| Author |
Message |
    
Arnie Brulhardt
New member
Username: arnieb
Post Number: 1
Registered: 07-2009
| | Posted on Monday, July 06, 2009 - 05:35 pm: | 
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....Hello: I have a 2003 Merc 60 4stroke. I recently had my thermostat and impeller changed. My situation is this: Before when I throttled up the gauge used to read 10 psi and over 10 minutes it used to reduce to a constant 5 psi after reaching 3500-4000 RPM. After having the thermostat and impellar replaced the first time I took it out I noticed that when I started to throttle up the pressure only reached about 7 psi and after 10 minutes reduced to about 3 psi. Do pressures flucuate that much after thermostat or impellar changes? I had no alarms sound so it's not so bad that the sensors think it's over heating. Anybody have any ideas or similar experiences??
Thanks, Arnie |
'Bandit
Advanced Member
Username: timebandit
Post Number: 774
Registered: 09-2007
| | Posted on Monday, July 06, 2009 - 09:41 pm: |
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12-25 PSI at WOT |
Arnie Brulhardt
New member
Username: arnieb
Post Number: 2
Registered: 07-2009
| | Posted on Wednesday, July 08, 2009 - 10:01 pm: |
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Thanks. Do you mean the pressure can fluctuate 12-25 psi depending on thermostats? Pardon my ignorance.
Arnie |
Graham Lamb
Senior Member
Username: galamb
Post Number: 5603
Registered: 05-2007
| | Posted on Friday, July 10, 2009 - 06:47 pm: |
|
The cooling system is controlled by a thermostat and a poppet valve (or neither).
At idle speed up to about 1500 rpms or so the waterpump creates upto about 4psi. At that pressure the thermostat completely controls the engine temp, opening/closing as required to try and keep the motor at approx 145-170 degrees or so.
As the rpms increase past fast idle the water pressure increases into the 4-9 psi range and the thermostat is (effectively) bypassed completely. The poppet valve (spring controlled diaphram) opens/closes based on the water pressure (min 4 psi before it starts to open) to control the flow of cooling water through the head - the higher the rpms, the higher the water pressure, the wider the poppet opens.
At full throttle (not a static number, say over 4500 rpms) the water pressure will exceed 12 psi. At that point the thermostat is bypassed and the poppet is locked fully open allowing the cooling water to flow "unrestricted" through the motor.
Depending on the condition of the waterpump and the rpms the psi could reach 25.... |
Arnie Brulhardt
New member
Username: arnieb
Post Number: 3
Registered: 07-2009
| | Posted on Saturday, July 11, 2009 - 09:11 pm: |
|
Thanks for the explanation! |
