Coolant woes..

[bcredliner]

If the coolant is full when you shut if off then any pressure 'leaking' will occur in the next few minutes and with that magnitude of coolant loss you should be able to see the source though you may have to remove the plastic covering under the engine. Coolant will leave a white residue and is almost always visible especially on plastic parts such as on the expansion tank if the cap is involved. A bright white LED flashlight will highlight the residue. I would start with areas that are above the level of coolant when it is a quart low.

There are symptoms associated with a blow head gasket or other internal problems associated with coolant. Engine runs rough, loss of power, sweet smelling white smoke out the back, indication of coolant or oil in the coolant.

I am not suggesting a pressure test won't be beneficial. I am saying that I have never needed to resort to a pressure test to find any type of coolant leak in the last 5 decades. I love an excuse to buy new tools but as few times as I have had a coolant leak over the years I wouldn't suggest buying one. If you want go that route, I would take a trip to local radiator shop, or almost any chain type auto repair shop.

[sunny5280]

Originally Posted by jdstrickland

I'm confused. How is it possible that it leaks AND holds pressure well enough that the needle stays in the middle of the scale?

If it leaks, then it has to NOT hold pressure, that's why it is leaking. I can understand that you can't find where it leaks from, but I cannot understand the objection to a leak-down test. I have to admit, I'm not sure what such a test will tell you, but it should tell you that the system has lost integrity and does not hold coolant any longer.

Coolant is collected at the bottom of the radiator and fed into the engine where it circulates, then is expelled into the top of the radiator where it falls to the bottom and cools, then starts over again. Just because you have lost a quart of coolant, the coolant that remains should still flow to the heater to heat the cabin.

My guess is that you have, among other issues, a clogged radiator, although this should also cause over heating troubles. Restricted coolant flow can affect coolant that goes to the heater core, and this will result in cold temps in the cabin. A clogged heater core will also give poor heating performance inside the car, but not affect cooling of the engine.

My point is, the loss of a quart of coolant should not be the reason why the heater blows cold. And, the repeated loss of coolant is either onto the ground, or out the tailpipe. Your description of the symptom set is not clear that the coolant is in a puddle under the car, or simply missing into thin air.

I believe the leak test being referring to is not a leak-down test but rather a pressure test to reveal a leak. Leak-down test is a test to help determine the state of the engine.

[StephenVA]

Like BCredliner mentioned, coolant leaks are quite obvious and will leave behind a stain that can be traced to the source. Run the vehicle up on some ramps, lay on your back and look up. Follow the drips to the source. If you need a larger stream to determine the source then think about a coolant pressure tester. NOTE: This is a simple hand pump that adds a little pressure to the cooling system via the overflow/expansion tank which in turns pressurizes the entire cooling system. It NOT rocket science, guys.

Common sources: The normal stuff, Expansion tank, Thermostat, major hoses to the Rad, the Radiator itself, heater hoses, heater control valves, and the heater hoses themselves. All will go "POP" when pressurized and then crack.

Heater "BYpass Valve" (AKA heater control valve)
Genuine BMW Heater Bypass Valve 64128374995 - Free Shipping

Note: All plastic + 10 years who knows what is left....

[bcredliner]

Originally Posted by jdstrickland

I'm confused. How is it possible that it leaks AND holds pressure well enough that the needle stays in the middle of the scale?

If it leaks, then it has to NOT hold pressure, that's why it is leaking. I can understand that you can't find where it leaks from, but I cannot understand the objection to a leak-down test. I have to admit, I'm not sure what such a test will tell you, but it should tell you that the system has lost integrity and does not hold coolant any longer.

Coolant is collected at the bottom of the radiator and fed into the engine where it circulates, then is expelled into the top of the radiator where it falls to the bottom and cools, then starts over again. Just because you have lost a quart of coolant, the coolant that remains should still flow to the heater to heat the cabin.

My guess is that you have, among other issues, a clogged radiator, although this should also cause over heating troubles. Restricted coolant flow can affect coolant that goes to the heater core, and this will result in cold temps in the cabin. A clogged heater core will also give poor heating performance inside the car, but not affect cooling of the engine.

My point is, the loss of a quart of coolant should not be the reason why the heater blows cold. And, the repeated loss of coolant is either onto the ground, or out the tailpipe. Your description of the symptom set is not clear that the coolant is in a puddle under the car, or simply missing into thin air.

A leak down test induces air into a particular cylinder to test for loss of pressure due to valves, heads, head gasket, rings and pistons. The source of the loss of pressure could be allowing coolant to leak but I wouldn't do a leak down test unless there were symptoms such as, loss of power, missing, oil in water or water in oil.

A coolant leak can be caused by pressure that only exceeds the cap release point when the engine is first turned off. This is due to percolating that can happen when there is no cooling benefit such as an auxiliary fan that does not run for a minute or two.

Heater not blowing hot is not always low coolant but when there is also loss of significant coolant it is often the case.

[crystalworks]

Originally Posted by bcredliner

I wouldn't do a leak down test unless there were symptoms such as, loss of power, missing, oil in water or water in oil.

What about exhaust leaking into the cooling system from a blown head gasket or cracked/warped head? I've had an E36 and an E30 with this problem... never overheated and ran great, but leaked exhaust into the coolant system causing loss of coolant through the vent hose.

The above is kind of a worst case scenario and I wouldn't jump to that conclusion or anything OP. First things first, find out where the coolant is going. Pressure test will reveal that. If you don't see any external leaks (hopefully you do), and the system won't hold pressure... time to pull the plugs and see if you have coolant going into the combustion chambers.

[bcredliner]

Originally Posted by crystalworks

What about exhaust leaking into the cooling system from a blown head gasket or cracked/warped head? I've had an E36 and an E30 with this problem... never overheated and ran great, but leaked exhaust into the coolant system causing loss of coolant through the vent hose.

The above is kind of a worst case scenario and I wouldn't jump to that conclusion or anything OP. First things first, find out where the coolant is going. Pressure test will reveal that. If you don't see any external leaks (hopefully you do), and the system won't hold pressure... time to pull the plugs and see if you have coolant going into the combustion chambers.

Yes, that can happen though with this amount of lost coolant it is a long shot. Also, Recall I said in an earlier post--if the cooling system is full when you turn the engine off. In this case since the coolant loss seems to be overnight there are no fumes to force coolant anywhere when the engine is not running.

[crystalworks]

Originally Posted by bcredliner

Yes, that can happen though with this amount of lost coolant it is a long shot. Also, Recall I said in an earlier post--if the cooling system is full when you turn the engine off. In this case since the coolant loss seems to be overnight there are no fumes to force coolant anywhere when the engine is not running.

Gotcha. Forgot he was seeing coolant loss only overnight. Weird there is no visible coolant with that much loss every night...

Get that pressure tester and find out where that coolant is going.

[Buguyed]

UPDATE!!

Problems solved. I wanted to come back and let you guys know what happend.

It turned out when I installed the new expansion tank, I made a mistake. Well me or shotty products, who knows. On the bottom of the ET there is a large opening that has a rubber seal, which is held in by a conical piece of plastic like a washer. On mine, for some reason, this plastic piece fell down slightly and covered the grooves the wire clip slips into when you install to hold it onto the hose. This cause the expansion tank to basically just be sitting there and not clipped in place. It was in there good enough to not cause issues but resulted in a slow leak. I couldn't see anything just laying under the car until I added some pressure with the pressure tester.

Corrected this, reassembled, added coolant, bled, checked oil for coolant or discoloration (just in case), and all was well. I feel like an idiot but i'm happy now it's all done!

Thank you everyone for the tips/tricks/help.

[StephenVA]

Success is a great feeling. Congrats!

[bcredliner]

If you haven't had screws or bolts leftover, had to do back and redo something or replaced a part and it didn't fix the problem you can't call yourself a real DIYer.