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Discussion Starter #1
Can someone explain what actually occurs when they do an engine coolant flush?

The reason I ask...just had a new hose put on radiator due to rodent damage. Shop replaced the hose and filled up the coolant to proper level. I get it back and the expansion tank is cracked. I replaced it and thought I would just top off the coolant lost in the process. However, my expansion tank was full of black particles. Lots of stuff. So I am guessing that I do not want to just top the coolant off but actually replace all of it. Will just replacing the coolant clean it out or do I need to do something else to "clean" out the radiator.
 

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If you go to the auto parts store, they sell an item called a flush. You need to be careful, because the block of your car may react to the ingredients in the flush. There is all sorts of chemical reactions occurring in engine, there are anticorrosion compounds in the anti freeze but even with those compounds problems can arise resulting in antifreeze contamination.
 

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Discussion Starter #3
Mensra, so based on the stuff floating around in the expansion tank, I do need to do a flush and not just empty and refill the coolant?.?
 

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It depends on how much there is. If it's a trace amount I wouldn't worry about it too much as there always will be something. However if it looks like alot there, I would recommend doing it. Just make sure you use the correct flush.
 

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Products labelled "Radiator flush" are usually 90% water and 10% Sodium Citrate. Sodium Citrate is a Sodium salt of citric acid. I noticed the MSDS of Prestone Super Flush states ingestion is not harmful. So when I do a rad flush I just flush with the garden hose and if there is a large buildup then use a bit of baking soda and citric acid. A friend of mine drops in an Alka Seltzer Gold (no asprin) tablet and looking up the MSDS for that he is right. So if you have Alka Seltzer Gold or a little citric acid with sodium bicarbonate (baking soda) you could drop that in but otherwise water will do it.

Gordon
 

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Discussion Starter #7
Due to inability to get rid of the used antifreeze, decided to let a shop do the flush. However, when I try to add antifreeze back to the system to get it full to take it to the shop, I run into a problem. The expansion tank will fill to full. I crank car and run a minute or so and the expansion tank empties. It seems I have a large air pocket in the system.

How do I fill the system and purge the air pockets?
 

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Discussion Starter #8
Also just realized the Zerex G05 does not mention that it is pre-mixed 50/50. I have already added 2 qts of Zerex directly into the system. Can I just add 2 qts of distilled water or do I need to drain system and pre-mix before adding into system
 

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You will be fine just adding 2qts of water on top of the pre-mixed coolant.

I'm not sure if your engine has bleed taps on it, but if you grab hold of one of the 'low down' coolant hoses, and squeeze it gently and repeatedly, this will help to 'burp' the air out of the system.

It is not a good idea to run it without the coolant topped up - you could end up with localised heating in the cylinder head, which could lead to head gasket failure.

Once you've got the coolant up to level in the header tank, then run the engine with the heater on full. Watch for any bubbles coming out of the header tank, and make sure the heater gets toasty. Finally, check the level again, and tightly secure the header tank cap.
 

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Lots of different questions/issues here, so here is my take.

The cooling system on your car I believe is on a 3 year service interval. Starting with my 2003, they went to a 15 year/150,000 mile interval. The proper coolant is important and Zerex GO5 or the Mercedes branded coolant are about your only two options. The Zerex comes in two flavors, one is a 50-50 mix and the other is full strength where you have to add distilled water to it to get to your desired mixture. Mercedes also has their own recommended products for cleaning your system. I personally would not ever use a McParts store cooling system flush. A home remedy is to deoil first with something like liquid Tide or dish washing soap and then descale with citric acid. However, if your system has been serviced regularly and the coolant comes out looking nice and clean, then it's unlikely you will need to do any type of serious flushing. Most oil change shops will take your old coolant. Some jurisdictions allow you to dump it down the drain and let the city sewer treatment system take care of it. Your cooling system should be self bleeding, but it probably wouldn't hurt to raise your front end and let the car run with the cap off for awhile.

Len
 

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Discussion Starter #12
Here is latest update. Went out this afternoon and the expansion reservoir was full. Drove long enough to get temp to 80 with heat on. in the past car would run at about 85. Then drove another 5-6 minutes with heat on, then turned air on to see if the temp would raise for another 5-6 minutes. Stayed at 80 the whole time. Parked the car on slight incline and will check the tank level in about an hour. Unfortunately I have to take the cap off to see since the zerex is so light in color, you cannot see the level from the outside.

If I have air pockets or not enough coolant, shouldn't I be getting some sort of warning light?

Back to Woolly's comment about the localized heating, will there be any warning that all is not right or could the damage just occur without warning?

Thanks again for all the support
 

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If the temperature gauge is registering close to normal running temperature, and you have warmth coming out of the heater, then you should be fine. Remember, if you have the cabin heater on, then this acts as additional engine cooling, so it will take longer before the engine reaches it's normal running temp and the thermostat starts cycling.

If you are running the car with no/not enough coolant, the temperature gauge sensor can just show the ambient temp (as the sensor is not immersed in coolant) and yet the engine can be seriously over-heating. The only warning you will get is when something lets go.
 

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Discussion Starter #14
Great. Thanks for the clarification. Even last night when the expansion tank was low, there was still coolant flowing through the overflow and the temp gauge was taking the normal amount of time to get to normal running temp.
 

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Hey big guy, I thought the sensor was actually attached to the cylinder head, it only reads the temperature of the coolant itself?
 

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Hey big guy, I thought the sensor was actually attached to the cylinder head, it only reads the temperature of the coolant itself?
Exactly, so if there's no coolant around it, it will just read the temperature of the air in the coolant space, plus that which is transferred to it by conduction from it's mounting. This could be at a reasonable level, whereas areas of the head (especially around exhaust valves ) could be a lot higher than they should be.
 
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