Recent hot running of M-25xp

[Patches]

Stumped right now on the elevated running temp of my M-25XP.

Went to a new Oberdorfer raw water pump about a month ago.  The impeller on my Sherwood pump shredded, which led to very high water temp--220 as read on my engine panel temp gauge.  Shut it down and sailed back.  Swapped in the new Oberdorfer. Took apart the input end of the heat exchanger and removed the bits of Sherwood impeller.  Primed the raw water intake, strainer, new pump and hoses. And everything worked.

After swapping out to the new Oberdorfer, the temp initially stayed below the 160 degree mark.  We have a lot of plant life in the water right now, and on a charter I noticed the temp climbing above 180.  I pulled over to an empty dock, found the strainer full of plants, emptied and continued on.  The temp went back down and good, strong flow on the raw water stream.


The last few days, however, the temp wants to go to 180 and hold. So yesterday morning I went back through everything from the new pump to the thru-hull valve.  I checked every hose, every elbow, the impeller and insured no obstructions.  Re-primed everything back to the pump.  Started the motor and--again--very strong flow out the back.

On the way back from Seattle last night I took the opportunity to watch my gauges while motoring.

On MY instruments:

2500 rpms:  5.8 knots, and 180 degrees

2000 rpms:  4.7 knots, and 170 degrees

1500 rpms:  4.2 knots and 160 degrees

I did notice that--at the higher 2500 rpms--the temp gauge needle would bounce "down" from 180 to 160 momentarily, then back up to 180 where it would stay.  On the other lower (1500) rpms, it would occasionally jump "up" from 160 to 170, and accompanied by same kind of sound in the shift in RPMs as when the external regulator steps in to limit charging. 

Any ideas about what may be happening?  Is it time to check the thermostat (which has given trouble free operation since I've owned the boat)?

Thanks in advance for for your input!

Patches

[Kyle Ewing]

I had similar symptoms once and burping the engine coolant solved the problem.  Maybe overheating the engine somehow introduced an air bubble.  Search "burp engine" here.

[KWKloeber]

You haven't mentioned coolant level.
Or whether the hoses to/from the Hx are cool warm or hot ( an indication whether the Tstat is opening correctly.)

Could be blockage at the injection wye (but you say there is good seawater flow?)
Could be (in no particular order):
   Faulty gauge
   Faulty temp gauge sender
   Faulty TStat
   Air lock.

Are you sure the engine is actually running hot (vs a faulty gauge reading)?  Maybe check it w/a thermometer.  If the engine isn't hot, check all connections and panel for wiring issues.)

Also use the gauge troubleshooting guide I put on the wiki.
Replacing the TStat is very cheap insurance if it's that old (or check it in a water bath.)  You can also check the sender resistance in a bath, and do the very coarse check that the gauge is zeroing/full scale. Replacing that (the sender) is also cheap insurance.)

[Ron Hill]

Patches : Do as Ken & Kyle mentioned.  If you don't have a Coolant Recovery system make one!!  I wrote a Mainsheet tech note article on the "How To".                       

All you need is a couple of feet of small diameter hose and a Rubbermaid quart plastic bottle!!

A few thoughts

[waughoo]

I give another vote for the coolant recovery bottle.  I had nearly identical symptoms and post coolant bottle, they stabiliazed.  I also had a gasket issue at the strainer.  It didnt seat well and would pull air now and again.

[Patches]

Thanks for the replies!

I have a coolant recovery bottle, so that is not the issue.  The symptoms (water temp reading of 180 degrees) remain after double checking for good exhaust water flow.  No smoke, as has indicated blockage in the raw water intake and/or plumbing in the past.

I'll follow the "burping the engine" path, and report back.

Again, many thanks.

Patches

[Jon W]

Hi Patches, I experienced the same temperature variability at different RPM's. I had good/normal raw water exiting the transom. Raw water strainer was properly sealed, clean, and I could see good water velocity flowing thru it. The new engine coolant level was correct, and the coolant recovery tank was fine. I had previously burped the engine coolant system so no airlocks causing overheating, and had no leaks.

First thing I did was check and clean the electrical connections at the sender and the gauge. The second thing I did was disconnect the coolant lines at the thermostat housing. I used my Handy Par pump with a very long ~1/4" tube attached to pull coolant thru the system and fed it back into the reservoir utnil mostly solid coolant. Next I put a ball valve and long hose on the top of the thermostat housing and spent ~ 45 minutes bleeding all the small and medium size air bubbles out of the system with the engine running.

I haven't had the temperature variation since. Last time I mentioned this I got skepticism. Everybody's boat and experiences are different. All I can say is the problem went away, has not returned.

[waughoo]

I'd be really curious to know more about this ball valve bleeding proceedure.  Do you have a thread where you provided more detail?

[KWKloeber]

Look on the TechWiki - I had put RCs info and pictures on there.

-k

[Jon W]

Hi Alex, no I did not make a write up. What I did is a similar process to what RC (Mainesail) suggested, but with different parts. There isn't enough clearance between the top of the M25XP and the soundproofing to have something there all the time. Plus with a shaking diesel, I do not want a cantilevered load from a relatively heavy horizontally mounted ball valve.

I permanently removed the petcock on top of the thermostat housing, and replaced it with a plug for everyday configuration. When I need to bleed the system, on a cold engine, I remove the plug and thread the ball valve vertically into the thermostat housing. The ball valve has a male thread and a female thread with a hose barb installed. I attach a long 1/4" clear tube to the hose barb, and tie it so the open end is above the companionway hatch. Turn on the engine, let it come to temperature, then open the ball valve. The coolant will percolate, and in my case initially rose up above the entry steps due to all the small to medium air bubbles. After a while the coolant had minimal to zero air bubbles, and the level in the tube dropped to what you see in the photo I posted in the previous reply. If you look at the upper left of that photo you can see some coolant droplets. That's when I shut the ball valve, shut down the engine, let it cool, removed the ball valve and reinstalled the plug. FWIW - This is not a regular maintenance task for me. I won't be threading and unthreading the plug often, so am not concerned about wearing the threads and risking sealing problems.

The above I would describe as "fine tuning" to deaerate the coolant. It is not the way I remove an airlock. For that I follow the "burping" procedure written up on this website. Hope this helps.

[waughoo]

Great explanation and it now jogged my memory that ive seen/heard it discussed before.  I found out the hard way how to burp the coolant while underway (heat exchanger 7/8" tube to pump had a rather large air pocket in it.).  I like the idea of getting the remaining bubbles out.  Thanks for writing it again. 

[Ron Hill]

Guys : Goodness!! I've never had any trouble "burping" my old or new engine - never!!  I just use the "Handy Par pump" and slowly move coolant from the heater hose back into the reservoir until the flow is all coolant!!

It almost seems that if you have new/residual bubbles? that it must be an air leak? from the outside causing more bubbles?? 

I just took a jug of 50/50 Prestone & water mix and shook it up. It is immediately milky and translucent, but in 5-10 minutes it is clear just like it was before the   
shake-up!!

I don't believe that the surface tension of that mix is substantially different from that of water!!

A few thoughts   

[Stu Jackson]

Ron, I think Jon covered it quite well in his post.  It works for him.  I do not doubt it.  I wrote the "burping" 101 based on your input over the years.  Doing what we do avoids immediate overheats which any large air bubble will cause.  Jon and others take it to the next step and are successful.   Who's to argue.  I think we can give it a break, 'cuz I'm one of the guys Jon mentioned!   

[Ron Hill]

Guys :  "Who's to argue.  I think we can give it a break, 'cuz I'm one of the guys Jon mentioned!" 

Not Arguing - All I was trying to point out is that with a coolant recovery bottle, it should be a closed perpetual system.  If you have to "burp" again because of more than just microscopic air, more air is coming in to the system from somewhere ?!?!

My thought

[Jon W]

More air is not coming in to the system. The "burping" process gets enough air out to stop the engine overheating, but it does not get all of the air out.

Do you mean closed pressurized system?