My 2009 E63 had the head bolts replaced under warranty after a dealership tech noticed “a coolant leak,” which I think was really more of them hooking me up with that repair before the warranty expired. That was 3 years and 20k miles ago. The car has 90k miles on it now. A couple weeks ago I had a “top off coolant” message come up, which had happened occasionally every 6-12 months I guess, and I would just put a bit more water in and be on my way. This time I didn’t have quite enough water on me to fill the reservoir (I had about a quart), but I could see it in the bottom when I was done. I dropped the hood and went on my way. No more message, and I drove home about 20 minutes on surface streets. Close to home I saw some steam coming out, and when I got home I realized I had forgotten to put the radiator cap back on. A good amount of fluid had boiled out of the reservoir and into the engine bay (not sure how much). Radiator cap was still sitting there and I put it back on.

A couple days later (had it parked) I put in a gallon of 50-50 mix of the appropriate blue coolant. I drove it 10 minutes and checked the fluid level. I found the dreaded milkshake coolant instead. Drove it back home (downhill) and parked it. The car never overheated at any point during this episode. There was no visible coolant in the oil filler area (cap) or the dipstick. The car never ran rough or exhibited any other issues. Had it towed to my indy a few days later and let him look at it.

My indy pressure tested and found a leak in the plastic radiator end tank, so we went ahead and started that project and this may be why I was losing coolant. He found cloudy coolant in the radiator and upper and lower hoses. Not so much in the block though. Still, my guess is that this is a head gasket failure, but is that likely given what happened? The car never got that hot, the temp gauge only got slightly above halfway and the auxiliary fan was on when I had the boil-over, is that enough to ruin the head gasket? The only other oil/water mixing potential would be the transmission cooler I am told, but my milky coolant is grayish-green, not the brown clay color tranny fluid would cause. The oil cooler is separate from the radiator and coolant so no potential to mix there, right?.

We are going to test the coolant for exhaust gas, which will be definitive for the head gasket. Assuming that is what it is, would the oily coolant have damaged anything else? The indy said the radiator hoses get soft when exposed to oil, what about any other seals? I already had a new rear main seal replaced under warranty, would that be compromised? I ask because a head gasket job is one thing, but if there is a lot of other stuff that is ruined it might be cost-prohibitive to repair. I am seriously considering Steel Seal head gasket sealer (what have I got to lose?) but I might not do that if it is “only” a head gasket. I might use it anyway, as I guess I could still do the head gasket repair if the Steel Seal doesn’t work.

My question is: Am I missing anything here? Could it not be a head gasket? Is there something really bad about using the Steel Seal other than the mickey mouse aspect of it? I’d have to dig a little deeper than I want to right now to swing the head gasket repair, but it is cheaper than buying another car is how I look at it. Still,

I am not going to throw 10k at it if there’s more to worry about here. Last, did my simple oversight with the radiator cap being left off cause all this? (Please say no).

Thanks for any insight!


Coolant color

 

Your E63 has a separate transmission cooler, so engine coolant and transmission fluid will never mix. Pull your oil dipstick, if coolant was introduced in the oil, you would definitely know. Also since you didn't have the coolant reservoir cap on, something could have been introduced that caused your coolant to change color. This needs further investigation, could it be a head gasket - yes, could it be a broken head bolt - yes. But it could be other things, as well.

 

Yes, the exhaust gas coolant test should be done today, and that will be the best indicator. I just don't know what else could be introduced to the coolant to make it look like that, and only in a 20 minute drive with the radiator cap off?

 

I've been giving this some thoughts, and I can't for the life figure this out. Have you check your oil dip stick, to see if coolant has mixed with the engine oil. That would give you some insight.
If the engine coolant hasn't mixed with your engine oil, then it's isolated to just the coolant system. This would indicate that you don't have a head gasket issue. Just contamination due to a open reservoir cap.

 

Correct, no coolant on dipstick or on oil filler cap, and area underneath cap looks normal. I think once the exhaust in coolant test is done I will have better intel. I worry a bit about the test, since we have to run the engine to make the test (we didn't test the coolant before draining it) but as I mentioned there is no smoke out of the exhaust and no rough running. Could boiling coolant cause it to cloud up like that? The coolant from the block drained clear, no cloudiness, but the upper and lower hoses had the milky stuff. I did not see any milkiness to the boiled over coolant that was coming out when I discovered the radiator cap being off. I put in a gallon of blue 50/50 after the boil over incident, drove it 10 minutes, then checked it. It wasn't even hot enough to wait to open the cap (just warm), and that's when I saw what is in my picture.

 

I would recommend draining the entire coolant system, as you don't know what the damages are, by having contaminated coolant. Then refill with new coolant, then closely monitor it, over the next few days, to see if the contamination comes back.
This will give you a better idea of what's going on. As you stated, there isn't any coolant mixing with the engine oil, so that rules out blown head gasket, or even broken head bolt. Could it be a problem with mixing different engine coolants together.
Possibly an adverse reaction, of two different chemicals. As Mercedes has their coolant, then there's everyone else's. I think that this could be a strong possibility. As I can't think of anything else at the moment.

 

So the exhaust test was done today and there was no exhaust in the cooling system. I consider that quite good news. I am having the car buttoned up and the water we put in for the test replaced with 50/50 coolant. I will do what you suggested and drive it and monitor it frequently until my paranoia subsides. It is very strange. I will update this post in the next few days as I keep checking. I appreciate your input.

 

If you mix the older **** yellow G05 coolant with the factory fill G48 blue you can get a feces brown, no issues otherwise.

 

That is good to know, I try to avoid mixing brands of coolants, just for this very fact.

 

No problem, glad to assist, It’s fortunate, that this a relatively cheap fix, because it could have been expensive. Remember keep that reservoir cap on, So that your system doesn’t get contaminated. 🤔

 

I see what looks like oil in the coolant.Running with no cap will not turn it that color. That white frothy look is what bothers me. That is a "forced" mix to get it that way.
Maybe a seal in the front cover leaking ?? into the oil??

Hopefully not.

 

I would put my finger in it, then rub them together and smell it to see if there is any traces of oil in it. Or have an analysis done.

 

What I am wondering is if there is a way for oil to get into the coolant, but not exhaust gas, and without coolant getting into the oil? Is there some section of the head gasket that could fail that would only allow oil out into the coolant and not vice versa? And could this happen with no signs of overheating?

 

Update on my issue: We tested the cooling system for exhaust gas 3 times and it was negative. My indy went ahead and put the coolant mix in and ran it with the radiator cap off since the radiator had been replaced and he wanted to circulate coolant. It ran for 10 minutes with the heater on and burped coolant out of the reservoir. He thought at first it was a bad hose connection (the upper and lower hoses were done also) but realized that it was coming out of the reservoir. He added more coolant and it did it again. Both of these times when he shut off the engine the coolant in the reservoir pulled back into the cooling system. The third time he left it running longer (with the cap on now, I believe) and the heater still running. It finally started giving heat to the heater. He tested for exhaust gas one more time and still negative. When I picked it up there was that same milky stuff floating on top of the coolant in the reservoir. It was just on the top and he said it must be that he could not get all of it out when he drained it. We also thought maybe the burping was air since the block was drained.

I took the car and drove it a couple days, maybe 40 miles total. Heat worked, engine ran just fine and no overheat or hint of overheat. I did notice the shift from 2-3 was slippy under normal acceleration, and became a bad stumble under harder acceleration as if traction control interfered. This did not happen in M mode though. Was thinking it was the transmission learning my driving again after essentially sitting for a week. I took it in this morning to have a look. The coolant in the reservoir was a brown color before I drove it (and it was low, but no top off coolant message). When I drove 10-15 minutes to the shop, he took the cap off and it boiled over briefly before the coolant was pulled back into the system. He felt that this was not normal since the engine was not hot. The coolant that came out was perfectly blue in color, for whatever that's worth. I am having him check the transmission fluid level and condition, but it seems to me this bubbling is coming from somewhere. I am not sure how much burping has to be done when the block is drained, but perhaps it is still air in the system?

 

This doesn't sound like your shop used a suction device to extract your coolant. My shop used a device that suctions out the old, creating a vacuum effect that then pulls the new fluid throughout the coolant system, thus eliminating any air pockets in the cooling or heating system.
Also this devices will alert you if there is a leak, as the suction will fail.

 

Do you think the bubbling out is due to air in the system then? It is not hot enough to be boiling over it doesn't seem.

 

The bubbling is due to air in the system getting burbed out. The machine that my shop utilizes gets all the air out, while sucking the coolant thru every passage In the engine, while also topping off the coolant reservoir.

 

I thought I would post a quick update on my issue: There have been no issues since we changed out all the coolant (using the suction device) back when this all went down. Coolant level has remained constant. We did have to siphon off a bit of residual film floating on top of the coolant in the expansion chamber (looked a bit like oil) but that was just because those baffles were hard to clean out in there. We did that twice in about 10 days right afterward. Coolant is now blue as normal and has been that way since. So I am rolling on a couple thousand miles later, my paranoia is pretty much gone, and hoping we didn't miss something. That's all for now. Thanks again for the help!