30+ Overheating- Solution in Hand?

[bigd14]

I noticed an overheating situation late last summer.
· Universal M18 Diesel, 14HP
· Campbell Sailor 3 blade 13RH P7-
· All new cooling/exhaust system hoses and exhaust mixing elbow 2 years ago
· Oversized aftermarket heat exchanger, boiled clean 2 years ago
· Oberdorfer water pump that moves water through the system just fine with fresh impeller and no airlocks
· Surface Water Temperature 80 degrees F
· Tachometer accuracy verified with handheld tach
· Cruising RPM 2200 temperature stays around 180
· Max RPM achievable under power 2600 (should be 3200 as per engine spec) and engine temp climbs to 200+. No smoke or steam.

During the purchase process there was quite a bit of confusion about the actual RPM's as measured by the mechanic (I always thought it was low at max throttle, mechanic thought it was OK even after I convinced him to revisit the boat with a handheld tachometer ). I also noticed that the boat moves really quickly at idle and requires lots of shifting in and out of gear. All this lead me to believe the boat was overpropped and the warm river water of late summer caused overheating at load. The boat's former life was in the Salish Sea with cold water temps and the situation probably never manifested itself. I called West by North to ask about re-pitching the current prop. Kelsey seemed to think that the Campbell Sailor 13x7 was too big for the boat (even though that is what West by North recommended 17 years ago) and recommended a 12x7. The new Campbell Sailor prop arrived this week. Unfortunately installation (and all other boat projects) will have to wait. I sure hope this is the solution!

 

[Frank Langer]

Hmmm... it's definitely a beautiful new prop!! I really hope you're right about it being the solution to your overheat problem, but I'll be a bit surprised if it is. Did the prop consultant think it would make that much difference?
It sounds as if you have checked and replaced just about everything in your cooling system, but is it possible that there is a problem part that you've overlooked - - a partial kink in a hose, a partly corroded, clogged raw water intake, an incorrect thermostat, etc. that only comes into play when you push the engine to high RPM, but is ok enough to appear normal at your lower 2200 RPM?
I may be totally wrong, and I'm not a mechanic, but just wondering...
I'll be interested in what others suggest, especially if anyone has resized their prop and can report on how much that affected engine temp.
Frank

 

[supersailor]

We had an overheat problem on one of our Club member's 42 footer. I turned out to be a fouled prop. He had a diver clean the barnacles off and the problem went away. The engine was working too hard and overheated.

The fact that your engine is not coming close to it's rated RPM's would point toward an overpitched prop. Call a local prop shop and ask what size and pitch are recommended. That new prop can be repitched.

 

[bigd14]

Great points Frank. I did look through the whole cooling system with the exception of the thermostat when I noticed the problem last year. Everything checked out OK, plenty of water coming out the exhaust, no clogs in the intake, strainer basket clean, coolant full, etc. I only noticed the overheating one time in September when the water temps were warmest and the guy manning the helm had the throttle advanced more than I would have. Once throttled back the temps went down to normal. I throttled up again and the temps very slowly went up to 200 before I backed off again. There was never an overheating issue prior to that day, but I was always conservative on the throttle. The nagging concern that I had since the survey that the boat was overpropped may have colored my thinking, but I scoured the internet and this fine website for answers and all directions seemed to lead to an overpropped situation. The only thing I have not done is check the thermostat. I did boil it a couple years back when I had the system apart to check function and it was fine then. But you have me thinking I should just go ahead and replace it, so I am going to add that to the list. Thank you!

Bob, luckily we don't have a barnacle problem or zebra mussels (yet!), so I know the prop is not fouled. I talked to Kelsey at West by North about re-pitching the existing prop. They had the records of the prop sale for this boat which indicated it was 17 years old. Kelsey said the prop was oversized and he recommended cutting it down to 12 inches. He also said the age of the prop and likely some dezincification may cause the prop to break during the process and he couldn't guarantee success. Given my troubles having to replace a severely dezincified strut and the appearance of some pink spots on the prop, I figured it too risky to cut down. So, new prop. I think the Campbell Sailor props are sized differently than traditional props to account for their "airfoil" shape so I am not sure the prop shop calculation would match up. For example VicProp calculator indicates a 12.8x7.5 three blade prop for my setup, which is basically what is on the boat now. Once installed and tested I will see about repitching if needed. Not sure when that will be though.


Thank you both for your thoughts!

Doug

 

[Kenneth K]

I think you're on the right track with your over-propped theory. The fact that the temp usually stays at 180 might indicate that the thermostat is doing what it is supposed to.

I followed your exhaust system re-build and I think it's top-notch--should be no problems there. After rebuilding my exhaust system, I can still get the engine to over-temp. It'll run at hull-speed all day long at 24-2600 rpm and 180 degrees. If I push it up to 2800 rpm (I can't get it much higher than that in gear) I don't pick up any speed--the stern just squats lower in the water and the temperature starts to climb. I ran it like that intentionally last season to test the over-temp alarm. After 5-10 minutes at 2800 rpm, the temp hit 200, the alarm sounded, I backed off to 1500 rpm, and all was good again within a few minutes.

I'm still running the original 2" heat exchanger, but it seems to do okay in the cool Puget Sound waters. If I re-prop, I'd like to be able to reach 3000 rpm in gear without over-temping, but for now I'm happy with what I have.

Sure is a beautiful new prop....

 

[markvone]

Doug,

It sure sounds like an overprop situation to me. However, one additional thought is a blockage in the freshwater cooling side that would limit the maximum cooling capacity which would only show itself under the worst conditions.

Mark

 

[Rufus McCool]

I don't have much experience with an over-propped boat, but it seems the symptom most will agree on is that the motor cannot reach its maximum rpm under load. Both Doug and Ken's examples identify this. As I read everyone's experience, I became intrigued as to why exactly would this over-prop situation cause overheating. Naturally, the first thing that comes to mind is that the engine is being over worked. But is it? And if it is, how is it being over worked?
Please indulge me here, because I must run this out in my mind.

I'm inclined to agree that yes, this condition could indeed cause overheating. And the lower achieved rpm below peak design rpm, the more likely overheating could occur. As the engine speed is increased to match the load, the throttle is at some percentage of full throttle (or maximum governor setting). If the load becomes too great, the rpm ceases to increase. At that point we push it further open. The engine attempts to deliver more fuel and advances injector timing slightly. And on and on it goes. But with no increase in rpm the cooling pumps run slower and raw water pumps run slower, and maximum combustion temps start to approach. If that condition is maintained, then the cooling system is taxed and overheating begins. Makes sense, right?

I appreciate being allowed to ramble on here. I know this issue wasn't necessarily in question. I suppose I just needed to convince myself.
However, I can see that any deficiency in the cooling system would be compounded in an over-prop condition, and may cause misplaced blame.
I would hope a healthy Universal cooling system has some surplus cooling to cover such matters.
I hope the smaller prop will fix the problem.

 

[supersailor]

When the engine is not coming up to speed, the water pump is pumping less volume of cooling water so there is less cooling for the load. There should be enough cooling to make up for this but if there are any obstructions or blockages (like in the heat exchanger) overheating can occur. It occurs at the higher throttle settings. When I cleaned my heat exchanger, it was about 1/3rd blocked. I now clean it every other year. I wonder how many ever get cleaned. Don't forget to exchange the pencil zinc in the heat exchanger every year. Catalina Direct is a great place to source it.
k

 

[Loren Beach]

On the subject of the pencil zinc in the stock M25XP diesel, You have reduce the length of most of the stock ones on the market, before they screw in all the way. Thus there is less zinc present than you might imagine. When you open up the HE, you may find thin pieces of old zinc's laying around, slowing up the flow of water. As Bob advises, do overhaul the HE regularly.

 

[bigd14]

Good point on the pencil zinc. I'll add that to my list. If I could only find my notes with the thread size of the zinc in the weird aftermarket heat exchanger. I did have the HX boiled out 2 years ago and its in freshwater so it should not have developed clogs unless the zinc decayed. Speaking of which (thread drift alert!) its a true zinc pencil anode in freshwater which I know is not optimal. I have magnesium anodes on the prop shaft but could not source magnesium pencil zincs. Does this matter?

 

[Loren Beach]

Good point on the pencil zinc. I'll add that to my list. If I could only find my notes with the thread size of the zinc in the weird aftermarket heat exchanger. I did have the HX boiled out 2 years ago and its in freshwater so it should not have developed clogs unless the zinc decayed. Speaking of which (thread drift alert!) its a true zinc pencil anode in freshwater which I know is not optimal. I have magnesium anodes on the prop shaft but could not source magnesium pencil zincs. Does this matter?

I have changed to the now-preferred aluminum shaft zinc's several years ago. I am not aware of any change in HE anodes, tho.
What with fears of our underwater metal wasting away and us sickening from the present rampant virus, there is a bit more free floating worry around than I would like!

While I hate to miss most of this year's outdoor activities, must admit that I am becoming eager for the arrival of 2021 ! (sigh)

 

[Kenneth K]

As I read everyone's experience, I became intrigued as to why exactly would this over-prop situation cause overheating. Naturally, the first thing that comes to mind is that the engine is being over worked. But is it? And if it is, how is it being over worked?

Here's a good article on the subject (see propeller power curves, p2), https://www.gerrmarine.com/Articles/EnginePowerCurves.pdf, but yes, the engine overheats because it is being overworked by doing more work at a low rpm (where it is inefficiently creating more heat per unit of work) while, additionally, the cooling system is circulating less water through the block than it would be at a higher rpm. I think of it like riding a bike up hill in too high a gear.

 

[eknebel]

for what its worth, my 30+ with a 16hp 5416 came with a two blade 12x12 prop. I replaced it with a Varifold 2 blade Shaft Propeller 14 x 11, which is a little under pitched when spotless(2900rpm max is 2800 rpm). I will look into getting it pitched a little more when I send it in for alignment in 2020 haul-out. here is a picture of the old prop, which lost a blade shortly after picking up a stray floating rope at idle. the engine stalling was the first indicator of a problem. my son calling a week later and saying there is "quite a bit of vibration" was the final step. 2 heavy hammers and a prop puller allowed me to replace it in the water. definitely use a umbrella to catch things you will drop.

 

[Tin Kicker]

Took my heat exchanger out partly because it was leaking and partly because all the hoses were crunchy old and everything appears to need a close look. For most of its' existence, Rag Time was owned by a doctor who would go sailing and bring it back to his very reputable marina (Port Annapolis) for any squawks. The point is that he was probably typical of somebody who pays for maintenance, and for the most part the receipts indicate that he got good service. It was a lot of money.

With the heat exchanger out and the cap off it didn't look too bad inside, other than needing a stiff cleaning, then after a mild acid soak it sounded like a baby rattle when shaken. Took a while with safety wire, forceps, and a lot of hot water flushing to get FIVE old pencil zincs out.

There are only 13 cooling passages in the 2" diameter heat exchanger so with the water flow these were probably causing some serious blockage for 4 or more. That's at least 31%.

A sticker at the port for the pencil zinc says they must be checked monthly but that sticker is mounted upside down and mostly on the bottom. Not very conspicuous.

Morals of the story are:
1. Know the zincs really do need to be checked regularly.
2. Replace them when they are a little worn, BEFORE they fall off inside the heat exchanger. They can be found on Amazon for as little as $4 each.

 

[Christian Williams]

Yep. And on my boat checking the zinc is neither easy nor enjoyable, but I need to do it more often. Maybe every three months.

I need to find a schedule where I will automatically change the zinc, not just check it. That is, when it's suspiciously porous yet not much reduced in size. That would beat "looks OK," which always leaves me wondering when I need to check again.

 

[bigd14]

Yuck! I will definitely add zinc check to the list. The stuff you find inside the cooling system while it (mostly) continues to work is amazing. As I was replacing all the hoses and fittings, I discovered a blockage in the outlet elbow of the raw water pump caused by a broken impeller vane. This had been there for some time as the existing impeller was intact. The engine had been run for many hours prior to this discovery, including a 6 hour delivery run entirely under power. Despite this major blockage the engine had not been overheating, I think due to the cold water of the Salish Sea.

 

[tilwinter]

Took my heat exchanger out partly because it was leaking and partly because all the hoses were crunchy old and everything appears to need a close look. For most of its' existence, Rag Time was owned by a doctor who would go sailing and bring it back to his very reputable marina (Port Annapolis) for any squawks. The point is that he was probably typical of somebody who pays for maintenance, and for the most part the receipts indicate that he got good service. It was a lot of money.

With the heat exchanger out and the cap off it didn't look too bad inside, other than needing a stiff cleaning, then after a mild acid soak it sounded like a baby rattle when shaken. Took a while with safety wire, forceps, and a lot of hot water flushing to get FIVE old pencil zincs out.

There are only 13 cooling passages in the 2" diameter heat exchanger so with the water flow these were probably causing some serious blockage for 4 or more. That's at least 31%.

A sticker at the port for the pencil zinc says they must be checked monthly but that sticker is mounted upside down and mostly on the bottom. Not very conspicuous.

Morals of the story are:
1. Know the zincs really do need to be checked regularly.
2. Replace them when they are a little worn, BEFORE they fall off inside the heat exchanger. They can be found on Amazon for as little as $4 each.

I hope you are not disparaging doctors. I always did my own maintenance work including changing my own pencil zincs and greasing the zincs in the rudder shaft.

 

[bigd14]

I finally got the new prop installed today. I gained about .5-.75 knots and a few hundred RPM. Max RPM is only about 2700 but it cruises now at 2400rpm at 185 degrees with no overheating whereas before anything over 2000rpm before led to a quick rise in temp. Temps do rise to about 190 at WOT but I didn’t see how long I could run it there. There is much more cooling water flow out the back.

The best part about it is how much less vibration and noise is present. It’s quite a dramatic difference and sounds like a much different (and happier) engine.

Since I am still not up to max rpms I may take the prop in for a re-pitch next time I haul it out for bottom paint. But it’s night and day better for now!

 

[eknebel]

Congratulations!!

 

[bigd14]

Coming back to this issue even though consensus says overloading engine is source of overheating. When motoring at WOT I can push 200 degrees before I chicken out and back it down. Takes a long time (10 minutes) to cool down to normal temps (~170). I can motor for hours at 2200 rpm with temps at 170. Cooling water flow looks like this:

Does that look like adequate cooling flow at speed? If not I might look into a new freshwater pump. Or maybe I need a new coolant pump? Or both…