No raw water on an AQD21A - any suggestions?

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tillergirl

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New impeller and water hoses on the raw water side today but on restart no water going through. Impeller is in the right way round and there's drive to it. Back flush from the heat exchanger did not suggest any air locks - but still no water being pumped through. Any suggestions from you clever people please?
 
with our sabres one of them requires priming we do this by releasing the clips to the first cooler from the jabsco pump in our case the intercooler and fill the pipe with water, then refit the pipe and start up and voila there is water coming out of the exhaust, but the other week we found a pin hole in the pump casting which could be our problem, at present it is being held by a blob of araldite pending replacement.
 
Thanks for both answers. I did think of an air leak preventing a vacuum. I think tomorrow I shall redo all the bits I did today: maybe I'll find one. I tried the priming bit exactly as you said but no luck. Thinking on this, when I removed the strainer cap there was a sound of air entering ie there had been a vacuum. That suggests a water inlet blockage but having primed 'both' end, water added to the strainer found the water line level suggesting water could flow out. A blockage perhaps only inwards?
 
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Thinking on this, when I removed the strainer cap there was a sound of air entering ie there had been a vacuum.

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That could simply be because waterlevel is lower than strainer cap so level drops as you open it.

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That suggests a water inlet blockage but having primed 'both' end, water added to the strainer found the water line level suggesting water could flow out. A blockage perhaps only inwards?

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Not sure if the AQD21A marinisation is exactly the same as the 6 cylinder AQD31A but if it is the water goes thru the oil cooler before it gets to the raw water pump. In fact, on the outdrive version the cooling tubes almost acted as a strainer and did get blocked up.
 
This has had a mod bypassing the outdrives and drawing the water direct from the transom. Yes it goes through the oil cooler prior to thepump but they are newish. The air entering was a pronounced 'hiss' so there was clearly a vacuum there. I think I need to try a dinghy pump down the inlet.
 
Just cos the oil coolers are 'newish' doesnt mean the tubes havent got blocked and that would stop water getting to the pump. It's an easy job to take the end of the oil cooler off and check. In fact you could probably check simply by removing the hose from the outboard enfd of the cooler and rooting around with a finger. Happened to me.
 
After further thought, you would need to drain down the engine oil before you could remove the end cap on the oil cooler safely to get at the tube stack.
I remember that I was able to get my finger into the outboard end hose connection quite easily (its 25-30mm I think?) and was able to feel foreign matter in there that had found its way up thru the leg grill.
If you have the big 5" diameter filter with the clear top its the same as I have now and I get the vacuum release of air when I undo it.

As you say, probably first step is to blow back from filter to sea to make sure thats clear.
 
The oil cooler is clearly different on this engine. It is all one part and no way to get at or remove the tube. The water entry/exit pipes are 28mm ext. So it'll be a blow through. Actually by removing the water pipe at the impeller and blowing through from the strainer I will get a good idea of whether there is any blockage. Thanks again.
 
Hi,
If the engine is as original it should have a hose coming from the Stb side of the leg, around the back of the engine and on to the oil cooler under the oil filter. Then connected via a short rubber hoseto a pipe that runs to the water pump on the front of the engine then via another hose onto a saddle tank set on the front of the engine. This is bolted onto the water jacketed exhaust manifold and the cooling water exits out via the exhaust bend. There was no water filter fitted. The cooling sytem may have been modified though. With care the oil cooler can be cleaned in situ. You need to remove the hose from the outdrive and wedge it so the end is above the water line so water doesnt come gushing in. There is a bolt that goes through from the back of the oil cooler into the front cover. Remove this and you can take both covers off and see the condition of the tubes. If they are blocked they can be rodded out with care from the front towards the back. I had a knitting needle which I used for this job, can't remember what size it was though (No 8???) and dare not ask the wife to see which one is missing!! These used to block quite frequently especially when in shallow muddy water as on the East Coast. Other options are piece of impeller in the copper pipe blocking it (remove the pipe to check) or worst case scenario a blocked cooling matrix. These are built like a car radiator rather than a tube stack and can be very difficult to clean. The good news is that this is on the pressure side of the pump so is less likely. I had a lot of trouble with this system on my engines and eventually replaced the lot with a Bowman combined header tank exaust manifold which worked well.
Hope this is of assistance.
Regards,
Eddie
 
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