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Old 26 September 2007, 16:50   #1
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Country: UK - England
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Boat name: Max Power
Make: Cobra 7.5
Length: 7m +
Engine: Mercury Optimax 225
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Optimax 225 - Overheating ? ? ?

I have a 2005 Mercury Optimax 225.

On two separarte occasions the engine temperature has risen significantly with the alarm coming on when idling from cold?

The first time we were seeting off from cold, engine running stationery for about 5-10 minutes whilst family getting ready, temperature goes up & alarm comes on. Turned off left for a couple of minutes & set off on journey, no further problems.

Used several times since.

Today, went from Sothampton to Port Solent for lunch (bit cold & rough, but great fun !), had lunch waited for lock on tick over, whilst waiting alarm came on again. Turned engine off in lock, set off on journey no further problems?

Can anybody shed any light or give me any advice.

Many Thanks.
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Old 26 September 2007, 17:05   #2
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Engine Overheat

Most overheat at idle problems relate to blocked waterways (unlikely in such a new engine) or a worn impeller. These items are easily damaged especially if the engine is run without water even for very short periods.
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Old 26 September 2007, 17:25   #3
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Check the intakes - mine had a bit of black tape stuck 1/2 over it that would flap around - could also be weed.
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Old 27 September 2007, 07:16   #4
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check water pressure on smart craft gauges.. if pressure fine it could be stuck shut thermostat..
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Old 27 September 2007, 15:10   #5
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Country: UK - England
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Leeway, any idea what the water pressure should be?

I think from memeory mine is 4-5 psi.

Don't know if that is right or wrong?
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Old 27 September 2007, 15:55   #6
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Are there any signs other than the gauges and audible warning that the thing is running hot? Does it smell hot or is it warm to touch? Could be it's the sender or gauges arsing about. If you switch off and re-start do you still get the overheat warning?
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Old 29 September 2007, 13:32   #7
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Quote:
Originally Posted by Mollers View Post
.... Does it smell hot? ...
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Old 30 September 2007, 05:11   #8
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Ok, is there a smell indicating that the engine may have gotton hot?

I've heard that the skiing is very good in Fiji.
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Old 30 September 2007, 06:57   #9
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Fiji for the RWC 2007
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Old 30 September 2007, 16:19   #10
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Idle water pressure is 1 - 3 psi, Wide open throttle is 12 psi. optimax and other di 2 strokes run very hot at idle. Warning buzzer comes on at about 75 celcius, if you leave your boat on idle for long enough the warning will come on, but open the throttle and it should cool very quickly. Although check this with the smartcraft controls so you dont do any damage. If the tempreature doesnt come down consider the thermostats. I think there are 2, one on each cylinder head cover at the top, they are black with a blue piece of plastic round them and lie at the top of the block on eithier bank of cylinders. Here are the instructions from the workshop manual. Use a pan and a thermometer as a thermostat tester
"1. Inspect thermostat covers and cylinder head covers (thermostat opening) for cracks and
corrosion damage that could cause leakage. Replace parts as necessary.
2. Remove and discard gasket from each thermostat.
3. Wash thermostats with clean water.
4. Using a thermostat tester, similar to the one shown, test each thermostat as follows:
a. Open thermostat valve, then insert a thread between valve and thermostat body. Allow
valve to close against thread.
b. Suspend thermostat (from thread) and thermometer inside tester so that neither
touches the container. Bottom of thermometer must be even with bottom of thermostat
to obtain correct temperature of thermostat opening.
c. Fill thermostat tester with water to cover thermostat.
d. Plug tester into electrical outlet.
e. Observe temperature at which thermostat begins to open. (Thermostat will drop off
thread, that was installed in Step a, when it starts to open.) Thermostat must begin
to open when temperature reaches 140-145 F (60-63 C).
f. Continue to heat water until thermostat is completely open.
g. Unplug thermostat tester.
h. Replace thermostat, if it fails to open at the specified temperature, or if it does not
fully open.
NOTE: BE SURE that water in thermostat tester is allowed to cool sufficiently [below 110F
(43.3 C)] before testing the other thermostat."

If they are ok consider the impeller, and i am asuming that you will have checked the inlets for blockage.

hope this helps
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