I went in to Honda today to get my coolant flushed and filled on my 08 si. They ran a pressure test, and there were no leaks. When they checked the overflow tank, it was empty but the radiator itself was full. I was at Honda for an oil change 2 weeks ago and they claim to always fill the coolant up. I don't know if that means into the radiator and overflow tank, or just the overflow. It could have been a bit low in the radiator, and thus got sucked back into it. They performed a cylinder pressure test to be sure, and the results were:

CYL1 : 5%
CYL2: 3%
CYL3: 2%
CYL4: 2%.

The tech said this was very good, but I'm confused. I drove another 100 miles today and now my coolant overflow has gone from full to minimum. Is this something to be worried about? They said that since I passed the cylinder pressure test then that for sure rules out a bad head gasket. I don't have any signs of head gasket failure such as milky oil, smoking or power loss.

Should the overflow tank remain full when the engine is hot, or does it go down when hot and then "refill" as it cools down? Thanks. I'm also wondering if maybe the "loss" of coolant was just from the initial fill and that it's not losing any. Definitely no leaks at all, but I wanna get this down 100% before too long. I've got a 2000 mile road trip in a few days.

 

If I remember, I'll check my level at start up then at full operating temp and let you know.

 

Coolant expands when heated. This causes pressure in the system. When it gets high enough, the coolant is allowed past the radiator cap and into the overflow tank. As it cools, suction is created. The suction pulls the coolant from the overflow tank back into the system. There are "min" and "max" level marks on the overflow and roughly indicate what the levels should be at cold and hot conditions.

FWIW, the overflow on our '08 Civic was empty after about 18 months. The dealer claims it was due to evaporation and refilled it. I have my doubts as my '03 Acura didn't show any drop in level after 3 years. I swear I smell a faint whiff of coolant whenever the Civic comes home and is parked in the garage. Can't find any leaks or seapage though.

 

Not sure if 2008 civic's were in the effected range of the faulty engine blocks that seep coolant

 

I thought that was only non-Sis?

As for the original question, I don't remember ever having to add coolant on my '08 Si.

 

That's the R18 (non-Si). I was told by the dealer that "Civics and Odyssey eat coolant" but I'm sure they referred to the R18.

I ended up driving around several times today. I filled the radiator a few more ounces. When I took the cap off and added some, it made a glug glug sound. Must have been some bubbles in the system. I drove 15 miles and checked the overflow tank again. It was down to minimum when hot. I let the car cool for about 5 hours, and when I went out to get some food I filled it in the radiator again. After my drive it was at the Full line in the overflow, and full in radiator. I assume I got all the bubbles out of the system, but will watch it. I do smell coolant from under the hood, but never while driving or inside the car. All the HG tests came back negative for it being blown, so who knows. I just really hate the smell of coolant lol.

 

Si or not?

 

Oops, meant to quote that for perfectionist! I checked mine today, was just under the max line when cold and 1/2" higher at operating temp.

 

It an EX, not Si.

 

It sounds like you dont have enough coolant inside the whole engine. As I repair many cars, I alwasy check the coolant when the engine is cold. It might since line you have enough coolant when you fill up to the max. But actually it might have some space around the engine and the heater.
Use a coolant bleeding kits ( like this image http://www.autotraderclassics.com/im...1950/81950.jpg ) place at the coolant cap, fill coolant in REMEMBER TO PUT SOME MORE FOR SPARE. Then turn on the engine and turn on the heat " NOT THE A/C " to the highest with the highest fan. You might see air came out from the coolant. Let it run until all air gone.