Morris Minor Owners Club

To keep a long storey short. Last year I went to drain the radiator to replace coolant and I noticed that the drain tap on the rear of the engine block had been replaced by a bolt. On removing this bolt no water drained out presumably due to the block being full of rust / muck. I got as much of the water out as I could by removing the radiator and bottom tube. I then replaced the tubes and thermostat and replaced the coolant temporarily with a fluid ( I have forgotten its name) which claimed that it dissolves the rust / muck in the engine as it runs. While I have not used the car over winter I have run it a few times to circulate this fluid hoping to give it plenty of time to dissolve the muck.
Recently the car has become harder to start and has occasionally backfired but once going seemed to run fairly smoothly. However the other day I noticed that a small amount of oil was leaking from the rear of the head gasket just above the blocked drain plug. I thought, rightly or wrongly, that this might be due to this area of the engine overheating due to the lack of coolant circulating in this area, and, as I have never done this job, I thought that I would change the head gasket and try to see if there is any way to clean out the water channels in the block while I was about it.
Well the head is off and I would now like to ask if anyone has any ideas how I can sort out the issue of the rust / muck in the engine block coolant channels.
The “coolant holes “in the block are all clear.( I presume that they supposed to be different sizes) and I have managed to syphon out most of the residual coolant but of course the muck / rust remains and the side drain hole still appears to be blocked.
I have read in the forum about pouring citric acid solution into the channels and leaving it to dissolve the rust / muck away. My only issue with trying this is should I try to cover the cylinder head / pistons with anything to protect them from any spillage or is it just a case of taking care and wiping up any spillage straight away. Also is there an optimum strength for the solution and how long should I leave it.
Thanks as always for any help and advice.

The drain tap was latterly replaced by a threaded plug.
The drain hole does not go straight and level into the main coolant gallery, it rises over the rear main/oil gallery so restricting any brush or wire worked into the hole to break through the crud into the main coolant gallery. All you can do is keep poking away at it.
Citric acid put into the coolant gallery should break down the crud. Length of time for the crud to break down will depend upon how bad the crud is.
The coolant transfer holes between block and head are different sizes. Just make sure that they are free of crud.
Below is a section of the rear of the 'A' Series block.
The drain plug hole can be seen on the R/H side about half way up.

Just have to keep rodding it until water flows… and refill with SOFT or de-mineralised water.

Thanks to all for your helpful replies. I will do as you suggest and hope for the best.

Just to let you know that the citric has finally worked. After much poking around and changing the citric acid solution water is finally draining from the drain hole at the rear side of the engine block. I will give it a few more weeks with the citric acid solution and then will try to put the engine back together. ( I had to take the head off to get to the blocked channels.) I expect I will be seeking advice when I try this…but a big thank you for all your help with this problem.

Is this citric acid just plain old lemon juice or are you using citric acid powder and adding that to a cooling system that’s just water?

Addendum: Google knows all and I see it can be bought in packets

cadetchris wrote: ↑Tue Apr 25, 2023 7:35 pm Is this citric acid just plain old lemon juice or are you using citric acid powder and adding that to a cooling system that’s just water?

Addendum: Google knows all and I see it can be bought in packets

Yes it can be bought in crystalline form quite cheaply in bulk. It is used for making bath bombs amongst other things. Also used in preserving/pickling. It's very good for descaling shower heads, kettles, coffee machines, washing machines, dishwashers etc. I run a hot wash in the washing machine with a cup of citric acid crystals every few months and it keeps the machine spotless (I live in an area with very hard water). Does a great job of descaling shower heads too. Works best when the solution is hot but will work albeit quite slowly cold.

Andyhereford wrote: ↑Mon Apr 17, 2023 6:29 pm Just to let you know that the citric has finally worked. After much poking around and changing the citric acid solution water is finally draining from the drain hole at the rear side of the engine block. I will give it a few more weeks with the citric acid solution and then will try to put the engine back together. ( I had to take the head off to get to the blocked channels.) I expect I will be seeking advice when I try this…but a big thank you for all your help with this problem.

Well done, a very satisfying outcome. I would like to clear my drain hole but as the car runs without any problem whatsoever, I never get round to doing anything about it!

myoldjalopy wrote: ↑Wed Apr 26, 2023 10:22 am

Andyhereford wrote: ↑Mon Apr 17, 2023 6:29 pm Just to let you know that the citric has finally worked. After much poking around and changing the citric acid solution water is finally draining from the drain hole at the rear side of the engine block. I will give it a few more weeks with the citric acid solution and then will try to put the engine back together. ( I had to take the head off to get to the blocked channels.) I expect I will be seeking advice when I try this…but a big thank you for all your help with this problem.

Well done, a very satisfying outcome. I would like to clear my drain hole but as the car runs without any problem whatsoever, I never get round to doing anything about it!

Maybe have a go when there is a good reason for draining the coolant.

Yes, maybe - and get the radiator drain tap working and the fan guard re-soldered to the radiator at the same time!

myoldjalopy wrote: ↑Wed Apr 26, 2023 12:34 pm Yes, maybe - and get the radiator drain tap working and the fan guard re-soldered to the radiator at the same time!

Radiator drain tap is pretty useless. It’s only marginally lower than the bottom hose outlet so taking off the bottom hose gets a far better flush than a tiny drain tap.

Surely the biggest issue is what to do with all the coolant once it's out.

As an example, my local council says it must be taken to a local recycling centre for correct disposal and point out that you can't put it either into ground or into the sewers, but none of the recycling centres round here say they accept it.

Chief wrote: ↑Wed Apr 26, 2023 1:31 pm Surely the biggest issue is what to do with all the coolant once it's out.

As an example, my local council says it must be taken to a local recycling centre for correct disposal and point out that you can't put it either into ground or into the sewers, but none of the recycling centres round here say they accept it.

Yes, it's a problem all over the UK, the responsible authorities haven't got a clue, they say it needs recycling, but then don't provide the resources.
It was a topic of discussion back in 2017.
See this topic, in particular the post I made: viewtopic.php?p=617651#p617651