Heat exchanger repair

[Bobc]

And what cools the exhaust gasses in the manifold fresh water or raw water

Raw water of course, which is why it gets eaten away

 

[rogerthebodger]

Raw water of course, which is why it gets eaten away

If you look at MagicalArmchair diagram showing the various flow it looks like the raw water goes through the stack cooling th fresh water which in turn cools the exhaust.

My mobo I have in the UK had a manifold /heat exchanger like that supplied by bowman

 

[MagicalArmchair]

Just to flesh this out, so I understand the cooling route - the below shows the 'full' circuit of the fresh water.

Red is fresh water, blue is raw. Clearly I have left the rest of the raw water bit off, and the header tank off. Have I got it right?

If so, it'll be fun pressure testing it

 

[earlybird]

IMHO, that casting is close to scrap for a repair of any durability, but bearing in mind the ridiculous price of a replacement, I'd try a specialist repairer eg here
Perhaps Google some others as well and Email them a picture to see what they say. It'll have to come off the engine no matter what and it could go in parcel-post if distance is involved. Probably make a hole in your wallet anyways by the time it's filled and machined!

 

[Bobc]

Just to flesh this out, so I understand the cooling route - the below shows the 'full' circuit of the fresh water.

Red is fresh water, blue is raw. Clearly I have left the rest of the raw water bit off, and the header tank off. Have I got it right?

If so, it'll be fun pressure testing it

That's about right.

 

[Bobc]

If you look at MagicalArmchair diagram showing the various flow it looks like the raw water goes through the stack cooling th fresh water which in turn cools the exhaust.

My mobo I have in the UK had a manifold /heat exchanger like that supplied by bowman

It's not difficult to understand. The coolant system removes the heat from the engine (runs around the engine and header tank in a closed loop, powered by the coolant pump). The raw water removes the heat from the coolant by being pumped through the tube stack (by the impellor) and then the hot raw water is mixed with the exhaust gasses in the exhaust elbow.

 

[Bobc]

Look at post #7 on the Bavaria forum thread you started.

This is the place to give a good hefty prod with a screwdriver to make sure it's solid.

 

[rogerthebodger]

It's not difficult to understand. The coolant system removes the heat from the engine (runs around the engine and header tank in a closed loop, powered by the coolant pump). The raw water removes the heat from the coolant by being pumped through the tube stack (by the impellor) and then the hot raw water is mixed with the exhaust gasses in the exhaust elbow.

So are you saying there is no cooling of the manifold itself and the exhaust gasses are only cooled once the raw water goes into the exhaust elbow.

Sorry but the exhaust manifold needs cooling from the first flow of exhaust gasses from the engine exhaust valve/ exhaust port.

My current engine has a fresh water raw water heat exchanger and my exhaust manifold is cooled by the raw water exiting the heat exhanger then entering the exhaust manifold.

Most combined have the fresh water enveloping both the exhaust manifold and the rw water tube stack. so in effect the fresh water cools the exhaust then transfers the heat from both the engine and exhaust manifold to the raw water through the cooling stack the raw water then exits through the injection manifold.

My previous boat with a perkins has a fresh water exhaust manifold and a separate fresh water / raw water heat exchanger.

 

[Bobc]

So are you saying there is no cooling of the manifold itself and the exhaust gasses are only cooled once the raw water goes into the exhaust elbow.

Sorry but the exhaust manifold needs cooling from the first flow of exhaust gasses from the engine exhaust valve/ exhaust port.

My current engine has a fresh water raw water heat exchanger and my exhaust manifold is cooled by the raw water exiting the heat exhanger then entering the exhaust manifold.

Most combined have the fresh water enveloping both the exhaust manifold and the rw water tube stack. so in effect the fresh water cools the exhaust then transfers the heat from both the engine and exhaust manifold to the raw water through the cooling stack the raw water then exits through the injection manifold.

My previous boat with a perkins has a fresh water exhaust manifold and a separate fresh water / raw water heat exchanger.

Apologies. I now understand where you're coming from. On this engine, the manifold is built into the header tank, so is cooled by the coolant.

 

[MagicalArmchair]

IMHO, that casting is close to scrap for a repair of any durability, but bearing in mind the ridiculous price of a replacement, I'd try a specialist repairer eg here
Perhaps Google some others as well and Email them a picture to see what they say. It'll have to come off the engine no matter what and it could go in parcel-post if distance is involved. Probably make a hole in your wallet anyways by the time it's filled and machined!

I'm a fan of reusing where I can as well, from a waste perspective. I don't mind paying a professional - and I've had some cracking responses back from some local firms who seem unphased by welding aluminum (as its their bread and butter). They all caveat it with "We need to see it first" of course...

That's about right.

Thanks Bob, I thought so. That means to pressure test it I will need to seal up the port that feeds the fresh water into the block here (as well as the reverse side that the thermostat goes in):

 

[Bobc]

I'm a fan of reusing where I can as well, from a waste perspective. I don't mind paying a professional - and I've had some cracking responses back from some local firms who seem unphased by welding aluminum (as its their bread and butter). They all caveat it with "We need to see it first" of course...



Thanks Bob, I thought so. That means to pressure test it I will need to seal up the port that feeds the fresh water into the block here (as well as the reverse side that the thermostat goes in):

Correct. As you see, this one has been tested.

 

[rogerthebodger]

Do check with the various guys you have on connected if they will do the pressure testing

 

[MagicalArmchair]

I've found a local company (www.gotoengineering.co.uk) who are open all over Christmas, can pressure test the unit and weld ally - so, fingers crossed. I've booked a half day tomorrow to drain down the system and drop it off, hopefully I'll be able to get it to them before they close tomorrow.

 

[jwfrary]

You can pressure test it using the raw water spigots. It’s what most rad shops would do.

the bit your concerned with holds exhaust gas anyway and not Coolant or raw water and has simply a result of a failed gasket and the corrosive nature of the gases being allowed to escape over time.

it’s pretty common to have none water cooled sections of an exhaust, just insulated with wrap or shields on bigger engines the small part on these that isn’t is cooled by the adjacent coolant.Might be a hot spot of course next time I’m called out to a d2 I’ll take the flir camera with me.

a good Ali welder should sort it but it’s not really an amateur friendly job, hence the brazing suggestion.

while you have it off I would give it a good service as well. - take it to a radiator shop they will be able to sort it out.

 

[jwfrary]

I've found a local company (www.gotoengineering.co.uk) who are open all over Christmas, can pressure test the unit and weld ally - so, fingers crossed. I've booked a half day tomorrow to drain down the system and drop it off, hopefully I'll be able to get it to them before they close tomorrow.

I tend to use a a bit of good tape to cover holes abs stop forgign bodies. Too many horror stories of shop rags left in engines!

 

[superheat6k]

Yet, the green paint will only withstand 170 deg C. How do you suppose that survives "way, way hotter" than 250 deg C ?

Exhaust hose is typically rated up to 100c, i find it hard to believe that one side of the elbow can only be 100c max, yet the other side is way, way above 250c

I would respectfully suggest that you may be mistaken here.

Because 170oC is the maximum working temperature of the paint you cite (which in this instance is a meaningless comparision BTW), does not mean it will break down at 171oC, and with no actual impinging gas flow may well be ok with temperatures way above its rated temperature . And neither is this an exhaust hose, which requires a permanent presence of cooling water. When my engine raw water cooling recently failed and took my engine out , the insurance inspector did not even bother to look at the exhaust. "Oh yes, that will definitely require replacing" was his comment in regard to my inclusion of a new exhaust hose in the new parts list.

In this case the port temperature before the water injection point could easily reach 400 - 500oC, and I am not sure recommending a product not suitable for even a domestic oven's temperature and without the violent gas flow is quite so wise.

So yes 500oC one side of the injection elbow and <200oC the other is quite feasible. But the very corrosion observed is a product of very high temperature and high velocity gases impinging upon the surface, and as a result so badly eroding / corroding the material.

My major concern here is using a temporary get you home at low revs fix, that then becomes forgotten about, and instead as some form of permanent repair, will later fail with potentially dangerous results when the possibilities are: engine failure; severe exhaust ingress within the vessel; flooding from the wildy leaking cooling water; and even risk of fire from the very hot exhaust gases. I would add that when my stbd engine failed in August, my immediate concern was that I was on fire, and secondary that I had lost that engine. So I stand by concern not to use a cheap fix on such a component.

So I shall disagree with your view I am mistaken, and instead comparing this with paint and rubber hoses is simply irrelevant.

 

[PaulRainbow]

So I shall disagree with your view I am mistaken, and instead comparing this with paint and rubber hoses is simply irrelevant.

Having seen the latest picture, showing the true damage, i have advised against using epoxy.

However, i find your suggestion that the mating surface could be at 500c whilst the hose is at less than 100c, the fresh water is at circa 80c and the sea water is simply "hot", whilst the whole assembly is pained with a paint that has a max temp of 170c is somewhat unlikely.

 

[jwfrary]

I would assume the temps have reduced considerably from the exit of the cylinder to the point at which the elbow mates but it will still be significant. I burnt myself pretty bad with a glancing blow of a similar area (bigger engine) so I wouldn’t doubt the ability of the component to get to considerable temps. The. Paint will of course have the surrounding air keeping it cool. Though, if it’s flaking off anywhere around the exhaust ports and elbow are usually the first to fail!

 

[MagicalArmchair]

Thank you all for your input. It is a cracking community here.

@superheat6k yes, we have moved on from the epoxy answer and are going for a pressure test and weld up by an engineering firm who specialise in such, failing that, a full on, bankrupting replacement . It's not so daft, a marine engineer suggested the epoxy if it was only very minor, and did not require building up the inside of the flange. When I raised the point that the flange there would reach 500 degrees C, he said that was the temperature of the gasses, and the flange would not get near that temperature (as @jwfrary says above) - and like @PaulRainbow, when the engineer heard the extent of the corrosion, he said it was a proper repair or replace job too. Thank you @superheat6k for being the first to raise the high heat issue, as that started me off down a different path.

Half day holiday today to get it off - the engineers are working on a project late tonight, so I should be able to get it to them so they can pressure test it and see if the unit is kippered. I have high hopes!

 

[MagicalArmchair]

The heat exchanger is off! I didn't have the right four sided socket to undo the drain plug, assuming my standard sockets would suffice... no chance... so I whipped the pipe off the bottom of the fresh water pump and that proceeded to dump the coolant into the bilge under the engine perfectly well. I sucked that up with my little 12V electric pump, took off all the hoses, and unbolted the heat exchanger. Very simple indeed.

I next took it to the guys at Welding Services in Kent | Go To Engineering. They were the only solitary lights still on in the trading estate. We were greeted by a very tidy, clean and professional engineering shop. The engineer that (socially distantly) greeted me was very well informed and helpful, and explained everything to my eight year old boy, who had helped with getting the unit off. The engineer cleaned up the corrosion there and then, and to test if it was possible, tried welding a bit to build it up. He confirmed it would be no trouble to weld as they did lots of delicate aluminium stuff (as evidenced by the array of metal work around their shop).

We spoke about pressure testing, and we agreed that it would be fine to just pressure test the raw water cooled side, else we would need to make up lots of plates and gaskets etc. What PSI should he test it at I wonder? That unit above has 30psi written on it? Is there a psi that would damage it I wonder?