Cooling System Flush?

[c0rbin9]

I'm planning on doing a multi-stage cooling system flush this weekend which will involve needing to flush the system with a garden hose numerous times between chemical flushes - I'm not 100% clear on where to hook up the garden hose in order to thoroughly flush the block.

HALP?

Basically my plan is to drain coolant, flush with tap water, fill with Prestone Super Flush (or oxalic acid), run car up to operating temperature, drain and flush again, and then fill with proper coolant/distilled water.

Also my coolant drain plug on the engine block snapped off when I did a drain and fill, so now there is a threaded portion still stuck. Anybody familiar with the location of this have any tips for removal? I'm a newb mechanic and know nothing about removing sheared bolts, let alone ones with limited access like the M42 coolant drain plug.

[iPee]

I would fill it through the overflow reservoir and drain until it's only water coming out.


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[roguetoaster]

Removing a broken block drain is going to suck. But be sure that it's not just the short bolt and accumulated crud fooling you. So if you pulled any threads with the head be sure to give the drain hole a good few stabs with a screwdriver.

If you do need to drill it out you may want to take it to a shop as they might have the tight access tools to make it easy.

[AndrewBird]

You are going to want to run it with tap water for a few minutes, then drain and repeat a few times to get the "flush" product out. You can't just "hook up the garden hose" to it, doesn't work that way.

[c0rbin9]

Thanks for replies, gonna be trying this this weekend. Really hope I can get the broken block drain plug out. How is such a thing removed?

[roguetoaster]

A broken plug would be removed by drilling it out and using an extractor or just drilling it/chiseling. Considering that the bolt is very short either method ought to be effective.

If for some reason you cannot get to rest of the bolt out you can always use the rad drain and add more flush steps.

[crash n' burn]

I used distilled water. drain, fill, ran until it hit operating temperature for about 5 minutes, then repeated. drained and refilled using coolant and ran the engine with that purge bolt open on the water neck, added coolant until it flowed out. closed it up and good to go

[TobyB]

I'm with Rogue on this one- that plug is pretty beefy. Can you post a pic of what came out?

I've pulled plugs on 'original' engines before, and they were so silted up that I had
to use a drill to get through the silt- but I've never broken a plug before
(that's the problem with leaving the 'original' coolant in for 20 years)
I HAVE rounded the heads of the plugs over, by not being careful.

But if it's really sheared off in there, it's big- careful drilling with a right- angle head,
a cut- down drill, and a short easy- out ought to do it.
I have found that customizing tools by cutting them down is almost a necessity when
working in close spaces like this...

hth

t

[c0rbin9]

People are telling me forget about the plug and just flush the system without removing it. If I decide to remove it, I'll be using your advice Toby.

For the flushing, can't I just connect a hose to either side of the thermostat housing after removing the thermostat and have it come out the other side, flushing all the coolant passages in the process? Same thing with the small heater hose going to the bottom of the radiator...

Otherwise I'm going to have the drain and refill numerous times to actually flush all the crud out.

Any recommendations on which flush product to use? Will be going to the chain parts store tomorrow.

[c0rbin9]

I'm considering doing a citric acid flush, which apparently is Mercedes Benz factory recommended maintenance, in which case I will want to inline flush with a hose to flush the system thoroughly. Repeated drain and fill won't flush completely. Anyone know how to do this on an M42?

[roguetoaster]

I believe the above diagram is accurate, and seems to make sense as far as I can remember.

Therefore, your best bet outside of the block plug might be to fill through the passenger side and drain out of the radiator drain with the engine running.

Also be aware that most any tap/hose water has minerals in it, so when you flush the system you should really run a few gallons of distilled water through to remove as much of that as possible.

I have had good luck using a pressure washer on the radiator (out of the car) by spraying alternately through each fitting, and am always surprised at amount of gunk that comes out. So it may be prudent to try that first instead of freeing all of that stuff to just send it in to the block/heater core.

[c0rbin9]

Oh my god, thank you for the diagram. I've been looking for one of those.

[c0rbin9]

New development: I found an old inline hose fitting spliced into one of the heater hoses near the firewall.

[c0rbin9]

Update: I ended up removing the thermostat and flushing through the upper radiator hose. Not sure how effective this was, but now the car is all put back together with Prestone cooling system flush in the system, which I will leave in for a few days before draining and refilling with coolant.

[c0rbin9]

Flushed again and filled with coolant, car now seems to run considerably cooler, so I'm happy with the results.

Unfortunately my coolant loss issue seems to have gotten considerably worse, with the car losing an inch or two per 30 miles.