As the title says. Any other spots I may have missed to look for leaks?
It does not drip in the garage.
I was affected by the bad thermostat gasket, I replaced it myself.
Went through little under half gallon in about a week. I filled up the reservoir over the full line a bit. A while ago the car overheated at a light, temp went down a second later as I started moving. I figured it was a burp since it hasn't happened since (when I was low on coolant).
I looked around the engine, can't see anything. Nothing immediately obvious as to being wet, or signs of dried coolant.
However, the hose clamp right under the fill reservoir does have evidence of dried coolant. The heatshield underneath, not so much. I am aware of the separation issue. However, mine, when hot, does not seem to bubble at the seams and it does hold pressure.
I plan on cleaning it thoroughly to see if spots come back. If that fails, I will inject a red dye or something.
I did look around the thermostat and it looks clean and again, no drips so I did the install right.
Coolant looks clean, no greasy film. Changed oil this week-end and oil also looked normal. So I strongly doubt I am having headgasket problems.
This problem seems to have gotten worse after the thermostat change and coolant flush done, around November. In the sense that, since that time, I have had no significant coolant loss that I was aware of.

Any other ideas? Suggestions?

 

Get the cooling system pressure tested.
It sounds like your loseing coolant when it's under pressure.
Possibility that system still has air in it.

 

I am thinking I should start by NOT opening the fill reservoir while the thing is hot. It lets pressure out and I am guessing maybe sucks air in. Level went down again yesterday when I checked, it was at the level of the bottom crevices or whatever you call them. I will let it cool down today and THEN top it off and see if it gets better. If not, I will have it pressure tested.

 

To add on to this, I did some searching but came up empty. How would I go looking at the weep hole on the water pump? Where is it located exactly?

 

How long ago did you replace the thermo gasket? Many people have issues with air bubbles in the system - could you just be evacuating those over time?
The water pump is on the back of the supercharger - near the middle of the engine, in front. Not sure if there is a weep hole in it.
Overheating at a light sounds like you have a fan issue. How hot did it get? Do you have gauges, or did the idiot light come on? Have you confirmed that your low speed fan is working?

 

Let's take'em one by one
The thermostat and gasket I replaced sometime in December. The car has not been driven that much over winter.
It is entirely possible there was a good amount of air trapped in the system still, let's say my install, by following the DIY, for sure introduced air.
Both the low and high speed fan work. At least I think they do, because the fan runs, and then kicks into the high-pitched-noise mode when the AC is turned on. So it functions at 2 speeds, not just one. I have not seen it not run, ever.
I also verified yesterday that the power steering fan under the car comes on, just because.
At the light, the needle started creeping above the mid mark. I did not let it creep above 3 quarters. I shut the engine off for not even a minute. Turned it on, went right away down to mid-level and never crept up since.

I checked the coolant level again today after the drive to work. Seems it has kept level since yesterday, it is at the same place. Maybe it's still burping air. I hope I will be able to get off this easy It would definitely be strange to lose a quart in 2 days and none at all after that. Maybe this indicates that I do have an unsighted leak at the overflow seam, which lets coolant spill until it gets too low to happen anymore.

I will note that before the whole thermostat gasket thing, coolant has never gone down. So the only two "variables" introduced since then was a coolant flush in November and the gasket change about a month later. The flush was done at Valvoline, while I was watching them do it, using Zerex G05. They bled the system using the one bleeder on the big hose to the radiator.
Maybe I should open up this screw and see what happens?

 

Def check the weep hole by the waterpump....then work to "burp " the system...pressure test might help...
many different posdibilites...some are kinda bad.
I would check the oil....maybe have asample tested, so you are 100% certain the antifreeze is going somewhere other than the oil....
A tiney crack somwhere is a certain posibility.....but a aged hose, (or something else) leading to fluid loss is more likly....sounds like you are working to rule this stuff out first, good move.
The overheating at the light....did you find it low on fluid then?
Interesting to know if it was low (or blocked by a bubble), and that caused the overheating....simplest answer...so mostlikely before you freakout!
def rebleed it....plan on loosing a few quarts of coolant while getting rid of the air...if this was not done after work....wow...100% needed to be done. Sometimes more than once....

 

I changed the oil. With 2 quarts of coolant in it, it would have definitely showed. However, it looks just fine.
How would I go about inspecting the weep hole/water pump? I hope it's something I can do without pulling off anything major.
Yes, when it overheated, it was low on coolant. Lower than it is now. I am guessing it passed an air pocket by the thermostat, possibly.

I appreciate everyone's help and suggestions

 

When mini did my cooling system flush on the maintenance plan, the coolant level in the catch can started dropping. No leaks. Took it back, they flushed it again and were careful with the bleed screws. It dropped about 1/2 inch, then stopped. I'm monitoring now. Dealer has no idea...

 

My 04 MCS leaks about a quart per week because the radiator has a small leak where the aluminum meets the plastic. I plan to replace, just havn't gotten around to it.

It doesnt leak on the ground and took me a lot of looking around to figure out where it was leaking....fyi.

 

OCKOLBY, is that on the bottom of the radiator?

 

did you find the source of the leak? mine is doing the EXACT same thing.So I made sure the water pump gears were good on the supercharger,and when removing the air inlet tube on the bottom,coolant spilled out!? gotta find out where it's coming from 2morrow.

 

removed head with help from father in law and .003 feeler gauge slides REALLY easy under straight edge on the outside center of the head.Noted a clumpy coolant/oil residue on the timing chain opening edge of the head and the same found on the block side as well.Looks as though coolant was leaking from the water jacket through the gasket and into the timing chain area.I could tell it must have pin a pin-hole type of leak because of the "stain" pattern that it left.What helped me pinpoint it was the fact that the previous owner must have put some stop leak additive in it,so it left some chalky/clumpy stains.Having the head milled and I will report back with what I have found,but seeing all of the similar postings I am thinking that this may be a common issue with R53 cooper s coolant leak mysteries!? If there was not any residue or staining,I never would have seen where it was leaking at!

 

Never pinpointed the leak because I don't think I have one, I certainly HOPE I don't. Ever since I opened this thread the coolant level has not gone down anymore. I plan on topping it off again and if it goes down, it has got to be the overflow tank leaking at the seams. Right now it is sitting at where it was before, at the level with those grooves.

 

front of the tank can look OK while the back is the problem

I pulled this one last week ... it was less than 3 years old

 

the overflow bottle. I had this on a 2006 high end Audi. Mysterious tiny drop in coolant bottle if tracked by marking the bottle. Dealer "could not replicate"/verify. Eventually I found a pinhole leak at the radiator core seam w/ the panel. Dealer then could verify and happily replaced whole radiator and flushed coolant.

Never dripped on ground...both because Audi's have a belly pan underneath, but ALSO because radiator heat itself burned off the wet coolant. Since then I realized to also look for slight chemical deposits (like in the coolant bottle pic above, complete w/ the antifreeze color [on Audi's it would be pinkish white] and either wet looking or dry powdery), which the chemicals in the antifreeze leave behind even if it evaporates w/ heat. Have seen the same deposits at hose clamps where there is a tiny leak or the hose is rotted internally near the clamp.

You are right that the starting point is monitoring the overflow bottle. I would just check it cold over time (weeks or more), and mark the bottle w/ pencil or grease pencil to compare later.

 

What makes it even trickier is the Zerex coolant is almost the same color as the overflow tank, a light yellow. However I wiped all the hoses around the tank and the tank itself really well, so if something shows up I will know it.
I will keep you guys updated. I certainly hope I don't have a pinhole anything anywhere else leak, it will be a pain in the *** to track down.
The fact that the coolant has not gone down now at all is encouraging. I will try to top it off and if it disappears again, then it's got to be either the overflow tank or I kept introducing air in the system by always checking it at hot.

 

If you are looking to let air out, you can try the "hard" bleeder screw buried on the left side of the engine. I would do that with the engine cold so you don't have to worry about the cap.

 

put a shot of blue food coloring in the coolant tank. A GOOD shot, half an oz or more.

If everything is working right little of that will find its way into the motor

if your spillage is blue you'll have a clue

 

One place to look....as our cars age, many are starting to leak where the plastic sides of the radiator is connected to the metal tubes....very common on many makes with this basic desgin....very hard to find due to the shrouding/fan till it gets pretty bad.

 

That's exactly where mine is leaking. My 04 MCS has 103K. I havnt replaced the radiator yet, but planned too....easy fix. Radiators on Ebay are about $100 shipped.