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MG MGB Technical - Cleaning cooling system

Now cleaning cooling system (3brg motor)
Advice from Archive was to test the thermostat, and also to flush system with some sort of descaling / degunking solution for the recommended period. Then add new fresh coolant.
Well I soon decided a new thermostat was needed . When I poured water in at the thermostat hole, the water ran freely out the bottom radiator tap, and i guess i could just keep flushing this way until the water is clear.
Question, do I need to take out the drain plug on the block in order to flush the whole block? In other words, if I don't, will there be a section of the block that could stay clogged up with crap?

If I do need to remove the plug, then replacing it with a drain tap seems a useful idea. Opinions?

John

John Minchin

I'd remove the drain plug on the block. If you're lucky, stuff will come out of it too!
If nothing comes out, or it looks scary (lots of crud), then you might want to remove the water pump as well. Lets you see inside and around the first couple of bores and it gives you a good indication on what the rest of the block might be like.
Just flushing through from top hose to bottom can work, but it's best to let the scale/rust out wherever you can.
RoadWarrior

You really need a hose with good flow to forwards and reverse flush block, radiator and heater using the hose ports. The flow out of the tap is so little under gravity it isn't going to disturb sediment other than immediately around it.

By all accounts you will be *very* lucky to get anything out of the block tap/plug at all! Several posts in the archives on this, in many cases it seems that casting debris was never removed, so the drain was never functional let alone after 40 years.
PaulH Solihull

I start by assuring the heater valve is closed. Then I drain the block and add a descaling agent. Run the car for the recommended period of time, and drain it.

I build a radiator cap with a hose fitting to do the flushing.

Once done with this, I take the heater valve off and clean it out as I find it gets reduced from scaling.

I then flush the heater radiator by backflushing it from the heater tube on the carb side.

I then put the heater valve back on and backflush the entire engine. (I am not as comfortable in flushing the radiator with the engine as I have a concern about getting stuff in the heater radiator.

I had the block plug out once when I had the engine out. It took a good hour to get it open. I normally don't use it for flushing. You can get the block pretty clean with a descaler and a good flush.
Bruce Cunha

Prestone makes a kit that includes a tee fitting that fits inside your heater hose. It has a male hose fitting that allows the included coupler to be hooked to a garden hose. You can then flush the system until the water comes out clear. You may get lucky and have water come out of your engine block drain, but this is rare. Expect to have to ream it out with a small stiff wire. After this, you can install a new thermostat, drain the block and radiator and then install a mixture of antifreeze and distilled water. RAY
rjm RAY

I flushed the engine by connecting a hose to the thermostat housing (thermostat removed) and a drain to the bottom radiator hose. the water ran clear very quickley. While this was happening i removed the drain plug on the block - nothing came out (as predicted by others) so I scratched around with some wire and only got a tiny bit of rusty goo on the end.

Next stop will be to use a cleaner additive and run this through the system for the designated time.

Has anyone ever connected a hose up at the engine drain and tried to flush that way with a bit of pressure?

Am I right in assuming that if I fill the system via the radiator (engine cold) there fill be air trapped in the engine as the thermotat will be closed. So should I do an initial fill via the thermostat hole, then top up via the radiator?

John

John Minchin

John
Usually I remove the thermostat and refit the housing
Pour your radiator flush ( I find the Wynns one as good as any but there are undoubtedly others as good or better ) in the radiator filler hole and top up with water till full. Run it for 1/2 an hour or so - you will probably need to cover a fair bit of the front of the radiator with a piece of cardboard to get the temp up without a thermostat but keep an eye on the temp. to ensure you don't get it too hot. Once it's hot you can remove some of the cardboard to allow a bit of airflow but try and keep it nice and warm/hot.
After it's run for 1/2 hr diconnect the front of that copper pipe that runs over the top of the inlet manifold and fit a short piece of hose to it out onto the ground Stick a cork or something in the hose you pull the pipe out of
Then start it up and feed hot water into the filler neck of the radiator till the water coming out the hose comes clean. A couple of bucketfulls usually does it or if you hook your garden hose up to a hot water tap , better still
After it's all come clean fit a new thermostat refill the coolant and it's done
If the motor isn't going and you can't get it hot you're wasting your time The only way to clean it cold is with one of those air pressure fed gurgling power flushing machines that some workshops have
Hope this helps Willy

Have you been out to Baskerville Historics today
William Revit

Thermostats should have a jiggle-valve, hole, or little nick in the edge of the seat the moving part closes against which prevents air-locks *below* the thermostat. I've never had any problems filling a system without an expansion tank purely from the radiator - heater valve open. As the radiator fills coolant will run through the bottom hose to fill the block, bleeding through the heater and thermostat jiggle-valve or whatever, then as the level rises will run through the top hose to fill the space above the thermostat. 2 or 3 heat/cool cycles should be enough to fully burp the system, nose up slightly helps, level will burp eventually, nose down probably won't. Systems with an expansion tank have a separate filler point to fill the engine and rad, the expansion tank is filled last to halfway, then burped as before.
PaulH Solihull

This thread was discussed between 09/10/2011 and 15/10/2011

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