I bought a 2006 F350 with 56K miles on it, the owner had a shop do all the maintenance on it and doesn't what what type of coolant is in the system.

I don't want to do a chemical flush as the oil cooler seems to be functioning within spec but I do want to drain and replace coolant.

Is the process drain fluid, add distilled water, heat/circulate, drain, rinse and repeat?

How many drain/fills should clear out the old coolant?

Is it safe to mix coolants?

 

yes don't use a chemical flush unless you are about to change the cooler afterwards.
taking the T stat out makes things go a little quicker
use only distilled water, and drain it back into the gallon jugs so you can see the progress you are making.
once it is looking good top it off with concentrate and you should have a 50/50 mix with the amount of water thats left in there after draining.

 

I do at least 4-6 drain/fill cycles.

 

You can do the first 2 with a garden hose and then go to the distilled to save a little cash.

 

I'll offer a little different take on this subject, certainly not what most members here would recommend.
Personally, I like this approach in these videos followed by a couple flushes with distilled to get the tap water out. There are many types of coolant and many different formulation within each type. Some play well together and some don't. Using only water to flush, a lot of residue can be left inside the engine in the form of protective rusty jell. The cleaning chemicals remove this coating and allow the specific formulation you're using to perform at its best. I understand being concerned about freeing this residue up and clogging the oil cooler, many have posted they believe that's exactly what happened to their own truck. You really have to decide for yourself if you're willing to take the risk. For myself, I'll use chemicals every time, if the oil cooler clogs, I'll change it. If the cooling system is that contaminated I want that stuff out of there. Check out how the coolant blasts out of the block drains when the engine is revved in the video. That's getting something done. Carefully draining into jugs is much less effective in my opinion. I try to catch the old coolant on the initial drain for recycling but the garden hose is going to be running for an hour or more during the flushes.

Sr master tech coolant flush
Part 1. Part 2.

 

I need a new thermostat so i figure i will do a distiled water flush when i put the new one in. My truck has green coolant in it now and from what ive read its not suppose to have green in it. It was in there when i bought the truck 2 years ago and Im not sure how long it has been in there. Is this bad??? Im planning on installing a coolant filter and putting red ELC back in it.

 

I was not expecting the "chunks" of stuff to come out during the flush while revving the engine. My coolant has always came out black after the flush with VC9 but I have never seen any chunks of stuff come out.