Coolant levels drop but no signs of leak

After dealing with a bad overflow hose and fix that my oil/water temps have been better than before. But now I'm noticing a significant drop in coolant level (from max to below min) but there is 0 signs of leaks.

I filled my coolant yesterday morning to max, this morning i checked coolant lvl and it is below min.

I guess i should probably get a coolant pressure test, but is there anything I can check for at home before I find time to take it to a shop?

Should i risk driving it? It is currently my only car at the moment and I need it to get to work.

What are the chances of a cracked cylinder head or something that can cause an internal leak? or is it more likely the cap that is faulty?

Appreciate any insight.

Any smoke out the tail pipe?

Not that i noticed while driving. And no smoke while idle in the garage.

First time I had a coolant issue (on the highway when my overflow hose popped off the thermostat) I lost all my coolant, and the max I saw my temperature gauge go to was 125 C (so like 257 F) but would get lower if I was cruising at a higher speed.

***CORRECTION: after looking at some photos I took when this happened max temp was 112/115 C ***

Do you think that was warm enough to warp the cylinder head or cause any damage to the gasket... I would think not, but now im just second guessing everything...

Depends on how long you drove it like that. Do a cylinder compression test. That should let you know.

Have you vented the cooling system? Air is often entrained when filling the cooling system, which can cause improper cooling. It is important to vent the cooling system every time you repair the cooling system.

That wouldn't explain the disappearing coolant though.

roastbeef wrote

Depends on how long you drove it like that. Do a cylinder compression test. That should let you know.

Probably about 10 min (maybe 15) it took for me to make it home when that happened.

jun_e92 wrote

Have you vented the cooling system? Air is often entrained when filling the cooling system, which can cause improper cooling. It is important to vent the cooling system every time you repair the cooling system.

The first time it happened I didnt, and i noticed higher temps than before under full load, 2nd time I did run the car with cap off to get air bubbles and now my temps are good. under full load 20C outside max I saw the temp go to was 105C.

If you are using BMW coolant it dries and leaves a white crusty residue, so if you look from underneath you may spot small areas of this on hose ends or other coolant related parts. Regular coolant would be a little harder to spot but generally does not dry completely and leave a wet residue.

Driving a car with a cooling issue is a bad idea in all respects. As mentioned get a pressure tester and check the coolant system, and/or do a cylinder compression test to see if there is gasket damage.

From personal experience, I have had a head gasket problem turn very quickly into a cracked head, so I would not drive the car until you know what is going on. The fact that you drove the car when it was overheating leads me to think you have possibly damaged a head gasket. Lets hope that is not the case, but I would err on the side of caution.

I just went through some pictures and I was mistaken it didnt go to 125 C it went up to the halfway between the middle and the first dot. So 112 maybe max 115C

There's no way that is considered overheating, enough for gasket damage tho right ?

I'll get some tests done but I mean I have no other option right now for getting to work. And I start my new job on Monday.

So far the engine temps while driving around and spirited driving stays under 105 C

have you peeked inside the crank to see the oil color? keep in mind, you're looking at oil temp. its somewhat sympathetic to water temp, but its not dead on. anytime you're running a car without water is not good.

How would I go about doing that ?

I opened up the oil cap and looked down and no signs of like creamy substance or anything.

I'll lift up the car tomorrow and remove the skid plate and see if I can see any small leak.

Yes, look down the oil cap into the crank.

Kk I will get a good flash light and look again. Thanks for your help I really do appreciate it.

As im trying to recall everything I've done since i had the overflow hose fail on me causing me to lose my coolant and start this mess, when I fixed the line and added new coolant in, I put in maybe 4-5 Litres of coolant back in before it hit Max.

So that means I must of had about 40-50% coolant left in my system while making my trip back home. Which is a lot better than having 0 coolant in the system which lowers the chances of having the gasket or other components fail.

What im leaning towards is I didnt properly bleed the system when I filled it back in and I had a bunch of air. So the next day when I went out and ran errands the coolant dropped a bit due to air escaping i guess?

Im going to bleed the system again tomorrow and see. If it holds by end of day tomorrow I should be good. At least enough until I can get it into a shop for some tests.

The system is self bleeding. So it makes sense that the level drops at first. Read the last 2-3 paragraphs of the OP in this thread.

DIY parts & procedures for replacing e92 M3 belts, tensioners, and water pump https://www.m3post.com/forums/showthread.php?t=1733739