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Discussion Starter #1 (Edited)
My engine is mixing oil and coolant. I will have to make a decision soon since this is my only car, so your thoughts and suggestions will be appreciated.

The car is a 2005 ZHP 6-speed manual. It had 131K miles when I got it three and a half years ago. The cooling system was done a few months after that and the thermostat is less than a year old - all OE components except for the water pump (Stewart).

The engine has never overheated while in my possession. It is still running at normal operating temp (at around 97C), and the car is still driving fine with no codes.

The first warning sign was a low coolant light about two weeks ago (the car is now at 164K miles). I didn't think much of it since coolant hasn't been topped off for seven or eight months. Incidentally I was under the car that very same day and admired the underside of the engine - clean with no leaks of any kind.

The next low coolant light came a week (and about a 150 miles) later, indicating that there is indeed a problem. This time I filled the expansion tank with distilled water, looked again for leaks, found none under the car, couldn't feel any moisture inside the passenger compartment or on the front carpets.
I decided to stop driving the car and do a leak-down test ASAP. Still had to take it to a friend's place to use his air compressor. The rate of coolant loss seems to keep increasing since I needed to add more water after that short trip.

While preparing the car for the test, it already became obvious where the coolant was going:



Not the most welcome sight to see under the valve cover. The oil level is fine (the oil was changed 2K miles ago).

Surprisingly the leak-down test didn't reveal anything alarming. For each cylinder, it was measured at 98 PSI with the piston at top dead position:

1: 4.1 %
2: 6.1 %
3: 4.1 %
4: 6.1 %
5: 9.2 %
6: 3.1 %

These numbers are not dramatically different from my previous test, done about a year ago, with the exception of cylinder 5, which was at about 5% then. For all cylinders, the air was leaking primarily through the piston rings.

One obvious way this could have happened is a head gasket failure, which hasn't significantly affected the cylinders yet, but allows coolant to enter the oil passages. Of course, this could be due to cracks in the head or even in the engine block.

Another possibility that crossed my mind, about which I would particularly like to hear opinions, is a potential lower chain case metal gasket failure. This gasket (#6 here) separates the timing chain compartment from the water pump socket. Has anyone seen coolant sipping through this gasket down into the oil pan?

So, the car is now parked at my place and I will only drive to a shop where the work is going to be done.
At this point I am considering a more extensive engine rebuild rather than limiting the work only to a head and head gasket job. At the same time I will be looking at the locally available M54B30 engines if it turns out that engine swap (or engine and camshaft swap if a non-ZHP engine is sourced) will be a better option. Not ready to let the car go.

Sorry for the long post, I thought it would be better to provide more details at the beginning. Please let me know what you think.
 

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That looks like a lot of mayo to me. If leak down was good but your still worried maybe you could try a block tester. It's basically a chemical that will change color if exhaust gasses are present in coolant. Change the oil and see how it looks. I would check out the oil filter also. If oil and coolant is really mixing you'll know it. Also check your spark plugs for any that are cleaner than the others if that makes sense.

My coolant light use to come on occassionally and would get a bit low, so I thought I had a blown gasket as well since my whole cooling system was new. I had a lot of mayo as well, so I was really freaked out. After a while my fan exploded and I had to replace most of the cooling parts, and my coolant light hasn't come on since. Level hasn't changed at all either. I think the coolant light was from a stubborn air pocket in the heater core or something that would set it off occasionally. The mayo? Idk probably from not driving hard as much as I usually do.

If you really haven't overheated the car I would not be too worried.
 

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Discussion Starter #4
Hard to tell from the blurry photo, but is that truly oil/coolant milkshake, or just the common mayo? How does the oil on the dipstick look?

If it still drives fine then take some time for more testing.
Sorry for the cell phone photo.

This mayo is something I've never seen in person before and it does look to me like an oil/coolant emulsion. The car has not been anyplace cold for quite a while.
I can post photos from my valve cover gasket and oil pan gasket jobs later, there was nothing remotely resembling this.

I should mention that the CCV setup is OE with O2Pilot mod and the crankcase vacuum is higher than stock. In the current situation this is probably a good thing since it should be more efficient in removing water vapor.

The oil on the dipstick doesn't look bad.

Any suggestions what other tests would be helpful? I've added more than half a gallon of coolant and water since this started. If all that leaked into the crankcase, I'd rather drive the car only with a very specific goal in mind.

Of course I can change the oil right away, but at this rate of coolant loss the amount of water in the oil will be back where it is right now in less than 200 miles.
 

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Discussion Starter #5 (Edited)
That looks like a lot of mayo to me. If leak down was good but your still worried maybe you could try a block tester. It's basically a chemical that will change color if exhaust gasses are present in coolant. Change the oil and see how it looks. I would check out the oil filter also. If oil and coolant is really mixing you'll know it. Also check your spark plugs for any that are cleaner than the others if that makes sense.

My coolant light use to come on occassionally and would get a bit low, so I thought I had a blown gasket as well since my whole cooling system was new. I had a lot of mayo as well, so I was really freaked out. After a while my fan exploded and I had to replace most of the cooling parts, and my coolant light hasn't come on since. Level hasn't changed at all either. I think the coolant light was from a stubborn air pocket in the heater core or something that would set it off occasionally. The mayo? Idk probably from not driving hard as much as I usually do.

If you really haven't overheated the car I would not be too worried.
So you suggest to take a look at the oil filter - that sounds to me like a good idea, thanks. Here in SoCal it is not common to see this kind of condensation, which people in colder climates have to deal with during the Winter. Here's a random pic from my valve cover and VANOS job for comparison:


I also did check the spark plugs while doing the leak-down test - all six of them look fine.

I don't think there is any chance this was an air pocket though. My last cooling system job was in September - replaced a leaky thermostat. Since then I've not touched the cooling system except to look under the ET cap before long trips (always found the coolant at proper level).
However, since the first low coolant light the level keeps going down at what appears to be an increasing rate...
 

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That small amount of milkshake at the oil cap is completely normal for these cars, and nothing to be alarmed about by itself. You should drain and check your oil for signs of coolant, and as mentioned, check the oil filter. If it's not visually obvious, you can send it off to be tested or perform other tests of your own, like the splatter test, or this one: https://www.youtube.com/watch?v=A8duzWvjBzY

Coolant leaks aren't always in obvious places, so for checking that, I'd suggest letting the engine warm up, then park and open the hood while running, and look for any steam.
 

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Appears to be a classic case of a soft thermostat causing the engine to run too cool, short driving trips (how far do you drive one way each day?) and possible coolant leak at the lower temperature sensor mounted in the lower radiator hose. You will not see this leak, it only leaks when the engine is cold and the O-ring that leaks need to be replaced every 5 years. I see you replaced the thermostat a year ago, however, this by no means the engine is getting up to temperature and that the thermostat is in fact still working properly and if you make trips less than 20 minutes one way and never get the car out for 45+ minute drives this will happen because it takes about 3 times longer for the engine oil to get up to temperature than the coolant.

Suggest you read this carefully - Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Replace the O-ring on the temp sensor in the lower radiator hose, this requires no tools, on a cold engine leave the expansion tank cap in place, vacuum in the crankcase will keep all but maybe 1 cup of coolant from leaking out.

Lower hose temp switch O-ring - BMW #13621743299

You should also read this thread as the CCV and/or CCV hoses may need to be replaced along with the dipstick tube probably needs to be cleaned out as well. The car is of the age all of these items are in need of replacement - Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Also read this, Mayo need to also be managed - http://forum.e46fanatics.com/showthread.php?t=1118566
 

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Drain the oil for inspection. If your losing that much coolant into the oil you'll see it when you drain as it won't just be a couple of milky streaks your oil will look like a light chocolate milkshake. If you can after draining it, pour it into a water bottle jug (clear). The oil and water will separate and you'll see exactly how much of each is in there.
 

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Oil fill cap mayo is, as jfoj has noted, not uncommon in these engines. I recommend you take the car on a 20mile+ trip on the interstate. Let the engine sing in the 3000-3500rpm band. That'll get rid of the mako. As far as loosing coolant, I bet it's not getting into the oil. Your best option is, as mentioned, to have coolant checked for combustion remnants. This is a quick and cheap test. Then, see if you can add a fluorescent dye to the coolant to find the leak. At that mileage I bet the hard plastic hoses under the intake are going bad.

I've never been a fan of the Stewart water pump. It increases water pressure as it pumps 20% more coolant than an OEM pump. I say ditch it.
 

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Isn't the oil pressure greater than the coolant pressure? All times oil and coolant have met in my cars, the mixing of fluids was always in the cooling ststem and not in the crankcase.


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That makes me think that you might have condensation in your crank case rising to the top


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That makes me think that you might have condensation in your crank case rising to the top
This is exactly the problem, these engines have 7 quart oil sumps and the oil often never gets up to proper temperature to "cook" out the condensation. This is due to weak thermostats and short drives, also a faulty CCV system and hose does not help matters.
 

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First order of business is confirm whether or not oil and coolant is mixing. Add dye to the oil and see if it makes it into the coolant. Or vise versa. Buy UV dye kit for $20

Then, if confirmed, you might have a headgasket leak (most common scenario, probably), particularly if you're seeing leakage in one of your cylinders over time (leak test).

Sorry, bud. Hope that's not the case. But in SoCal driving, particularly with your verified good water temps, I don't see how that mayo can be attributed to your commutes. Let us know what you find.
 

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Discussion Starter #16 (Edited)
That small amount of milkshake at the oil cap is completely normal for these cars, and nothing to be alarmed about by itself. You should drain and check your oil for signs of coolant, and as mentioned, check the oil filter. If it's not visually obvious, you can send it off to be tested or perform other tests of your own, like the splatter test, or this one:
Coolant leaks aren't always in obvious places, so for checking that, I'd suggest letting the engine warm up, then park and open the hood while running, and look for any steam.
Unfortunately this is not a small amount of milkshake for SoCal. I have never seen any amount of it my ten years of E46 ownership.
There is not a drop of coolant anywhere under the car, the underside of the engine is dry, I spent a considerable time looking for leaks with the engine running or not.

Appears to be a classic case of a soft thermostat causing the engine to run too cool, short driving trips (how far do you drive one way each day?) and possible coolant leak at the lower temperature sensor mounted in the lower radiator hose. You will not see this leak, it only leaks when the engine is cold and the O-ring that leaks need to be replaced every 5 years. I see you replaced the thermostat a year ago, however, this by no means the engine is getting up to temperature and that the thermostat is in fact still working properly and if you make trips less than 20 minutes one way and never get the car out for 45+ minute drives this will happen because it takes about 3 times longer for the engine oil to get up to temperature than the coolant.

Suggest you read this carefully - Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Replace the O-ring on the temp sensor in the lower radiator hose, this requires no tools, on a cold engine leave the expansion tank cap in place, vacuum in the crankcase will keep all but maybe 1 cup of coolant from leaking out.

Lower hose temp switch O-ring - BMW #13621743299

You should also read this thread as the CCV and/or CCV hoses may need to be replaced along with the dipstick tube probably needs to be cleaned out as well. The car is of the age all of these items are in need of replacement - Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Also read this, Mayo need to also be managed - http://forum.e46fanatics.com/showthread.php?t=1118566
Hi jfoj, I wish it was a simple thing such as a soft failing thermostat or an o-ring leak. It's not. I am familiar with your threads and I did check the operating temp - the engine warms up fast and reaches 97C in less that five minutes from cold start. CCV, hoses, engine gaskets - all this is taken care of.

Oil fill cap mayo is, as jfoj has noted, not uncommon in these engines. I recommend you take the car on a 20mile+ trip on the interstate. Let the engine sing in the 3000-3500rpm band. That'll get rid of the mako. As far as loosing coolant, I bet it's not getting into the oil. Your best option is, as mentioned, to have coolant checked for combustion remnants. This is a quick and cheap test. Then, see if you can add a fluorescent dye to the coolant to find the leak. At that mileage I bet the hard plastic hoses under the intake are going bad.

I've never been a fan of the Stewart water pump. It increases water pressure as it pumps 20% more coolant than an OEM pump. I say ditch it.
The hard plastic hoses are not replaced yet. I spent extra time trying (and hoping) to find leaks at the driver side or the back of the engine, but it's dry.
I perfectly understand that people can have strong opinions on aftermarket parts such as the Stewart pump, but let's keep the thread focused on the issue. I don't drive the car hard anyway, so the supposedly increased coolant pressure should not be a major concern.
Also need to mention the car has not seen a short trip for years - the shortest one way route for me is six miles, then I drive back before the engine had time to cool down. In the past ten years of driving an E46 in this climate, there has never been any mayo to manage.
 

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Discussion Starter #17
Drain the oil for inspection. If your losing that much coolant into the oil you'll see it when you drain as it won't just be a couple of milky streaks your oil will look like a light chocolate milkshake. If you can after draining it, pour it into a water bottle jug (clear). The oil and water will separate and you'll see exactly how much of each is in there.
Alright, you convinced me. I will drain the oil and will check how much water is in there. If all that coolant went into the oil, there should be quite a bit of water in it even though the O2Pilot mod should help remove at least some of it. Anyway, if there is one thing I know, it's how to separate water and organic phases - I do that at work often.
It will take a few days until I can get under the car again, but I'll post the result when it's done.

First order of business is confirm whether or not oil and coolant is mixing. Add dye to the oil and see if it makes it into the coolant. Or vise versa. Buy UV dye kit for $20

Then, if confirmed, you might have a headgasket leak (most common scenario, probably), particularly if you're seeing leakage in one of your cylinders over time (leak test).

Sorry, bud. Hope that's not the case. But in SoCal driving, particularly with your verified good water temps, I don't see how that mayo can be attributed to your commutes. Let us know what you find.
This will be the next thing to do if I can't see water in the oil.
 

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Discussion Starter #18 (Edited)
Isn't the oil pressure greater than the coolant pressure? All times oil and coolant have met in my cars, the mixing of fluids was always in the cooling ststem and not in the crankcase.
Yes, that makes perfect sense, but it's not what I see in this current situation.
This is why I asked if anyone has seen coolant leaks at the timing chain cover steel gasket. This is one place where the coolant is at higher pressure than the oil - crankcase vacuum on the passenger side, water pump pushing hot coolant in a pressurized compartment on the driver side...
 

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I guess if you were to take off the cover to check, you'd have to get some gaskets and a new tensioner.

What makes you think the timing case has less pressure then the rest of the motor, though? It's not sealed off from the rest of the crank case


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Discussion Starter #20 (Edited)
I guess if you were to take off the cover to check, you'd have to get some gaskets and a new tensioner.

What makes you think the timing case has less pressure then the rest of the motor, though? It's not sealed off from the rest of the crank case
Not sure I understand this. I didn't mean to say that the timing chain compartment is isolated from the rest of the crankcase. I compared the pressure in the crankcase to that in the coolant passages.
The oil passages in the block and the head of course are under even higher pressure while the engine is running.
 
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