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Old 01-09-2023, 14:20   #1
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Correct Temp differential in heat exchanger

Hey all, my Yanmar 4jh2e had always run great with the exception of a few minor things, one of them being reliably overheating at 3k or more. Now it's happening at lower RPMs.I noticed at 2500rpms, the heat exchanger in/out hoses for coolant were 185 and 170.

Does that sound like enough? Planning a barnacle buster
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Old 01-09-2023, 14:47   #2
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Re: Correct Temp differential in heat exchanger

Could be your heat exchanger needs service.
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Old 01-09-2023, 17:37   #3
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Re: Correct Temp differential in heat exchanger

Do a cleaning first but have read that yanmar doesn’t recommend Barnacle Buster. Use hammerhead descaler. If that doesn't help then may need to take it apart and look for impeller bits etc. when was last time you took the exhaust elbow off and cleaned it?
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Old 01-09-2023, 18:48   #4
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Re: Correct Temp differential in heat exchanger

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Do a cleaning first but have read that yanmar doesn’t recommend Barnacle Buster. Use hammerhead descaler. If that doesn't help then may need to take it apart and look for impeller bits etc. when was last time you took the exhaust elbow off and cleaned it?
I couldn't get the exhaust elbow off at first, and I'm not about to replace the exhaust hoses...yet. I'll try to at least get the barb off and then I can check it more. I am able to blow through it though. The barb where the water injects is totally clear with zero build up, but I can't dig further into the elbow. It doesn't seem like the exhaust puts out a lot of water tbh. At ide, nothing happens for 5 seconds and then water gushes out in intervals.

I checked the heat exchanger a year ago just by pulling the front cover off and it looked very clean, which is why I'm trying to see if anyone knows what a normal temp differential is.

New impeller, new raw water hoses, clean strainer. Problem has been happening for years.
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Old 01-09-2023, 19:58   #5
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Re: Correct Temp differential in heat exchanger

Here’s a thing to check for the long term overheating problem. Your 4JH2e has a “2 pass” heat exchanger, the raw water does a u turn through the tube stack and if the core is incorrectly fitted, not only does it lose a lot of cooling ability on the seawater side, the ability of the coolant to enter the outside of the tubestack and reject heat is also compromised because the shroud is not in the optimum position relative to the coolant flow. The gasket, the core and the flow divider in the end cap all need to be lined up if the locating pin is not present.
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Old 02-09-2023, 02:10   #6
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Re: Correct Temp differential in heat exchanger

I suspect that you'd have to consult the Heat Exchanger manufacturer, to determine their design Delta T's [cooling seawater & engine coolant], and flow rates.

What most users do, is to watch for a gradual reduction in the Delta T [or just 'seawater exit temperature].

Failures rarely happen suddenly, if you’ve been paying attention. Most problems develop gradually, so continually monitor temperatures [watching for changes], replace zincs, and look for visual signs of leaks.

You might be interested in:

Shell and Tube Heat Exchangers - Basic Calculations
https://www.pdhonline.com/courses/m371/m371content.pdf

How to Calculate the Efficiency of Heat Exchangers
https://www.linquip.com/blog/efficie...eat-exchanger/
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Old 02-09-2023, 10:31   #7
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Re: Correct Temp differential in heat exchanger

Ok, well I was able to get the exhaust hose off while it was hot. Everything is as clean as a whistle (i mean there was a coating of black soot but less than 1mm or thereabouts.)

Here is a video showing how much water comes out of the exhaust at 800 and 2k rpm. It was like this after an impeller was replaced; always was similar to this amount. I don't think i could fit a bucket under the exhaust to measure it but to me it doesn't look like enough; however I don't have much to compare it to.

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Old 02-09-2023, 10:34   #8
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Re: Correct Temp differential in heat exchanger

That looks like nowhere near enough water to me.
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Old 02-09-2023, 14:18   #9
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Re: Correct Temp differential in heat exchanger

Man hard to tell on the water. It will be cyclic like that either way. Have you check the hose intake from your seacock? And what does the water flow look like through the strainer?

Back to your temps… those don’t seem unreasonable. What does your panel temp gauge say at 2000 rpm after 15 minutes? And are you able to do a load test at the dock with it in gear at that rpm? What skipperpete said is critical so when you pull the aft side cap on the HE you have to get it back just right with the cross piece gasket in place. I put a dollop of silicone lube on the gasket to hold it while assembling.
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Old 02-09-2023, 14:38   #10
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Correct Temp differential in heat exchanger

Not nearly enough water in my view. Time to start systematically searching for an obstruction in the raw water path.

Edit: once I had poor raw water flow with the old engine. Did all the right stuff with refacing the raw water pump, cleaning the exhaust elbow injection point, intake fitting, filter basket. Round and round, eventually I started pulling the raw water circuit apart and sampling the water flow at each point. This helped me track down the problem which was a small chunk of sacrificial anode that had flaked off and lodged out of sight in the exit elbow of the heat exchanger.
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Old 02-09-2023, 16:38   #11
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Re: Correct Temp differential in heat exchanger

Do not forget to check the pump itself. A worn cam or face plate will dramatically reduce water flow. Also using a gasket thicker then the paper original.
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Old 02-09-2023, 18:37   #12
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Re: Correct Temp differential in heat exchanger

The hose from seacock to impeller is brand new (Well 1.5 years now and no change in function). However, now that I know the exhaust elbow is clear, at least I've narrowed down the issue.

Thanks for the tips
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Old 02-09-2023, 20:35   #13
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Re: Correct Temp differential in heat exchanger

Quote:
Originally Posted by sv_sharky View Post
The hose from seacock to impeller is brand new (Well 1.5 years now and no change in function). However, now that I know the exhaust elbow is clear, at least I've narrowed down the issue.

Thanks for the tips


Congratulations, you’ve eliminated about 1% of the possible causes. Don’t give up.
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Old 02-09-2023, 20:47   #14
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Re: Correct Temp differential in heat exchanger

Quote:
Originally Posted by GreenWave View Post
Man hard to tell on the water. It will be cyclic like that either way. Have you check the hose intake from your seacock? And what does the water flow look like through the strainer?

Back to your temps… those don’t seem unreasonable. What does your panel temp gauge say at 2000 rpm after 15 minutes? And are you able to do a load test at the dock with it in gear at that rpm? What skipperpete said is critical so when you pull the aft side cap on the HE you have to get it back just right with the cross piece gasket in place. I put a dollop of silicone lube on the gasket to hold it while assembling.
At 2250 RPMs moving, it was hovering at around 82 deg C.
2500 RPMs will get it right around 100 deg C indicated. I took a temp reading at the hose and indeed it showed around 195 deg F.
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Old 03-09-2023, 05:08   #15
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Re: Correct Temp differential in heat exchanger

Quote:
Originally Posted by sv_sharky View Post
Hey all, my Yanmar 4jh2e had always run great with the exception of a few minor things, one of them being reliably overheating at 3k or more.
"reliably overheating at 3k or more" and "Problem has been happening for years." is not within the definition of "Runs great."




Quote:
Originally Posted by sv_sharky View Post
I couldn't get the exhaust elbow off at first, and I'm not about to replace the exhaust hoses...yet. I'll try to at least get the barb off and then I can check it more. I am able to blow through it though. The barb where the water injects is totally clear with zero build up, but I can't dig further into the elbow. It doesn't seem like the exhaust puts out a lot of water tbh. At ide, nothing happens for 5 seconds and then water gushes out in intervals.

I checked the heat exchanger a year ago just by pulling the front cover off and it looked very clean, which is why I'm trying to see if anyone knows what a normal temp differential is.

New impeller, new raw water hoses, clean strainer. Problem has been happening for years.
Do you mean you've already replaced impeller, raw water hoses, etc.?

Obstruction from previous old impeller bits and pieces? Collapsing hose (esp. if not new).

Raw water pump actually working to spec?

Otherwise, I suspect you'll need to pull it all, from thru-hull to exhaust... to find an obstruction... or verify working... perhaps one at a time.

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