Overheat - Steam vs. Water

[jrys]

My atomic4 has been overheating at 3/4 throttle (6.2 knots) but not at 1/2 throttle (5.5 knots).
Even when I would pull back on the throttle when the temp reached 200, it wouldn't stop rising and I would have to shut her down. After 2 hours I would restart and appear to get little flow from the discharge, although lots of steam (smoke?) and the engine wouldn't cool down.
I ran many blockage tests (after the pump, after the manifold, etc.) - No flow problems. I removed the thermostat and no flow problems at idle and under load for ~ 5 minutes. Temp reached ~140/160 and thats it.
I tested the thermostat at home last night and it opened only ~1/4. Therefore my conclusion is bad thermostat blocking flow to cool the block. When I thought about the low trickle flow while overheating, a nearby sailor told me that if the engine was hot enough (240) the water could be vaporizing into steam instantly and that's what was coming out of the discharge with the trickle.
Can the water vaporize that quickly with a hot engine?
And can I run it (temporarily) without a thermostat to get her home to avoid the overheat?
Thanks,
Joe Rys

[Jim Booth]

Did you make it home? I would think limping home without a thermostat is safer for the engine than risking overheating.

Jim

[jrys]

Yes, I got her home. Barely. It was really bizzare. I was able to control the heat with no thermostat and a clamp on the bypass hose all day.
Then, 1 hour away (already going 7), she wouldn't cool, I pushed it and it pegged, then smoked and I finally shut her down. I had to get a tow the final mile into my slip.
I don't know if I totally ruined and fried my engine or not, but I'm ready to throw out and get a diesel.
I just bought the boat and feel cheated. Do I have any recourse here?

[hobbit91]

Don't forget to check the exhaust system. It turns out that all of my overheating problems came from a blockage in the water inlet tube on the riser. Hot exhaust turned what little water was getting through to steam. The gunk that blocked the tube made everything quickly backup and block the manifold. Once I cleared the tube, flushed the rest of the exhaust system and used a compressor to blow out the manifold and did another acid flush, I have more water coming out the back than i thought possible. Last year it would hit 180 to 200 or more in less than 1/2 hour. Last weekend I ran it for 10 hours over 2 days. it took 1 to 1/2 hours to reach 140 and another 2 to reach 160 and fluctuated in between for the rest of the trip at a steady 5.25 knots.

[jrys]

hobbit91,
what do you mean by water inlet tube on the riser?
Is that where the water hose leaving the manifold eventually hooks into the exhaust tube before the water muffler? It doesn't appear that there is much to check there?
Thanks,
Joe

[hobbit91]

Yes. I have a rubber hose going from the end of the manifold to a 1/4 (maybe a little larger) diameter copper pipe that directs the hot water into the hot exhaust section before the water lift muffler. This pipe was clogged and very little water was getting through. The water mixing with the hot exhaust helps to cool the rest of the exhaust system. If This pipe is blocked or restricted the flow through the engine is restricted as well. If insufficient water is flowing through the hot gas exhaust can make the little bit of water getting through steam out of the tail pipe. Just about any restriction along the rest of the exhaust system may let hot gasses escape while restricting the water flow. We dismantled the rubber hoses on either side of the muffler and flushed them out with a garden hose. Got a load of black gunk out. You may also want to check the exhaust hoses. From what i understand they start to rot out from the inside. Sorry this was so long but i spent half of last season and the first month of this one fixing this. If i had known then what i know now I could have fixed in 2 weekends.

[wavdancr]

Don't forget to check the exhaust system. It turns out that all of my overheating problems came from a blockage in the water inlet tube on the riser. Hot exhaust turned what little water was getting through to steam. The gunk that blocked the tube made everything quickly backup and block the manifold. Once I cleared the tube, flushed the rest of the exhaust system and used a compressor to blow out the manifold and did another acid flush, I have more water coming out the back than i thought possible. Last year it would hit 180 to 200 or more in less than 1/2 hour. Last weekend I ran it for 10 hours over 2 days. it took 1 to 1/2 hours to reach 140 and another 2 to reach 160 and fluctuated in between for the rest of the trip at a steady 5.25 knots.
Hi
I'm interested in acid flushing my A4. How does one deal with the acid and gunk that comes out? Does the boat have to be out of the water? Thanks, Bob

[Don Moyer]

Bob,

It's somewhat easier to go through the acid flush procedure while the boat is in the water. Otherwise, you have to provide water via a garden hose for the water supply and you'll have to fabricate some sort of method of catching the cruddy water that will come out with the exhaust so that it doesn't splash on some innocent passer-by.

In most cases, the weak acid solution (specified in the acid flushing procedure recommended in our service and overhaul manual) will neutralize during the 15 minutes of sitting time before restarting the engine to flush raw water through the engine and exhaust system.

Don

[Michael L]

Reading your woes sounded a little familiar. I found that reverse flushing the block would clean out my spontaneous blockage/ overheating problems, and its easy. Remove your thermostat, block (clamp) your bypass hose. To the outlet on the bell housing for the thermostat, connect a garden hose, with a presurised water source on the other end. Undo the outlet hose on your watepump and direct towards bilge, then turn on the tap. All the loose crud bouncing around in the water jacket will be blown out by the pressure and volume of water rushing through it. I carry 2 hoses on board now, one I can hook up to a municipal source and to the bell housing, and a lenght that I can run between the outlet of the water pump, and the bell housing. The later is used to reverse flush the system using the motors waterpump, although you only do it for a minute because theres no water going to the exhaust, but this has saved me when far from shore. Works for me.
Michael

[Don Moyer]

Good for you, Michael!

We've heard from at least one other person in the past year that reverse flushing the head and block (from the thermostat housing back toward the
pump) resulted in the removal of additional crud after completing a flushing operation through the drain ports and out thorough the thermostat housing outlet.

Bottom line is that the flushing procedure that is effective and easy to accomplish on your particular boat is the best one for you.

Regards,

Don