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AQ200D overheating when in idle

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snoopy5

New member
Hi Guys

Hopefully you can help, am at my wits end.

I have a Volo Penta AQ20d. It is raw water cooled. When I start her up there is plenty of water pumping from the sterndrive. Problem is when it gets up to operating temp (around 140 degrees) and put her into idle the water stops pumping through the sterndrive aout 850 - 900 rmp. If I increase the revs the water starts pumping again.

I have changed the impeller, thermostat, checked all the pipes, checked the circulation pump (no broken fins or leaks) Taken off and cleaned the manifolds and risers.

At a loss what to do next. Any help much appreciated.
 
What is the environment, i.e., running conditions? it is almost impossible to tell if you have water flow with the boat in the water and running it on dry land with "muffs" is often problematic . Running it in the water with the drive tipped up enough to see the exhaust port is a no-no... at least long enough to have the water temp rise above ambient at all.
 
Hi

Sorry to take so long to reply, been a the boat all day. Boat is out for the winter. I a running it in a large container (plastic cold water tank from the loft) It is big enough to submerge the leg, also keep the hose running so plenty of cold water. Done this for last 8 winters with no problems.
 
A tiny suction beach may be causing what you describe!

Remove the water neck fitting.
Check for excessive slop at the upper pivot tube bushing.

If need be, replace the bushing, water neck fitting and special beaded gasket.


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Last edited:
snoopy5 said:
1..... I have checked the pivot tube it is ok.

2..... It is the crankshaft jabsco pump that I replaced the impeller.
Click to expand...

1..... The pivot tube can have no play at the upper end.
If it does have play, the water neck's special beaded gasket will not seal for any length of time.

2..... OK, if this is an old Jabsco pump (six cover screws), and if it's the large volume pump (1.990" deep body), you'll need to know that the impellers for both the Jabsco and Johnson large volume pumps are almost identical.
They share the same blade count, same diameter, same shaft splines.... but the length is not the same.

The Johnson F6B-9 pump impeller measures 1.900" in depth, whereas the large volume Jabsco impeller should measure 1.990" in depth.
If the more current and more common Johnson 1.900" impeller is used in the Jabsco pump body, it will be shy by .090" .
This .090" difference in depth will cause the pump to fail, and more than likely at low rpm.

Parts counter people get this wrong all too often, and will send a customer out the door with the wrong impeller for the Jabsco pump.

Check your pump body depth against the impeller depth.
When fully inserted into the pump body prior to the cover being installed......, the impeller should sit proud by approx .006" to .008" or so.


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