Hi. I have a 1997 civic lx. I just got the rear main seal fixed along with the belts and waterpump. Now whenever I drive it for a while, it starts overheating. I noticed that when that happens the overflow radiator compartment is full of coolant(water) even more than i filled. It appears as if the coolant from the radiator came into the overflow tank too and didn't circulate back. If i let the car cool down for an hour or so, the coolant level decreases in the overflow tank. Once I even heard a gurgling noise when that happened
Its not leaking out of the car though.
Could anyone help me figure put what the problem might be before I take the car to the mechanic? Anxiously awaiting your replies. Thanks.

 

Try purging the air out. Any time the coolant has been drained, you have to rather carefully refill it to get the engine and radiator completely full.

The process is to park the car on level ground or facing uphill so that the radiator is the highest part. Wait until the engine is completely cold, then take off the radiator cap and fill the radiator to the top. Start the engine with the cap off and set the heater dial on full hot. Rev the engine a few times. If a bunch of bubbles and coolant blows out of the radiator, the head gasket is blown, so you can stop there.

Otherwise watch the radiator and keep adding more if the level drops as the engine runs and warms up.

While you're waiting for that, look closely at the rubber seals on the cap. The one near the top is important for getting the coolant to return from the bottle to the radiator.

When the engine starts to get warm, the radiator should start to overflow. Put the cap on then. Make sure there is coolant in the bottle and test drive until fully warm (and hopefully not overheated.) Park again in the nose-up position and wait until cold, then check that the radiator is still full.

 

Just followed the procedure u suggested:
I filled the radiator to the brim. Since the car was on, I could see the coolant vibrating inside the radiator but none was coming out.
But whenever I revd the car some coolant spilled out (a couple tablespoons in amount) thus lowering the level a bit. Reving the car more didn't spill out any coolant although it did rise within the radiator. I assume that is what you meant and the gasket is blown (pls correct me if I misinterpreted) I will take it to the mechanic in the morning. Will let you know what he thinks.
Thanks for the detailed and we'll explained response.

 

If it just surges a little it's probably OK. If you get a steady stream of bubbles or a constant flow there's a problem.

 

So I took the car to the mechanic today. His initial diagnosis was that I might have blown the gasket. However after connecting an instrument to measure the pressure in the radiator(he replaced the radiator cap with another steel cap that had a pressure gauge attached to it), he reached the conclusion that there was nothing wrong and it might have just been air. The car hasn't overheated after I purged the air out as mk378 suggested.
Bad news is, when I drive the car for more than 15 mins and check the coolant reservior, it's completely full up to the brim. Moreover the coolant is muddy(chocolate brown) and fuzzy (some bubbles) and the car seems to be driving heavy and shifting late (it's an automatic). I feel like the mechanic might have under diagnosed and it's a matter of time before whatever is partially functional (e.g gasket) will stop working altogether.
Any help is greatly appreciated. Thx

 

The level in the reservoir is supposed to rise and fall as the engine heats up and cools off. Maybe it is just overfull. When cold, the bottle need only be full to the line on the side. The rest is space for expansion. For the next several days check the radiator before you use the car the first time that day. It needs to stay full.

If there aren't major problems, you would next want to drain and flush the system to try to get most of the brown stuff out.

 

Oh ok. Makes sense. I will start checking from now on. Will get the flush done in a week if nothing goes wrong. Thank-you for the accurate and timely advice. I will keep you updated until the flush

 

Today a friend was reversing my car for me and I noticed the smoke coming out was white in color similar to cigarette smoke. Does that signify something?

 

Today, after a couple of weeks, the problems have manifested themselves enough for the mechanic to diagnose a blown head gasket. Will be getting it replaced soon. Thank-you for all the help and advice.