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Old 21-07-2006, 09:33   #1
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Yanmar overheating

My salt water cooled Yanmar is overheating (the alarm goes off after about an hour and a half of motoring). There is plenty of water coming out of the exhaust and I checked the water filter. Could the thermostat sensor (alarm) be set too low? I just got a new one. Any other ideas? Thanks.
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Old 21-07-2006, 13:28   #2
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OK, to clarify, has this problem just started after installing the new sensor? or did you replace the sensor because it seemed it was overheating??
Check impellor anyway!!!! Water can be flowing but maybe not enough.
If you are unsure about the temperature, you need to confirm it with another device, before you go anyfurther, or you could be chasing red hearings.
If upon testing you do find it is overheating, then first suspect will be impellor. Water maybe going through..oh yeah I already said that.
Next will be heat exchanger, but less likely.
I sugget you inspect the impe....oh yeah, I said that didn't I
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Old 21-07-2006, 14:23   #3
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Could you please identify the model of Yanmar.
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Old 22-07-2006, 00:31   #4
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I seem to recall a lengthy discussion on an overheating Yanmar but cannot locate it.
From memory it came down to the coolant?
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Old 22-07-2006, 06:33   #5
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Just posted a link on the engine forums about problems of Yanmar 3YM30 overheating (design fault)

see http://cruisersforum.com/forums/showthread.php?t=4576
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Old 22-07-2006, 07:16   #6
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What RPM's are you doing. Every diesel will overheat after an hour or so if run at maximum RPM's for that long.

Mike
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Old 22-07-2006, 08:26   #7
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Talbot,
The statement "design fault" I think is inappropriate. Yes Yanmar has increased the cooling capacity of the 3YM30 after the instalation in many new boats. This was due to the boat builders increasing the demand on the cooling system by adding extra hose and water heaters. The water heater acts as a heater for the coolant instead of wicking heat away from the engine. Yanmar added raw water passages to the cooler bundel to pass more raw water and counter the effect of the water heater.
I wouldn't consider it a design defect because the engines that were installed without water heaters are running fine according to the info I'm hearing.
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Old 22-07-2006, 09:08   #8
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I would hope that you have better information than me!
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Old 22-07-2006, 11:56   #9
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It perhaps is a design fault. I have two 3ym30's. If I run the engine that has the water heater above 2800 RPM's for more than 5 minutes the warning buzzer starts sounding. I have to bring the RPM's back down to 2200 or so and it will cool enough to turn the buzzer off. If I run the other engine at 3000 RPM's for more than 15 minutes, the buzzer goes off. The specs say I should be able to run the engine at:

"Cruising Speed (3400 rpm or lower) for less than 90% of total engine times (9 hours out of every 10 hours)"

My max RPM is a bit over 3500 RPM, so I should be able to run my engine without excessive thermal load issues at about 3150 RPM. I can't do that for more than 15 minutes, not the specified 54 minutes. So, it is either a design, or specification issue.

One might argue I have additonal devices on the engine that are increasing the thermal load. In this case, we have an engine that has absolutely nothing additional on it. No high output alternators, compressors, water heaters, it is bone stock. The other engine has a heater, but not HO alt, or compressor. hoses are recommended sizes, coolant is DEX, which they require. I even changed the impellor, thinking that might be a source of the problem. The installation was certified by a Yanmar dealer. All the maint requirements have been followed, almost to the letter (ask me about changing the oil in the Saildrives every 100 hours! Grrrr!!). We will see what Yanmar says about the issue on Monday.

Great engines though! I do love them. (Not the saildrives though! )

Cheers

Keith
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Old 22-07-2006, 14:56   #10
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No Kieth, you have a slight error in your understanding of duty cycle. That 90% part is only based on a specific industry standard measurment time. I have got my technical book here in front of me, but the time is measured in minutes. It is 90% of say 30minutes or something. If it was 90% of the total running time, then you could also be accurate in saying if the engine was going to run for 10days nonstop, then it should be able to run for 9days at full RPM without overheating. See what I mean?
15mins at full RPM and load is about what I would expect.
As for the lesser time on the one with the heater, it is highly likly it is a cooling speed problem. I don't know all the ins and outs of this setup, but with many engines, if cooling water is allowed to circulate too fast, it won't cool very well. It's why removal of a thermostat in an engine can most of the time cause it to overheat. The water flow must be controlled to allow it to have sufficient cooling time int he heat exchanger.
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Old 22-07-2006, 15:44   #11
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Wheels, I think you are wrong about the reason removing some thermostats cause some engines to overheat. Some thermostats close when hot, thereby forcing the coolant to flow through the heat exchanger. Some thermostats open when hot, allowing more coolant to flow through the heat exchanger.

If you remove a thermostat that closes when hot you will not get enough coolant flowing through the heat exchanger.

Deep.
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Old 22-07-2006, 16:09   #12
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Alan;

I think the greater point I was try to make is that the engine should not overheat after running for 15 minutes. Not when it is has a rated

"cruising speed of 3400 RPM".

Besides, I was just quoting the Yanmar Marine International 3YM30 service manual on the thing. In section 2, page 9, Product Explanation (GB section). Perhaps it is their wording in their literature, not my understanding. They say

"The engine is designed for pleasure boat applications

Maximum throttle(3600-3800 rpm) for less than 5% of total engine time. (30 minutes out of every 10 hours)

Cruising Speed (3400 rpm or lower) for less than 90% of total engine time (9 hours out of every 10 hours)"

I doubt VERY seriously it is a cooling speed problem. If it is, then that is a SEPERATE design issue. BOTH of these engines were install new in January of last year. They both have about 400 hours on them now. I followed the recommended break in procedures.

I am overheating at 2800 and 3000 RPM's. My max RPM on the engines is about 3550 or so. My max RPM is only 50 rpm's less than the rated max throttle range. This is I account for because I have probably 1 inch more pitch in my props than I should have ( I had the repitched by 2 inches, should have only done 1 inch.). Still, with both engines, I can get the boat up to hull speed. So, I believe that may account for my not obtaining max RPM. Could be my tacometers too1? There was no difference in speed or overheating after I had the boat pulled, props cleaned, hull completely stripped, faired, resealed and painted.

I don't know if this problem has existed since the engines were new. I only took the engines up to max throttle for more than a minute after I had reached the 130 hour mark. But, after that, I have only had occassion to run it at 3000 for longer than a couple of minutes a few times.


I haven't removed, or altered the thermostat from the original. I bought both engines new from the distributor. Picked them up and pulled them from the crates myself. I HOPE the right thermostats are in there! I haven't thought to pull them.

Like I said. I had the installation certified by a Yanmar rep. We even went on a sea trial. They gave the installation approval, after I changed the coolant to Shell DEX-Cool. (they could tell by the cooler). Nothing fancy about the water heater installation. Yanmar sells a kit that you you can use to tap into the fresh water cooling circuit. It routes water that has gone past the thermostat up to the hot water tank, then back to the engine heat exchanger. Aside from that, and exchanging the saltwater intake valve for a seacock, the installation is completely stock.

Keith
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Old 22-07-2006, 22:58   #13
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Food for thought.....
All the diesels, I worked on, in the fishing fleet overheated when run for a period of time (all different) over spec'ed cruising RPM's.
The design flaw is built in by the manufacturers.
The heat generated by a diesel running at max is tremendous. The water jackets surrounding the cylinders and heads are as big as the manufacturers can afford to make and still make a profit...
Remember the companies want to spend the least, and get acceptable results.
Acceptable???? Yeah just do not run 'em wide open.

Spec'ed rpm and overheating rpm may be different for each install....

We tried everything to cool a smoker that we," wanted to"... "had to" ....
run at max. Bigger intake/thru hull, hoses, high flow water pump, bigger heat exchanger, straight coolant....nothing helped.
It was installed on a boat, much too large for the HP the engine was putting out.
That engine ran on the numbers all day, every day, for months......
bump it up 500 rpm's??? Bells and whistles ringing.

May not be worth the cost, to customize the engine, to run above specs....

Any other thoughts on this?????? Any fixes????

Fred
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Old 23-07-2006, 01:29   #14
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Hang about, maybe I wasn't very clear. I am only suggesting idea's in general. Not that a thermostat is faultyu or missing, it is just a genral comment that may help this situation and maybe some others reading.

Deep, I have yet to see a reverse operating thermostat that closes Off the water circulation. Anyways, It dosen't matter how the thermostat works, that's not what I am trying to suggest.
What I am trying to suggest is that cooling water is MAYBE being diverted to this heater thing in such a way that it is not being allowed to cool to a low enough temp before being feed back into the block. Maybe not enough water is going through the heat exchanger because it is also cyling through the heater thingy.
BUT!!! I don't know the setup of this heater thing, so I am only suggesting a consideration, not saying it is a problem.
It was also kinda directed at Pat as a potential idea he may find helpful. Pat know's what I do and why I would suggest something.

Deep, yep it is indeed a very common problem that occurs with removing a thermostat. It happens when someone has had a faulty stat and they remove it, only to find the engine still overheats and sometimes even overheats worse than when the thermostat was faulty. Upon replacing with a new stat, the temp behaves normaly. The cooling water is being circulated through the cooling system too fast and isn't being cooled properly.
For others reading this, here is a tip that may help with diagnosing a faulty stat. Watch the temp rising on your instrument display. If you notice that the temp tends to stay low for sometime and suddenly jump up, it is a sure sign that the stat is requiring replacment. It is sticky and suddenly opens allowing the water to flow. Problem is, the water has become very hot in the engine and suddenly gets to flow at a good seepd. It usually doesn't cause a problem, but it is possible in an extreme case that it could, due to thermal shock. However, it pays to replace the stat before you "Have to"

OK kieth, back to your issue, just because the manufacturer says the engine is good for X amount of RPM for X amount of time, doesn't always translate to real world in the boat. Now don't get me wrong, I am not saying this IS your problem, it's just some general info that may or may not help you or others.
All engines have a series of specs based on loads and RPM. At some point, the engine reaches a "critical point" of where it can not have the heat it is creating being removed at the same rate. Operation at and above this point is a short term rating. Now, there are also different ratings. SAE, DIN, and several others. Each is derived in different ways. Also remember, these ratings are also derived on a test dyno under specific test conditions. This conditions are NEVER repeated in the real world. There are simply too many factors that make to many differences. It's not a simple case of just because the paper work says X, the engine is going to perform X in the boat. Taking the same engine and placing it in different boat hulls will result in a different operation. Things like where the water is taken from on the hull, the length and diameter of exhaust, how much water is going into the exhaust, the exhaust outlet placing, the angle of engine and hull at different speeds, the loading on the engine and so on are all so different and affect the heat created and the means of taking that heat away form the internals.
So to recap, please understand I am not saying your wrong in this situation, just that there is more to it than only what the specs on a piece of paper says.

I am concerned though, why did the installation guy not pick up a heating problem???
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Old 23-07-2006, 21:19   #15
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I would think most major manufacturers would come close to meeting their specs. Yes, there are all kinds of variables and one always should be aware that "your milage may vary". But, there has to be some semblance of coming close to published performance numbers. I should be able to run at 83% of full throttle for at least 15 minutes. Not to be able do so suggest there is an issues. At least, it gives one pause to say, what is sufficiently different from my installation to warrent that much of a variance. I believe that is the basic determinate for ascertaining whether one has an issue. We always looked at expected value and how much variance from that expected value. I have a rather large variance from an expected value. One next must try to ascertain the cause. Clean hull, slight over prop, middle of the range in terms of weight, installation independantly varified. Belts not slipping, impellor new, pump not rusted. Decent flow from the exhaust, flow not especially hot, but never tested when engine was overheating. Sea strainers clear, lines to heat exchanger clear. Never checked lines to water heater. It would be nice if I had someway of measuring flow through the heat exchanger, alas, no. I thought of scale in the system, and indeed, that was what I was going to look at next. Taking the exchangers off and having them cleaned.

So anyway, If there is a higher capacity heat exchanger, I think that may be a solution. I was thinking about exploring a higher capacity raw water pump, but if the heat exchanger is marginal, that seems like more of a bandage and not a good solution.

The reason we did not find an issue during the sea trials was because I was just looking for maximum RPM and speed at the point of the trial. The engines run fine for a while at full throttle. We only were at full throttle for 3-5 minutes or so. Indeed, as I have only experienced an issue a couple of times. I usually run one engine at 2000 - 2100 RPM when I am cruising. I have run it for 24 hours straight at that speed, no issues. I then switch to the other engine to balance the run times, Only burns .5 gallons an hour at that rate. I have run them for extended periods at 2800 RPM, probably about 5 hours or so. No issues, that I know of, there. Fuel use is closer to .75 gallons per hour at that speed though, so I have found it unecessary to run at that speed. So, like I said, I'll call my dealer/distributor and see what they have to say. They are still under warrenty, so I expect no issues.

Keith
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