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Back flush cooling system?

Started by Richardonly, August 28, 2012, 07:42:30 AM

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Richardonly

Hello,

I understand what back flush is and why it is done.  I have been told that a garden hose can be used and run through the heater system. 

1.  Where exactly do you connect it?

2. Do you open the petcock or remove a hose (which one?) at the water pump?

3.  Do you run the engine or merely flush the system, and if flushed or running, how long?  I assume until the water is clear.

4.  This still leaves any crud at the freeze plugs.  Should it be done at a shop the 1st time?

Thank you, Richard
1948 Cadillac Fleetwood 60S
1995 Lincoln Towncar, Signature Series
1995 Jaguar XJ6
2001 Chrysler Sebring Convertible
1986 Yamaha 700 Maxim X motorcycle

TJ Hopland

I believe 'back flush' just means you are going to try and flush in a direction opposite the normal coolant flow.   This is most commonly done on something like the heater core because its internal passages are smaller than the inlet so its possible that crud from the system got in but is not able to flow through.  The idea if you reverse the flow is that you can then force anything that is loose back out the way it came in.  To do this you would usually disconnect the heater core and connect the garden hose directly.  This could also be done on the radiator but since that is usually easier to remove if you have a radiator problem most people would just remove them and take them to a shop where they can use other methods to clean it. 

The classic system flush is / was (i think it has changed now days that you are not supposed to just dump coolant on the ground) to insert a T fitting on one of the heater hoses.  This T fitting had the garden hose fitting on it.   You would remove the T stat then connect things back up and start the car.  Usually part of the 'kit' was to first add a bottle of flush solvent.  Some of the kits I remember were a 2 part system. You would add the first bottle a few hours or days before and drive the car.  The second bottle was added just before the flush.  You would then start the engine and let it warm up.  It wont usually get that hot because it does not have a stat but the heat is supposed to activate the chemical.  The last part of the kit was a elbow that snapped in place of the radiator cap that directed the coolant hopefully over the paint and grill usually onto the front bumper.  You snapped in this elbow and slowly at first turned on the garden hose.  You wanted to do it slow at first so you did not suddenly shock anything with the cold water.  The engine running with no stat keeps the internal flow going and the pressure from the garden hose pushes some of what ever is in the system out the radiator.   The theory is that the chemical loosened crud and the circulation from the water pump will eventually get the crud into the radiator where it will then be ejected.    Often after this process is done is when you would then disconnect the radiator and heater core and back flush those because of the likely hood that loose stuff may have got trapped.   They still sell those kits but I am not sure how they intend a typical do it yourself person at home to use them since we are supposed to take used coolant to or local hazardous waste disposal site. 

You mention the likely hood of crud being trapped around the freeze plugs.  That crud may be all that is currently sealing them so flushing it may cause a leak.   Same tends to be true about radiators and heater cores.  I would not do an aggressive flush unless I was prepared to make major repairs.  You may be fine but chances are also good you could end up with a loose freeze plug and those can sometimes be quite a project to replace especially with the engine in the car not to mention inconvenient if one happens to fall out while you are out on the road.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

harry s

Richard, There is a flushing procedure in the shop manual that explains how to flush the crude out of the rear cylinder area. This area seems to accumulate the most crude and causes over heating problems. It requires removing head bolts and use of a tool that inserts into the coolant passage. I have never seen the tool in question, but maybe some of the flathead members have or have made one up.    Harry
Harry Scott 4195
1941 6733
1948 6267X
2011 DTS Platinum

Glen

Remember that the garden hose can have pressures a lot higher than the radiator and the heater core can stand.  So don’t restrict the outlet when flushing with a garden hose.  Also you probably want to not open the hose bib all the way.   
Glen Houlton CLC #727 
CLCMRC benefactor #104

Richardonly

Getlemen,

TJ Hopland, 

What a detailed explanation and quite thorough.  So it seems from what I have been told and what you have written is that the crud water would be expelled from the top of the radiator rather than it's petcock.  Kind of hard to comprehend as the water does not flow that way, but it is what I have been told "in general" from other sources.  You gave me so much more and I thank you.

Glen & Harry,

Thank you also for the needed precautions.

Perhaps I should have this done professionaly the 1st time to avoid unseen problems appearing.

Thank you again, All.

Richard
1948 Cadillac Fleetwood 60S
1995 Lincoln Towncar, Signature Series
1995 Jaguar XJ6
2001 Chrysler Sebring Convertible
1986 Yamaha 700 Maxim X motorcycle

harry s

Richard, One other thought. When flushing you can open the drain plugs on each under side of the block. They are small brass thrunb screws just behind the motor mounts. If you remove the plug and nothing comes out you can stick an awl or something simular to break up the hardened crud.. Good Luck,    Harry
Harry Scott 4195
1941 6733
1948 6267X
2011 DTS Platinum