Tuesday, March 18, 2014

Hot Engine

Once returning to the boat, the first order of business, maintenance wise anyway, was to determine the state of the engine.  We had obviously overheated the engine, but without the alarm the engine could have been hot for anywhere between 10 seconds and 10 minutes.  My hope is that it was at the shorter end of that spectrum.

Since a prior mechanic had done a fair amount of work on the cooling system of that engine, I decided I should have another mechanic (an unbiased third party) come help determine what had happened.

Now, before I left I knew that the coolant was down quite a bit and suspect that the missing coolant was the cause of the steam in engine room.  The plastic overflow bottle was empty and the cap was found elsewhere in the engine room. The secondary coolant reservoir (this is the engine that is plumbed into the hot water heater) was empty and I couldn't see coolant in the engine when I removed that radiator cap either.  These are not good signs. I had looked around and didn't see any loose or broken hoses or missing clamps either.  On the bright side, there did not appear to be any contamination in the oil.

The mechanic arrived and did similar inspections and could find nothing wrong either.  Then we checked the impeller.  For those not familiar with a boat impeller, it is the working part of the raw water pump.  Unlike your car that uses air to cool the engine coolant that then cools the engine, a boat uses sea water (raw water) instead of air to cool the engine coolant.  Since sea water can contain contaminants, the pump needs to be more forgiving of the liquid it pumps and so the working part of the pump is a series of neoprene rubber fins attached to a hub kind of like a water wheel..this is the impeller. When the impeller rotates, it moves water and if you restrict the clearance on one side of the impeller chamber, water will flow in one direction and you have a pump.

Impeller conceptual drawing - found on the internet.

So, you might have guessed that this little piece of rubber is fairly important.  When we opened up the impeller housing, we found that the impeller had self destructed. As a result the engine wasn't getting cooling water to cool the engine coolant and this was the direct cause of the overheat (just as if you had completely blocked the radiator in your car).

A new impeller on the left, the one from the engine on the right.

As the impeller spins, it rubs against the metal housing of the pump body.  As you can imagine this causes quite a bit of friction.  When it is pumping water, the water lubricates and cools the impeller, but if the water supply is blocked, the impeller will generate heat and rip itself apart.  It is our best guess that this is what happened.  Maybe a piece of plastic or other trash was sucked up against the intake and blocked cooling water.  The truth is we will probably never know.

We removed the pump, dug out all the parts of the impeller (as shown in the above picture), did our best to confirm we had all the pieces of the impeller and checked the raw water entrance to the heat exchanger (radiator) for any additional impeller pieces.  We checked the strainer and the hoses to ensure there was no blockage anywhere in the system (and we found none) and then put it all back together.  When we added coolant we found that it took about half the amount of an empty engine (so at least we didn't boil it all out).

We then tried to start the engine.  It was a little hard to start but did start up and didn't appear to smoke or do anything out of the ordinary.  We carefully watched the temperature as the engine ran and it came up to it's prior operating temperature.  Watching the needle, we could see when the thermostat opened and the temperature stabilized.  Since the temperature needle stopped at 188°F and the prior mechanic indicated that the gauge was indicating 15~20 degrees high, we again checked the temperature of the engine using a laser thermometer on a number of engine locations.  At the temperature sensor, the temperature was actually 168°F and the hottest temperature we could find was 172°F.  So we did confirm that the gauge was reading a bit high as was previously reported.  Guess I'll need to see what options I have to make this system more accurate.

The other issue was why the high temperature alarm didn't go off.  We tested the circuit by grounding the wire and the alarm did sound...albeit not as loud as I would like.  I'll have to pull the sensor and put it in some boiling water to see if it is working at some point.

But the good news is that the engine is alive and that is a relief...particularly to my bank account.


  1. Doesn't sound too bad. Hopefully you didn't do any real damage to the engine.

    When you had the steam in the engine room, were you also finding any antifreeze on the floor? Just curious where all of the antifreeze went.

    I am also curious if the earlier mechanic changed the impeller. That should be part of standard maintenance and he should have. I change mine each year. I know others let it go longer but for a $15 part its not worth risking the engine.

    Good luck and fair winds,


    1. Hey Jesse,

      I completely forgot...I did pump some fluid out of the bilge before I left the boat...didn't want it discharging anything into the marina. I had a fuel leak prior and I don't think the other mechanic cleaned up some of the spilled fuel...so what I pumped out was reddish in color (the installed antifreeze wasn't red). Some of that was likely antifreeze though.

      The impeller was changed as part of the standard maintenance that was performed on the engine a month or so ago after I bought the boat. So, it was only in the boat a few months and a probably under 24 hours of opoeration...although it was a spare that came with the boat so I don't know how long it had been stored (I did all the standard maintenance stuff myself with the aid of a fellow cruiser that made sure I did things right...like using the lube to install the new impeller).

      Oh, and the impellers that fit these engines seem to only be available through Westerbeke for $50...they have a smaller center pin than the one in the picture above. Some boat parts seem to be a lot like aircraft parts as far as inflated prices go.


    2. Mike,

      I guess I exaggerated on the cost of the impeller. I just checked my supply spread sheet and its $37.99. So same ball park as yours.

      If I was in your situation there are two things I would think. First would be that the impeller could have been old and that's why it failed. But the fact that you didn't have pieces in the heat exchanger makes me think that you didn't have water. Whenever I have seen a failed impeller and there was water flow, you had some pieces in the heat exchanger. Running a impeller dry will destroy it and result in what you have from your exiting impeller.

      So my next thought would go to external strainers/screens. Do you have these on your boat? If so, plan a haul out and remove them. See here: http://www.pbase.com/mainecruising/external_strainers.

      Good luck,


      PS another thought would be that your engine was air bound. But since you have the issue with the impeller I would think that is more of the issue but you could also have several issues coming into play. Did the mechanic bleed the air from the antifreeze side of the system?

    3. Yeah, the most likely hypothesis is that something temporarily plugged the intake through-hull and cut off or severely diminished the water supply. We checked the internal strainer and it was fine. We actually also poured water in the strainer to see if it would flow from the strainer back through the intake through-hull and it appeared clear (there may be an external strainer but I don't recall from the haulout and can't locate a picture to check...will definitely pay attention to it the next time it is hauled...and probably have it checked the next time the bottom is cleaned). We did inspect the entire raw water path and found nothing.

      And after reassembly, water is flowing as it should and the engine is running at normal temperature. Once we refilled the engine, we did bleed air out of the antifreeze side (don't know what the prior mechanic did...but given the that the petcock was broken, probably not).

      The bigger issue for me is why the alarm didn't go off. Would like some other warning than trying to watch a needle down by my knee at the helm...or waiting for steam to pour out of the engine room.

    4. Oh, I guess I should mention that some of the fins of the impeller were jammed into the out flow tube of the pump. So, if the larger pieces were jammed in first, then only very small bits could pass...ones that would likely have passed all the way through the cooler.

      So, it is possible that the impeller was just old and broke apart I guess. Makes for an interesting academic discussion.

  2. Hmm. My experience on cruising cats is admittedly limited. But on monos one of the things that most skippers learn is the sound of their engine pumping water. Also, you get in the habit, or should get in this habit, of checking for water flow every time you turn on the engine.

    On the occasions that you pick up some seaweed or something that clogs your intake, you can hear the difference.

    To your point of wanting the alarm to work and not wanting to have to look at the gauges all the time. Welcome to cruising and boat ownership. I never rely on the alarms. I scan my gauges about every 20 minutes. It just becomes part of your routine. On longer passages I will open up the engine access and check it with my IR thermo a couple of times. My boat came with gauges for temp, rpm's and battery charge; it has alarms for high temp and low oil pressure. The only time alarms have gone off is when they were broken. I purchased the parts to add an oil pressure gauge but haven't gotten to it yet (another part of cruising I hear). I would rather rely on gauges then alarms and I check the accuracy of the gauges often.

    Of course the goal is to not be powering on longer passages since we own sailboats but since we are still weekend warriors when it comes to cruising (i.e. still stuck in the rat race) it happens more then I would like to admit. If there is no wind on Sunday and you need to cover 50 nm to get back to home port so you can work on Monday, on goes the engine.

    Good luck. I hope it just ends up being a bad impeller.


    1. Hey Jesse,

      Oh, I hear you (no pun intended). With two engines one may mask the other a bit, but I'm sure it provided some signs that weren't picked up on. I knew there was a problem as soon as I got back to the cockpit. Can't blame my wife though, she is just too new to the boat...and the boat is pretty new to both of us...that's why I'd like the alarms to work. Redundancy is a good thing and given that the entire instrument cluster is "fly by wire", any or all of them can pretty much fail at any time.

      Thanks to my pilot training I'm used to scanning gauges regularly and had been trying to...even though it requires hopping down from the helm chair to do so. Certainly can't scan as often as if they were in the field of view, though. The whole issue occurred in just a few minutes in the time we engaged the engines and dropped the main. I've heard a dry impeller can self-destruct in just a couple minutes and that supports the working theory of a temporarily blocked intake.

      And I totally hear you on the sailboat thing. Need to get out of the ICW where we can actually be a sailboat and not a tall motorboat...but as you say...schedules sometimes dictate other measures.

      The engine now has a recently purchased Westerbeke impeller and hopefully it will run a long time without issue...but I'll definitely keep an eye on it.

      As for getting around to it...that list is very long and every time one of these issues pops up it just puts others on hold. ;-)

      So, how did your book swap work. I've got books that I need to pay forward as well...of course that is also on the above list.

      Take care,

  3. Someone messaged me privately and suggested that these may help improve impeller life in a run-dry situation. Thought I'd throw it out here for info and comment as well.