v 6 Mercruiser 2004 Model.

[testlab]

Hi Paddles,

Can you tell me how dose one check this,to see if you need the risers and manifold parts replaced. Is is easy to check this.

I need to check this before I buy this boat.Dont want a 2k bill 3months down the line.

thanks.

How to put this politely.... no offence, but do you know what you are looking for if you took them off?

I am not familiar with the 6 cylinder Mercruisers but I know my way around the V8 (350/5.7 and 454/7.4) and I assume (at the risk of living out my signature slogan) they are similar.

There are different types of risers, manifolds and riser extensions, some are wet joint, some are dry joint and different gaskets are used for FWC and RWC. The manifolds are different for RWC, full system FWC and half system FWC.

The seawater that is used to cool the engine (after the heat exchanger in a FWC system) is injected into the exhaust riser after the elbow to keep the exhaust system cool and is then expelled with the exhaust gasses.

Prior to this the water has travelled up galleries between the outside surface of the riser and the internal exhaust cavity. This water is then mixed with the exhaust gasses after the elbow for expulsion.

The gaskets at the manifold riser joints can perform different functions depending on the system.

Risers need to be replaced because they carry salt water and they rust out between the sea water galleries and the exhaust cavity. When this happens sea water leaks into the exhaust cavity (with the engine off) and into the cylinder heads and cylinders. Likewise the gaskets leak due to corrosion of the mating faces. You can't tell if a riser is crook from outside inspection or in place testing.

Proper testing of the riser requires removal and pressure testing between the galleries and the exhaust cavity to eliminate pinholes and then visual inspection. If they are OK then the correct gasket is critical for reassembly.

Hope this helps. Sorry if it doesn't apply the V6's but I am sure it will be a similar system.

[PADDLES]

g'day testlab, i've got dry joint ones and they're pretty much identical to the v8 ones, i've not personally done mine, (because i just got mine inspected when it was serviced) but the guys at northside marine told me you can generally see excessive corrosion if it's present and with the dry joint ones you'll hopefully see leaks to the outside of the riser/manifold before they go into the exhaust ports, ie. they can't hide. like you say though, pinholes to the inside will be very hard to spot, but also very hard to actually create in a dry joint type, but pinholes to the outside will show themselves quite easily i would have thought, still, pressure testing is a good idea if you're suss.

my riseres are actually corroding from the exhaust side of the riser, into the gap between the cooling water passage and the exhaust pipe, it's apparently from condensation dribbling down the inside of the exhaust pipe from the riser and catching in the little upturned bit of the gasket and just sitting there and causing corrosion.

with the dry joint ones i thought the only difference between closed water cooled and raw water cooled was a different gasket that blocks off the cooling water passage, and a different hose arrangement to seperate the coolant from the raw water at the joint between the riser and the manifold.

[Suiblonde]

hi there i agree with snatchy 100% i just fitted the mercruiser v6 220hp 4.3lt alpha leg in a 24ft bertram, i have only done 45 hours. fuel consumption is spot on

[testlab]

with the dry joint ones i thought the only difference between closed water cooled and raw water cooled was a different gasket that blocks off the cooling water passage, and a different hose arrangement to seperate the coolant from the raw water at the joint between the riser and the manifold.

Thanks for the useful info on the dry joint ones. The manifold/riser gasket has two holes blanked off in the fully FWC ones and the different hose arrangement. The half FWC systems (manifolds are on seawater) are different again (but I haven't seen one) - there are occasional variations in manifold/gasket/riser between engine models. I don't know enough to say which goes with which but there are few variations but I don't know how significant/important they are.

Cheers
Dave.

[PADDLES]

hi testlab, i reckon it's a very clever/simple setup and the dry joint risers/manifolds are a huge step ahead of the old style. i've got mates with the older style and the only good thing about them is they're heaps cheaper to buy and replace. like you say, with the old style it'd be extremely hard to find leaks because the water galleries wrap around the exhaust pipe and everything's hidden away and you have no idea looking from the outside whether you have a leak into the engine. but these newer dry joint ones are a very clever design where they've stepped away from what you'd best describe as an automotive style of manifold cooling to what is essentially a seperate cooling water passage cast into the side of the manifold/riser.

like has been mentioned in an earlier post, mercruiser engines still do have that stigma attached to them, and it's come from those people who have experienced the heartache of the older design failing and then had an engine self destruct from water ingress, even though the newer designs have somewhat eliminated the corrosion issues of the past. that being said though, i'd never like to leave one in the water, but i wouldn't like to leave an outboard in the water either.

[testlab]

like has been mentioned in an earlier post, mercruiser engines still do have that stigma attached to them, and it's come from those people who have experienced the heartache of the older design failing and then had an engine self destruct from water ingress, even though the newer designs have somewhat eliminated the corrosion issues of the past. that being said though, i'd never like to leave one in the water, but i wouldn't like to leave an outboard in the water either.

I've had a few over the years and left them on a mooring - I will be doing so again (soon I hope). It helps when you can do some of your own maintenance, at the least checking things to make sure they won't fail unexpectedly. I think they are as reliable as any powerplant stuck in a hostile environment. Even diesels need the risers changed every once in a while.

[MarkIC]

Hi guys
I have a couple of questions regarding the whittley 660 cruiser with a 220 v6 mpi mercruiser too.
I've only just purchased this boat and so far it seems in immaculate condition for a 2005 model with 380 hrs. It is raw water cooled and has not been stored in the water. The owner was religious in using Macs salt remover to flush when returning from each trip. The boat has full receipts and was serviced each year.
The risers have never been off and and although there are no signs of rust or leaks it will be interesting to see what I find when I pull them off in a few weeks to inspect. I will keep you posted

Q1, should I also remove the manifolds for inspection as well if the risers are not in bad shape, they are the new dry joint type

Q2, the boat is running a merc High Five SS 17" prop and performs well with 4750 wot and a nice sweetspot cruise of 3370rpm for 42kph with a alpha II leg. Seems funny to run a 5 blade on a cruising boat like this even though this was Whittleys std ss prop option. Would a merc revolution 4 blade prop be a better cruising prop for these boats? I've only ever really seen 5 blade props on high hp ski and performance boats boats before. I'm looking for a good all round prop with best economy. The boat has smartcraft hooked up to a navman so fuel use at cruise is 1.35klm/lt with the high five, nice and smooth with good hole shot and no signs of cavitation at all.
Cheers Mark

[terryc]

It is not that hard to pull off the risers to inspect, though you will need a couple of riser gaskets to reinstall. My thoughts would be that if the risers are good then the manifolds should be good. It seems that the risers deteriorate quicker than the manifolds.
I have the same rig as you and find the standard 5 blade prop more than adequate, i doubt whether it could be much improved upon.
I reckon they are a great boat and hull design i take mine outside fishing off the Gold Coast and find it handles the sea excellent.
regards, terry

[PADDLES]

we've just replaced our risers and manifolds on our 2004 cruiser 660. they lasted 8 years and it's raw water cooled like yours and terry's. the 5 blade prop works fine. the big thing i've found with ours is that it responds really easily to weight distribution when you want to get it up on the plane. if i've got more than just us (1 wife + 1 kid) on board, i generally ask anyone on the back seats to jump forward a bit to let us get on the plane quickly and then they can sit back down and enjoy the ride. the 660 has a superb hull in rough conditions.

[The-easyrider]

I did my rmanifolds last year on a 2004 v6 mercruiser that had been well looked after. The out let for the exhaust was well restricted and this is in an area where salt water never goes so the first thing would is pull an elbow of and have a look up the riser.
Aarons iphone 281.jpg

[MarkIC]

hi guys, thanks for the replies so far. The -easyrider I don't seem to be able to open the attachment, can you pm me an email or link to see it please
I agree with the handling comments, so far I'm very impressed with the ride and cant wait to add more hours.
Cheers Mark

[The-easyrider]

There you go fixed, I went for stainless was only 150 bucks dearer than cast so far so good but only time will tell they should outlast the mercruiser ones. There is a noticable improvment in power and economny but the way the old ones were restricted there was bound to be. I run a 3 blade ss prop on mine after canging the manifolds i did some prop testing and the 3 blade ss gave better results than the 4 blade ss and the 3 blade alli. I cruise at 44kph for 29l/h at 3250 rpm on good water with 4 POB