e36 coolant reservoir ??

[jamin325i]

after many years servicing my coolant system i still do not understand my reservoir action when i check it to top it up. the last 3 years have had a slow leak which evaporates leaving no trace of location. my question is, when removing my cap and before i add any coolant, the reservoir begins to fill itself with a gurgling sound. why? and please keep answer simple for me.

[MarcoZandrini]

The cooling system can leak in places you can’t readily see. How much coolant are you loosing and how frequently are you checking the coolant? Are you checking the coolant level when the engine is cold?

Next time, before you remove the expansion tank cap, squeeze the upper hose:
- easy to squeeze means the head gasket is likely ok
- hard to squeeze means the head gasket is suspect.

[bmwdirtracer]

The very first step is to get a cooling system pressure test, and find the leak. Step two is to replace whatever's leaking, and then vacuum-fill the system with correct blue coolant and distilled water, making sure you don't overfill it.

When the cooling system is intact and correctly filled, the gurgling should stop.

[jamin325i]

The cooling system can leak in places you can’t readily see. How much coolant are you loosing and how frequently are you checking the coolant? Are you checking the coolant level when the engine is cold?

Next time, before you remove the expansion tank cap, squeeze the upper hose:
- easy to squeeze means the head gasket is likely ok
- hard to squeeze means the head gasket is suspect.

i check level w/engine cold. last 3 years i estimate i add a cup about every 2 weeks. i add the cup amount immediately after removing cap and before the gurgling/ self filling completes. strangely, last week heat gauge showed overheating after idling a few minutes after running engine an hour. shut car off, allowed to cool 15-20minutes. released some pressure thru bleed screw on top for few minutes. gauge showed down to about normal running temp so removed cap, started car and added about a quart. this appeared to fill radiator. topped off when reached home and am monitoring temp gauge for another sign of overheating. will top off at 2 weeks as before waiting for a more serious event before replacing parts. i have $200 of 2 year old coolant parts sitting in garage for use.

[jamin325i]

The very first step is to get a cooling system pressure test, and find the leak. Step two is to replace whatever's leaking, and then vacuum-fill the system with correct blue coolant and distilled water, making sure you don't overfill it.

When the cooling system is intact and correctly filled, the gurgling should stop.

i should do that test although i am not optimistic. because have not located water undercar with newspaper test nor seen dry watermarks in engine compartment.

[bmwdirtracer]

"waiting for a more serious event before replacing parts"

Um, really, there is only one event more serious than an overheat which did not toast the engine. You do realize that every single cooling system part in your car should have been replaced at least twice already, with brand new OEM parts?

[jamin325i]

"waiting for a more serious event before replacing parts"

Um, really, there is only one event more serious than an overheat which did not toast the engine. You do realize that every single cooling system part in your car should have been replaced at least twice already, with brand new OEM parts?

they have been except for long lines to heater core, h.core and cover for thermostat.