I hate to be a bearer of bad tidings. The 'bubbles' in the radiator indicate combustion gases are escaping the combustion chamber and into the coolant passages. The new head gasket my be leaking. The head may be cracked, There may be a hole in the head (caused by pitting corrosion on the water side. You might first try re-torquing the head bolts---a slim chance this will correct the situation, but quick and no cost. The head will need to be removed and carefully inspected and pressure tested to locate the leak. It can probably the repaired by welding. A 'head shop' will know just how to do it right. Aluminum heads must be pre-heated to at least 400F before the welding (TIG welding only) DO NOT 'mill the head' to correct any warping. If the warpage is too much (over about 0.030" in any direction) it can be straightened by heating to about 600 F and then clamping it tightly to a flat surface (it has to be FLAT to within 0.002 or less) to improve the warpage. After cooling, re-check the warpage. Repeat as necessary.
During inspecting try and determine how severe the corrosion in the water jacket has become. If extensive and severe, or deep pits, consider getting a used head. Sometimes pitting corrosion is caused by prolonged operation under light knocking (detonation), Another insidious cause is cavitation when the coolant boils on the metal surface --too low a pressure cap for the temperature and coolant mix.
You may have a warped or cracked cylinder head remove head and have it pressure tested if ok check for flatness, if warped don't shave. aluminum are to be stress relieved, that's were it's torque down onto a plate and set in an oven for 24hrs and left to cool for an other. if ok after stress reliving recheck for flatness. if head is found to be cracked then it must be replaced. one from a recycler would be cheaper, just pressure test it be for installation.
SOURCE: 1999 micra eating water.
Hi mate unfortunately you do have a serious problem. The bubbles is from your combustion chamber when the engine had fired and the cylinder pressure is at its most and air from the cylinder is entering the cooling system. The water that is disappearing, is actually entering the combustion chamber when the cylinder is on its inlet stroke.
Ways to rectify
1. Buy a coolant test kit from your local spares shop that will test for exhaust gasses in the coolant, which we know will be possible so just start at my next point.
2. Remove your cylinder head and send it to your local engineering shop to be checked out for a crack or cracks, (the best way to crack test it is the Cummins way,to pressurize the cooling side inside the head to about 8-10bar and drop it in a hot water tank by the time the head is warm it will start to bubble.)
3. If this did not work make sure they had given you the right gasket and it looked the same with the holes and every thing.
4. If the head checked out OK, you will have to remove the block you might have a cracked cylinder. Get the block tested out also then
Try stopping on a steep incline--does the heater stay warm? If yes, what you have is an air bubble that hangs at the heater hose until pressure from the water pump blows thru it as the engine speeds up. Park on an incline, open the radiator cap, run the engine until the thermostat is open, turn the heater on, crack open any/all bleed ports to release any trapped air, and fill the radiator to the neck. Wait until the level stops dropping and make sure bubbles don't continue to come up. If they do, you may have a blown head gasket that will keep forming these bubbles until you change the gasket.
Try stopping on a steep incline--does the heater stay warm? If yes, what you have is an air bubble that hangs at the heater hose until pressure from the water pump blows thru it as the engine speeds up. Park on an incline, open the radiator cap, run the engine until the thermostat is open, turn the heater on, crack open any/all bleed ports to release any trapped air, and fill the radiator to the neck. Wait until the level stops dropping and make sure bubbles don't continue to come up. If they do, you may have a blown head gasket that will keep forming these bubbles until you change the gasket.
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