Princess 32 overheating

[Fishpond]

Have just replaced the starboard impeller on my 1975 Princess 32. raw water is not circulating & there is back pressure & slight smoke evident if you remove the top of the raw water strainer. Should add that this is first time I have seriously run the engines as it has been out of the water during a re-fit. Any ideas?

 

[James L]

Have just replaced the starboard impeller on my 1975 Princess 32. raw water is not circulating & there is back pressure & slight smoke evident if you remove the top of the raw water strainer. Should add that this is first time I have seriously run the engines as it has been out of the water during a re-fit. Any ideas?

Try a new one.
It's a while ago but I had one impeller and for whatever reason it just didn't work.
Given you have run it dry long enough for the engine to overheat, it's likely toast now anyway.

In my boat, when it goes back in the water I have to remove the strainer lid to let water in or the pump sometimes stays airlocked.

Is the strainer before or after the pump?
If after I would open the lid and let water in, if it doesn't fill, then when you start the engine loosen the lid slightly and see if water sprays out.
On mine that is enough to get it primed.

If it's before the pump, I would think try filling it with water. See if that helps prime the pump.

 

[Fishpond]

Thanks James. Fortunately didn't run it dry & there is evidence of water in the pump so impeller is OK. The strainer is before the pump & I took the top off to try priming it, that's when I noticed the turbulence which I assume is back pressure due to the direction of flow. There is water there I'm just not sure the water is getting round or in what volume. While running the engine the temp was well within the norm but as the collarifier runs off this engine it would take longer to overheat. It's the back pressure that puzzles me. Someone suggested it could be build up of exhaust gas but I can't see how. There were two partial pieces missing off the old impeller, found the one in the pipe between pump & strainer. I'm down the boat next weekend & intend to take the hose off the outlet of the pump to see if the missing piece has lodged there causing a partial blockage. Any thoughts? Regards Ian.

 

[dragoon]

Thanks James. Fortunately didn't run it dry & there is evidence of water in the pump so impeller is OK. The strainer is before the pump & I took the top off to try priming it, that's when I noticed the turbulence which I assume is back pressure due to the direction of flow. There is water there I'm just not sure the water is getting round or in what volume. While running the engine the temp was well within the norm but as the collarifier runs off this engine it would take longer to overheat. It's the back pressure that puzzles me. Someone suggested it could be build up of exhaust gas but I can't see how. There were two partial pieces missing off the old impeller, found the one in the pipe between pump & strainer. I'm down the boat next weekend & intend to take the hose off the outlet of the pump to see if the missing piece has lodged there causing a partial blockage. Any thoughts? Regards Ian.

Which engines do you have?

 

[James L]

Thanks James. Fortunately didn't run it dry & there is evidence of water in the pump so impeller is OK. The strainer is before the pump & I took the top off to try priming it, that's when I noticed the turbulence which I assume is back pressure due to the direction of flow. There is water there I'm just not sure the water is getting round or in what volume. While running the engine the temp was well within the norm but as the collarifier runs off this engine it would take longer to overheat. It's the back pressure that puzzles me. Someone suggested it could be build up of exhaust gas but I can't see how. There were two partial pieces missing off the old impeller, found the one in the pipe between pump & strainer. I'm down the boat next weekend & intend to take the hose off the outlet of the pump to see if the missing piece has lodged there causing a partial blockage. Any thoughts? Regards Ian.

You say engines, so I assume there are 2.
Is one working ok? If so try swapping the impellers, as I said one year I had a new impeller that for whatever reason just wouldn't pump, looked perfect etc.
If both are not working, what work did you do?
I'm just wondering if the engines have opposite rotation and the pumps have been switched? Some old boats used a different rotation on each engine to simplify the gearbox (as far as I've read on here).

 

[BruceK]

back pressure? I have seen a couple of blades on an impeller reverse direction presumably because the engine may have been cranked in the wrong direction during a tappet / valve clearance service. I wonder if that could cause back pressure?

 

[Fishpond]

Which engines do you have?

Hi Dragoon, thanks for responding.
they are AQD21As I'm thinking of using an industrial wet vac connected to the inlet on the heat exchanger to suck back any debris. To do this I would raise the leg so the exhaust is just clear with the inlet still submerged. On completion I would then run the engine with the leg still in same position to check water flow. Are there any problems doing this? Any thoughts? Cheers, Fishpond

 

[James L]

Hi Dragoon, thanks for responding.
they are AQD21As I'm thinking of using an industrial wet vac connected to the inlet on the heat exchanger to suck back any debris. To do this I would raise the leg so the exhaust is just clear with the inlet still submerged. On completion I would then run the engine with the leg still in same position to check water flow. Are there any problems doing this? Any thoughts? Cheers, Fishpond

I can't see how that would do any damage, but probably worth checking with someone who knows their stuff. The System is designed to be under pressure rather than vacuum.
If you have access to fresh water, try removing the the pump outlet and see if the water from the hose flows through from there. If it does then you know there's no blockage.
then replace it and open the strainer and place the hose into the strainer outlet, you should see if over flowing and when you start the engine if it's still overflowing you know the problem is the pump.

 

[dragoon]

Hi Dragoon, thanks for responding.
they are AQD21As I'm thinking of using an industrial wet vac connected to the inlet on the heat exchanger to suck back any debris. To do this I would raise the leg so the exhaust is just clear with the inlet still submerged. On completion I would then run the engine with the leg still in same position to check water flow. Are there any problems doing this? Any thoughts? Cheers, Fishpond

Hi Fishpond,
I doubt as it will hurt to try that. If the problem is bits of rubber impellor blocking things you might be lucky. If it's blocked due to crud and salt build up, I doubt it will help.

I think James above offers good advice. Once you establish that the pump is running, you can work your way through the raw water circuit one component at time and establish where its blocked.

In case this helps here is a link to the exploded view of those engines Exploded views / schematics and spare parts for Volvo Penta AQD21A, AQD21A - MarinePartsEurope.com - MarinePartsEurope.com

Cheers,
Paul