Diesel engine heat exchanger and manifold repair

Barry Pickthall

Barry Pickthall explains how he carried out engine repairs on a budget after a couple of years of Covid-19 lockdown neglect

TAGS:

Diesel engine heat exchanger and manifold repair on a budget

How many of us follow the full engine winterising schedule, especially if you keep your boat in the water?

I’m probably one of many who have limited this to simply changing oil and filters and ignored flushing through the engine cooling system, especially when the engine intake skin fitting is difficult to get at.

Well, we ignore these things at our peril!

More often than not we check that the water is flowing out through the exhaust, and eyeball the system for any tell-tale signs of obvious leaks, then let sleeping dogs lie, not realising that an unseen build-up of salts can seriously restrict the amount of water running through the diesel engine heat exchange manifold.

Crystallized salts in a diesel engine heat exchanger and manifold

Crystallized salts had almost completely blocked the manifold’s cooling tube stack and ‘welded’ it to the inner casing. This was all dissolved in a bath of brick cleaner. Credit: Barry Pickthall/PPL

I learned a hard lesson last spring after leaving my boat – and its inboard marine diesel – unused for two seasons because of Covid-19 restrictions.

The saline water in the cooling system crystallized and gummed up the tube stack within the manifold, and because of the mix of an alloy manifold casing and bronze fittings, it also suffered electrolytic corrosion.

Continues below…

There were no outward signs of trouble, the problems were all hidden inside the manifold or at the back end of the engine – which in Sea Jay’s installation is hard to see in the restricted engine space under the deck.

A cheaper option

The shock was all the more when I learned the cost of replacement parts – £279 for a part-exchange tube stack, and £439 for a new manifold casing.

With fitting, it was going to cost around £1,000, simply for not following the full winterising programme – Gulp!

Corrosion in a diesel engine heat exchanger and manifold

The level of corrosion due to electrolytic action between the alloy manifold and bronze fittings were not noticed until the engine was removed from the yacht. Credit: Barry Pickthall/PPL

The pain was largely relieved when an engineering friend told me what a £12 bottle of brick and patio cleaner could do to dissolve the mess.

“Simply put the manifold in a bucket and pour in the liquid. It’s hydrochloric acid and will dissolve the crystals and free up the tube stack within a couple of hours.”

The result was brilliant, the acid bringing up the components like Coca-Cola once used to clean old coins until they changed the recipe.

A yellow bottle of Sika Brick & Patio Cleaner

Sika Brick & Patio Cleaner – hydrochloric acid – used to bath and dissolve the salty deposits that were blocking the waterways within the heat exchanger manifold.. Credit: Barry Pickthall/PPL

I hope we weren’t drinking hydrochloric acid back in those days!

The tube stack slid out of the manifold like a new pin and the bronze end caps came up clean and shiny.

There was still some calcium type build-up in some of the tubes, but rodding them through with a welding rod sorted that out.

Rebuilding the metal

But what about the electrolytic damage that had occurred at one end of the alloy manifold?

The cleaning showed the full extent of corrosion.

bronze end caps, tube stack and manifold casting fresh out of the hydrochloric acid bath which dissolved all the salty residue.

The bronze end caps, tube stack and manifold casting fresh out of the hydrochloric acid bath which dissolved all the salty residue. Note the corroded casing however. Credit: Barry Pickthall/PPL

The coned bronze end cap would still fit and seal the hole, but for how much longer?

A website search showed that the alloy manifold could be brazed to rebuild the metal that had been eaten away.

A man cutting metal

Cutting the hole with a tank cutter through the braze-welded repair to the manifold to accept the bronze inlet/outlet end plate. Credit: Barry Pickthall/PPL

A phone around to local fabricators and engine specialists pointed me to Task Welding in Portsmouth (taskwelding.com), a company specialising in carbon and stainless steels, aluminium and titanium.

I sent them a photograph of the damaged manifold. “No problem…Bring it over… We’ll soon have it looking like new” was the response.

A man grinding a diesel engine manifold

Grinding the manifold with a Dremel multi-tool attachment and hand file to fine-tune the fit for the bronze end plate. Credit: Barry Pickthall/PPL

Using a torch brazing technique, their skilled welder built up the damaged metal, re-drilled the hole for the end plate with a tank cutter, fine-tuned the fit with a Dremel multi-tool attachment and cleaned up with a power grinder.

the engine manifold aluminium housing fully restored

The engine manifold aluminium housing fully restored and almost ready to re-assemble with its core and end plates. Credit: Barry Pickthall/PPL

The final task was to solder the brass water filler cap base to the manifold to ensure a watertight bond.

The final task was to solder the brass water filler cap base to the manifold to ensure a pressure- and watertight fit. Credit: Barry Pickthall/PPL

The final task was to solder the brass water filler cap base to the manifold to ensure a pressure- and watertight fit. Credit: Barry Pickthall/PPL

The whole job cost little more than £200, and once re-coated in heat-resistant paint, the manifold did indeed look ‘as good as new’ with a service life long extended.

A reminder on winterising a marine diesel engine

  • Drain all water from the cooling system
  • Run antifreeze through the engine by closing the intake seacock, removing the intake hose and putting it in a bucket of antifreeze
  • Change the oil and fuel. It’s always a good idea to remove dirty oil and fuel through the winter so there is less chance of sediment forming in the engine
  • Keep moving parts moving. Fill a grease gun with waterproof marine grease, lubricate all the fittings and wipe away any old hardened grease
  • Give the engine a check over. Look out for any parts that are showing wear and need to be replaced. Obvious parts to look at are hoses and clamps
  • Cover the engine
  • Fill the diesel tank to avoid condensation building up inside that can lead to the growth of ‘diesel bug’
  • Disconnect the battery, charge and store it

Enjoyed reading Diesel engine heat exchanger and manifold repair?

A subscription to Practical Boat Owner magazine costs around 40% less than the cover price.

Print and digital editions are available through Magazines Direct – where you can also find the latest deals.

PBO is packed with information to help you get the most from boat ownership – whether sail or power.

        • Take your DIY skills to the next level with trusted advice on boat maintenance and repairs
        • Impartial in-depth gear reviews
        • Practical cruising tips for making the most of your time afloat

Follow us on Facebook, Instagram and Twitter