Overheating

[Drmoise]

01 325i recently had head gasket and valve cover gasket replacement mechanic filled expansion tank with water only will this cause car to continue to overheat?

[shadowpuck]

seems like there's much more to the story here...

why was the head gasket replaced?

no, using water alone is not a reason to cause an overheat; however, i'd say its an odd practice to use water after a repair is complete and confirmed good.

i can only think of a few reasons to use water:
testing the system and expecting issues so i don't want to waste coolant
various forms of system flushing
race car
by the side of the road and need something in the system to make it home/to my destination, etc.

what's the story here?

[dworthy]

Modern BMW's are rather difficult to bleed, more so if it's a E-85. The newer models with an electric water pump is a breeze.

If the Mechanic isn't using a vacuum bleeder to fill the cooling system, then you will have air, thus causing it to overheat.

[bmwdirtracer]

And curiously, a master tech at my shop just had an issue with, of all things, an E46. He swears that he vacuum-filled the car after water pump, thermostat and ECT sensor replacement. Then he drove the car for several miles, no issues, and we sent it home. It came back next day, with the same original problem: ECT temp rose incredibly quickly, both hoses remained cold.

While watching temps via the two sensors (lower hose and back of cylinder head) and an infrared temp gun, cap open, I did a manual, old-school bleeding, ended up adding another two quarts of coolant, and suddenly all the temps went to the correct values, and the coolant stream began in the filler neck.

I absolutely love my vacuum fill system, and it always works...except maybe once a year, almost always with E85 Z4's. (Remember, I probably do ~100+ cooling system fills a year).


NOW, to the car in question in this post:

Your mechanic did a head gasket replacement? Did the head go to a machine shop to get milled flat and tested for cracks? When the head was bolted back on, was the mechanic able to achieve the full angle-torque specs, using new bolts?

You DID use a BMW specialist mechanic, didn't you? Because non-BMW guys just don't know that the M54 head gasket does NOT fail on its own: it fails because the car overheats, the head warps, and when the head warps, it rips the threads out of the engine block.

The most cost effective fix is usually to replace the engine. Sure, you can Time-Sert the bolt holes for the head bolts, but you're talking about a lot of hours, and several special tools.