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ivndrago · 22-06-2010, 14:17

Just purchased a newly used Irwin 37' Ketch with a Perkins 4.108 not knowing the "real" condition of the engine. Once she was in the water, we hired a mechanic to get the Perkins started. He had to severely adjust the idle but he got her going. After running and overheating, we decided to get the injector rebuilt. We installed the new injectors, bled the system, changed the oil, a new muffler and got her started. She starts without problems and she runs at average operating temperature. Here is where my problem lies, under power (in gear) she only generates enough power to max speed of 2 knots at around 1500. Anything over 1500 rpms and she starts to overheat without any gain in speed.
I am stuck! I will probably continue to troubleshoot but if anyone has any ideas on where to focus, it will save me time and most likely some moula!!
Thanks!

DeepFrz · 22-06-2010, 14:24

Could be the exhaust mixing elbow is partially plugged.

That is where I would start because you say it starts and runs well at lower RPM.

Have you checked the sea water pump impeller?

slacker · 22-06-2010, 16:05

Before you pull apart the exhaust elbow have you checked the prop? A dirty, barnicle encrusted prop could easly reduce your speed to 2 knots and cause you to overheat.

DeepFrz · 22-06-2010, 16:09

slacker, right. I forgot to ask what RPM it will run at WOT out of gear and if it will run at WOT out of gear without overheating.

ivndrago · 23-06-2010, 05:19

The boat was recently out of the water so everything on the bottom and the prop is clean.
The boat runs very cool at idle. At 1500 rpms she runs are around 150 degrees.
Under power, (2000 rpms) she runs at average temperature (around 190-200). She starts to overheat at higher rpms all the while not increasing speed.
I have not checked the exhaust elbow but she seems to be discharging at a regular rate.
The impeler is also new.

perchance · 23-06-2010, 05:49

What colour is the exhaust smoke under load?

ivndrago · 23-06-2010, 05:54

white.

donradcliffe · 23-06-2010, 06:40

If you can catch the exhaust water in a bucket, run it up to 2000 rpm in neutral at the dock, and see how many gallons per minute are coming through the raw water side of the engine.

slacker · 23-06-2010, 09:06

So, if you can run it up to 1500 or so in neutral with out overheating then it must be a problem with overloading.

Your engine should run just shy of 180 all once it warms up. If it runs at 150 you may have a problem with your thermostat.

Can you grab the prop shaft coupler and turn the shaft by hand? If so, that eleminates a cutless brg. problem.

When you spin the shaft by hand (in neutral) do you feel any excess drag in the transmission? BTW, is it a Borg Warner?

Seahunter · 23-06-2010, 11:01

From the Perkins manual:

perchance · 23-06-2010, 12:38

The white exhaust, as opposed to grey smoke may be an indicator of a problem with the head or gasket. Is this a raw or closed cooling system and is it run in salt or fresh water?

johnar · 23-06-2010, 13:30

man I feel for you, for 3 years I had a Perkins 4108 that would start and run great at anything below 1600 RPM any higher it would over heat. I made around 3 to 4 knots so it did not stop me from sailing but for the life of me i could never figure it out. In the 3rd year it overheated and blew the head so i replaced that never changed that 1600 RPM thing. The replaced head did not last long at all before it blew.

I desided to repower the boatmy choice was another Perkins 4108 that I found for $5K it arrived with a head problem (injector would not seat) bit it is my belief that the motor will out live me now. The one thing I would have don different is where I got the motor. There are reasons people buy from TranAtlantic aka. TAD. even at a higher price.

The point I am tryin to make is before you spend a dime on fixing it, think about repower. any Perkins around has to be over 20 years old.

Dutch

DeepFrz · 23-06-2010, 14:39

Quote:

The point I am tryin to make is before you spend a dime on fixing it, think about repower. any Perkins around has to be over 20 years old.

I think that is really jumping the gun. Check the cooling system right through from the inlet to the exhaust mixer and you should be okay. Some of the older ones needed a larger heat exchanger but that is a lot cheaper than re-powering the boat. Bill Trayfors has commented on his heat exchanger upgrade here on this forum, a search should find it. If the engine is in good repair it should last a long time.