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TOPIC: Perkins-Sabre M215 heat exchanger maintenance

Perkins-Sabre M215 heat exchanger maintenance 10 years 5 months ago #1

On my early Perkins-Sabre M215 engine, the main engine cooling is achieved by means of a heat exchanger where the closed circuit cooling fluid is passed through a heat stack that is cooled by a continuous flow of pumped sea water.
In order to maintain maximum efficiency & prevent high running temperatures, the heat stack should be cleaned ideally every year but no longer than every two years.
The following notes are my personal experiences regarding the removal & cleaning of the heat stack.
Its’ housing is a long cylindrical item mounted on the rear port side of the engine about half way up. Two hoses attach to the rear end cover whilst the front cover will have either nothing attached to it or it may just have a small bore water take off pipe to feed a drive shaft seal.
Before commencing any work please take note of the following vital warning.
WARNING. The end caps on my heat exchanger are retained by screws that have hexagon shaped recesses in the heads (known technically as hex socket cap head screws). It is vital to ensure that you have exactly the correct size of hex driver to fit these. If you use a slightly undersize driver there is every likelihood that you will damage the hex in the screw heads which will make the screws virtually impossible to remove.
I would recommend fitting new replacement screws especially if there is any sign of rust in the hex recess. You will also need a quantity of replacement coolant (15 litres should be enough)
There is no need to perform any special draining of the coolant as that will happen as part of the removal process.
My suggested sequence of tasks is as follows:-
Remove the engine cover if practical to give maximum access.
Remove the air filter assembly from the turbo.
You will see two pipes going across the top of the gearbox (port to starboard) both of which connect via hoses to the rear cover of the heat exchanger. One is a continuous solid pipe held onto a metal plate by two P-clips.
Undo the fixings for these two P-clips then slacken the jubilee clips securing the short hose that goes between the heat exchanger & the end of this pipe.
Loosen this hose then withdraw it from the spigot on the end cap of the heat exchanger.
This will then allow the pipe to be swivelled out of the way.
The second “pipe” is in fact the gearbox oil cooler.
Undo the jubilee clips holding the two hoses that connect the right angled pipe between it and the end cover of the main heat exchanger. Carefully remove the right angle pipe noting which way round it fits plus the connecting hose at the heat exchanger.
With the hoses removed, feel under this end of the main casing of the heat exchanger where you will find a largish head of a bolt. This has to be removed to allow the inner heat stack to be removed later. Removal also causes a fair amount of coolant to drain into the bilge.
With this bolt removed, carefully loosen the end cap retaining screws taking note of the earlier vital warning.
Make a note of the orientation of the tubes protruding from the front end cap as it is necessary to refit this end cap exactly as it was.
The end cap may need to be dislodged by means of a tap with a large lead weight or soft mallet. Note that the end cap is sealed by an O ring in a groove in the housing body which may be reused provided it is not damaged.
Remove the front end cap in a similar manner which also has an O ring seal.
The inner heat stack can now be withdrawn to the rear but may need a tap with a large lead weight or soft mallet to get it moving.
It will probably appear to get stuck half way out but a bit of manipulation should see it come all the way (providing you remembered to remove the drain bolt.
Wipe both O-rings clean & examine them for damage. They will have taken on a triangular section which is quite normal & is no cause for concern. If undamaged, carefully store ready for refitting.
The inner heat stack consists of a number of densely packed small tubes going down its length & attached to end plates.
Use a pressure washer to clean the outside of the tubes as much as possible.
They should show no sign of corrosion. If they do then you should consult an expert.
The inside bores of the tubes should be treated with great care. If you can find a length of threaded rod that is a good fit down the bore and can be slid in and out by hand without having to force it then that would be workable. Each tube should be cleaned out with care.
It is possible to obtain special brushes for this purpose but they are not cheap.
Additional cleaning may be achieved by soaking the entire assembly in an appropriate cleaning fluid obtained from somewhere like a radiator refurbisher. The use of Cillit-Bang lime & grime has become popular due to its acidic formula. Whatever is used should be thoroughly washed out after.
Reassemble the heat stack into the housing, noting that it will probably be necessary to do a bit of jiggling to get it back in.
Place the O ring seal over the front protruding end of the heat stack & reassemble the end cap, preferably with new screws. I would recommend filling the ends of the screws with heavy grease after they have been fully tightened.
Repeat for the rear end cap but making sure the end cap is fitted in the same orientation as when it was removed,
Refit the drain bolt at this point taking care not to tighten excessively as it is probably made from brass/bronze which is easily damaged.
Refit the right angle pipe that connects to the gearbox oil cooler making sure that it is fitted the correct way round plus the connecting hose(s). Tighten all jubilee clips.
Refit the hose that connects to the long straight pipe. Tighten the jubilee clip(s).
Re-secure the P-clips that hold this pipe to the metal plate.
Do a final visual inspection that all is in place, screws & jubilee clips fully tightened etc.
Refit air filter assembly.
Top up coolant reservoir to normal level (I use 50:50 antifreeze & distilled water rather than tap water)
Start engine with filler cap off.
Check for obvious leaks.
Coolant level will drop after a few minutes so top back up to normal level.
If no leaks, fit coolant filler cap and run engine to normal temperature.
Check for leaks now that system is pressurised.
If no leaks, go for short run at operating speed to check that engine shows normal temperature (may be a degree or two cooler that before).
If all is well, allow engine to cool and check coolant level again. Top up if necessary.

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