What could cause a lot of coolant consumption on my 03 Accord?
 

The past few months, I've noticed the temperature gauge on the car was slowly creeping up so I checked and the coolant was pretty low. I topped off both the reservoir and radiator with Honda coolant, and within two weeks the reservoir was almost empty again.

There aren't any typical head gasket symptoms at all. No leaks, no milky oil, no backfires or white smoke, and it isn't overheating (the gauge stays steady a little bit below the halfway mark). I also checked the radiator cap and there weren't any visual signs that it was damaged. I'm at a loss at it would be. Any suggestions or tests I could try before I take it to the shop?

I had this happen with two of my Honda Accords. In the first case it turned out to be due to a couple of hairline cracks in the radiator. The second time it turn out to be a bad radiator cap.

Thanks for the reply! I might as well replace the radiator cap since it's so cheap just to be on the safe side. Were you able to find the hairline cracks yourself or was it a garage that found them?

Honda service finally found the cracks. One or two along the seam under the upper portion of the radiator. Another long one lower down towards the bottom not visible from above. These cracks just sort of bubbled and were damp. No coolant on the ground. Very tricky. RE: the radiator cap, it fell apart. We fished the spring out of the reservoir. Good luck !

Update: So I took the radiator cap off (when the car was cold) and started the engine. I had someone lightly press the gas pedal and noticed that the coolant level started to increase and spill out of the radiator but there wasn't any bubbling or anything. I had heard that one of the symptoms of a bad rad cap since it's not holding pressure. Is this true?

The easiest way to test for a leak in the coolant system is to get a radiator pressure tester. Check your parts stores for the loaner tool, where you place a deposit for the tool and get your money back when you return it. There are some good youtube videos on how to do this as well.

Another vote for the pressure tester. When you pressurize the system cold, it's easier to find the leaks because the leaking fluid doesn't immediately evaporate.

Seems like a bad cap or hairline cracks in the radiator would more likely result in low coolant in the radiator while the reservoir is still full. But a leak somewhere down lower, would suck coolant back in from the reservoir.

Agreed on the pressure tester. Get it from the Zone, as they are the only ones who have the small radiator cap size in their kit (I went searching). It costs about 267 to rent, but you get your money back when you return it. It'll also allow you to test the cap as well as the radiator.

Thanks all! I won't be with the car for another few days, but will post my findings once I return!

So sorry for the delay! When doing the pressure test, I heard a noise and noticed there was coolant spitting out from one of the radiator hoses in a spot I I couldn't see. I'll be replacing that over the weekend, so hopefully that fixes the issue. Thanks for the responses everyone!