(Maybe) How to break the Water Heater

[papawads]

Our 2001 model has a water heater with a relief valve now dropping about a litre every 2-3 minutes into the bilge. This continues despite the temperature of the water inside.

Never happened before, but I think is linked to …

Today we where running the engine fast to get to a bridge raising, and the engine overheating alarm sounded. As the too-hot engine cycles water around the water heater, I’m guessing the relief valve is stuck on :-(

So it’s a lesson learned.

Quite what I do about a stuck 20 year old relief valve is a conundrum I know nothing about. Any views most welcome.

[rene460]

Hi Papawads,

Sounds like time to replace that pressure relief valve.  If you search General Jeanneau topics for pressure relief valve, you will find several posts with recommendations of where to purchase the replacement.  The same item tends to be found in RV’s or caravans when they are fitted with a hot water tank, but there are other sources that forum members have found satisfactory.

Some have even dismantled and cleaned the seats of the valve, always worth a try, but considering the age probably worth replacing.

rene460

[zaphod]

On land it is normal to replace T&P valves periodically, and on boilers it is mandatory every 5 years. You are doing well if yours lasted 20 years!

[sailingabe41ds]

20 years!  I think I would get a new one....sooner or later something else will break down after 20 years.

Abe

[papawads]

Thanks for the responses.

T&P valve replaced.

Lessons learned.

1) Running engine above 2800 rpm, even for a few minutes, both overheated the engine and triggered the T&P valve!!! Have read other threads on high revs overheating these engines.

2) Carry a spare T&P and replace working one every few years.

QUESTION:

There’s no ability to close the water circuit from the engine to the water heater. If some problem with the heater, meant no water in the heater tank, would it be unsafe to run the engine?

Thought appreciated :-)

Joe (Sandpiper of Harwich)

[rene460]

Hi Papawads, I’m glad that you were able to source a suitable replacement valve and get it installed.

However, your first lesson learned is not so straightforward.  I don’t know the specified maximum continuous rpm for your engine (it will be in the manual for the engine), but I would not expect to overheat the engine unless the cooling water flow was shut off or blocked, or perhaps the heat exchangers blocked or fouled.  No reason you should not be able to run the engine all day if you have fuel and the cooling system working properly.

First make sure the engine cooling water intake valve is open and the strainer not blocked.   And check that the exhaust is splurting out water regularly.  Then check the water pump impeller.  If all is ok there, I would have to call the mechanic, as it sounds suspiciously like your engine cooling system is not doing its job.  Could be one of any number of items, but worth checking out.  Unlike your car, your marine engine is built to run near flat out all day, so long as you have fuel, air, oil and a working cooling system.  It should not overheat in that time.

Regarding the water tank, I would not worry.  Cold water enters at the bottom and exits at the top, so it is quite hard to empty to protect the electric element.  We are lake sailors so don’t have sea room to run all day, but in when the water is glassy, we regularly run for four hours at about 2900 rpm.  Max continuous rpm for our model engine is 3600 rpm, so 2900 is about 80%.  Noise and fuel consumption make me prefer the lower rpm.  Ours is a 3YM20, but check the specs for your in the manual as it may well be different.  The mantra for a Diesel engine is “at least 80% load, at least 80% of the time”.  This does not overheat the engine or hot water tank, nor does it cause the water tank prv to weep.  The engine cooling coil tends to be self limiting through limited heating area, but in your case it seems like the engine may be overheating, with only the hot water tank for cooling, so heating the water more than the designer intended.


I hope this helps.  Please keep us all informed.

rene460

[papawads]

Thanks rene460 I’ve now done more research and came across this great thread, well worth anyone reading. www.cruisersforum.com/forums/f54/yanmar-4jh3-te-overheating-at-full-load-30869.html

That looks like a project for the start of next season, as I leave the boat this week. If I come across an obvious culprit I’ll update this post. FYI we ran all day at 2500rpm without a hitch.

Cheers -

Joe (Sandpiper)

[andreshs1]

something I learned with one of my previous boats is that barnacles also grow inside the head exchangers and overtime the water flow decreases to the point of full blockage

ever since that happened, on a yearly basis I flush the engine, A/C and generator with barnacle buster, highly recommended

www.trac-online.com/products/descalers/barnacle-buster


cheers