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Old 06-06-2011, 11:20   #1
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Perkins 4.154 running hotter - thermostat?

My Perkins 4.154 has been running hotter in the last several months. It used to run at about 180 - 185 at about 75% load (1800 rpm? the tach is fairly squirrely), maybe push 190 when I pushed the engine harder to fight a current or make a bridge opening or anchorage by nightfall.

In the last couple of months, with lots more motoring than normal (we have put just over 300 hours on since early March 2011), the operating temps have climbed so that I can't run over about 50% load without the temp climbing over 180, and it gets up to 195 or so - very close to 200 - if we increase RPMs over 1800.

I have just flushed the raw water side with a circulating solution of Ospho (phosphoric acid) using a bilge pump (see this link heat exchanger cleaning for the method), and no change when I ran it - still heats up to near 200 when I load it up to cruising RPMs and higher.

I understand the normal range is 169 to 197 degrees, but I hate being on the hottest side of the range, and the fact that this is worsening over time indicates something.

I have not replaced the thermostat yet - do they go bad in a way that allows slowly increasing engine operating temps, or do they just go all the way bad?

Thanks in advance,
Dave
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Old 06-06-2011, 13:57   #2
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Re: Perkins 4.154 running hotter - thermostat?

Dave

First thing to check is the water pump">raw water pump. Pull the old impeller, put in a new one and make sure if any blades were broken to follow the hoses and clean everything accounting for all the pieces. You might have to take the caps off the heat exchanger. If impeller checks out OK and water flow is normal normal - ideally measure the output by putting a bucket under the exhaust, calculate water flow gal/min and compare to spec for pump, then it might be the thermostat. Easy to change. I am assuming you have made sure the fresh water side has coolant.
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Old 06-06-2011, 14:00   #3
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Re: Perkins 4.154 running hotter - thermostat?

Your description of gradual increase leads me to believe your problem is on the seawater side as well.. Follow Jon's advise
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Old 06-06-2011, 14:13   #4
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Dave,

I had the same problem last year and what John us saying is absolutely right. I had a beat up impeller and impeller bits in my heat exchanger. I am now going to replace the impeller every year, worth it just for the peace of mind. After watching the temp go up as I cut through woods hole mass last year I learned this :-) not fun throttling down when the current is pushing you around!!!
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Old 06-06-2011, 14:14   #5
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Re: Perkins 4.154 running hotter - thermostat?

As anove,

Check both impellers and change
Check thermostat
Rod out heat exchanger core
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Old 06-06-2011, 15:39   #6
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Re: Perkins 4.154 running hotter - thermostat?

Thermostats are designed to fail in open position not closed so unlikely.
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Old 06-06-2011, 16:54   #7
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Re: Perkins 4.154 running hotter - thermostat?

I would also check the exhaust mixing elbow.
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Old 06-06-2011, 17:17   #8
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Re: Perkins 4.154 running hotter - thermostat?

Diesel engines run better at high temperatures. #1 If your engine has a thermostat accessible, check that it is opening correctly. #2 check water pump impellers, #3 Check sea water intake strainer and valve.
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