Pseudo Nim

Appreciate any advice here. I think I have a very minor coolant leak. After all the horror stories, I'm pretty particular about checking fluid levels, and I've been noticing the coolant level drop every few days by a few mm from the level meter in the expansion tank. Like it's not a lot, but I fill it up when cold right to the top of the horizontal bar, and after driving a few days, it always drops below the bar. I've been adding maybe 50mL every few days. This started happening after I got a "low coolant" warning a couple weeks ago, so I've been monitoring it since. The car did have all headbolts done etc, and I don't see anything obvious on the dipstick, so I don't think it's going into the engine (also, no codes thrown in the ECU, so no misfires etc), but also don't see anything underneath the engine / on the floor. The car did move from a very hot climate to a very cold one, so I don't know if it's related or not, but not sure how to debug this. I cleaned the O-ring on the coolant reservoir cap, for what it's worth. Any thoughts welcome!

Plutoe

yea get the system pressure tested.

Pseudo Nim

Thanks. Do I need a dealer for that or can indy usually do that? Will it help figure out the leak source as well, or just tell me that there is one?

gsfent

Any Indy can do it. The reason you pressurize is to look for/listen for the leak. Shouldn't take very long.

Regards,
Jerry

chassis

Also look at the exhaust when the engine is warm to see if steam is coming from the tailpipe. Smell the exhaust and note a sweet smell which is coolant.

Also smell around the engine bay. Leaking or weeping components will generate a coolant smell. My GLE with M276 engine has a weeping/sweating circulation pump, which is fairly common phenomenon for this cheap and widely used Mercedes component.

Smell inside the vehicle for potential leaks in the HVAC.

Pull the spark plugs. If they any are "washed" clean, that is a sign of coolant entering the combustion chamber from a failed head gasket. Also look down into the combustion chamber with a bright light and note if the top of the piston is "washed" clean which indicates coolant in the combustion chamber.

Rough idle is a symptom of coolant in the combustion chamber, with or without check engine light.

Look under the oil fill cap for chocolate milk sludge. This indicates coolant in the oil.

Who changed the head bolts, when were they changes, and by which method were they changed?

Pseudo Nim

Thanks. I will check into all of those points, though I don’t feel like I saw any (especially exhaust smoke, rough idle or generally smell of coolant or anything “obvious” like that). But I will recheck to confirm.

The bolts were done about 30K miles ago by Mazdeuce. It’s THAT R63. Hehe.

focalxplosion

I just had a bit of a nightmare coolant experience. I had an indy shop replace my alternator. About a week later my coolant pipe came loose from the water pump. It turns out that it was badly corroded and the shop just jammed it back in the water pump without mentioning it to me.

Next phase of the nightmare, that coolant pipe is unique to our R63. The dealer was able to coble one together from R350 and ML63 parts but the OEM part is no longer available. $600 in rubber hoses later and I'm running like new.

Like the others said, pressure test it.

ygmn

Check engine oil and coolant for signs of one or the other in the wrong place.
I.e. Coolant in crankcase = BAD
Oil in Radiator = BAD

Pseudo Nim

Thanks. The issue is that there hasn’t been THAT much disappearing - so I feel like I’m going to have a hard time tracking it down. For example, I drove around all day yesterday and the level hasn’t dropped at all, or maybe just an oz or so (the rib in the reservoir is maybe a mm or 2 more visible than the previous day. I should do day to day photos to compare). There’s no way I’m going to find this anywhere - I almost wonder if I’ve overfilled it before and it was its way of ejecting it from the system. But I have a friend doing a pressure test tomorrow. Let’s see.

chassis

This post comes off as hoping against hope that there is no problem. Understandable but not realistic.

Watch the situation over time and take note of all the observations suggested to you. Have the coolant system pressure tested. You need data. You have insufficient data at this point.

190Efan

Go to your local parts store and buy some engine dye. The see if you can see any of the engine dye seeping out anywhere. If you see anything, that's likely where your leak is.

Pseudo Nim

Update! Leak discovered. So we lifted the car, and discovered there was a slow drip on the right hand side (when facing the car). A taste test definitively established coolant (although DAMN, Mercedes coolant tastes awful! I liked my Audi coolant more, it was sweeter... although maybe it was the brain releasing sweet, sweet endorphins to protect me from the impending realisation that any coolant leak in a V10 RS6 usually required an engine drop). We did a pressure test just in case, and did confirm pressure dropping.

We took off the underbelly, and traced a leak to this fat hose on the right side of the radiator:



We first thought it was a radiator leak (bad!), then we looked more closely and it really looked more like a hose leak (less bad but still bad) but then we REALLY looked closely, and realised it has one of those insanely annoying clamps that don't really clamp anything, and are more of a decoration. So we decided to swap that useless clamp for a proper one that actually holds the hose down:



Now we vacuumed out some loose coolant and did a vacuum test on the system, and this time, the vacuum held! So we refilled the coolant, closed everything up, and I was on my way. Checked the hose when I got home, dry as a bone. Will keep an eye on it.


Offender:



I don't know if it was a cold climate switch, but I guess I'm somewhat worried other clamps will go loose with time - Audi had similar clamps, and I simply cannot stand them. But I think this panic is avoided this time! Thank you everyone for your advice!

chassis

Well done!