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Old 18-05-2021, 15:34   #31
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by robert sailor View Post
Maybe your heat exchanger needs a good cleaning?
Something is seriously FUBAR

Iím using an 1,100 gph bilge pump to pump 4:1 barnacle buster in reverse flow front the elbow to the output of the water pump">raw water pump

Its literally coming out at teaspoons a minute. Yes, pump works fine when unplugged.

Elbow itself looks fine. Iíll try the airpump on the through hull but rn this heat ex is not looking good.

Passed a 5 min full power run without showing abnormal temps in early April. IR gun checked during run.
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Old 18-05-2021, 15:37   #32
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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The OP said "Thereís water spitting out the exhaust.". He said nothing about 'gushing'. Also this boat is 'new to him' so he has no idea how much water should be coming out.
Correct. Iím a total newbie. I donít even know what I donít know. I donít have a clue what is the current amount of exhaust water. Seriously. Climbing the (hopefully steep) learning curve.
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Old 18-05-2021, 15:48   #33
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by flightlead404 View Post
Something is seriously FUBAR

Iím using an 1,100 gph bilge pump to pump 4:1 barnacle buster in reverse flow front the elbow to the output of the raw water pump

Its literally coming out at teaspoons a minute. Yes, pump works fine when unplugged.

Elbow itself looks fine. Iíll try the airpump on the through hull but rn this heat ex is not looking good.

Passed a 5 min full power run without showing abnormal temps in early April. IR gun checked during run.
Did you remove the impeller from the rw pump?
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Old 18-05-2021, 16:15   #34
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by kenbo View Post
Did you remove the impeller from the rw pump?
Iím not passing anything though the raw water pump

Pumping in reverse to normal direction Iím going in at the hose that connects to the elbow and out at the output (not input) of the raw water pump.

If I reverse the direction and pump the barnacle buster mixture in the normal direction of flow I get a little better, like maybe a pint or so a minute, but certainly not what Iíd expect with an 1,100 gph pump.

I did notice a slight kink in the hose from the heat exchanger heading up to the siphon break, lousy design on Yanmarís part IMHO, it needs. 30 or 45 degree fitting there. I may attempt to fabricate something.
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Old 18-05-2021, 16:16   #35
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by flightlead404 View Post
Correct. Iím a total newbie. I donít even know what I donít know. I donít have a clue what is the current amount of exhaust water. Seriously. Climbing the (hopefully steep) learning curve.
Donít know the *correct* amount of water.

I looked in the Yanmar service manual for a flow rating for the raw water pump but could not find.
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Old 18-05-2021, 16:21   #36
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Re: Overheat at low rpm - 3JH4E on Hunter 38

I understand that you are running reverse flow but I don't understand if you are trying to run the BB reverse flow through the RE pump with the impeller still in the pump. The impeller will block the flow. Sorry if I don't understand your description.
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Old 18-05-2021, 16:27   #37
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by kenbo View Post
I understand that you are running reverse flow but I don't understand if you are trying to run the BB reverse flow through the RE pump with the impeller still in the pump. The impeller will block the flow. Sorry if I don't understand your description.
The OP isn't pumping the BB through the raw water pump!

The OP states he connected the BB flow to the OUTPUT of the raw water pump. This means the plumbing or hose that attaches to the raw water pump, not the pump itself.

Ergo, the BB does not try to flow through the raw water pump.
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Old 18-05-2021, 17:26   #38
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Re: Overheat at low rpm - 3JH4E on Hunter 38

Flighthead,
the output of cooling water from the muffler/exhaust at idle to slow speed (1,000-1,200 RPM) should be a shot every 5-10 seconds, a trickle shows it, the elbow mixer, is not getting enough water flow or the mixing elbow is "choked with exhaust build-up. I've had to replace mine every 1,000 hrs or so, and believe this is common, esp. if you cruise at 1,700 RPM like I do, 30hp Yanmar 3QM30H on 37 ft Hunter Cutter.

Pull the hose to the elbow off and direct it to the bilge, run the engine at idle, if you get good flow it's the elbow mixer, poor flow and it's up stream and likely the heat exchanger or strainer.

To test the Heat exchanger, HE, pull one end cap off and inspect, if it looks questionable, pull other end cap & shine a light through the tubes. If any tubes have any kind of blockage a trip the the radiator shop, or using BB on the HE is in the cards.

I've forgotten if you tested the HE by disconnecting the output hose, and tested the raw water pump by sending its output to the bilge or not.

The key to successful trouble shooting is to start at one end and go through each possible problem area one at a time in order to isolate the malfunctioning device.

Mechanics that are experienced in that mfg. and particular model can usually shorten the test procedure since they "know" what to expect at each device in the system. And have a great feel on what normally goes wrong in the system.

I hope this helps & please keep us informed on how it goes,

Wayne
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Old 18-05-2021, 21:33   #39
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Re: Overheat at low rpm - 3JH4E on Hunter 38

we had a similar over heating problem recently with one of our 4JH yanmars.

ran ok up to about 1700 rpm when started blowing steam. output water definitely low. checked every where / every thing...could not find the problem. suspected obstruction in sail drive leg but take the hose of there and heaps of water.

decided must by sw circ pump

however eventually...almost by accident...discovered the problem was the length of suction hose from sw intake to sw circ pump was delaminating. outside of hose stayed round...inside was sucking closed.

changed hose...now no problem

ps : anyone want to buy a brand new un-used genuine yanmar sw circ pump ??

cheers,
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Old 19-05-2021, 05:38   #40
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Re: Overheat at low rpm - 3JH4E on Hunter 38

Its not the elbow. First, elbow isnít in the path of the BB flow.

Second, Iíve inspected with a mirror and flashlight, its completely free of any blockage.

I ran the BB overnight, no change. Reverse flow is around 1/2 cup a minute, normal direction maybe cup per minute.

Iím going to put everything back together, then plumb in a line to use the RW pump to pump this ďoldĒ BB through the entire system and out the back.

Once that is done Iíll let it sit for a few hours, then Iíll try again. If thereís no change Iíll pull one or both end caps.

Can I use something stronger than BB/phosphoric acid on the heat ex?
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Old 19-05-2021, 06:34   #41
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by flightlead404 View Post
I...........

Can I use something stronger than BB/phosphoric acid on the heat ex?
You can but as with all things, more aggressive chemicals require greater caution.

I have used hydrochloric acid (muriatic acid) with great success but you do really need to be careful with it. The fumes destroy lungs and do not get it on your skin or eyes. It used in the building industry to clean concrete and masonry and for adjusting the pH of swimming pools.

It destroys calcium carbonate in a flash. 30 minutes will sort out any calcium carbonate build up in the heat exchanger. Dunno about your part of the world but here it is available at hardware stores and pool stores at 33% concentration.

Rinse well after use and it doesn't hurt to run some base like bicarbonate of soda through the system to neutralise any remaining acid. Then rinse again.

Let me repeat, use with caution!!!!!!!
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Old 19-05-2021, 07:20   #42
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Originally Posted by flightlead404 View Post
Its not the elbow. First, elbow isnít in the path of the BB flow.

Once that is done Iíll let it sit for a few hours, then Iíll try again. If thereís no change Iíll pull one or both end caps.

Can I use something stronger than BB/phosphoric acid on the heat ex?

Do not know how you have your BB flush set up but will say the normal exhaust mixing elbow will have the raw water/salt water system exiting your engine at the exhaust elbow.

If you do not have full flow at the hose at the mixing elbow w/your external pump you need to work backwards (removing hoses/fitting) to systematically go through the engine plumbing to find the blockage/until you get full flow.
The BB/strong acids will breakdown organic material (e.g. calcium carbonate), but will not dissolve rubber vane pieces or other non organic matter. If The BB doesn't dramatically increase flow after sitting over night, wouldn't jump to a stronger acid (muriatic) expecting better results. You will need to pysically locate the blockage and remove it. A bit of a pain but in the end it will be worth it and should give you a good working motor for years.
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Old 19-05-2021, 08:24   #43
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Re: Overheat at low rpm - 3JH4E on Hunter 38

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Do not know how you have your BB flush set up but will say the normal exhaust mixing elbow will have the raw water/salt water system exiting your engine at the exhaust elbow.

If you do not have full flow at the hose at the mixing elbow w/your external pump you need to work backwards (removing hoses/fitting) to systematically go through the engine plumbing to find the blockage/until you get full flow.
The BB/strong acids will breakdown organic material (e.g. calcium carbonate), but will not dissolve rubber vane pieces or other non organic matter. If The BB doesn't dramatically increase flow after sitting over night, wouldn't jump to a stronger acid (muriatic) expecting better results. You will need to pysically locate the blockage and remove it. A bit of a pain but in the end it will be worth it and should give you a good working motor for years.
Literally the only thing in the path is the heat exchanger and a couple of feet of rubber hose.

Interestingly I looked in the exit hole of the heat exchanger and just the half dozen tubes I could see looked clean from the outside.
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Old 19-05-2021, 08:43   #44
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Re: Overheat at low rpm - 3JH4E on Hunter 38

OK, should be fairly simple then to disconnect the hose from the front of the heat exchanger to test the flow w/the external pump. If full flow at the disconnected hose, then it's a clog in the exchanger (if you aren't getting full flow after the exchanger). Wouldn't discount impeller pieces causing the problem.
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Old 19-05-2021, 08:45   #45
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Re: Overheat at low rpm - 3JH4E on Hunter 38

Just for giggles I decided to put everything back and run the engine expecting the engine driven pump to have a little more oomph than the bilge pump.

I *feel like* thereís more water out the exhaust. But no quantitative measurement and, as I mentioned before, not enough experience to know if its the appropriate amount of water (or just me being hopeful). I took some video at idle and in neutral at 2,000 rpm which Iíll figure out how to link here.

I took some temperature measurements after running the engine in neutral at 2,000 rpm for 10-15 minutes.

Incoming sea water: 24 c
Top of heat exchanger: 63 c
Top of pressure cap: 69 c
Body of elbow: 34 c
Bronze water injection fitting to main elbow: 35 c
Heat exchanger end cap (coolant out fitting): 39 c
Coolant pump body: 68 c
Top of thermostat: 75 c

Here is a video of the exhaust at idle

Here is a video of the exhaust in neutral at 2,000
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