MD7A chemical flush of raw water cooling system

[Sailing newbie selsey]

Hi took my boat out for the first sail of the season last weekend, after 15 mins at 2500 revs the engine temp alarm sounded. I cut the revs to around 1200 and the alarm and warning light went out after a few minutes.
At all times I had a good flow of water from my exhaust port and I have always had a little white smoke. I removed the thermostat and tested it, it seems to be operating ok, my next step will be to flush the raw water cooling system with barnacle buster in an attempt to clear any blocked channels. I will also replace my thermostat with a new one just to make sure.
can anyone advise me on flushing the system, I intend to disconnect the raw water inlet pipe at the gearbox entry point of the system ( sea cock closed of course!) and attached a hose for the inlet, via a drill pump and hose back from the pump into the barnacle buster bucket. I will remove the impeller from the pump so this does not hinder the flow. From the top fitting of the thermostat housing I will attach my outlet hose returning flow back to my barnacle buster bucket. I intend to saw out the spring and closing plunger on my old thermostat so that it remains in the open position for the flush process.
I understand that I may need to block a bypass opening for the flush, I am not sure what opening this is. I have attached pictures of the thermostat housing and exhaust manifold where it attaches, can someone please point out the hole I need to plug for the flush.
I intend to flush the system for a few hours using the drill pump.
thanks in advance

 

[rosie]

The bypass is the small hole just to the left of the copper pipe which connects to the thermostat housing. The hole in the housing with the rubber o ring lines up with it.
I have experienced the by pass itself becoming blocked so no cooling water flows until the thermostat opens. It might be worth trying to clean the bypass with a bit of wire. You could also run your flushing pump with the closed thermostat in place.
The thermostat housing looks to be in good condition. Look after it because it is worth its weight in gold!!

 

[VicS]

Hi took my boat out for the first sail of the season last weekend, after 15 mins at 2500 revs the engine temp alarm sounded. I cut the revs to around 1200 and the alarm and warning light went out after a few minutes.
At all times I had a good flow of water from my exhaust port and I have always had a little white smoke. I removed the thermostat and tested it, it seems to be operating ok, my next step will be to flush the raw water cooling system with barnacle buster in an attempt to clear any blocked channels. I will also replace my thermostat with a new one just to make sure.
can anyone advise me on flushing the system, I intend to disconnect the raw water inlet pipe at the gearbox entry point of the system ( sea cock closed of course!) and attached a hose for the inlet, via a drill pump and hose back from the pump into the barnacle buster bucket. I will remove the impeller from the pump so this does not hinder the flow. From the top fitting of the thermostat housing I will attach my outlet hose returning flow back to my barnacle buster bucket. I intend to saw out the spring and closing plunger on my old thermostat so that it remains in the open position for the flush process.
I understand that I may need to block a bypass opening for the flush, I am not sure what opening this is. I have attached pictures of the thermostat housing and exhaust manifold where it attaches, can someone please point out the hole I need to plug for the flush.
I intend to flush the system for a few hours using the drill pump.
thanks in advance

The thermostat should just start to open at 60C and be fully open at 75 C. It is so horrendously expensive you'll not want to replace it if it is working correctly.

Barnacle Buster, which is phosphoric acid based, is also very expensive . Consider Rydlyme , which is hydrochloric acid based or Fernox DS-3 central heating boiler descaler, which is sulfamic acid based.

Remove the thermostat.
The bypass passage which ideally you will need to block is in the thermostat housing between the top and bottom connections. I do not know how practical it is to block that.

 

[Refueler]

To flush my raw water system ... I do this every autumn as winter knocks on the door. Perkins 4-107 43HP.

I close seacock ... open top - remove filter ... stick a coke bottle that is cut in half into the top of seacock (the screw neck) ... then have Anti-Freeze or whatever flushing medium ready in 5ltr containers ...

The exhaust I have a short length of pipe sticking out of transon - I take a plastic large bore drain pipe and prop that up so exhaust is blowing into the pipe .... end of pipe into a large bin ...

Start engine ... pour flushing into the coke bottle ... collecting it in the large bin. Once the flushing is through ... Stop engine .... if I want to flush again ... I transfer back into 5 ltr containers and repeat. This way - I never have the flushing getting hot .. it has time to cool ...

I would not flush by external pump with engine stopped ... I will always use the engine itself for the job to avoid any problems of fluids going where they shouldn't ... with engine running - all fluid is blown along exhaust instead of possibly collecting ..

 

[VicS]

>
I would not flush by external pump with engine stopped ... I will always use the engine itself for the job to avoid any problems of fluids going where they shouldn't ... with engine running - all fluid is blown along exhaust instead of possibly collecting ..

The OP says, " From the top fitting of the thermostat housing I will attach my outlet hose returning flow back to my barnacle buster bucket."

Therefore his chemical cleaning solution will not be going into the exhaust, or anywhere else that it shouldn't.
.The downside is that it will be cold and will tale longer than it would with a bit of warmth from the engine being run

 

[Refueler]

The OP says, " From the top fitting of the thermostat housing I will attach my outlet hose returning flow back to my barnacle buster bucket."

Therefore his chemical cleaning solution will not be going into the exhaust, or anywhere else that it shouldn't.
.The downside is that it will be cold and will tale longer than it would with a bit of warmth from the engine being run

Yep - should have gone back to read his post again ...

Anyway - its a point well worth noting for anyone thinking to flush all way through to exhaust ...