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Old 27-07-2015, 11:18   #16
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Re: Overheated

You said the coolant flow was good. How was it measured? If you are sure that the raw water system is clean and you are getting enough water flow then the problem can only be the coolant side of the system. Have you checked the air bleed screws as mentioned in an earlier post? Next task would be to remove the water pump and have it rebuilt, IMO.

By the way have you actually measured the raw water flow? There have been instances where the impeller actually slipped on its hub when the pressure built.
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Old 27-07-2015, 12:01   #17
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Re: Overheated

More information would be helpful.




Assuming you have a 6LPA-ST series?

Do you have a straight inboard, or an I/O?

Are you the original owner, or did you inherit the problem?

What does 'peg the temp' mean? The alarm comes on or does the gauge read 250 after 30 seconds?

Did the problem start all at once or come on gradually?

Can you modulate the temp with speed, or does it overheat at anything above idle?

What is the ambient temperature and condition of hull and running gear?


Based on what you've said so far, I'd guess, in no particular order, overpropped, airlock in the freshwater side, switched hose, faulty freshwater pump, reversed thermostat, seriously dirty hull, flow restriction after the riser.

Couldn't find a good cooling schematic, so the above are somewhat obviously all guesses....
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Old 27-07-2015, 12:45   #18
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Re: Overheated

Quote:
Originally Posted by jimbunyard View Post
More information would be helpful.




Assuming you have a 6LPA-ST series?

Do you have a straight inboard, or an I/O?

Are you the original owner, or did you inherit the problem?

What does 'peg the temp' mean? The alarm comes on or does the gauge read 250 after 30 seconds?

Did the problem start all at once or come on gradually?

Can you modulate the temp with speed, or does it overheat at anything above idle?

What is the ambient temperature and condition of hull and running gear?


Based on what you've said so far, I'd guess, in no particular order, overpropped, airlock in the freshwater side, switched hose, faulty freshwater pump, reversed thermostat, seriously dirty hull, flow restriction after the riser.

Couldn't find a good cooling schematic, so the above are somewhat obviously all guesses....
I have straight inboard engines and you are correct on the series. I have owned the boat for two years and am the second owner. The temp will go to just over 200 on the gauge then the alarm will sound just after I power up. The hull and gear was just done while I had it out of the water last month. Think I'll try the freshwater airlock idea, or even the pump, haven't done that. thanks a lot for the input, I appreciate it.
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Old 27-07-2015, 12:51   #19
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Re: Overheated

Quote:
Originally Posted by DeepFrz View Post
You said the coolant flow was good. How was it measured? If you are sure that the raw water system is clean and you are getting enough water flow then the problem can only be the coolant side of the system. Have you checked the air bleed screws as mentioned in an earlier post? Next task would be to remove the water pump and have it rebuilt, IMO.

By the way have you actually measured the raw water flow? There have been instances where the impeller actually slipped on its hub when the pressure built.
Thanks for the response. I only checked the that the coolant was moving in response to throttle and it seem to react but I don't know how to check the flow. Also, I haven't checked the air bleed screws yet it's on my list to do next. I'll try the freshwater pump too. again thanks!
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Old 27-07-2015, 13:27   #20
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Re: Overheated

Where are you located, and will the engines reach at least maximum rated rpm in gear with proper trim and full fuel?
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Old 27-07-2015, 13:32   #21
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Re: Overheated

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Where are you located, and will the engines reach at least maximum rated rpm in gear with proper trim and full fuel?
I'm in South Florida and yes, she ran perfect up until 40 days ago. Still pops right out and levels off just like before but port side gets hot quick. Starboard stays at 170 or so, which is where they always ran.
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Old 27-07-2015, 14:22   #22
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Re: Overheated

Well that eliminates overpropping and climatic extremes.


The very rapid heat rise indicates that heat is not being exchanged efficiently, which as previously noted can be the result of several things.

A hand held infrared thermometer can help troubleshoot. If possible, shoot the raw water temp where it comes into the boat; then where it leaves the r/w pump; then where it leaves the inter or aftercooler; then where it leaves the oil cooler; then when it leaves the oil cooler; then where it leaves the engine heat exchanger and then where it enters the exhaust riser and then (as best you can) at the lowest part of the riser where the hose exhaust hose connects . Generally speaking the raw water temperature should get incrementally higher at each stage, any anomalies might indicate where the problem is.


Since you have a correctly operating twin you can also shoot the well behaved engine at the same spots to compare the two...
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Old 27-07-2015, 14:55   #23
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Re: Overheated

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Originally Posted by dspringer View Post
Would anyone know besides water flow what would cause over heating of a Yanmar 315? I have cleaned every cooler replaced perfectly good impeller and even replaced the thermostat. At idle and at higher rpms the water is moving, yet as soon as I put it under load to come up on plane the temp still pegs within 30 seconds.
I had a Westerbeake with the identical problem, went thru most of ideas that have been recommended. What fixed it was a mechanic showed me a bleed port in the engine head that had accumulated a crust that was blocking water flow. The hole was about the size of a pencil lead. Replacing the head fixed it although had I had the time , perhaps a vinegar soak would have done the job cheaper.
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Old 27-07-2015, 15:08   #24
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Re: Overheated

Quote:
Originally Posted by jimbunyard View Post
Well that eliminates overpropping and climatic extremes.


The very rapid heat rise indicates that heat is not being exchanged efficiently, which as previously noted can be the result of several things.

A hand held infrared thermometer can help troubleshoot. If possible, shoot the raw water temp where it comes into the boat; then where it leaves the r/w pump; then where it leaves the inter or aftercooler; then where it leaves the oil cooler; then when it leaves the oil cooler; then where it leaves the engine heat exchanger and then where it enters the exhaust riser and then (as best you can) at the lowest part of the riser where the hose exhaust hose connects . Generally speaking the raw water temperature should get incrementally higher at each stage, any anomalies might indicate where the problem is.


Since you have a correctly operating twin you can also shoot the well behaved engine at the same spots to compare the two...
That's great information, thank you. I'm heading to get a gun right now.
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Old 27-07-2015, 16:20   #25
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Re: Overheated

Quote:
The hull and gear was just done while I had it out of the water last month. Think I'll try the freshwater airlock idea, or even the pump, haven't done that. thanks a lot for the input, I appreciate it.
So you had a bottom job done just prior to the problem showing up? Take a look at these pictures courtesy MaineSail at Compass Marine. Great place to check.
External Strainers - OMG Photo Gallery by Compass Marine How To at pbase.com
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Old 27-07-2015, 17:00   #26
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Re: Overheated

I had the bottom done after the first overheating incident. I had it hauled to check for intake obstruction and did the bottom a little early since she was out. She's very clean from bottom up
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