Hello everyone,

My 2005 CLK 320 - M112 engine with 181,000 km (112,000 miles) started displaying a low-coolant warning since the summer. Back then, it would take a month to reappear and I would add coolant/water each time until a month ago when the low-coolant warning started happening every 4-5 days. The oil cap was inspected and the yellow milky/creamy stuff was found on the bottom of the cap, but the coolant tank is clean.

After confirming a coolant pressure leak using the appropriate kit, we replaced the oil cooler first and cleaned the cap and filler neck. That didn't solve it as the car kept displaying the low-coolant warning every 3-4 days now and milky/creamy stuff remained on the bottom of the oil cap.

We then inspected the floor beneath the footwells inside the cabin and found that the heat exchanger was leaking water into the floor which was pretty wet. Here, we replaced the heat exchanger since we were able to trace the coolant leak to it and then changed the engine/oil filter and topped up the coolant/water mix. This was last weekend and I thought that the problem is solved.

Unfortunately, a couple of days later, the low-coolant warning came up again and the milky/creamy stuff was back at the bottom of the oil cap.

Mind you the car idles fine, there's no smoke from the exhaust, and no current or stored errors using STAR. Something to note is that after we did the oil change this past weekend, even though 8L of oil were poured in, the dash displayed an error for 2 days saying that the car needed 2 liters of oil. This error disappeared on its own. About a month ago, I got a Defective Oil Level Sensor error on the dash but it went away after the next driving cycle. Something tells me that either the oil level sensor is defective or something inside the oil is causing it to display erroneous warnings.

What I want to know is whether I'm looking at a bad head gasket which needs replacement even though the car drives and idles normally or could this be something else? Where else could the coolant and the oil be getting in contact with each other thereby resulting in the contamination? I keep reading online that these engines rarely suffer from a bad head gasket. The car never overheated before.

I had already replaced 2 years ago the Valeo radiator with a Behr one along with the transmission pilot bushing, connector plate, filter, and fluids.

Thank you in advance for your help in diagnosing this.

Picture below of the milky/creamy stuff at the bottom of the oil cap.

 

I did not see that you included what may be the most important fact - what does your oil look like other than on the bottom of your oil cap? Either when you changed it or do you have a dipstick? A cap can sometimes look like that simply from a bit of moisture under there. But a leak of the size you describe will make all your oil look like a milkshake.

Edit: Unless, of course, you have a head gasket leak where 99% is going into the combustion chamber, and only a tiny amount into the oil. But the oil still has to make its way to your oil cap from there, so just the cap would not be milky.

 

Also, just spitballing but I don't know if the lack of oil in your expansion tank necessarily means you don't have a leak in the system. You have two fluid systems (coolant and oil), which are not supposed to come into contact. Both are under pressure. If a gasket that separates them fails, the system under higher pressure will leak into the lower pressure system. I tend to think hot coolant is the higher pressure system, but Rodney will correct me if I'm making stuff up.

 

When the oil was changed this past weekend, it looked perfectly fine without any residue of the milky substance. The mechanic said it's very clean since it had less than 2k Km on it. That's what lead us to believe that the oil cooler was the problem and the leak was caused by the heat exchanger. Turns out not. We're all baffled as to how much coolant the car is consuming, how light the milky stuff is, and how there's no smoke out the pipe or any performance loss. Where is it going?

 

How much are you adding? Have you investigated the water pump? Leaks there are common, but hard to detect because the leaking fluid gets spun out by the pulley and atomized.

 

0.5 to 1L every 3-4 days. I'll have the mechanic inspect the water pump tomorrow. Thank you for all the pointers. That's what I need to pinpoint the problem.

I also read that doing a cylinder compression test and watching if the pressure will rise in the cooling system resulting in air bubbles in the coolant reservoir will mean a head gasket failure. Will dedinitely try that tomorrow as well.

 

Yes, that is the test you need to do.

 

Oh, the pressure you put on me! (pun fully intended). Oil pressure is generally supposed to be about 10psi per 1000 rpm. Coolant pressure is more like 15psi at operating temperature. So, at idle, or even after shutting down the engine, the coolant would have more pressure, but during acceleration and at highway speeds, the oil would win out.

 

Short version: it's the head gasket.

Long version: the mechanic disconnected the fan and removed it and we ran the engine until it reached 100c so by then the coolant pressure was high. We then started inspecting for any visual leaks or anything.

We were able to identify the head gasket as the problem because we could see the water drip from the exhaust tip.

The car is currently being repaired. It'll cost a maximum of $200 including new head gaskets.

 

Well, at $200 you don't have much to lose. That's an amazing price. At a US dealer it would be $200 for the paper they put down to protect the carpet. Did you confirm what is coming out the exhaust is coolant and not just water? Water is normal under some circumstances until the exhaust itself is good and hot.

 

Yeah, labour rates in Lebanon are pretty low so that's a good thing.

Because of how much water I've been adding, there's barely any coolant if any in the cooling system so water is all there is in it and we saw it accumulated in the exhaust and dripping.

I'll keep you guys posted with updates.

Below is a picture with the valve covers removed. Engine internals look decent enough.

 

Latest update:

Upon removal of the head gaskets, no visual cracks or anything was found. Nevertheless, the head gaskets were replaced, the engine internals cleaned thoroughly, and everything put back together. The car started up nicely and we let it run for an hour and we conducted a coolant pressure test and there were no leaks.

I drove the car home (20 mins drive) and next time I started it, the idle was rough and even rougher when I put a gear in it as if it's about to stall but it never stalled. No check engine light and no errors using SDS/STAR.

I drove it back to the mechanic and we pulled both valve covers and removed both camshafts and everything was normal. We did some tests with the coil packs as well. Anyway, after some diagnosis, he had to correct the timing with the chain where it needed one unit of adjustment. He had to skip the chain one tooth underneath the valve covers. This improved things, but the rough idle is still there although less. He told me to drive it for a couple of days, and to bring it back on Friday if the problem is still there. I had paid a total of $233 for this job (150 for labour and 83 for parts) and he said he will get it back to normal without taking a single extra penny.

Now all this was Saturday.

On Sunday, I took the care for a drive and after 30 mins, I got the following errors on the dash:

-Add 1L of oil
-Oil Quality error
-Oil Level Sensor error
-Check Coolant Level

I have since, up until this morning (Monday), added water twice (0.25 L yesterday + 0.75 L this morning) and the milky stuff is back on the oil cap. I also added this morning 1L of oil.

I am going to continue monitoring the car until Friday, but I am not too hopeful. The coolant leak warnings are back, the milky stuff is back, and the car is idling rough. I'm afraid the head gasket was not the cause of the leak, but in all cases, I won't be paying an extra penny until the car is repaired.

I had read somewhere about putting some sort of a safe-to-use dye in the cooling system and driving the car and then checking to see if the dye had leaked somewhere where it could be visible. I might have him do that next if the coolant level warnings don't stop and we're back at square 1.


Anyway, what do you think of all the above?


Oh and I forgot to say that I'm already looking for a 2012 W204 C300 because I've had enough with the CLK. I've done nothing but baby it with maintenance these past 3 years and the repairs keep coming one after the other.

 

That's an awful lot of coolant to be mixing with the oil. My confidence level in said mechanic would be diminished at best, seeing how he failed to get the timing on point the first time. Are you confident he did a good job replacing the headgasket? Did he check to see if the block was warped in any way when he replaced the headgasket? A gasket won't do much if the mating surfaces aren't straight. The only other thing I can think of, provided you checked the usual places for an external coolant can leak, is a cracked block somewhere. I would stop driving the car until issues are fixed.

 

Thank you for the pointers. Yeah my confidence level is not so high but I have to stick with him to get the car back to normal without paying much so that I can sell it soon. That's why I have turned to the forum to get enough pointers so that I tell him what to do next time I visit.

When I asked him about the block, he said that it was inspected and it looked perfectly fine without any cracks. But let's see he's not sure, wouldn't adding a dye to the cooling system end up exposing an external leak like this one?

I am posting below pictures of the old head gaskets and the oil cap from this morning:

 

The Check Coolant Level warning is now always on regardless of the fact that the coolant reservoir is topped up which leads me to believe that the sensor is faulty.

In addition, the car is now needing water/coolant every day leading me to think that something's up with the engine block/surfaces because before the attempted repair, it would take 3-4 days for the coolant to get low. So I guess when the block was removed and reinstalled, the crack got bigger and it's leaking more water now.

 

Or the initial problem was never discovered and it's now getting worse. I wouldn't jump to the worst conclusion just yet. The dye would help with an external leak. You could give it a shot and see if the coolant is getting blown around like mentioned before. I used the dye for an oil leak and it worked pretty well.

I would start trying to pinpoint the leak by doing some individual pressure tests like all separately so you can eliminate components one by one - radiator, individual cylinders. I would also drop the oil pan and check if the timing cover is leaking directly into the oil pan...or at least check all seals associated with the timing cover.

 

Thank you for the suggestions. I will definitely add them to the list of things to check.

I was told on another forum to check the o-ring seal between the timing chain rear cover and the engine block which what you're suggesting as well so that's definitely going on the top of the list of things to check.

 

Yeah unfortunately we're all spitballing here. Leaks are hard to find sometimes. My suggestion is to approach each component individually and check it removed from the system, if possible, so you can isolate the problem.

Also, again, gaskets can be very very tricky. In some cases the surfaces need to be perfectly straight and absolutely clean for the gasket to work. Ask me how I changed one of the valve cover gaskets on an Audi like 6 times until it actually worked

 

So I'm at thw mechanic and here's what we thought. Before we changed the head gasket, the car was loosing 0.5-1L of water every 3-4 days. After the head gasket change, the car started loosing almost 1L every day which leads us to believe that the movement in the heads caused this.

So, in order the check the timing cover o-ring and the heads and the block, we decided to remove the entire engine and inspect it meticulously.

If we find the o-rings are bad, we will replace them and put the engine back. If not, we will inspect the heads and and test them for leaks. Otherwise, we might just put a new engine for $500-600.

I'm staying at the garage while this is unfolding so I'll keep you all posted.

 

The first o-ring we got to was ripped as seen in the picture below.

We're continue to dismantle the timing cover to get to the second o-ring.

 

I can now confirm that the passenger side o-ring was ripped and the driver side one was swollen and leaking as well but the passenger side one was far worse.

We confirmed that too by the oil pan which had the milky stuff in its bottom, in a decent quantity, on the passenger side.

The timing cover is out now along with the oil pans. We'll clean everything, replace the o-rings, and put it back together and hopefully that's it.

 

Aaaaand there we have it. That should be the end of it. German cars really are terrible with seals in general.

 

Wow! Great work. I hope that is the end of your troubles. I just found out from my mechanic that the oil filter housing on my CLK is leaking and needs replacement -_-

 

Yeah it doesn't sit very right with me that an engine needs to be taken out for 2 $8 seals to be replaced. That's BMW territory.

Does it need new seals or the entire thing needs replacement? The one I bought which has the oil cooler attached to it was BEHR and made in Germany. It cost me $80.

 

He called me late yesterday afternoon so I'm going to go Monday and talk to him and take a look. I don't see how the whole thing could be bad especially if it is leaking from the top, which is the most likely area if the cap is bad or something. I'd assume that's more common.

But I hope your problem is resolved. That took a lot of patience and I think I personally would have lost my mind.