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Old 21-02-2015, 23:03   #1
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perkins 4.108 over heat on high rpm

Hi I have a 4.108 that works perfectly in fact I have sailed from Norfolk to NY and back and I run the engine most of the times
the only problem I have if I push the rpm over 1600
the engine over heats '230 degree' but then If I push the rpm back down temperature goes back down to 180 degree
I changed the impeller
I cleaned the strainer
the exhaust is pushing enough water so there is enough water for cooling
I cleaned the heat exchanger tube
and nothing seems to work
the engine still over heats on rpm over 1800


any advice would be appreciated
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Old 21-02-2015, 23:51   #2
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Re: perkins 4.108 over heat on high rpm

What are the max RPM free running in fwd gear it will do???

Hull condition?

Seawater temp?

Aux drives in use?

Using any coolant?

Exhaust colour?

Marine conversion company?
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Old 22-02-2015, 00:22   #3
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Re: perkins 4.108 over heat on high rpm

I think the max I went on fwd was 2000 rpm
and the water temp was just not a factor it over heated on the summer and fall as well I was sailing back on oct 2014 from ny to va and it was overheating if I keep it over 1700 rpm
and the higher the rpm the faster it over heat but again if I pull back the rpm to 1500 or below it cool down to 180 and stay there
the hull in good condition no barnacles
the boat is 40 ft 17000lbs


exhaust is clear no smok
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Old 22-02-2015, 01:16   #4
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Re: perkins 4.108 over heat on high rpm

Thermostat stuck closed?


Do you see any water circulating with the cap off? (Don't open it hot!)
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Old 22-02-2015, 01:56   #5
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Re: perkins 4.108 over heat on high rpm

If 2,000 RPM is the max--flat chat in gear revs obtainable it is over propped to blazes ie. OVERLOADED!
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Old 22-02-2015, 04:39   #6
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Re: perkins 4.108 over heat on high rpm

You should be able to obtain 4000 RPM in gear and at full power when running free.
(Not tied to a dock)
If not, over-propped
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Old 22-02-2015, 06:03   #7
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Re: perkins 4.108 over heat on high rpm

I've dealt with my 4-108 for 25 years now, and love it. Had major overheating years ago, but fixed it.

Some of the factors which cause overheating were noted above. However, from what you describe, it seems to me:

1. you are WAY overprop-ed. You should be able to get upwards of 3,000 RPM (not 4000) underway at maximum throttle.

2. The 4-108 likes about 2200-2300 rpm at cruising speed. 1600 RPM is way too slow.

3. I'd bet your problem is the heat exchanger. The 4-108 heat exchanger is too small for that engine. I changed mine many years ago to a larger one from a 4-236 and have had no problems since.

4. even if the heat exchanger seems clean -- or has been recently "serviced" with, e.g., muriatic acid -- it could still be part of the problem. I replaced a 4-108 heat exchanger some years back which had recently been "serviced", put on a new one, and ...voila! All the difference in the world. This was a few years before I went to a larger heat exchanger.

Many other conditions could cause overheating, but my bet from what you describe relates to the prop and the heat exchanger.

Bill
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Old 22-02-2015, 06:12   #8
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Re: perkins 4.108 over heat on high rpm

Everybody seems spot on here... overpropped...

My sweet spot is 1800-2200 (175), and I'm overpropped... higher than 2200, we see 210+

33'/20k lbs
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Old 22-02-2015, 06:42   #9
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Re: perkins 4.108 over heat on high rpm

Had the same problem with a 4-154, did everything, flushed out system, clean heat exchg, put new heat exchg on, etc, it turns out the fix was simple. The salt water pump had play on the shaft which was not allowing enough water to circulate, even though it appeared there was lots of water exiting the stern. Did that 2 yrs ago and life is good. Engine is 35 yrs old with 3400 hrs on it.


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Old 22-02-2015, 08:10   #10
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Re: perkins 4.108 over heat on high rpm

Quote:
1. you are WAY overprop-ed. You should be able to get upwards of 3,000 RPM (not 4000) underway at maximum throttle.
Yeah, there are different models of the 4-108,
Mine had a max RPM of 4000 and and would see 4000 at full throttle.
Max Continuous RPM is 3000 and 4000 should be considered "emergency" power, which I have had to use a few times, like when a bridge was closing as I was going through...
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Old 22-02-2015, 09:28   #11
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Re: perkins 4.108 over heat on high rpm

Quote:
Originally Posted by mohamedshaheen View Post
Hi I have a 4.108 that works perfectly in fact I have sailed from Norfolk to NY and back and I run the engine most of the times
the only problem I have if I push the rpm over 1600
the engine over heats '230 degree' but then If I push the rpm back down temperature goes back down to 180 degree
I changed the impeller
I cleaned the strainer
the exhaust is pushing enough water so there is enough water for cooling
I cleaned the heat exchanger tube
and nothing seems to work
the engine still over heats on rpm over 1800


any advice would be appreciated

If it's always done this since you bought the boat - it may need an oil cooler fitting. I marinised an old BMC taxi engine a long time ago and that was fine at low revs, but push it hard and it overheated. Fitting an oil cooler solved the problem completely.

Of course, if it has been OK in the past and is now playing up (or if it already has an oil cooler!) then this won't be the answer.
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Old 22-02-2015, 10:23   #12
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Re: perkins 4.108 over heat on high rpm

If you have not flushed the fresh water side of your cooling system in a couple of years that might be your problem. Old coolant will become thick and restrict the heat transfer to the raw water side of your system. Also check your heat exchanger cores for scaling. It is always a good practice to run your engine at max RPM for a short time on a regular basis to detect problems before they become serious.
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Old 22-02-2015, 10:34   #13
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Re: perkins 4.108 over heat on high rpm

I had a similar problem with a 4-154. Shortly after I bought the boat, I discovered that the rubber pieces on each end of the heat exchanger were bad, and the engine was cooling with straight salt water. It was an ex charterboat and it probably had run that way for a long time. I changed out the exchanger end pieces (and cleaned the exchanger) and everything seemed fine except that it would overheat above 2000 RPM. I did all of the things mentioned in this thread with no results, so I simply lived with it for 8 years of cruising. I ran at 1800 RPM and had no trouble. I could rev much higher for close quarter manuvering, as long as I didnt keep it high for more than a few minutes. Since I started cruising in an engineless boat, I was happy with 1800 RPM. When I finally sold the boat, I told the new owner about the overheating, and how to live with it. He had more of a need for speed than I did, and kept overheating it. He finally had the head pulled and discovered that the cooling passages were almost completely rusted shut. This was on a supposedly fresh water cooled engine. I suspect that the rubber end pieces on the heat exchanger had been bad for years, and it was basically a salt water cooled engine. There are a number of products on the market that claim to remove rust and salt build up in the cooling passages. I would give one (or more) of these products a try. ____ I just reread your post, and you dont say if above 1800 RPM there is lots of black smoke out the exhaust. If there is not, then you are probably not overloading your engine, so the problem would more likely be the engine rather than the prop. Another thought might be the injection timing. That can cause overheating. Many good ideas in this thread. I would try the cleaners first, before changing the prop. When you find the solution, please report back so we can all learn from it. Best of luck. _____Grant.
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Old 22-02-2015, 11:07   #14
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Re: perkins 4.108 over heat on high rpm

I'm thinking overpropped too ... or the prop is infested with barnacles. You should be getting near 3000 rpm wide open. 2400 was always the sweet cruising spot on mine.
Mine was in a 44 ft boat and strangely, I never had an overheating issue like some mention...
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Old 22-02-2015, 11:39   #15
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perkins 4.108 over heat on high rpm

Always interesting to see the range of RPM suggestions. With our 4.108 we cruise at around 1800. This moves us at about 6 knots. Max hull speed for us is 7. At this speed the engine feels right. It's also the speed where we get our most efficient mileage. I keep reading that we should be up around 2200 to 3000. We can do this but the engine uses twice as much fuel to gain that extra knot, and just feels wrong.

I do a high rev run every week or so just to blow out any buildup, but 1800 seems right four our arrangement.

And so far no overheating problems.


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