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Old 06-01-2016, 17:57   #1
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Yanmar Overheating

Yanmar 4JH-HTE 1989 1500 hours on it. Meticulously maintained: Oil and filter evey 100 to 150 hrs. Fuel filter on engine every 200. Dual Racors that until recently ran 4 Micron but recently switched to 30's. Obvious stuff done: Dove the intake, completely removed the clamshell. Checked water flow from inside the boat with hose off: Lots and Lots of water. Hose from inlet seacock to strainer is not collapsed and is in good shape. Strainer is clear on both ends and strainer allows water thru. Replaced the impeller several times, and the fins are going the correct way according to the manual. Seen into the air cooler and looks very clean. Fresh water flushed and flushed and flushed. Looked into lube oil cooler and it looked clean. Today I took off the Heat Exchanger which everyone has told me to check, even though I had it off entirely and serviced 24 months ago and I found some stuff I don't understand. There appears to be carbon on the exit side of the fresh water... Pics to follow.

Overheat:

While in San Francisco Bay I overheated half a dozen times over a 3 year period but lowering RPM and putting it in reverse usually fixed the problem. One time was just stupidity having forgotten to refill the coolant. The boat used to not have a sub tank but I have since added one. From San Francisco to La Paz, I overheated only once. In La Paz I had the high pressure fuel pump off and serviced and replaced the fresh water pump since it had a tiny leak. From La Paz to Mazatlan, no probs. Boat ran 85 - 90 C at 2800 to 3100 rpm, mostly 2800... Max Prop was cavitating in fast following seas which was the only time I ran it at 3000 or higher.

I get to Nuevo Vallarta and the boat sits from April to November. Pull out of there and it's overheat city... Boat would run fine, tho hot, 90 to 95C at 2000 to 2400 rpm so we had a mechanic look at the engine in Ixtapa. Turbo was frozen. Took off turbo and bingo. Now we only overheated at 2800. so we ran the rest of the way to Huatulco at 2450.

Since removing the clamshell I was able to motor at 2800 at 85 - 90C and 3000 at 95C. Normal operating temp for the motor is 80 to 85C

Forgot to mention... water heater is completely disconnected from fresh water pump and due to sizing of posts, Temp sender and switch are reversed but the dealer said that was ok. Previously it had been plumbed with water heater in/out on left side of pump, switch in current location (with fixture to feed turbo) and sender on the far right.

Anybody got any ideas??
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Old 06-01-2016, 18:19   #2
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Re: Yanmar Overheating

Did this start acting up after you disconnected the water heater?
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Old 06-01-2016, 18:49   #3
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Re: Yanmar Overheating

There are so many possibilities here meaning all that anyone can do is toss in a few ideas and hope for the best. At least I have a 4JH3 which can't be too different so here goes.

1. You don't mention fresh water (antifreeze). Have you been watching the level in the reserve tank?
2. Having the heat exchanger serviced can mean many things. Was it pressure tested?
3. Replace every rubber hose which carries raw water and that includes the ones which might lead to the water heater. It only takes a hairline crack to start sucking air and that crack could be under a hose clamp.
4. It sounds like the elbow should be removed and cleaned. That should be done every 500 hours.

Hopefully, you will locate the culprit sooner rather than later.
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Old 06-01-2016, 19:33   #4
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Re: Yanmar Overheating

ever replace the thermostat?
have you tested the antifreeze level in the cooling water?
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Old 06-01-2016, 20:18   #5
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Re: Yanmar Overheating

What does "overheating" mean?

How do you measure engine temperature?

Do you use an IR heat sensor to measure the raw water and coolant lines at various locations?

Do you use an IR heat sensor to measure the heads, exhaust ports, intake ports?

In other words - why do you think it is overheating - WHAT are the symptoms?

95C (on the temp gauge) at higher power (3000 RPM or 42HP at the prop with the 4JH-HTE) in 85 F- 90 F degree raw water (ocean water in Banderas Bay) seems acceptable. The normal 4JH-E thermostat does not fully open until 90C

You said "Temp sender and switch are reversed" That means the temp sender is on the upstream side of the thermostat. IF the thermostat is not fully open then you may be getting a misleading reading.

Have you tested the water flow out the exhaust pipe? It should be about 15 - 16 gallons per minute?

I've worked a few of these Yanmar problems in the 21-years I've operated a 4JH Yanmar. The KEY is precise temperature measurement at each point in the flow path for both RAW and FRESH(coolant) circuits. You should be able to document temperature drop and raise at each RPM at each point in the circuits and then see where the problem occurs.

Measure (for example) at various RPMs (2400, 2700, 2900, 3000, 3100) under LOAD.

Before and after:
- the thermostat
- the heat exchanger
- the oil cooler
- turbocharger
- freshwater pump

I had a problem similar to your description and it was caused by an air bubble introduced while I was working on the hot water circuit. I eventually put an air bleed valve in the highest point in the freshwater (coolant) circuit and it solved all my over heating problems.
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Old 07-01-2016, 04:22   #6
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Re: Yanmar Overheating

If you find you have an air block problem, this is usually solved by drilling a very small hole (1/16" or so) in the thermostat plate. This allows air to pass thru the thermostat when it's closed. The air should end up in your highest point to be purged.
Corrosion or scale occurs in both the sea water side and the coolant side.
I've fixed a number of overheat problems for people that had the heat exchanger serviced, changed various parts and pumps, etc., by descaling the coolant side.
I use Rydlyme for both sides. It's legal to dump over the side in most locations. It should be available on Ebay or Amazon.
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Old 07-01-2016, 05:15   #7
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Re: Yanmar Overheating

My Yanmar 3gm30f was running about 10 degrees warmer when I brought it down here to Ft. Lauderdale. I used Barnacle Buster and temperature came right down.


If you use one of the calcium type cleaning agents it important to do the compete system. The cleaning gadgets they sell are a rip off, I used an extra bilge pump and bucket. I connected a hose from the pump in the bucket to the inlet of the strainer. Then disconnected the exhaust hose from the elbow and put the bucket under it.
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Old 10-01-2016, 10:38   #8
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Re: Yanmar Overheating

I have tested the engine 3 different ways and here are the results:

Keep in mind, there is no thermostat installed. The 'coolant' for this test was filtered water, tho I usually use the pink stuff. The "front" cover of the exchanger is the fresh water/coolant in/out and the rear is the seawater in/out.

Scenario 1:

2650 RPM Forward Gear at the dock run for 15 minutes or until gauge quits moving:

Temp at Gauge: 93-95
Thermostat Housing: 85
Temp at Switch Fitting: 85
Temp at Sender: 86
Back Cover of Heat Exchanger: 55
Front Cover of Heat Exchanger: 45
Coolant Cap: 66
Top Front of the Heat Exchanger: 84
Top Back of the Heat Exchanger: 71

Scenario 2:

2800 RPM Reverse Gear at the dock run for 15 minutes or until gauge quits moving:

Temp at Gauge: 85
Thermostat Housing: 75
Temp at Switch Fitting: 73
Temp at Sender: 73
Back Cover of Heat Exchanger: 43
Front Cover of Heat Exchanger: 48
Coolant Cap: 58
Top Front of the Heat Exchanger: 74
Top Back of the Heat Exchanger: 65

Scenario 3 - Overheat, meaning the Overheat Alarm goes off

2850 RPM Forward Gear at the dock run for a little over 15 mins before alarm sounded:

Temp at Gauge: 105
Thermostat Housing: 92
Temp at Switch Fitting: 92
Temp at Sender: 89
Back Cover of Heat Exchanger: 46
Front Cover of Heat Exchanger: 51
Coolant Cap: 74
Top Front of the Heat Exchanger: 93
Top Back of the Heat Exchanger: 78

The alarm stopped sounding at Gauge reading of 95

Cool Down at 1600 RPM readings are as soon as the alarm quit sounding

Temp at Gauge: 95
Thermostat Housing: 79
Temp at Switch Fitting: 75
Temp at Sender: 72
Back Cover of Heat Exchanger: 44
Front Cover of Heat Exchanger: 51
Coolant Cap: 66
Top Front of the Heat Exchanger: 71
Top Back of the Heat Exchanger: 59

Any thoughts?

If the pic actually posts this time, it is of the back of the heat exchanger. The dark part is where the sea water enters the exchanger.
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Old 10-01-2016, 10:43   #9
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Re: Yanmar Overheating

Oh, forgot to mention.... Every Single hose on the engine was replaced 24 months ago. Not that that means they aren't cracked or damaged somehow, but I doubt it. While the turbo was off and being serviced, I visually inspected the mixing elbow and it looked almost new inside. I physically inspected it and found it to be in pristine condition.
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Old 10-01-2016, 11:06   #10
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Re: Yanmar Overheating

Also, the water heater is completely disconnected and those ports are plugged on the fresh water pump if not already mentioned.
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Old 10-01-2016, 12:19   #11
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Re: Yanmar Overheating

Put a thermostat back in, I don't pretend to understand exactly why, but my 4-JHE thermostat is a little unusual, there is an additional washer that moves as well as the normal thermostat part.


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Old 10-01-2016, 12:32   #12
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Re: Yanmar Overheating

Let me ask a real basic question - are you sure the engine really is overheating? Are you saying it is overheating just because the alarm goes off?

Both of the boats I've owned had Yanmar engines and both had temperature "problems". Both boats problems were really wiring, temperature senders and gauges. Neither boats had an engine problem.
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Old 10-01-2016, 12:43   #13
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Re: Yanmar Overheating

Any idea what product to buy down here in Mexico?
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Old 10-01-2016, 12:53   #14
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Re: Yanmar Overheating

I have tested the engine 3 different ways and here are the results:

Keep in mind, there is no thermostat installed. The 'coolant' for this test was filtered water, tho I usually use the pink stuff. The "front" cover of the exchanger is the fresh water/coolant in/out and the rear is the seawater in/out.

Scenario 1:

2650 RPM Forward Gear at the dock run for 15 minutes or until gauge quits moving:

Temp at Gauge: 93-95
Thermostat Housing: 85
Temp at Switch Fitting: 85
Temp at Sender: 86
Back Cover of Heat Exchanger: 55
Front Cover of Heat Exchanger: 45
Coolant Cap: 66
Top Front of the Heat Exchanger: 84
Top Back of the Heat Exchanger: 71

Scenario 2:

2800 RPM Reverse Gear at the dock run for 15 minutes or until gauge quits moving:

Temp at Gauge: 85
Thermostat Housing: 75
Temp at Switch Fitting: 73
Temp at Sender: 73
Back Cover of Heat Exchanger: 43
Front Cover of Heat Exchanger: 48
Coolant Cap: 58
Top Front of the Heat Exchanger: 74
Top Back of the Heat Exchanger: 65

Scenario 3 - Overheat, meaning the Overheat Alarm goes off

2850 RPM Forward Gear at the dock run for a little over 15 mins before alarm sounded:

Temp at Gauge: 105
Thermostat Housing: 92
Temp at Switch Fitting: 92
Temp at Sender: 89
Back Cover of Heat Exchanger: 46
Front Cover of Heat Exchanger: 51
Coolant Cap: 74
Top Front of the Heat Exchanger: 93
Top Back of the Heat Exchanger: 78

The alarm stopped sounding at Gauge reading of 95

Cool Down at 1600 RPM readings are as soon as the alarm quit sounding

Temp at Gauge: 95
Thermostat Housing: 79
Temp at Switch Fitting: 75
Temp at Sender: 72
Back Cover of Heat Exchanger: 44
Front Cover of Heat Exchanger: 51
Coolant Cap: 66
Top Front of the Heat Exchanger: 71
Top Back of the Heat Exchanger: 59

Any thoughts?
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Old 29-01-2016, 09:19   #15
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Re: Yanmar Overheating

Crowlegs

I have a 4Jh-hte 1986 with 3,300 plus hours.

After running for an hour on 1,500 rpm on reverse the temp reads about 68c with a ir gun while the temp Meter shows 80c.

Is it possible you may have a partially clogged intake at the thru hull. I often find stuff growing inside the thru hull fitting .

Just a thought.




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