Correct Temp differential in heat exchanger

[sv_isara]

2 things that I've done since the last motoring (and reduction of 400 rpms or so of cooling) was: replace coolant and remove all hydronic hoses. There was previously an expansion tank that would get hot that is now disconnected.

So I believe that whether the issue is coolant or raw water, certainly the problem is with the heat exchanging. Next steps will be new impeller (again why not), barnacle bust, check heat exchanger, and put a hose backwards through raw water. Then a coolant flush with a mild acid, lots of rinsing, and changing from a green coolant to a Delo ELC coolant.

[rslifkin]

The low water flow on the exhaust would have me looking at the raw water side first. Have you measured the temperature rise on the raw water side of the heat exchanger? I'd expect it's pretty high, which would indicate that more flow will improve cooling.

[GILow]

Just systematically pull the connections at each point of the raw water path and measure the flow at each. You’ll very quickly discover just where the restriction lies.

[sv_isara]

Thanks, I'll let y'all know later this week ��

[Skipper Jethro]

Had same issues. Did all in reverse to find it was small hose between sea strainer and intake. It appeared to be flowing well but when the hose was removed the inside was puckered and clearly restricting flow. Also
Use only Yanmar antifreeze… don’t know why but multiple folks have told me and it seems true.

See photo of my hose inners…

[RedneckRedcoat]

The water coming out though the exhaust looks about the same as our boat . We have the same engine.

Check your raw water intake , the strainer should be full. I’d open the ends of the heat exchanger and see if there is a calcium build up on the inside.

Or You can call Doug Dykans at Yanmar or email him for advice. 727-522-9471;1208. dsdykens@mastry.com His job is to answer all our questions on yanmar engines and transmissions. He will tell you more about your engine than you will ever want to know.

[sinnerman]

Originally Posted by skipperpete

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.

VERY good point...

[sinnerman]

Maybe a long shot, but your FW (Coolant) pump may have issues...

Example: the impeller is slipping on the shaft.

Or thermostat not opening fully

my two cents

cheers

[OneBoatman]

So you did all of this: Cleaned your rawwater strainer, Replaced your rawwater impeller. checked your exhaust elbow for excessive carbon build-up as may restrict the flow of rawwater with your exhaust, and the engine tends to overheat at higher RPMs. It is most likely there are remnants of a previous, perhaps long ago overheat episode which left impeller bits or pieces restricting the flow thru the rawwater side your heat exchanger. Flushes designed to remove scale probably won't do much because that would require you to have a boatload of scale. Theoretically possible, by not likely. You have something obstructing flow through the raw water side of heatX. Disassemble at both end caps and check for restriction to the rawwater.

[Joe Okros]

Congratulations, you have just proven global warming is real. lol

[freshalaska]

Originally Posted by GILow

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.

Basically had the same thing happen to me as well. Piece of weed somehow got though the seawater strainer and got stuck in the 90 elbow on the exit side or the strainer. Better to use straight fittings and these things don’t always happen gradually as someone else said.

[col50]

Check the raw water temp at the heat exchanger exhaust. It should be warmer to the touch then at the input side, but not hot. If it is hot then there is not enough flow.
I it is just a little warmer the raw water flow is not the problem and you might want to make sure your heat exchanger is operating in the double-pass mode as previously mentioned.

[Ken of KC]

The actual answer is in your first post, you only have a 15 degree Delta 'T', you have covered all the why's and if I read it correct you did have some obstruction in one hose but at the end of the day you seem reluctant to open the HX and that is where I believe is most if not all of your issues. When you find your issue your Delta 'T' will double.

[sv_isara]

All really great info! This is great. Only thing that isn't is that I had a health issue and lost a week of work so won't be able to go back till next week. Itching to get this fixed after 1.5 years of reliable overheating

All advice is being considered, will start with raw water + all rw hoses

[sv_isara]

Originally Posted by Ken of KC

The actual answer is in your first post, you only have a 15 degree Delta 'T', you have covered all the why's and if I read it correct you did have some obstruction in one hose but at the end of the day you seem reluctant to open the HX and that is where I believe is most if not all of your issues. When you find your issue your Delta 'T' will double.

also replaced thermostat.

I peaked inside the raw water side, but only the front of the engine which may be the output. I will now open all sides and all hoses since I have new coolant, gaskets, and new hoses ready.
Also, I never checked raw water in/out Temps so will do that