Exhaust manifold and riser

[oGaryo]

Hi All.. I've been working on an overheating engine and so far have changed the impeller and thermostat.. it runs slightly hot at low revs but at the weekend was running at about 20 degrees above norm at 180 degrees when on the plane... not in the red yet though.

I suspect I have blocked water passages in the exhaust manifold and or riser and I can see rusty water marks around the gasket where the riser joins the manifold.

DIY commitments permitting, I'll be removing the manifold for a closer look this weekend as the exhaust tone sound louder than normal.. it's an MGM 3.0l with Mercab by the way.

Let's assume it's blocked.. is it typically worth fixing / unblocking or is it better to replace? boat performance seems ok at present getting about 4400rpm at WOT although she's slow coming on to the plane.

p.s. the boat used to be lanched from the beach so may even be sand blockage.. are there other things I should check other than the manifold where sand would normally accumalate in the system?

thanks for your advice.. cheers Gary

 

[tinkicker0]

Hi All.. I've been working on an overheating engine and so far have changed the impeller and thermostat.. it runs slightly hot at low revs but at the weekend was running at about 20 degrees above norm at 180 degrees when on the plane... not in the red yet though.

I suspect I have blocked water passages in the exhaust manifold and or riser and I can see rusty water marks around the gasket where the riser joins the manifold.

DIY commitments permitting, I'll be removing the manifold for a closer look this weekend as the exhaust tone sound louder than normal.. it's an MGM 3.0l with Mercab by the way.

Let's assume it's blocked.. is it typically worth fixing / unblocking or is it better to replace? boat performance seems ok at present getting about 4400rpm at WOT although she's slow coming on to the plane.

p.s. the boat used to be lanched from the beach so may even be sand blockage.. are there other things I should check other than the manifold where sand would normally accumalate in the system?

thanks for your advice.. cheers Gary

Corroded water tube in the leg, kinked water hose to transom shield, blocked water hose to engine, blocked riser ports, buggered circulation pump. loose drive belt. Oh and if you do not know exactly how old the manifold and riser is, change them.

3 years or so in salt water, 9 - 10 years in freshwater and you are on borrowed time.

If freshwater cooled it may be the heat exchanger that requires cleaning. Raw water cooled motors were really only intended for use in freshwater lakes.

 

[oGaryo]

thanks TK... I'm going to chnage them in that case as I don't think they've ever been changed.. boat's initial life seems to be scotish lochs from the stickers on the windscreen but I know it spent the last 5 in Abersoch and nothing on the maintenance shcedule copies I have show a minifold or riser change... the boat has had very little use in those 5 years though.... there were a few rusty metal shards in the lower leg when I changed the impeller (raw water cooled), which I presume has come from the manifold or riser.. water pickup tube looked fine apart from someone misaligned the guide and crumpled the top of it on refitting, that's been replaced and fitted correctly.

Have read up on the stories of water leaking in to cylinders etc so better safe than sorry and I'll replace them

Have you a good supplier in mind?

 

[MapisM]

are there other things I should check other than the manifold where sand would normally accumalate in the system?

Since you mention the previous low usage of the boat, a destroyed impeller springs to mind. It's not uncommon to have some rubber parts of previous impellers stuck somewhere in the circuit, in which case a change of the exhaust manifold could be useless, without a removal of the blockage. Were any parts of the previous impeller missing when you changed it?
Besides, some rusty water marks where the riser joins the manifold are rather normal if the engine was left for long periods filled with sea water and not flushed. And yes, internal leakage from there can be dangerous for the engine, but I don't think that's the reason for the blockage.
Last but not least, the rusty metal parts in the leg are weird. I don't know how the circuit is arranged in the 4 cylinder engine, but isn't it a too long way back, from the riser/manifold...?

 

[tinkicker0]

thanks TK... I'm going to chnage them in that case as I don't think they've ever been changed.. boat's initial life seems to be scotish lochs from the stickers on the windscreen but I know it spent the last 5 in Abersoch and nothing on the maintenance shcedule copies I have show a minifold or riser change... the boat has had very little use in those 5 years though.... there were a few rusty metal shards in the lower leg when I changed the impeller (raw water cooled), which I presume has come from the manifold or riser.. water pickup tube looked fine apart from someone misaligned the guide and crumpled the top of it on refitting, that's been replaced and fitted correctly.

Have read up on the stories of water leaking in to cylinders etc so better safe than sorry and I'll replace them

Have you a good supplier in mind?

Tricketts are pretty good and supply pattern parts at a quarter of the price of OEM.

 

[oGaryo]

Since you mention the previous low usage of the boat, a destroyed impeller springs to mind. It's not uncommon to have some rubber parts of previous impellers stuck somewhere in the circuit, in which case a change of the exhaust manifold could be useless, without a removal of the blockage. Were any parts of the previous impeller missing when you changed it?
Besides, some rusty water marks where the riser joins the manifold are rather normal if the engine was left for long periods filled with sea water and not flushed. And yes, internal leakage from there can be dangerous for the engine, but I don't think that's the reason for the blockage.
Last but not least, the rusty metal parts in the leg are weird. I don't know how the circuit is arranged in the 4 cylinder engine, but isn't it a too long way back, from the riser/manifold...?

thanks, I'll check all those out too.. interestingly, the old impeller was in remarkable good nick, not brittle at all and no damage but I changed it all the same... one thing of note already mentioned was the ill fitting of the water pipe guide where the lower gear case joins the upper.. it had been squished in such a way that water and crud was entering the forward section of the lower gear unit and that's where the metal shards were sitting (in and around the outside of the water pump housing).. it could be they've been sucked up from outside and deposited in that area due to the split water guide... there was certainly small pebbles and grit in there with the shards.

I guess it'll all be a mystery until I get the manifold off and have a proper look at the internal condition of the waterways and reverse flush for things like blockage from foreign objects.

 

[oGaryo]

Tricketts are pretty good and supply pattern parts at a quarter of the price of OEM.

cool, thanks. I'll benchmark them against Keypart that are just down the road from me and give me a 10% discount

 

[scej]

How about checking the thermostat as they corrode from salt water also, if it not opening properly it could be the source of the over heat, also check the hoses incase any are delaminating and restricting the flow of water.

 

[GrahamHR]

3 years or so in salt water, 9 - 10 years in freshwater and you are on borrowed time.

After 4 years use in salt water I took the manifolds and risers off my V8. The water galleries were remarkably clean and free of rust, so I have reused them. I have used the VP "Neutrasalt "system since new though, so it seems to do something.

Grahan

 

[oGaryo]

dont know if this helps.. ran her up tonight.. pipes in to thermostat housing from the leg are cold as expected.. short but large hose from top of thermostat down to the engine is hot to the touch, it's the one with the spring reinforcement inside if I remember correctly.. all other pipes leading off to the mainfold and the exhaust mainfold itself + the riser are luke warm.. water exisiting the exhaust is luke warm.... temp reads 180 degrees at idle which has increased from 160 at idle from the time I replaced the thermostat, impeller and sorted to duff water guide to this weekend's run... would suggest a blockage in and around the thermostat? or is this all quite normal?

 

[AndieMac]

After 4 years use in salt water I took the manifolds and risers off my V8. The water galleries were remarkably clean and free of rust, so I have reused them. I have used the VP "Neutrasalt "system since new though, so it seems to do something.

Grahan

I guess with water ingress being statistically the major reason of engine failure in these arrangements, TK is wise to give this advice, particuarly factoring in the permanently moored (seawater), raw water cooled boats, who do not have any annual checks or re-tensions.

Manifolds and risers in a fw flushed, etc.... trailer-boat will last longer, but as there are as many different kinds of owners, as there are ways to look after your boat, IMO its best to think of a minimal time frame.

With my own boat (trailered, raw water cooled V8), it will be going into season 7 with the same manifolds (stripped down every year for inspection), but of course don't do this at home!

After 20 years now, the inlet manifold is going to be changed as a precaution.

The newer breed of 'genuine' manifold/riser, apparently has a ceramic internal liner which lengthens the life span.

 

[GrahamHR]

With both my (VP V8 engined) boats that are moored for 6 months at a time I took the position that hot salt water was NOT something I wanted to be circulating through the engines ! So, both had had closed cooling sysytem added; the first after 1 year use in salt water, the second before it ever saw salt water. Both have had the Neutrasalt system fitted to protect the manifolds/ risers.

Graham

 

[tinkicker0]

I guess with water ingress being statistically the major reason of engine failure in these arrangements, TK is wise to give this advice, particuarly factoring in the permanently moored (seawater), raw water cooled boats, who do not have any annual checks or re-tensions.

Manifolds and risers in a fw flushed, etc.... trailer-boat will last longer, but as there are as many different kinds of owners, as there are ways to look after your boat, IMO its best to think of a minimal time frame.

With my own boat (trailered, raw water cooled V8), it will be going into season 7 with the same manifolds (stripped down every year for inspection), but of course don't do this at home!

After 20 years now, the inlet manifold is going to be changed as a precaution.

The newer breed of 'genuine' manifold/riser, apparently has a ceramic internal liner which lengthens the life span.

Absolutely correct. In situations where the engine can be destroyed, and you don't know who may be reading and disseminating the info; it is best to look at the worst case scenario.
A trailer boat manifold that is flushed through after each use will obviously last longer than one sat on a dock, full of warm saltwater for years.

Dunno why Merc don't provide for pencil anodes to be fitted to the manifold, or rather I do at £400 plus a time for OEM.


Another thought just occurred. My particular boat has the engine block and transom shield bonded to a 4" magnesium donut anode on the transom. Will this be affording some protection to my block and manifold? (freshwater use).
When draining the manifold and block for winter, the usual iron filings that come out are black, not rusty coloured.

 

[AndieMac]

Another thought just occurred. My particular boat has the engine block and transom shield bonded to a 4" magnesium donut anode on the transom. Will this be affording some protection to my block and manifold? (freshwater use).
When draining the manifold and block for winter, the usual iron filings that come out are black, not rusty coloured.

I can't offer an opinion on that TK, although I'm sure there are those who can. It's a rare vessel over here that sees only fresh water use, but as you mentioned earlier regarding manifold life, clearly the most favourable environment.

 

[AndieMac]

With both my (VP V8 engined) boats that are moored for 6 months at a time I took the position that hot salt water was NOT something I wanted to be circulating through the engines ! So, both had had closed cooling sysytem added; the first after 1 year use in salt water, the second before it ever saw salt water. Both have had the Neutrasalt system fitted to protect the manifolds/ risers.

Graham

The best way to go Graham (FWC) for either moored or trailered, but of course adding a considerable cost. The neutrasalt option has been here for a few years now with good results, as has an American product called Macs.
Part of the total care package, for those who want the most out of their boats

 

[Bobobolinsky]

Black rust, just means that there is insufficient oxygen in the system to produce red rust