Correct Temp differential in heat exchanger

[knotnline]

Collect discharge water for 30s or 1 min at known engine rpm.

Pump rpm=3250 at engine rpm=3600.
Pump flow at engine rpm=3600 is 3250 l/hr.

Do a bit of math and see if flow is good?

[Icarus]

Originally Posted by sv_sharky

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

cheers

I run 40hp ISUZU....the temp difference at the exchanger is about 30°C
Better check for blockages, pump impeller, clean the exchanger.

[sv_isara]

Ok updates: unfortunately I am having some life challenges so things are going very slow and I hesitate to actually take the boat out at this time. However I did do a barnacle bust and noticed a few things:

• heat exchanger copper tubes are (still) looking pristine

• there was *no* gasket in the rear side of the heat exchanger. I installed one

• The old impeller had 12 blades. New one has 9

• The old impeller was missing 5 blades

• I did find one small bit of impeller blade in one copper tube, and in the impeller housing. Maybe there are more around the rest of the system even though I reverse-circulated the raw water when barnacle busting.

• Comparing the videos, there seems to be a slight increase in flow, but not dramatic. see below

https://www.youtube.com/watch?v=8ZfhWiwYP08

Next steps:
My pace of working on this has slowed to a crawl unfortunately . I'm thinking in the next week I'll take it out and give it a spin. I'm guessing that it'll be good up to 3k like when I bought the boat rather than just 2500, but still shy of the 3600rpm max rated. If that is true then I'll remove the rest of the lines to check for obstructions and then replace the coolant.

[rslifkin]

The water flow in that last video no longer strikes me as abnormal (and it's definitely more than the first video), so I expect you've made some improvement.



When you test under load, do a brief run up to WOT and see if you actually reach the rated 3600 RPM. If you don't, you may be overpropped which could be contributing to the issue.

[skipperpete]

If the heat exchanger core is installed with the two air bleed holes anywhere other than at the the top of the housing (just near the filler neck) with the flow divider horizontal, it won’t matter how much raw water flow is happening…… Incidently, the best achievable flow (from the service manual data) is 3,500 litres per hr @ 3,600 rpm measured at the final exhaust outlet but very difficult to measure on your boat considering how low the outlet is.

[ranger58sb]

Originally Posted by sv_sharky

[/LIST]

• The old impeller was missing 5 blades

[LIST]I did find one small bit of impeller blade in one copper tube, and in the impeller housing. Maybe there are more around the rest of the system even though I reverse-circulated the raw water when barnacle busting.

Next step, I'd look for and remove the rest of the missing impeller blades.

-Chris