I've heard different things. Yesterday, my mechanic did a coolant change on my 2004 Civic LX. I couldn't see exactly what he was doing but it looked as if he Instead of pulling the drain plug, he disconnected the hoses up top to drain it. I asked what he did and he said an old mechanic short cut . Anyway, I started watching and when he filled up the radiator, it didn't even take an entire gallon of 50/50. There's still about 1/5 of the coolant still in the container. I'm thinking it wasn't completely drained. The old coolant was green, unknown manufacturer, and the new was blue Honda coolant type 2.

Let's say there was still a little of the old coolant in there. Does this normally happen and is there any problem of mixing the green with the blue.? I've read conflicting stuff on the internet and was looking for better opinions. Basically, is it alright and am I making a big deal out of nothing or not.

 

Unless the system was completely drained and flushed with distilled water, you will run a risk of coolant cross-contamination, which can cause the coolant to coagulate and clog the coolant passages.

 

To completely drain the coolant you must also remove the drain plug on the engine block itself. Shortcut means incorrect in most cases.

 

Me personally , I stay away from a plastic drain on the bottom in fear it will leak when closed , There's a lower radiator hose that can be pulled but you have to remove the dust shroud and all it's clips . Many things on a honda are held with these and there are a variety of them . It should be flushed , filled ( distilled water ) ran , drained , till clear water comes out . Now there's residual water left behind that can be blasted out with compressed air or vacuumed through the top hoses , or you can just add straight coolant and use a tiny hose , and I mean tiny , feed it in to get a sample from the radiator when done to check for proper mix . Then there's the air pocket problem you may or may not have , back to the smaller hoses on top , pull the one from the head and put it in a jug of coolant , a spare piece of hose ( clear ) can go at the head nipple and drawn with a shop vac. If all goes well air comes out and coolant gets drawn in . That's my story , your experience may differ .