over heating....

[RonE58]

Good afternoon,
I just had my stolen moments put in for the season. After letting the diesel run for 10 mins I motored out to my slip. After about 5mins or so my overheating alarm went off twice. Once I pulled back on the throttle for a minute the sounding alarm stopped, only to start again some 5 mins later. I pulled into the slip and left the yanmar running for a time and it seemed fine. I have the boat 3 years, I changed both fuel filters 2 days ago. I never changed the impeller or themostat, could that be the problem.
Thanks
Ron

[Joe Myerson]

Ron,

I had the same symptoms for two seasons.

When I took the boat to the yard, they replaced temperature sensors, etc., for big bucks. They also claimed to have checked, but not replaced, the impeller.

When the engine finally overheated, with no cooling water coming out of the exhaust, I had the impeller replaced. It turned out that the impeller looked OK, but the metal hub had separated from the rubberized blades.

I probably could have saved some bucks if I had checked the impeller myself.

--Joe

[Jim Cornwell]

Checking the impeller is a sensible first step. Easy to see a problem and easy to fix it, unless a fragment has been carried down the line. If the impeller is okay, the problem could be fouling anywhere in the raw water path. One year I discovered I hadn't adequately reamed out the raw water intake through-hull and little crater-head critters had barricaded it, way up inside. Lesson learned, that was....

[Neil Gordon]

It turned out that the impeller looked OK, but the metal hub had separated from the rubberized blades.

What Joe said. Sometimes the hub grabs and the impeller turns, sometimes not. That's why a change in rpm can (pretend to) solve the problem.

[Ken Cave]

Impellers are cheap, considering a total replacement of your
engine!

I replace mine on a Volvo 2020 once a year, and believe me,
there are some years that it really shows wear and damage.

For those who have a Volvo engine in their boat, try Marelco
out of Seattle. Bill Tibbits, the owner of the shop, has about
everything you need to rebuild your Johnson Pump, as well
as impellers. If you can't find him on the internet, call him
at 206 545 4224.

I have worked with him for over 11 years, and he has the best
advise ever when it comes to water pumps.

Ken Cave
Dragon Tale
LaConner, WA

[Steve Kuhar]

Ron,

I agree with all the suggestions to check the impeller, I am assuming that you check for a good exhaust flow every time you start. If you have a good exhaust flow you may also want to determine if you are really overheating. Yanmars are notorious for getting buildups on the sensors that cause a false overheat indication. Our local Yanmar expert recommends putting your hand on the valve cover and counting to five. If you can do that, you are not overheating. If you don't want to take your hand off at that point you are running to cold.

Steve Kuhar

[abcnuzeman]

I had a similar problem on my CD 25D the first season. I replaced the impeller, changed the oil and filter and changed the oil pressure sender unit. I was getting some water from the exhaust, but the alarm would start about 5 to 10 minutes after leaving my slip. Finally I pulled all the sea water intake hoses to find that all had calcium deposits to a greater or lesser extent. After a through cleaning, the problem disappeared. I didn't end up costing too much, but I lost a couple weeks sailing trying to find the problem. I now include water intake inspection in my spring commissioning program.
David Owens

[fsuhre]

Ron,
I feel your pain. Bought my CD27 in March of 2006, she was equipped with the original YSM8. Had intermittent overheating
issues through June 2008. Tried everything to fix the problem: impleller replacement, new thermostate and hoses,
coolent system flush, new belts. Still intermittent overheating. Never could predict when or where overheating would
occur. Finally out of frustration I put in a new water pump. Problem solved. Still don't know the real problem with
the water pump. Mechanically it seems very simple, the impeller, shaft, pulley and belt where not the problem.
Could it have been bearings, or seal failure within the pump??? Good luck in solving your problem. I you have any
thoughts on why my waterpump was intermittently failing, I like to hear them.
Bart

[moctrams]

Check your water filter, if there is one. It sounds like the pump is losing its "prime" by getting air into the water. I've seen a lot of that with boats having a Vetus filter. Not so much with th eGroco.

[RonE58]

Ok, I replaced the impeller, even though the old one looked fine.
My buddy and I motor her hard for 40 mins or so took her out and back. There was no alarm, no overheating and the flow coming out the exhaust looked better than I can recall. The yanmar sounded great, not sluggish at all. I took a few hoses off and showed them to a local marine supply and he told me they were fine. So I appear to be back un business. By the way removing the water pump and then removing the impeller was very easy.
Thanks everybody who chimed in with some great advice,
Ron

[Joe Myerson]

By the way removing the water pump and then removing the impeller was very easy.

Ron,

It sounds like you had the same problem with your impeller that I had.

You might consider installing a SpeedSeal, so you can change the impeller while on the water without removing the pump, and do it without using a wrench.

Sail on,

--Joe

[Ken Cave]

On the Yanmar, my friends carry an extra mixer elbow when they
are about to embark on a long voyage (Anacortes to Mexico)

It seems that they get clogged up with the exhaust coming out of
the manifold system and the water that also is injected to keep
the exhaust cool so it doesn't do damage to the muffler and all
its related parts.

Worth a thought anyhow

Ken Cave
CD 28
Dragon Tale
LaConner, WA