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Old 26-02-2020, 14:49   #31
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Re: Installing EGT Probe on Yanmar 4JH3

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Good advice on contacting Kubota for the EGT info, but I'm concerned that their data would be a bit different than for a marinized engine. The exhaust gases will be just a bit cooler than an engine without a heat exchanger exhaust manifold. Thanks!
IMO you should always go with the engine manufacture's specifications for EGT max and back pressure max. There are too many variable's that you either don't know or can't control that the marinizer can't evaluate. Those would be the sea water temp (32 to 90° F), size of your raw water intake, head pressure the water pump">raw water pump has to overcome and others. Go with the Kubota spec and derate it a bit for the cooling that occurs in the exhaust manifold. It won't be much especially when your really whipping the horses.
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Old 27-02-2020, 09:01   #32
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Re: Installing EGT Probe on Yanmar 4JH3

I haven’t read the whole thread, but 1200F is right about the temp that the aluminum used for pistons melts, now your piston won’t be running that hot because it’s oil cooled and through conduction to the cylinder walls, but 1200 is hot rod, short duration high.
I used to run my truck at 1400 for 12 sec or so and that was considered a temp that would cause cumulative damage.
My truck was common rail and was being way over fueled by fuel pressure being cranked way up and injector dwell longer than stock from custom programming.
Stock you couldn’t really get to 1200 F except by maybe holding it in a gear and lugging the motor some.
If you saw your EGT getting too high pulling a hill hauling heavy, the best way to reduce it was not to back off, but to accelerate, force a downshift, this raised RPM and temp would drop drastically with all the extra air the RPM brought with it. You would even accelerate pulling the hill, but at an EGT of say 900 as opposed to 1200.

It’s lugging a Diesel that drives the EGT through the roof, so be careful overpropping, a little is fine, but too much is damaging.

Most of us truck guys when drilling the exh manifold would put grease all over the bit and tap and go slow, that trapped pretty much all the chips and small chips aren’t likely to hurt anything anyway.
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Old 27-02-2020, 10:51   #33
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Re: Installing EGT Probe on Yanmar 4JH3

A64pilot, I agree 1200 F seems high to me as well but that's the spec given to me by Mack Boring for the Yanmar 4JH3 & 4 series, but that is the absolute max. What's more surprising to me is the exhaust back pressure Yanmar says the 4JH3 &4 can tolerate, it's 120" H2O or 4.3 PSIG. That really surprised me considering that most other diesel manufactures state less than 1.5 PSIG, some like Deere much less.
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Old 28-02-2020, 07:06   #34
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Re: Installing EGT Probe on Yanmar 4JH3

I couldn't find a way to contact Kubota so reached out to Beta Marine in the UK. They indicated the EGT should be around 450-520°C, which is 842-968ºF, taken in the dry part of the exhaust elbow. Thoughts?
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Old 28-02-2020, 07:35   #35
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Re: Installing EGT Probe on Yanmar 4JH3

That confirms, at least to me, that they want that engine heavily loaded. No surprise but it runs counter to many theories presented on this forum.

I'd assume they have access to Kubota's fuel maps and are basing that recommendation on that info.
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Old 28-02-2020, 08:04   #36
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Re: Installing EGT Probe on Yanmar 4JH3

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I couldn't find a way to contact Kubota so reached out to Beta Marine in the UK. They indicated the EGT should be around 450-520°C, which is 842-968ºF, taken in the dry part of the exhaust elbow. Thoughts?
Are they suggesting that is the good loaded cruising range, or the maximum for continuous? I would imagine the latter. I found this for the V2203 Kubota engine, which, while not apples to apples, seems to agree with those numbers.
AAC/Morgan's cloud speaks more generally about where minimums are and seem to agree that under 450-500 continuously is underloaded. So, I just think it's a good warning for those who are overpowered and "correctly propped" that they may be severely underloading engines unless motoring at an aggressive pace. Like I said, I hit 550-600 F with an overpropped engine (can't get more that 2450 of 2800RPM)
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Old 28-02-2020, 08:15   #37
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Re: Installing EGT Probe on Yanmar 4JH3

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Are they suggesting that is the good loaded cruising range, or the maximum for continuous? I would imagine the latter. I found this for the V2203 Kubota engine, which, while not apples to apples, seems to agree with those numbers.
AAC/Morgan's cloud speaks more generally about where minimums are and seem to agree that under 450-500 continuously is underloaded. So, I just think it's a good warning for those who are overpowered and "correctly propped" that they may be severely underloading engines unless motoring at an aggressive pace. Like I said, I hit 550-600 F with an overpropped engine (can't get more that 2450 of 2800RPM)
Good question. They didn't say if it was loaded cruising range or maximum continuous. I'll ask.

I would say if you can only get 2450 WOT that you are over propped. What is your EGT at 2450rpm?

Thank you for the attachment. Where did you find it?
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Old 28-02-2020, 09:30   #38
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Re: Installing EGT Probe on Yanmar 4JH3

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Are they suggesting that is the good loaded cruising range, or the maximum for continuous? I would imagine the latter. I found this for the V2203 Kubota engine, which, while not apples to apples, seems to agree with those numbers.
AAC/Morgan's cloud speaks more generally about where minimums are and seem to agree that under 450-500 continuously is underloaded. So, I just think it's a good warning for those who are overpowered and "correctly propped" that they may be severely underloading engines unless motoring at an aggressive pace. Like I said, I hit 550-600 F with an overpropped engine (can't get more that 2450 of 2800RPM)

My truck unloaded ran around town at 400 or so or less, and many I’d assume millions of PU trucks do so, day after day for hundreds of thousands of miles, as majority of PU trucks are not used as trucks but merely as personal transportation.
It would idle I believe below 200, numbers are in F not C.

Glazed cylinders on a properly broken in engine are very, very rare.
If your not “wet stacking” or slobbering your engine, it’s not under loaded.
If it is actually under loaded, then there is incomplete combustion and of course slobbering or wet stacking.
Best study I have seen on it was done by the US Army as they have many, many Diesel engines that are run every week but only very rarely out under any real load and they did a study to see if it was doing any harm.
https://apps.dtic.mil/dtic/tr/fulltext/u2/a151273.pdf
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Old 28-02-2020, 10:54   #39
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Re: Installing EGT Probe on Yanmar 4JH3

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Good question. They didn't say if it was loaded cruising range or maximum continuous. I'll ask.



I would say if you can only get 2450 WOT that you are over propped. What is your EGT at 2450rpm?



Thank you for the attachment. Where did you find it?


Yes that’s my point I’m overpropped so that I properly load the engine at the RPMs I use

Above 2200 my EGT starts to go up rapidly. Below that it is linear and stays below 900 and my boat digs a huge hole in the water at 2200 and 7.7 knots
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Old 28-02-2020, 11:12   #40
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Re: Installing EGT Probe on Yanmar 4JH3

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Yes that’s my point I’m overpropped so that I properly load the engine at the RPMs I use

Above 2200 my EGT starts to go up rapidly. Below that it is linear and stays below 900 and my boat digs a huge hole in the water at 2200 and 7.7 knots
Got it. Makes sense. I am replacing my old Perkins 4.108, Velvet Drive 1.91:1, and 3-blade 16" Max-Prop with the Beta 43, TMC 60A 2:1, and a 4-blade 16" Max-Prop pitched at 20º per PYI. We'll just have to see what happens once I'm up and running.

I'll probably miss the smoothness of the Velvet Drive, but I didn't have room to install the new engine with that beast hanging off the back end.
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Old 28-02-2020, 11:38   #41
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Re: Installing EGT Probe on Yanmar 4JH3

The trick to being overpropped and not hurting anything, is to realize your overpropped and the last third or so of the throttle isn’t for you.

The reason overpropping “works” is that if you look at the HP curve and engine makes per RPM and the HP curve the props absorbs, you’ll notice that in mid RPM range where most of us cruise there is a big gap, so that there is a lot of power that the engine is capable of making, but the prop can’t absorb.
If you overprop you will close up that gap considerably, but the curves will cross, which means that as the RPM goes above a set point that the engine is being overloaded, and as it can’t make the RPM necessary to drive the prop, it bogs, and in extreme example may even blow some black smoke.

A normal fixed prop only matches the engines output power at one RPM, that being the max engine RPM, any RPM less than that and the engine is capable of more power than the prop can use.

Not being 100% loaded up is one reason why in my opinion that small boat Diesels last so long.

Same with an automobile, whether Diesel or gas, almost all are operated at a small fraction of max power available, and they last often 250,000 or more miles.

Now some want to think that the average speed of an average car is 50 mph or something, but it’s not, it’s around 30mph or less, often 25 mph or so.
All that time sitting at red lights and stuck in traffic really kills the average speed. Some autos will display average speed and on our Prius it’s in the high 20’s since it was new.
So if you figure 25 MPH to make that math simple, at 250,000 miles a car engine has 10,000 hours on it, and 250,000 miles on a car really isn’t all that uncommon.

Not bad for engines that are operated always under loaded huh?
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Old 28-02-2020, 11:54   #42
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Re: Installing EGT Probe on Yanmar 4JH3

Very good info. Thanks, a64pilot.
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Old 28-02-2020, 12:14   #43
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Re: Installing EGT Probe on Yanmar 4JH3

I just don't get overpropping as much as Malbert has done. First rule of thermodynamics is that energy can neither be created or destroyed. Do you think you are saving fuel by overpropping? You need X amount of HP to drive your hull through the water at a given speed. You capture that HP by burning fuel, potential energy to kinetic energy, the only difference is your burning that fuel at a lower RPM. Since diesels don't have throttle like a gas engine, the air mass flow is controlled only by the RPM. Lower RPM = less air BUT you are still feeding the fuel needed to capture the HP to drive your boat. You are running a rich mixture all the time you are much over idle.

There is no magic in overpropping with a fixed pitch propeller. Only the "feel good" of the ability to get more knots at a lower RPM while leaving quite a bit of the HP on the table.

Both Deere and Cat have transitioned from using an hour meter to fuel burned method for scheduling overhauls. I believe overpropping is a false economy. If you want a larger displacement engine for the grunt AND you want to run at low RPMs, recalibrate the fuel injection pump and possibly use a smaller injector and get back to the correct stoichiometric mixture. Every single engine manufacturer cannot be wrong about properly matching a prop to the full loaded RPM
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Old 28-02-2020, 12:20   #44
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Re: Installing EGT Probe on Yanmar 4JH3

Ah, even more good info and some controversy to boot. Thanks kenbo.

The fuel burned method seems to make good sense.
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Old 29-02-2020, 05:13   #45
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Re: Installing EGT Probe on Yanmar 4JH3

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I just don't get overpropping as much as Malbert has done. First rule of thermodynamics is that energy can neither be created or destroyed. Do you think you are saving fuel by overpropping? You need X amount of HP to drive your hull through the water at a given speed. You capture that HP by burning fuel, potential energy to kinetic energy, the only difference is your burning that fuel at a lower RPM. Since diesels don't have throttle like a gas engine, the air mass flow is controlled only by the RPM. Lower RPM = less air BUT you are still feeding the fuel needed to capture the HP to drive your boat. You are running a rich mixture all the time you are much over idle.

There is no magic in overpropping with a fixed pitch propeller. Only the "feel good" of the ability to get more knots at a lower RPM while leaving quite a bit of the HP on the table.

Both Deere and Cat have transitioned from using an hour meter to fuel burned method for scheduling overhauls. I believe overpropping is a false economy. If you want a larger displacement engine for the grunt AND you want to run at low RPMs, recalibrate the fuel injection pump and possibly use a smaller injector and get back to the correct stoichiometric mixture. Every single engine manufacturer cannot be wrong about properly matching a prop to the full loaded RPM


Sure. But remember engine manufacturers assume boat operators are dumb and will pin the throttle every chance they get. So they are making guidelines that protect their engine from being quickly ruined via lugging. It’s the “decerebrate” approach and certainly safest.

Automobiles run with gears and no one runs at highway speed in second gear. A64 makes good points about under loading but I think the intermittent high load of acceleration is what makes them not suffer effects of under loading.

But I’m no expert - don’t take my word for it. But I read and spoke to a lot of experts and didn’t rely on dogma in my setup.

Read Nigel Calder, John Harries (Morgan’s cloud), and Steve Dashew’s approach. All have done the same thing or are proponents of it. Andy Schell did same on his repower and wrote about it.
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