based on the buildup of a sufficient volume of steam pressure to force water back through a normally operating pump, my guess is that a blockage develops in the fitting where the water enters the exhaust system. I have no explanation of why the blockage would only occur at an operating temperature of 185 degrees.

Don
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Old 05-22-2007, 10:50 AM
ChickenEye ChickenEye is offline
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Well, so much for the hope that it was something deceptively simple.

I guess it's time to start disassembling. My plan is to start with the fitting that injects water into the exhaust, then the manifold. If neither one of those is the culprit, it's going to be a long summer.
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Old 05-24-2007, 11:37 PM
ChickenEye ChickenEye is offline
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OK, it appears that I have fixed this problem, and it really was deceptively simple! After a little amateur detective work, I determined that the blockage was indeed in the manifold. I got the proper fittings to attach a garden hose to the inlet and outlet of the manifold and put a blast of 80 PSI water through it, which dispatched the clog in no time. I have normal water flow now. That's the short story.

**WARNING** Long-winded explanation ahead **

I also have a theory on why this blockage exhibited such strange symptoms. On initial startup of the engine, there was leftover water in the muffler/exhaust pipe which was expelled with the exhaust when the engine was started. At the same time, water was being drawn out of the bucket by the water pump and pushed into the empty manifold and block. This gave the appearance of "normal" water flow. As the small amount of water left over in the muffler was eliminated, the outflow from the exhaust slowed and stopped. Meanwhile, as the manifold and block became full, the pump was unable to draw more water in. What appeared to be a single event was in reality two separate but related events, as they occurred simultaneously (or close enough, to a single observer going back and forth from the engine compartment to the transom checking for water flow) and were both due to the blockage in the manifold.

While the engine was relatively cool, the water pump was able to keep the water in the engine. As the temperature of the engine rose above 180 degrees or so, the pressure of the water and steam rose enough to overpower the pump and blow back into the bucket, since the blockage in the manifold was severe enough to prevent anything but steam from escaping to the exhaust system. Because the water and steam were able to escape past the pump and out of the inlet hose, there was never enough pressure built up in the manifold to clear the blockage. This is what really had me fooled - the appearance that there was good water flow initially but blockage developed as the engine heated up. In reality, there was never good water flow through the manifold at any temperature.

Some steam did get through the blockage, as evidenced by the boiling I noticed in the manifold outlet tube after the engine was shut down, and I believe this to be critical in both my initial mis-diagnosis and the eventual solution. Since some steam was escaping the manifold and getting into the exhaust, but the engine was not running, there was no way for the steam to escape the boat before it condensed back into water, which again collected in the muffler and became an apparent through-flow of water when the engine was first started. I did notice that each time I started the engine after it had cooled, there was a smaller and smaller amount of water expelled through the exhaust even though the water drawn in remained fairly constant. It finally dawned on me what was happening and it took only a short time after that to clear everything up.

Again, this is just a theory but it certainly explains all the symptoms and it was the reason I did a high-pressure flush of the manifold which ultimately solved my problem and allowed me to put my boat in the water, finally.

Last edited by ChickenEye; 05-24-2007 at 11:41 PM.
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Old 05-25-2007, 07:21 AM
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Don Moyer Don Moyer is offline
 
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ChickenEye,

Thank you for your detailed analysis of a very intriguing sequence of events. What we seem to have learned in the event we ever encounter these symptoms again has most to do (it seems to me) with the observation of initial "normal flow" out of the exhaust. Your period of normal flow must have been very short - perhaps one discharge from the water lift muffler or even less.

We hear of quite a few severely blocked manifolds over the course of a season, but to my knowledge, none have reported your symptoms, so I'm wondering if we're still missing something. It seems odd to me that the pressure built up by the steam would have been able to expel enough water in both directions so that you could watch water come back through the pump and into your bucket while at the same time force enough water through in the normal direction to give you the impression of normal flow from the exhaust.

It seems that something in your system was functioning more like a heat controlled check-valve than a simple blockage. Was there anything unusual about the blockage in your manifold?

Don
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Old 05-25-2007, 09:32 PM
ChickenEye ChickenEye is offline
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Unfortunately, I did not get a good look at what came out of the manifold as I had the outlet connected to a garden hose and discharging overboard and, once it was apparent the blockage was cleared and there was no restriction in the manifold, I saw no point to any further disassembly. I'm going to save that for a winter project; assuming all goes well this season, of course!

In retrospect, there may have been some water flow past the blockage and I will theorize about that as well. When the exhaust was cold, this small flow was able to collect in the muffler and be lifted out as normal. As the exhaust heated up, this small flow boiled upon injection to the exhaust pipe, and exited the exhaust system as steam. This would account for the unusual amount of condensing water vapor I observed leaving the exhaust as the engine warmed and the water flow slowed and apparently stopped.
Again just a theory, but it explains the symptoms.

I plead guilty to not observing water flow from the exhaust for sufficient time to get an accurate picture of flow. Chalk that up partly to trying to observe at the same time how well the water was being drawn out of the bucket and partly to my inexperience.

I agree with you that I should have been more careful in checking water flow. I think I should have put a bucket behind the boat to collect and measure the exhaust water against what was being drawn in. My observation was very casual and the flow *seemed* to be slightly less than normal at the outset. I now believe it was significantly less than normal, a fact I could have ascertained immediately with a quantitative measurement rather than an observation. That probably would have led to a much more speedy and accurate diagnosis.
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Old 05-26-2007, 06:39 PM
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No problem. I didn't mean to question the accuracy of your observations. I actually found them to be far more detailed (and useful) than normal.

Don
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Old 05-29-2007, 05:05 PM
rkinghunt rkinghunt is offline
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Another strange water flow problem

This past Saturday I was trying to my '77 Catalina ready to go. The last task was to replace the impeller on the water pump (Oberdorfer). With that accomplished I started it up and it ran fine. I observed good water flow and continued to run the engine at various rpm's and then notice a change in the sound and the temparture rose quickly to 200 degrees and no water was flowing out the exhaust. Tried opening and closing the bypass but still no water flow. Read the post from ChickenEye and tried to find blockage on Monday. Removed hose from thermostat housing to the exhaust manifold, connected hose and flushed the water thru the manifold outlet with clear plastic tubing overboard. Got a good flow and ran until clear (water discharge was not as dirty as I expected, no chunks either). I then hooked the hose to a tee fitting on the hose for the supply to the water pump. Hooked my clear tubing to the bypass hose where it connected to the thermostat housing. Flowed the water and got water thru my clear tube and also out of the inlet and outlet of the thermostat housing. Not really finding a clear problem, I reconnected everthing and started her up. Ran the engine for 30 min. observed good water flow with either the bypass valve open or closed. Temperature remained constant at about 140 degrees with either to bypass valve opened or closed. Decided to go sailing, motored out and didnot observed any problems either with temperature or water flow. On way back in had issue with popping at the arrestor (see backfiring? post from 5/29). Went back to boat today and started up the engine again to see if I could further isolate or figure out the popping problem and I again ran into the same water flow problem. This time I didn't have my tubing or the fittings to find problem. Neither time though I didn't really observe any steam. Any sugestions?
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Old 05-31-2007, 07:28 AM
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Don Moyer Don Moyer is offline
 
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My first suggestion would be to examine the first few feet of exhaust hose coming out of the water lift muffler. Your symptoms (change in sound and then rapid temperature rise) are consistent with the inner layer of that exhaust hose collapsing in and blocking the exhaust.

Don
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