Here’s a real puzzler for you guys. First run of the season going down the channel to the sound and I knew something wasn’t right because the throaty sound from the exhaust tells me the water isn’t flowing right (and I also could see that the water output was down a good 50% versus normal) and sure enough the temperature is rising and so I back off on the power, and we nurse it back to the dock motor sailing. I checked to make sure that the water pump intake hose is properly clamped and it is. I then pull off the water pump impeller cover for an inspection and find that all the impeller vanes are just fine which they should be because I replaced it last season. I then lubed the cover and put it back on. I then removed the intake hose which you can do on this particular boat without causing a flood as it is above the waterline at the water pump. I then lower it and aim it under the motor so water would flow into the bilge and plenty of water comes out. I saw no debris. I then put the hose back on and clamped it properly. As a final check, I sprayed detergent on the connections while the engine was running to see if there were any tiny leaks and I did not see any. Now, of course I did not do this before. I started pulling things apart so I can’t say what it was like beforehand. I thenran the engine up at the dock And the gurgling sound disappeared and plenty of water is now coming out. I ran it pretty hard and the temperature did not elevate above 180 which is kind of where it tends to run at 3/4 throttle. So does anybody have an idea what is going on here? What are the things should I be looking at? Thanks in advance for any help you can offer.
Overheat adventure on 1985 Universal M12
- Thread starter odaydokay
- Start date
Any chance your fiddling could have knocked some crud out of the mixing elbow (assuming you have one)?
First off the vanes off the impeller being in place means nothing. There is a plethora of nothing finah made in Chine impellers that have a failed bonding between the hub and impeller. The best 2ways to confirm that the impeller is ok is to remove the pump plate and with the stop pulled have a mate engage the starter and watch the impeller spin at the same rate as the hub. OR remove the impeller. Insert a needle nose plier into the hub so that it locks against the key way. Now try to turn the rubber. If it spins over the hub, it's BAD!
All that said, the mixing elbow, thru hull and raw filter are next to check.
All that said, the mixing elbow, thru hull and raw filter are next to check.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 24,521
You might have powered over debris that partially blocked the through hull. When the engine stopped, no suction the flotsam fell away and the thru hull flow returned to normal.
Do you have a strainer on your raw water intake? Is it clear?
Certainly the exhaust elbow can be inspected.
If all is in order then it sounds like time to go sailing.
Do you have a strainer on your raw water intake? Is it clear?
Certainly the exhaust elbow can be inspected.
If all is in order then it sounds like time to go sailing.
Thanks, guys. Thru hull is cheese wedge South Bay Strainer so probably not debris there, but yes, possible. Impeller was OE, but yes maybe they do come from China and the starter handle out turn over test is good idea. Exhaust system quite new. Has a Y riser, no elbow. Unlikely an issue.
An chance I have an intermittently faulty thermostat? I actually did see some temperature "wandering" last season at constant RPM. It is original and so 41 years old.
An chance I have an intermittently faulty thermostat? I actually did see some temperature "wandering" last season at constant RPM. It is original and so 41 years old.
It's possible. At 41 years old, that thermostat doesn't owe the boat a thing. Replace it.
The thermostat on an M12 controls the fresh water coolant flow, but has no effect on raw water. So no thermostat issue would cause the reduced exhaust water you saw.
OK, thanks for that info. Won't spend time on that, but I think I will double clamp the intake hose at the water pump and inspect the end at the boat entry point to see if clamped. Am I right that an intake hose would likely not leak water at the pump as tell tale sign as it is suction.? But it is the critical hose as the pump will lose prime off an on with the smallest of air leaks, yes?
The thermostat is a genuine possibility.as well as the sending unit. For little money you can acquire a digital laser heat gauge. It will corroborate you cockpit gauge.
So are you in fact, saying that the reduced water flow can be caused by a faulty thermostat? David a sailor stated this would not do so. See above.
But it could leak when the pump/engine is off.
Engine Coolant Flow 101
Maybe this will help you understand the coolant flow:
Catalina30@groups.io | Wiki
If I can do so, without sharing off the bolts, of course. Maybe not such an easy deal as it looks.It's possible. At 41 years old, that thermostat doesn't owe the boat a thing. Replace it.
I don't think the raw water is affected by the thermostat. Only the coolant.
FRESH WATER CIRCULATION DIAGRAM
ALL MODELS EXCEPT M-15
Normal Range 165F to 195F
Sorry, I can't get the diagram to print here. Attached is a PDF.
FIGURE 13
1. Sea water enters through sea water inlet,
2. Through sea water valve when open,
3. Through sea water pump into heat exchanger to cool fresh water system,
4. From heat exchanger to sea water overboard through exhaust port.
FRESH WATER
1. Coolant (fresh water with antifreeze) is introduced into the system from the coolant section of
exhaust manifold by removing pressure cap and filling manifold tank to within one inch of
lower rim of fill port.
2. Fresh water engine driven circulating pump moves coolant from heat exchanger through
engine block circulating pump and thermostat back through exhaust manifold into heat exchanger
to be cooled.
The manifold serves as the engine expansion tank to allow for expansion of coolant as it is
heated. You also fill the system at this point. In some cases when hot water heaters are installed
an expansion or surge tank may be required to prevent air from entering the system.
Should your engine overheat, first check coolant level to make sure it is not low which would
cause air locks to develop. If air does enter the system, it may require a couple of fillings to
remove the air pocket. A momentary increase of engine R.P.M. to approximately 2800 to
3000 R.P.M. may aid in moving the air from the system. In some cases it may require doing
this 2 or 3 times. Do this just as you notice the temperature starting to rise above normal.
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Terrific, Richard. Many thanks. I had the coolant pump replaced two seasons ago at the very end and last year I did see some temperature wandering so I am certainly gonna be looking at the coolant situation. May need burping as you said. The lower than normal water flow was troubling, however, and I don’t love the fact that I am puzzled as to why I corrected it or it corrected itself.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 24,521
Sometimes it is best to accept the good things in sailing. Perhaps Possiden was feeling generous.
You probably realize this but burping does not affect the raw water flow. It sounds like all is well now. I might suggest being sure you have a spare impeller aboard.