Coolant leak AND high temperature alarm

[c34no1471]

I have a Catalina 34 MKII, hull number 1471.  This week-end I started the engine Sunday morning after anchoring overnight, and the high temperature alarm light went on and the buzzer sounded, immediately, and they continued to alarm, although water was being discharged out the exhaust.  I shut the engine down and checked the coolant and oil levels, which seemed o.k. I then managed to get the anchor up and sail (almost) into my slip, running the engine for (I'd guess) at most a minute or two, first very briefly to free the anchor, and second as I needed a bit of help maneuvering into my slip.  This second time I ran the engine, the alarm did not sound!

I then tried to start the engine after a couple of hours elapsed, and it alarmed again.  The coolant level seemed o.k. and the coolant was not warm.

I have since talked with the folks who regularly service my engine.  They agreed it could be a faulty alarm, but it also might be caused by an air bubble in the coolant line, I presume because that would be making the pump run dry rather than circulating coolant. 

My first question is--why would that trigger the alarm on startup?   Does the high water temperature sensor alarm simply because of an absence of flow?  The engine was clearly not yet running hot. Could the dry-running pump heat the sensor that quickly?

I have since found evidence (today) of a slow coolant leak--namely, coolant in the bilge.  I've never before seen that. I also tried starting the engine, and this time it did not alarm! Again, to be safe I only ran it for a few seconds.

I'm having a local expert mechanic come check things out with me Friday.  In the meantime I have read the many helpful posts on this forum, on the temperature alarm, and the many helpful posts on coolant leaks and replacing hoses.  But I'm stuck at my first question--why would the coolant pump (apparently) running dry immediately trigger the alarm and keep the alarm lighting and sounding? 

Thanks! 

George Alberts
Catalina 34 ("Breezing Up")
on the Chesapeake Bay

[Ken Juul]

The fact that it is intermittant and happening on a cold engine probably points to the sender or wiring.  Check all the connections; at the sender, instrument panel and any connections in between.

The reason an air bubble will cause the alarm to sound on a hot engine is that the air tends to get trapped in the thermostat housing.  This is where the sensors are mounted.  The metal in the thermostat housing heats up because air will not dissipate the heat, causing the alarm.

The coolant pump should be ok, it has a metal impeller and is much lower on the engine so it should have stayed submerged.  Find and fix your leak.  Refill and burp the system to remove any trapped air. Don't forget to make sure the lines to the water heater are full.  Start it up and see what happens.  You will not hurt the engine by running it for a few minutes.  Even on a hot day it takes a good 8-10 minutes to get the engine up to operating temp.

[c34no1471]

Ken,

Thanks for the quick and insightful answer.  It makes sense that the temperature sensor, being near the high point of the coolant cycle, could be sensing hot air. That should show up as a high reading on the temperature gauge, as well as triggering the alarm buzzer and light, right?

I'll do everything you suggest.  Finding the leak looks tricky if it is a hose or hose connection.  An earlier post on the forum suggested a coolant leak could be due to "weeping" from the pressure cap rather than a leak in the lines.  I'll certainly look into that. As you know, it's hard to get a good look at some of the hose connections--I believe I need to check the connections to and from the heat exchanger, as well as those going to and from the water heater, and to and from the "expansion" tank.

Regards,

George Alberts,
Breezing Up

[Jack Hutteball]

George, check the connections of the engine heater lines to the hot water tank.  They are hard to get at on the MK II, but that is where I found the leak on my boat.  The hose clamps were only on finger tight.  figured it must have been lunch time when they were working on that part of the boat and never got back to it!!

Jack

[Stu Jackson]

Hose clamps loose on new boats???

Seems very familair:  http://c34.org/bbs/index.php/topic,3117.0.html

[c34no1471]

Here's a quick report on the mechanic's visit--he put the cooling system under pressure (about 17 psi) and we found a leak at one of the two hose connections at the engine, running tothe hot water heater.  We found no other leaks. He "bled" coolant to and through the thermostat housing, I topped up the coolant in the overflow tank, we ran the engine for several minutes, watching the oil pressure (he attached a pressure gauge) and engine water temperature, and all was fine.  He checked the engine water temperature gauge by checking the temperature at various points on the engine, and it was working great.  He tested the temperature and oil pressure switches, and the corresponding alarms, and they seemed to be working properly.  He also adjusted the valves, and showed me how to do that.

He says the only remaining explanation for the intermittent triggering of the alarm would have to be an electrical issue in the engine panel.  I said I'd remove it at some point and examine it. 

So I'm back in business.  Thanks for all the helpful input.