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cardude01 08-28-2015 10:44 AM

Gauge reading vs infrared thermometer
My boat possibly has a little bit of an overheating problem if I push it over 2800 rpm. Engine max rpm is 3200 on the Yanmar 4JH4-hte. I rarely go over 2400 rpm but when passing barges sometimes I need to. I ignored the problem until I got it to the dock here in Texas, but it's here now so...

Anyway, I say "possibly overheating" because the temp taken with the heat gun at the head never seems to match my gauge. It's always about 10 degrees lower with the heat gun.

So maybe I don't have an overheating problem after all? (Hope hope. Wish wish). The heat exchanger access is not good. 😢
Or, is the creeping up of the temp more of an indication of overheating?

At what temp do I do damage and crack a head (or whatever breaks on these little engines)?

What temps should the various engine components read with the IR thermometer?

I seem to be Question Man today!

AusCan 08-28-2015 11:21 AM

Temperature gauges & senders are often out a bit. Also - engine coolant temperature will vary considerably depending where you measure it. Are you measuring right at the temperature sender with the IR heat gun?

I'd be just a little concerned about heat creeping up when you are above 2800 rpm.
It may be something minor such as your thermostat is not opening 100% and you aren't getting full flow with the coolant. A new thermostat is a fairly cheap investment if you don't know when it was replaced last. Cheaper that pulling and flushing your heat exchanger.

In regard to maximum temperature before damage being done - that is a tough call.
I'd say for most diesels, as long is there is coolant circulating in the engine you are ok in the short term. If it all starts boiling off and you lose circulation, you run into serious problems fast. Maybe someone with specific Yanmar experience may give you a better answer for that one.

C lectric 08-28-2015 11:23 AM

It's quite normal for the I.R. gun to not read the same as the guage. It's not in the coolant so there is some heat loss and temp. as it is transmitted to the outside.

The best place to use the gun is at the same place the temp sensor is mounted. Even better is some flat black paint put on the spot you wish to read . The farther the gun is held away the less accurate the reading will be as it will read more of the surrounding area.

Creeping temps are often indicative of a seawater low flow problem:

- R.W. pump needing a proper rebuild from a worn R.W. pump. Old vane pieces from previous failed impellers closing H.E. tubes, Sometimes impellers will take a set and not pump as effectively.

-restrictions from failing hoses especially on the suction side of the R.W. pump,

-ANY air leaks on suction side from loose clamps or hoses, seastrainer gasket failures.

-not fully open seacock valves, clogged through hulls and seacocks from junk or critters,
even the exterior scoop painted closed.

-the heat exchanger tubes can plug from debris over the years. Some times a cleaner such as muritaic acid or Rydlyme can help if the tubes are NOT blocked fully as the solution must pass through. Also impeller bits will not be dissolved, they must be mechaically removed.
David Marchand has written many times about cleaners like this. Look up his threads. I would caution about Yanmars though as they sometime use 'exotic' materials, compared to many engines, which may be damaged.
Also very important to use the CORRECT antifreeze with many Yanmars as the wrong ones can cause trouble.

-The r.w. injection point in the riser can block from rust buildup. Same for the actual shower holes where the R.W. is sprayed into the exhaust stream.

So what temps are you seeing specifically? Where did the temp used to sit? Have you double checked the wiring at the guage and the sender. Voltage off from poor connections will affect the guages ability to read properly.

Can't help with the point where actual damage is done. If what you have now is a slow buildup and then a quick cooldown when the power is reduced back to normal cruise then you MAY be ok to put it off untill the season ends. But that's a three-four thousand mile guess. Just keep an eye on it it if you go that route and watch for the temps to change more rapidly as that will tell you to not put it off longer. Use a marker pen to mark where it is now so there is no memory. Also to mark the high points. If creeping up then get after it.

Lollygag 08-28-2015 11:25 AM

I had a number of mechanics work on my perkins 4-108 trying to figure out the overheating problem. It turned out to be a cracked sending unit! Didn't always overheat in the beginning but then it started creeping up till it was pinned. A fisherman took a look and said it wasn't overheating. He said to hold a bucket under the exhaust and see if you are getting enough water out and if it's boiling. Of course it wasn't so I started looking for causes and found the cracked sender.

djmarchand 08-28-2015 11:33 AM

Yanmar JH overheating
1 Attachment(s)
I tackled this problem on my neighbors 75 hp Yanmar JH engine. I also have some perspective about how IR guns read engine temperature.

So first, a calibrated IR gun will always read about 5 degrees lower when shooting a thermostat housing than the underlying coolant temperature due to the slight insulation of the metal housing. Also the temperature gauge may not be exactly at the thermostat housing and it may not be calibrated. So having a 10 degree temperature differential is definitely possible.

Calibrate your IR gun by shooting a dark colored pan of boiling water and then go out and run your engine in gear at wot for ten minutes and shoot the housing. The overheat alarm will typically go off at 205 deg, so if your gun reads 200 or less you are probably ok. You could also take that sensor out and put it in a pan of water with an ohmmeter connected and measure the temperature that it closes to make sure it is working correctly.

Your coolant will not boil until it reaches about 225 deg due to the pressure cap and the higher boiling temp of the glycol mix, so there is quite a bit of head room over the 205 alarm point. But some areas of the engine get hotter than the measured temp, so don't rely on that headroom much.

If you have done everything- flushed the coolant and changed the antifreeze, rodded the exchanger tubes and acid cleaned them, replaced the impeller and measured the raw water flow and compared it against the pump spec, then there may be one other thing that is wrong.

There is an internal shield in the heat exchanger that directs the raw water flow that was installed backwards on some engines. See the attached service bulleting. This was what was causing the overheating on my neighbor's boat.


twistedtree 08-28-2015 12:27 PM

Keep in mind that the IR gun is usually measuring a much larger area than suggested by the laser dot. There should be a diagram on the gun that tells you the size of the sense area at different distances. In general, you need to be really close to whatever you are reading.

On my gun, here are the sense circles at different distances:

1.2" sense circle @ 12" distance

3.6" sense circle @ 36" distance

7.2" sense circle @ 72" distance

Given the above, in most cases you would want to be 12" or closer to the target.

caltexflanc 08-28-2015 01:06 PM

IR guns are a great tool, with the issues noted above. The keys are to take the various measurements at the same place everytime and log them. Cross reference them to the reading on your gauges.

I found having a set of mechanical gauges right in the engine room, for engine temp, drive oil pressure and engine oil pressure to be invaluable. This is what I cross referenced the IR and the helm gauges to. I had the mechanic verify the accuracy in the survey and again a few years later. They were dead on. The electric helm gauges often were not, but I had a variance table I learned.I never fully trusted them so always took the IR to the engine room checks, where I also checked oil filter temp, drive oil temp, alternator temp, temp at each turbo and intercooler and shaft log temp. Since I had base line numbers from the survey and the engine specifications, what we were really looking for was variances.

cardude01 08-28-2015 04:29 PM

Ok. Great ideas. I need to go check some things now.

1. Will the shoot at the sending unit area and keep the gun close.

1.5. Need to check thermostat.

2. It heats up slowly and cools down quickly. Will check RW flow.

3. Will try to calibrate heat gun with boiling water.

4. I have cleaned out system with barnacle buster. No better.

5. I suspect the HE is clogged or shield is installed incorrectly like David's bulletin says but want to eliminate other problems first because it's hard to get to.

Carolena 08-28-2015 04:33 PM

When you say overheating, what numbers do you get a cruise RPM vs when you bring her up? On our Cummins, I notice that she is rock solid from around 1200 RPM up to almost 2000 RPM, but runs about five degrees hotter if I push her to 2200 and above (WOT is 2550, about 50 RPM below the rated WOT). We usually cruise between 1400 and 1800.

cardude01 08-28-2015 04:38 PM

Gauge reading vs infrared thermometer
It runs at 180 from 1000-2400 rpm. It will creep up to about 200-210 at 2500-2800 rpm. Seems to hold around there but have only run it that fast for about 10-15 minutes.

Bottom is clean. New bottom job.

Never have had an alarm go off.

Carolena 08-28-2015 04:40 PM

Ok, yep, that sounds like enough of a climb to warrant further investigation.

FF 08-29-2015 08:07 AM

"My boat possibly has a little bit of an overheating problem if I push it over 2800 rpm. Engine max rpm is 3200 on the Yanmar 4JH4-hte. I rarely go over 2400 rpm but when passing barges sometimes I need to."

Perhaps it is not the heat , but the load the engine is under over 2400 RPM warming it up?

I would attempt to find a power graph for cont duty for that engine and see if you are not overloading the engine.Any Black smoke?

Sure the engine is rated to check the prop at 3200 RPM , but that's not the cruise RPM for more than yanking up a water skier.

Your instruments may not be lying.

twistedtree 08-29-2015 08:20 AM

FF has a very good point. That engine is rated at 3200 RPM. At wide open throttle, what RPM does yours make? It should exceed 3200 RPM.

cardude01 08-29-2015 09:07 AM

Gauge reading vs infrared thermometer

Originally Posted by twistedtree (Post 363640)
FF has a very good point. That engine is rated at 3200 RPM. At wide open throttle, what RPM does yours make? It should exceed 3200 RPM.

Interesting point. I think we ran it up to 3100 on the survey. Started getting hot so backed off. I have never run it up to or past 3200 rpm so I guess I need to try that? Are you thinking it's an overprop issue?

I thought from the survey it was determined it had the original equipment, proper size and pitch prop, so I never figured it was an overprop issue.

I did have some trans problems on the way home from FL. Found the oil very dark and had to flush it multiple times to get it "unstuck" out of forward. Before this oil flush it seemed like the engine was "dragging" a bit when putting into gear. Dropped RPM to about 800 for awhile after putting it into gear, and killed the engine at times when putting it into gear. The trans flush seemed to cure that problem. Could there be some internal resistance caused by my transmission?

So, if this engine is not running up to 3200 rpm I could have other issues causing it to get hot? If it's not overproped what else could cause that? What do I need to check?

I don't remember any black smoke at WOT but will check that.

twistedtree 08-29-2015 09:51 AM

Sometimes it's hard to see your own black smoke. If you can, have a buddy observe while you are running WOT.

At WOT, your engine should EXCEED 3200 RPM by 50-100 RPM. If it doesn't, you are over propped. Many people will tell you that's fine as long as you limit your power level at any give RPM, but I don't think most people have the discipline to do that.

Your trans issue is interesting - not sure what to say about that, but if it's working OK now I'd set that aside and stay focused on the other problem.

If you are over propped, it will contribute to high operating temps, but probably isn't the sole issue. It sure sounds like you have some limitation in your cooling system.

Probably the best thing to do is go through the cooling system from end to end and bring it up to snuff. I would focus on the raw water side, so start by making sure your intakes are clean and clear, and strainer is clean and clear.

Then open up the raw water pump, check the impeller, and replace it while you are in there. You might find that a few fins on the impeller are missing.

Then give the heat exchanger a good inspection and cleaning. You could have build up in the tubes that will restrict water flow and inhibit heat transfer. You can clear the tubes with a dowel or other such tool. Also check inside the cooler on the end where the raw water enters, and be sure there aren't any impeller parts bobbing around in there. When they break off the impeller, they will often get stuck in there rather than getting flushed through, then they block water flow.

Next take off the exhaust elbow and sprinkler and inspect it really carefully for corrosion, perforations, etc.

If the engine had an after cooler, that will need to be services too, and typically involves removing it from the engine, disassembly, cleaning, greasing up the mating joints, new o-rings, and a pressure test. Any salt water leakage from the raw water side to the air side will result in pretty much sudden death for the engine as it ingests salt water.

Based on your gear experience, it sounds like the power plant was not well maintained, so I think gogin through everything will be well worth while, and allow you to establish a good base-line for future maintenance.

what_barnacles 08-29-2015 06:59 PM


Originally Posted by twistedtree (Post 363675)
Many people will tell you that's fine as long as you limit your power level at any give RPM

Please suh, what does that mean?

BryanF 08-29-2015 08:31 PM

Well I think that whatever was going on in the transmission may still be going on and placing additional load on the engine. I think I would be looking there as well as going through the whole cooling system.
At least going over it all you will know what you have.

twistedtree 08-29-2015 08:54 PM


Originally Posted by what_barnacles (Post 363878)
Please suh, what does that mean?

Search for over propping and you will find way more info and debate than you could ever want. Enjoy :whistling:

FF 08-30-2015 07:41 AM

For about $100 or so you can purchase an EGT gauge to stick in the exhaust that will allow you to operate with out overloading.

High Wire 08-30-2015 08:07 AM

Another quick indicator of cooling system health is the length of the water vapor trail at the exhaust outlet. A foot or three of white vapor is normal at higher RPMs during a normal summer day. If it grows longer than say 5-10 ft or so before disipating, the reason is the water is leaving at a higher than normal temp and needs to be investigated. Cool, damp weather days also cause longer plumes.

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