I got a new radiator for my wagon and i want to flush motor befor putting on can i put a hose in the uppe radiator hose and flush it? Or what is the best way to flush it without a radiator? My old one is toast. The plastic deteriorated after a citric acid flush.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

A garden hose secured to the small hose that exits at the rear of the head is best. You want to connect to the side that goes to the heater core.

You also really want to open the block drain. It's miserable getting up there, but it's the only way to seriously flush these engines.

Be a bit careful with the garden hose. It puts out way too much water for the engine to handle and the pressure in the system might climb to levels that could be detrimental to the heater core. You want to flow some water into the engine but not pressurize it.

what concentration of citric acid did you use? I got real good results with about 5% conc and 20 minutes running my OM606.910 engine with the thermostat bypass blocked with a rubber cork. This setup forces all coolant through the engine and radiator and not short circuit in the block.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Thanks. Can you elaborate on your setup? I think 5% is probably good. I used 10%. 1.5 lbs acid in 15 lbs reverse osmosis water. I drove for about 20 minutes but I know how it takes a while to bleed the system and wanted to give it a good highway run in daytime. When I came out in morning
There was a ton of water on floor. I tightened upper hose on radiator and it just broke off in my hand. Do you think it was citric acid that did it?

Can that stuff do any damage inside engine and head?

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Thanks. I know that hose. It's got the fuel heater built in. Ill flush through heater core with low pressure.

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

On most cars, while the old radiator is still in, I drain and fill with pure water and Prestone SuperFlush (a citric acid product), drive it a while, then drain. I also put a wire screen in the radiator return hose (upper) to catch junk. I leave the wire screen in so the new radiator doesn't become the filter. I sometimes connect the 2 hoses together without a radiator and run flush that way, but only run the engine in short intervals because the water will get hot fast. Removing the block drains is good, if easy (not so for 300D). Often engines with little 1/4" plugs need a screwdriver to punch thru the rust junk and get them to flow.

The factory service manual advises to use an "open thermostat" SST to do the citric acid flush - I did not have that and used a rubber cork in the bypass port and put the flange back on without the thermostat.

The 5% solution cleaned out the engine nicely. A lot of rusty and milky water came out.

I then neutralized it too with some baking soda just to be safe.

The radiator pipe fitting breaking off is an age issue and probably also caused by the lack of the metal collar reinforcement. Its a known problem and citric acid does not cause it - infact if I were you I would consider it a good luck sign that it broke off in my driveway and not on the highway.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

ditto. the citric did not damage the plastic... age did. and green coolant, and age...

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