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Old 25-02-2020, 09:44   #16
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Re: Installing EGT Probe on Yanmar 4JH3

Something to keep in mind when using an EGT on an engine with a manicooler like Beta and Yanmar, the exhaust gas is cooled a bit by the time it reaches the probe installed in the riser. Not by much but a bit, maybe 50 degrees F. So err on the low side when reading the gauge.
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Old 25-02-2020, 11:12   #17
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Re: Installing EGT Probe on Yanmar 4JH3

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Originally Posted by kenbo View Post
Something to keep in mind when using an EGT on an engine with a manicooler like Beta and Yanmar, the exhaust gas is cooled a bit by the time it reaches the probe installed in the riser. Not by much but a bit, maybe 50 degrees F. So err on the low side when reading the gauge.
Good to note. Thanks.
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Old 25-02-2020, 19:16   #18
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Installing EGT Probe on Yanmar 4JH3

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Originally Posted by bbayne View Post
That would be great. Thank you! What temperature readings are you getting with your Beta 50?


Fast cruise speed, 7.2 knots in my boat (EGT gauge bottom right), about 525F
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As an aside, I deliberately overpropped as Nigel Calder and Steve Dashew, as well as Morganís Cloud suggest. In essence de-tuning a 50 HP engine down to where I am extracting my cruising speed at max torque and slow revs. The EGT validates the load calculations I estimated prior
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Old 25-02-2020, 20:36   #19
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Re: Installing EGT Probe on Yanmar 4JH3

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Fast cruise speed, 7.2 knots in my boat (EGT gauge bottom right), about 525F

As an aside, I deliberately overpropped as Nigel Calder and Steve Dashew, as well as Morganís Cloud suggest. In essence de-tuning a 50 HP engine down to where I am extracting my cruising speed at max torque and slow revs. The EGT validates the load calculations I estimated prior
Thank you! Any pictures of the probe and where you mounted it?

I had read somewhere that the EGT should be around 1200ļF or so. Not sure where I read that, but when I saw that you were only achieving 525ļF, I was astonished. I would have expected more. How much pitch did you over-prop by?
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Old 26-02-2020, 07:08   #20
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Re: Installing EGT Probe on Yanmar 4JH3

1200 is way too high. Itís really tough to feel published data from manufacturer which is interesting- but I found a document some time ago which Iíll attach when I can find it.
Morganís cloud has good discussions on this and most think 500-700 is a good load on engine. Lower is not ideal. Word to caution for everyone with ďideally proppedĒ engines that are way above 1.5-2 hp per ton. Unless you are running up high you are likely way under loading your engine
For perspective I can only achieve 2450 out of 2800 rpm.
These readings were ideal conditions- perfectly clean hull and calm sea state and breeze. Thatís whatís nice about EGT. With less ideal conditions my temps get up in 600s at 1900 rpm cruise setting
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Old 26-02-2020, 08:09   #21
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Re: Installing EGT Probe on Yanmar 4JH3

1200 F is the absolute maximum for the Yanmar 4JH3 and 4. 750 to 800 would be a good Target for the Yanmar. Yanmars are also tolerant to high exhaust back pressure unlike many other diesel makes.

The information is available if you contact the engine manufacturer. You may not get the complete fuel map but EGT and back pressure is readily available. If you have a Beta I'd contact Kubota. I often find that Beta's engine data differs from Kubota's.

The issue of over-propping always leaves me a bit uncomfortable as a sub optimal solution. Firstly you're leaving a lot of HP on the table. You are not changing the inherent properties of the engine just the ability of the engine to be fed the proper fuel/air mix. If you want the low end HP and torque that a larger displacement engine provides that's good but have the high pressure pump and injectors recalibrated for your lower target max rpm.

This isn't the same as a variable pitch prop. With an over pitched, fixed prop you're just rotating the propeller curve counter clockwise while leaving the HP and torque curve in place.
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Old 26-02-2020, 09:00   #22
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Re: Installing EGT Probe on Yanmar 4JH3

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Originally Posted by malbert73 View Post
1200 is way too high. Itís really tough to feel published data from manufacturer which is interesting- but I found a document some time ago which Iíll attach when I can find it.
Morganís cloud has good discussions on this and most think 500-700 is a good load on engine. Lower is not ideal. Word to caution for everyone with ďideally proppedĒ engines that are way above 1.5-2 hp per ton. Unless you are running up high you are likely way under loading your engine
For perspective I can only achieve 2450 out of 2800 rpm.
These readings were ideal conditions- perfectly clean hull and calm sea state and breeze. Thatís whatís nice about EGT. With less ideal conditions my temps get up in 600s at 1900 rpm cruise setting
I think you're estimate of HP/ton is bit light. Running the numbers on a few different boats in two separate prop calculators puts the HP/ US ton right around 4 to be able to drive a displacement hull to 1.34 x sq. root of the LWL. The guideline that I've always used was 1 HP / 500 # of fully laden displacement.
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Old 26-02-2020, 10:48   #23
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Re: Installing EGT Probe on Yanmar 4JH3

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Originally Posted by kenbo View Post
I think you're estimate of HP/ton is bit light. Running the numbers on a few different boats in two separate prop calculators puts the HP/ US ton right around 4 to be able to drive a displacement hull to 1.34 x sq. root of the LWL. The guideline that I've always used was 1 HP / 500 # of fully laden displacement.


Youíre right I meant 1.5-2hp per 1000 lb.
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Old 26-02-2020, 10:55   #24
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Re: Installing EGT Probe on Yanmar 4JH3

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Originally Posted by kenbo View Post
1200 F is the absolute maximum for the Yanmar 4JH3 and 4. 750 to 800 would be a good Target for the Yanmar. Yanmars are also tolerant to high exhaust back pressure unlike many other diesel makes.



The information is available if you contact the engine manufacturer. You may not get the complete fuel map but EGT and back pressure is readily available. If you have a Beta I'd contact Kubota. I often find that Beta's engine data differs from Kubota's.



The issue of over-propping always leaves me a bit uncomfortable as a sub optimal solution. Firstly you're leaving a lot of HP on the table. You are not changing the inherent properties of the engine just the ability of the engine to be fed the proper fuel/air mix. If you want the low end HP and torque that a larger displacement engine provides that's good but have the high pressure pump and injectors recalibrated for your lower target max rpm.



This isn't the same as a variable pitch prop. With an over pitched, fixed prop you're just rotating the propeller curve counter clockwise while leaving the HP and torque curve in place.


I agree that leaving HP on the table seems wrong. But most boats are given more HP than they ever need. it takes nearly exponential HP to get far above hull speed. And itís probably a <1% use case that boat owners need the full top end HP. So if youíre under loading the engine more than 95% if the time that is far worse than risk of running beyond overpropping.
So most boats are given much more than 4hp per ton and owners run them much less than loaded because they donít want the noise and fuel consumption. Until there are 2 speed marine transmissions or variable pitch props at a smaller scale to fit our sailboats, the optimal solution is downsize engine HP and run them faster (leaving HP on the table) or overpropping a oversized engine so that itís loaded at cruising speed.
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Old 26-02-2020, 11:15   #25
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Re: Installing EGT Probe on Yanmar 4JH3

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Have a strong vacuum hose right beside the drill bit when drilling.
Coat the tap flutes with a thick grease when tapping.


Another option is to tap it with the engine running. Exhaust pressure will force the chips out.
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Old 26-02-2020, 12:47   #26
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Re: Installing EGT Probe on Yanmar 4JH3

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Another option is to tap it with the engine running. Exhaust pressure will force the chips out.


Or just remove the elbow and take it to a bench
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Old 26-02-2020, 12:59   #27
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Re: Installing EGT Probe on Yanmar 4JH3

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I agree that leaving HP on the table seems wrong. But most boats are given more HP than they ever need. it takes nearly exponential HP to get far above hull speed. And itís probably a <1% use case that boat owners need the full top end HP. So if youíre under loading the engine more than 95% if the time that is far worse than risk of running beyond overpropping.
So most boats are given much more than 4hp per ton and owners run them much less than loaded because they donít want the noise and fuel consumption. Until there are 2 speed marine transmissions or variable pitch props at a smaller scale to fit our sailboats, the optimal solution is downsize engine HP and run them faster (leaving HP on the table) or overpropping a oversized engine so that itís loaded at cruising speed.
I agree to some extent and you are overpropping the safe way, using an EGT as long as you understand that you are running above the appropriate stoichiometric mix of fuel to air, i.e. wasting fuel for the HP achieved.
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Old 26-02-2020, 13:37   #28
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Re: Installing EGT Probe on Yanmar 4JH3

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Originally Posted by malbert73 View Post
1200 is way too high. Itís really tough to feel published data from manufacturer which is interesting- but I found a document some time ago which Iíll attach when I can find it.
Morganís cloud has good discussions on this and most think 500-700 is a good load on engine. Lower is not ideal. Word to caution for everyone with ďideally proppedĒ engines that are way above 1.5-2 hp per ton. Unless you are running up high you are likely way under loading your engine
For perspective I can only achieve 2450 out of 2800 rpm.
These readings were ideal conditions- perfectly clean hull and calm sea state and breeze. Thatís whatís nice about EGT. With less ideal conditions my temps get up in 600s at 1900 rpm cruise setting
Good to know. I have an AAC account and follow John's posts often. I'll have to take a look and see what I can find regarding EGT on the site.

I decided to include a pyro with this engine replacement so I would know if I was pushing the new engine too much or not enough.

Where exactly did you tap the exhaust elbow for the probe? Right as it leaves the heat exchanger or a bit farther downstream?
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Old 26-02-2020, 13:40   #29
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Re: Installing EGT Probe on Yanmar 4JH3

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Originally Posted by kenbo View Post
1200 F is the absolute maximum for the Yanmar 4JH3 and 4. 750 to 800 would be a good Target for the Yanmar. Yanmars are also tolerant to high exhaust back pressure unlike many other diesel makes.

The information is available if you contact the engine manufacturer. You may not get the complete fuel map but EGT and back pressure is readily available. If you have a Beta I'd contact Kubota. I often find that Beta's engine data differs from Kubota's.

The issue of over-propping always leaves me a bit uncomfortable as a sub optimal solution. Firstly you're leaving a lot of HP on the table. You are not changing the inherent properties of the engine just the ability of the engine to be fed the proper fuel/air mix. If you want the low end HP and torque that a larger displacement engine provides that's good but have the high pressure pump and injectors recalibrated for your lower target max rpm.

This isn't the same as a variable pitch prop. With an over pitched, fixed prop you're just rotating the propeller curve counter clockwise while leaving the HP and torque curve in place.
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!
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Old 26-02-2020, 13:41   #30
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Re: Installing EGT Probe on Yanmar 4JH3

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Or just remove the elbow and take it to a bench
I like this approach.
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