Volvo Penta AQ175A/280B overheating

[Privatear]

Hi Folks,
Hope you are all enjoying the season.

Raw water hose 'exploded.'
Starboard exhaust manifold very hot, port side cold.

1. Went to check impellar with a view to replacing but water will not stop flowing out of pump. I removed the long port side water hose that goes to the pump from the water intake elbow adjacent the bell housing but no water there. I can?t think where else water would enter the pump?

Any advice appreciated.
Cheers / Privatear

 

[captmello]

Re: Volvo Penta AQ175A/280B overheating

Raw water hose exploded? Which hose? the one from the pump to the thermo housing?

Is this a raw water cooled engine? Or do you have a heat exchanger?

Not sure on the manifold temp either. Do you run in salt water? you could have some blockage somewhere in the manifold/riser or in the thermostat housing perhaps.

you may want to pull the riser and take a look.

Let me get this straight, you removed the intake hose coming from the transom shield and no water is coming in from there, but you still have a constant flow of water coming out of the pump? Seems odd...

We'll get it figured out.

 

[Privatear]

Re: Volvo Penta AQ175A/280B overheating

Hi captmello,
Many thanks for your reply.

1. There are two large hoses from the pump to the thermostat housing. The one that blew is to starboard, on the side of the fuel filter. (Edit: I am not with my boat, this is from memory. Looking at an illustration online the starboard hose goes from behind the raw water pump to the thermo housing - or is that on a freshwater pump?)

2. It is a raw water-cooled engine.

3. I am moored in freshwater most of the time but go down river to the open sea occasionally and then into Poole Harbour (salt). On this occasion I did drift into a sandy clay bank in the harbour and then reversed out. Then moored for the night. The next morning I began the return journey and shortly after setting out the hose blew.

4. Yes, removed the intake hose from the rising metal elbow that comes from the transom shield. At it?s highest point it is above the waterline. There is no water there, yet water still comes out of the pump when I remove the cover, even after 15 mins of continuous running (with my bilge pump running and definitely discharging overboard. Edit: I only loosen the cover-so we are talking about a steady trickle-don.t know how long it would take for the manifolds to empty?). Yep, it?s a mystery to me too.

Thanks captmello / privatear

 

[Don S]

Re: Volvo Penta AQ175A/280B overheating

In the picture above, is this the hose that exploded?

All you need to do is disconnect the inlet hose from the pump and plug the hose. Even a rag will work. There will be some water still coming out of the pump until the water drains out of the engine.

After an overheat, you really need to pull the risers and replace the gaskets. They tend to leak once overheated.

 

[Privatear]

Re: Volvo Penta AQ175A/280B overheating

Morning Don S,

Thank you for loading the pictures, my memory is obviously as shot as the hose! Yes, you have correctly identified the hose I am referring to.

Next week I will follow your instructions Don S, and when the engine is drained down replace the impellar.

I still need to follow captmello?s advice to investigate a possible blockage that caused the hose to burst in the first place and subsequently (after my fitting a new hose) the starboard exhaust manifold to become very hot and the port one to remain cold/cool. I'll let you know how it goes.

Thanks again / Privatear

 

[Privatear]

Re: Volvo Penta AQ175A/280B overheating

Hi DonS,

Drained the engine down ok. (The constant flow from the inlet hose was siphonic so I disconnected it at the inlet elbow end to let air in.) Replaced the impeller, (no sign of any blockage), ran the engine for short while and starboard exhaust riser began to heat up again while port side remained cold.

So as captmello suggested I removed the starboard exhaust riser and it was virtually solid at the hose end with only a couple of the rifled slots still visible on the top and just a couple of inches of the round ?channel? where the water flows to the rifling. The rest was just solid with no sign of the channel or rifling.

I suspect they are the original exhaust risers from date of manufacture (1984). I realize now that the exhaust risers need to be inspected annually and perhaps replaced every 5years or so?

I have cleaned the the riser up (will do the same to port side) so all the rifling and the channel is clear. I thought I would run the engine first just to make sure it is still okay and cooling properly. The engine itself was replaced about 10 years ago so hopefully the water channels/ducts/pipes(?) in the block are okay. No point in spending ?700 on risers and manifolds if the engine has been damaged beyond economical repair.

Thanks again for your advice.
Regards / Privatear.

 

[Don S]

Re: Volvo Penta AQ175A/280B overheating

The biggest problem with manifolds and risers that are also plugged, is the gasket surfaces between the riser and manifold. Inspect them carefully. The web between the exhaust passage and the water passages needs to be at least 1/4" wide, and good solid shiny metal, not the black carbon that the metal turns into. That is what causes engines to go bad. When they leak water after shutdown and that water goes into an open cylinder and sets for a time, they can rust solid. Especially if used in salt water.

 

[Privatear]

Re: Volvo Penta AQ175A/280B overheating

Hi DonS,
Thank you for your advice. I removed both the exhaust risers and cleaned out the circular slots and rifling (both badly clogged). Cleaned and polished both surfaces (exhaust manifold and risers) and refitted them with new gaskets. Ran engine at 3000 rpm for 5/10 mins. and temp gauged registered just in the low green range as ?normal.?
Only thing is, part of the starboard exhaust manifold was ?hottish? and the hose that you identified was very hot, but not too hot that I couldn?t hold it. The thing is, I had never actually touched the hose or exhaust manifold prior to the engine overheating so I don?t know if that is normal. Can you advise please?
Thanks again / Privatear