Engine overheating

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John&Ria
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Engine overheating

Postby John&Ria » Sat Sep 03, 2016 7:38 pm

We recently experienced an overheating issue. I would be interested to know if anyone with similar engines - we are powered by 110 hp Yanmar 4JH4-HTE diesels - have had a similar experience, and what was done to correct the problem.

Here's the background:
- we normally cruise at 2600-2700 rpm, with engine temperatures hovering around 175 degrees.
- as a system test we decided to run the engines at WOT (3200-3300 rpm) for awhile; we last did this about 2 years ago.
- after no more than a few minutes at WOT the upper helm temperature alarm for the starboard engine sounded and we throttled back to idle to allow the engine to cool down; it did this fairly quickly.
- I checked the starboard temperature gauge at the lower helm shortly after cutting back to idle - it registered above 210 degrees (I understand the alarm is set to go off at 203 degrees).
- after motoring for a few minutes with both engines at their usual idle-speed temperatures, we powered back up to 2600 rpm; the starboard engine temperature went no higher than 190 degrees for the balance of the trip.
- the engines have approximately 1400 hours of use and last received regular maintenance in the spring of this year.

From reviewing other on-line forums for similar Yanmar overheating problems, I understand the likely cause is one of the following problems (in descending order of probability):
- faulty impeller (replace); the impeller was last replaced in January/2015 (approximately 250 hours ago)
- faulty thermostat (replace)
- restricted water flow through the exhaust elbow (remove and clean); the exhaust elbow was replaced in March/2015 (approximately 200 hours ago)
- restricted water flow through the heat exchanger (remove and have cleaned 'ultrasonically')

I'm not much of a mechanic so most of the engine servicing on His Idea is done by professionals. Before getting them involved and starting to ring the cash register I would appreciate any insights that others may have.

Thanks.

John

duetto
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Re: Engine overheating

Postby duetto » Sun Sep 04, 2016 7:20 am

hi john,

i'm not familiar with your model engines but here are some things i'd check:

1) i assume prop and bottom are free from growth

2) get an infrared heat gun and check the rw temps on the heat exchanger in vs out. the out should be approx 15 degree warmer than the in. lower readings would mean the heat exchanger is not transferring enough heat out of the engine.

3) if all the mechanicals checkout i'd start thinking about maybe being over-propped.
john & diane cummings
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John&Ria
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Re: Engine overheating

Postby John&Ria » Sun Sep 04, 2016 11:01 pm

Thanks very much for your input John.

Because the boat has previously performed well at WOT (22+ mph at 3300-3400 rpm, with the same props) I'm fairly sure it's a cooling issue of some sort. The 100 rpm I'm losing at the top end right now is likely due to some modest bottom fouling (light green slime, no barnacles), however I wouldn't think it alone would be sufficient to seriously overheat one of the engines.

I like your suggestion to use a heat gun to check the temperatures (it's a mechanical task I can probably handle). I'll definitely look into getting ahold of one.

duetto
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Re: Engine overheating

Postby duetto » Mon Sep 05, 2016 8:09 am

hi john,

i've gotten the heat guns from both sears and harbor freight. home depot may have them.

also remember that the engine fw heat exchanger is the last stop in the cooling system (at least on our 75hp). the rw has to go thru the transmission oil cooler and engine oil cooler. so if the engine water heat exchanger is the last one in line your problem maybe a clog, etc in one of the others. with the heat gun check the rw into the engine water heat exchanger. my guess is that it should be approx 10 degree more than ocean water temp. if its significantly more start working backward to see where the jump is happening.
john & diane cummings

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John&Ria
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Re: Engine overheating

Postby John&Ria » Mon Sep 05, 2016 11:18 am

I've located on-line what looks to be a decently rated infrared gun at my local Home Depot ($50 CDN), and plan to pick it up in the next day or two.

Thanks for the additional tips....

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Re: Engine overheating

Postby sailkane » Wed Sep 21, 2016 5:18 pm

You can do a overnight "pickle" with barnacle buster to clean out the raw water systems.this will be easier ire than taking apart the heat exchanger. Also check the sea strainer for some clogging.

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Re: Engine overheating

Postby Gusto » Tue Oct 04, 2016 5:28 pm

I have the 100 hp engines and had the same problem. We did everything you did. Problem not solved. I lowered the sea strainer until the water rose to the top of the strainer. That solved the problem. Go figure.

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Re: Engine overheating

Postby John&Ria » Tue Oct 04, 2016 8:55 pm

Thanks for the interesting suggestion Gusto. I'll have a look at the sea strainers to see if I can re-position them lower in the bowl. Never would have thought of that.....

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Re: Engine overheating

Postby John&Ria » Sat Oct 08, 2016 5:35 pm

An update on the overheating issue....

Purchased an IR thermometer and took temperature readings at various locations. Engine running at 1600 rpm and engine temperature gauge steady at 175, which is typical for that rpm.
- top of heat exchanger - 125
- cylinder head - 140
- injector fittings - 145
- side of block - 150
- back of block - 165
- turbocharger - 170
- exhaust elbow (after injection pipe for cooling water) - 65
- oil filter - 175

From what I have been able to discern from various online discussions of overheating issues these temperatures/differentials all appear to be within reasonable limits. Unfortunately I was unable to take readings under full load, which may tell a different story. Until I have an opportunity to do that I'm wondering if others have similarly taken readings from their Yanmars and could share them.

Thanks.

duetto
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Re: Engine overheating

Postby duetto » Sat Oct 08, 2016 8:12 pm

hi john,

i've been thru this at least twice. it's all about high rpm/under a load. when we had the problem, the minute we would backoff to lower than 3000 rpm (we have 75 hp) all measurements would return to normal. you need to make arrangements to help you get the temps at full throttle.
john & diane cummings

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John&Ria
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Re: Engine overheating

Postby John&Ria » Sun Oct 09, 2016 4:15 pm

Hi John,

Thanks for sharing your experience - I thought that might be the case.

Just to clarify, when you say you did it under load, was this at max rpm in neutral at the dock, or were you running at top speed out on the water? The latter sounds a bit daunting when one is stuffed down in the engine compartment trying to get a steady bead for the IR measurements. If so, I may have to find a fearless friend to help me out....

duetto
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Re: Engine overheating

Postby duetto » Sun Oct 09, 2016 7:13 pm

hi john,

it doesn't have to be at "max rpms" just at the rpms that make it overheat.

yes, someone is going to be on top of the engine with the ir gun taking readings and it will be loud and buzzing. i would start by making sure that person knows exactly where they will measure. i would start with engine heat exchanger. measure the rw in and rw out. this is the key starting point because it's the most common problem. if the out is less than 15 degree than the in then that's your problem. if the difference is greater than 15 then you start working back to rw oil cooler, then transmission oil cooler. it's all about localizing the problem.
john & diane cummings

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John&Ria
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Re: Engine overheating

Postby John&Ria » Sun Oct 09, 2016 8:19 pm

Thanks for the additional information John.

James Power
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Re: Engine overheating

Postby James Power » Tue Oct 18, 2016 7:58 am

Hey John, don't forget the hearing protection and no loose clothing while working around a running engine. James

John&Ria
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Re: Engine overheating

Postby John&Ria » Wed Oct 19, 2016 12:34 pm

Hey James, hope all is well. I appreciate the reminder about safety for this little exercise. Given what needs to be done and my lack of experience around engines I've decided to have my mechanic deal with this issue when His Idea goes in for annual service next year. Just one more thing to add to the list. Cheers, John


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