Why would your antifreeze level keep dropping if there is no leak evident?

Answer 1

Check to make sure that the cap is holding the proper pressure, also once the vehicle is warm make sure there is no steam coming from the tailpipe. ( headgasket ) I would have a Block test done to check for exhaust gasses in the cooling system also

a new radiator cap should fix it.small cracks in the gasket can cause fluid loss

Your radiator may be the culprit. Often the solder, braze, or plastic welding which connects the tanks, tubes, and cooling fin sections will corrode and leak through tiny holes when it is hot. Since most metals and plastics expand when hot and contract when cool, the majority of the fluid loss may occur while driving and you may never notice a large leak. Also, when the fluid is cooler the pressure is less and, hence, less leakage. A million micro leaks = one large leak.

Also check the auxiliary plastic filling tank ( if applicable ) for leaks at the seams or cap.

Test: Look for white residue (depends on coolant type)on the radiator and hose juctions and filling tank.

Fix #1: You must find any leak(s) elsewhere as well. Try an anti-freeze additive product that stops micro leaks. Even new cars have an additive from the factory just for this problem. Your local auto parts store can make a suggestion.

Fix #2: Change your hoses and make sure all the surfaces are clean and free of scratches. If the flanges are dented or gouged then smooth the area with some 400 grit abrasive paper. If the flaws are deep you can resurface it with solder or a metal filled two-part epoxy like "JB Weld" or "PC-7". Do not use the 5-minute set stuff because it easily breaks down from exposure to heat or water.

Fix #3: Replace the radiator, only at the suggestion of your mechanic.

Good Luck!

I had a leak on my 2001 Chevy Malibu V-6 3.1L Engine that was on the inside of the V and up under everything, center of the motor. No evidence of a leak as it only occured when coolant system heated up and pressurized and then evaporated away without dripping, puddling or "visible" residue. As I had only owned older vehicles with overflow tubes I didn't realize how sealed the new coolant systems are, so adding (initially) a little fluid every month seemed like no problem. Then, after adding more fluid more often, the gasket completely failed to hold fluid, warranty had just expired too. So I paid for the repair and inspection/repair of any additional damage and I learned a lesson to do my homework on my 'newer' cars systems.