My bmw 728i has an over heating problem, the radiator water filling bottle cracked with the pressure, i have to fill the tank with aprox 5 litres every 8 hours or so. the car has cut out on me twice while the tempreture gauge is showing max tempreture. is it the head gasket going or maybe the water pump ristricting normal water flow through my engine ?
The thermostat and water pump are both common failure points on BMW 6-cyl engines of this era.
I would recommend checking the thermostat first, then moving on to the water pump.
If the vehicle has overheated several times, you may need to remove the cylinder head and have it checked for warp.
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Flush coolant system again. Do you have a brown sludge in the oil. Do this get Preston coolant flush, drain radiator drain coolant tank, fill radiator with water, add the Preston run vehicle for about 15 min remove lower radiator hose from radiator. This will allow all residue to be removed from engine. Replace radiator hose. Fill radiator with appropriate amount of coolant. Disconnect tank from system and let water run through tank until it is clear. Reconnect tank and you should be good. Unless you have oil and coolant mixed which means a blown head gasket or cracked block
replace the faulty reservoir or radiator
what is happening is that the radiator cap is not raising the pressure in the cooling system because of a leak in the system
the excess water from heating is being pushed out probably onto the ground through the leak
when the cooling system cools down , water is being drawn back into the radiator
probably find a crack in the radiator tank that opens under pressure but seal off as the pressure is lost
flushing a radiator is a waste of time and money as blocked cores do not flush. Have a pressure test done on the coolant system and check for external leaks. have a compression test done to check for head gasket and cracked head. Have a flow test done on the radiator and if shows signs of blockage replace the radiator .. Always fill the radiator at the radiator cap and not the reserve bottle. The reserve bottle water will not go down until the engine coolant starts to cool so if it is going down when the engine is hot then you have a bad leak in the reservoir bottle.
You have a vapour lock. The coolant isn't flowing. The remaining water is not cooling your engine evenly so you could crack your engine block. The water that isn't circulating turns to steam. The water pump could need replacing if the impeller failed. You may need a new thermostat. Get someone knowledgeable enough to fill your radiator properly and then keep the overflow reservoir filled to half. Check that bottle at least every week.
need to perform a coolant pressure test. fill the reservoir and after the engine cools down fill the radiator, next start the engine and wait till the coolant system builds pressure then turn off the engine and using a mirror and flash light look for a leak.check water pump, hoses,radiator tanks for cracks,intake gasket at the corners espesically at the back next to the trans.also pull the carpet back and check for coolant leaking from the heater core,and last remove the sparkplugs and check for leaking head gaskets.hope this helped.
the thermostat (on bmw replacement parts) have an arrow that has to be installed facing upward.if this was done correctly,to bleed the system usually there is a bleeder screw on or near the expansion tank(where you fill the coolant) and possibly on the thermostat housing. i would recommend opening both bleeders and keep filling the system with coolant closing the lower bleeder first and then allow the rest of the air purge from the other bleeder screw.make sure the coolant stays full and be patient you can't wait TOO long.
there can be a yellow light in the cluster that looks like a small radiator or box with waves inside of it to indicate water. This light means that the coolant level sensor has detected a low coolant level. Typically the expansion tanks inside of these cars will crack from heat and age. A simple diagnosis is to check your coolant level and top it off. Do not forget to bleed it by unscrewing the bleeder screw found on the upper radiator hose while filling up the reservoir found on the right hand side of the radiator. once the coolant has been filled, tighten the bleeder screw back down but be careful not to over tighten. and finally screw on the expansion tank cap. run the vehicle to operating temperature and use a flashlight to inspect the engine bay for leaks. If there is a leak, it will need to be repaired. possible leaks are a cracked expansion tank, leaking radiator hoses, or a leaking water pump or thermostat.