[BeastMode335i]

So I was hit with the oil in coolant situation last week, when my oil cooler gasket decided to RIP. I replaced both the oil cooler gasket and the OFHG's, along with changing the oil + filter yesterday, but now I'm left with the fun task of removing the oil from the coolant.

After the parts were fixed, I began to flush the cooling system, which has drained out quite a bit of the oil mixed in the coolant. The caveat however, is that now after 5 full flushes/drains/bleeds of the system, I'm still able to dip a paper towel in to the reservoir and pull significant amounts of dark black oil out. After about 30 attempts at sticking paper towels in there to absorb it, the amount of oil goes down quite a bit, to where I'm almost pulling out clear liquid, but as soon as I top off the system and bleed it again, it's as if I hadn't put a dent in the job and I'm back at square one of this process.

I'm sure there's quite a bit of oil mixed in all of the coolant passages, but what would be the best/fastest way to flush out this remanence of oil? I thought about a backflush, but wasn't sure if I could do that on this engine w/o breaking anything. My thought was stick a garden hose on that lower corner line that I've removed, and open the cap on the reservoir to just let all that oil float up out the top. My hope is that someone has a less messy idea that will get me ahead of the game. I bought this Prestone Cooling System cleaner, but before I use chemicals I'd love to hear what others have had success with.

Thanks!

[yupetc]

There are coolant flush additives you can use to emulsify the oil if you're flushing it cold. Alternatively, I've used a 1:4 ratio of simple green and distilled water and did 5 flushes first, then 5 more flushes of distilled water after that using just the electric water pump flushing method. After all this, there will still likely be a film of oil left to be found. I've had to run the engine to operating temperature on just water and flush that 5 more times to get to an acceptable coolant purity. By the end of all this, the coolant reservoir ,being the highest point of the cooling system, gets replaced and I was able to do two more 1000 miles interval flushes to get the last visible trace of oil out. This happened on one of my customer's X5. I've also done plenty of similar work on VW's EA888 cooling systems. Their oil cooler is notoriously failing to have a brown-ed coolant reservoir.

The only worry I have while using the electric water pump to help circulate fluid during each flush is that I did a lot of it in just soap and distilled water. It wasn't until I get most of the oil out before I start using the 50:50 BMW coolant. And I can tell the lubricity is very different between just water and the 50:50. So how much damage is done to the pump due to absence of lubricity is unbeknownst to me.

[Jvac]

Originally Posted by yupetc

There are coolant flush additives you can use to emulsify the oil if you're flushing it cold. Alternatively, I've used a 1:4 ratio of simple green and distilled water and did 5 flushes first, then 5 more flushes of distilled water after that using just the electric water pump flushing method. After all this, there will still likely be a film of oil left to be found. I've had to run the engine to operating temperature on just water and flush that 5 more times to get to an acceptable coolant purity. By the end of all this, the coolant reservoir ,being the highest point of the cooling system, gets replaced and I was able to do two more 1000 miles interval flushes to get the last visible trace of oil out. This happened on one of my customer's X5. I've also done plenty of similar work on VW's EA888 cooling systems. Their oil cooler is notoriously failing to have a brown-ed coolant reservoir.

The only worry I have while using the electric water pump to help circulate fluid during each flush is that I did a lot of it in just soap and distilled water. It wasn't until I get most of the oil out before I start using the 50:50 BMW coolant. And I can tell the lubricity is very different between just water and the 50:50. So how much damage is done to the pump due to absence of lubricity is unbeknownst to me.

Great info for someone who's hoping this won't happen to me.

[SlumsToMills]

My OFHG is failing too and ive been leaking oil for a few months now. However, now I'm starting to see my coolant reservoir with oil. Doesnt seem like its too bad yet but there is definitely some.

I was wondering whats the best way to flush too but it seems like no one knows anything concrete. How does BMW techs deal with this? We all know tons of customers have probably had the same issue.

I bought some LiquiMoly coolant flush hoping that would help. I will do the job to replace my OFHG and cooler gasket this week then flush.

Whats the process for flushing coolant while its still hot? Whats the best hose to flush from while the coolant is warm/hot without getting burned? I cant find any info on that....

[yupetc]

Originally Posted by SlumsToMills

My OFHG is failing too and ive been leaking oil for a few months now. However, now I'm starting to see my coolant reservoir with oil. Doesnt seem like its too bad yet but there is definitely some.

I was wondering whats the best way to flush too but it seems like no one knows anything concrete. How does BMW techs deal with this? We all know tons of customers have probably had the same issue.

I bought some LiquiMoly coolant flush hoping that would help. I will do the job to replace my OFHG and cooler gasket this week then flush.

Whats the process for flushing coolant while its still hot? Whats the best hose to flush from while the coolant is warm/hot without getting burned? I cant find any info on that....

You can activate the electric pump manually to initiate the bleeding sequence and use that as a way of getting your coolant out. each time you do this, you'll get about 1/2 gallon out of the reservoir and it takes about 2 or so gallons for the entire motor. You'll just have to pull out the little return hose from reservoir and direct it into a dispel bottle. And while you're doing it this way, you'll also need to add the coolant flush mixture into the reservoir to keep the level above the minimum sensor trip signal (If it senses low coolant level, bleeding sequence will stop).

If you're going to run this procedure while the engine is still hot, make sure to use Polypropylene bottles to contain the fluid. PET bottles will deteriorate quickly upon temps above 145 deg-F and HDPE will have issues at temperatures above 180-190 deg-F. PP, HDPE, and PET are most common plastic materials you'll find off the shelves everywhere, so just mind the differences. PP should be your pick for high temp fluid containers. And there are different wall thicknesses to bottles, the thicker the better if you're working with something hot. You should never try to drain any coolant at boiling temperature. I'd say between 120-150 deg-F should be where you want to operate the flushes to get the oil out. I find it best if you're working with nearly hot coolant that has some sort of flushing compound added to it, Liquid Moly coolant flush is a great choice.

Also be ready to do this for many days because even if you are able to completely flush and displace the coolant in volume, you'll always be left with a thin film of oil still in the system. I had to perform a flush every few hundred miles to get that last bit of oil out (I added about 8-onze coolant flush additive during those to help emulsify and catch the oil). Lastly, after you get the bulk of the fluid flushed and cleaned, you'll be urged to change out your reservoir bottle (mine's see-through, so it's all browning badly) Even after I clear the fluid out, the brown is stained inside the reservoir bottle. I pretty much run about 5 flushes amongst 600 miles before I put a new bottle in, and from that point on, no more stain and no more oil to be found. Hope this helps.

[Polo08816]

Originally Posted by SlumsToMills

My OFHG is failing too and ive been leaking oil for a few months now. However, now I'm starting to see my coolant reservoir with oil. Doesnt seem like its too bad yet but there is definitely some.

I was wondering whats the best way to flush too but it seems like no one knows anything concrete. How does BMW techs deal with this? We all know tons of customers have probably had the same issue.

I bought some LiquiMoly coolant flush hoping that would help. I will do the job to replace my OFHG and cooler gasket this week then flush.

Whats the process for flushing coolant while its still hot? Whats the best hose to flush from while the coolant is warm/hot without getting burned? I cant find any info on that....

I've talked to them about this issue on a different platform.

They flush it with dishwashing detergent until they get all the oil out of the system.

And then they'll flush it with distilled to get the detergent out.

[SlumsToMills]

Originally Posted by yupetc

You can activate the electric pump manually to initiate the bleeding sequence and use that as a way of getting your coolant out. each time you do this, you'll get about 1/2 gallon out of the reservoir and it takes about 2 or so gallons for the entire motor. You'll just have to pull out the little return hose from reservoir and direct it into a dispel bottle. And while you're doing it this way, you'll also need to add the coolant flush mixture into the reservoir to keep the level above the minimum sensor trip signal (If it senses low coolant level, bleeding sequence will stop).

If you're going to run this procedure while the engine is still hot, make sure to use Polypropylene bottles to contain the fluid. PET bottles will deteriorate quickly upon temps above 145 deg-F and HDPE will have issues at temperatures above 180-190 deg-F. PP, HDPE, and PET are most common plastic materials you'll find off the shelves everywhere, so just mind the differences. PP should be your pick for high temp fluid containers. And there are different wall thicknesses to bottles, the thicker the better if you're working with something hot. You should never try to drain any coolant at boiling temperature. I'd say between 120-150 deg-F should be where you want to operate the flushes to get the oil out. I find it best if you're working with nearly hot coolant that has some sort of flushing compound added to it, Liquid Moly coolant flush is a great choice.

Also be ready to do this for many days because even if you are able to completely flush and displace the coolant in volume, you'll always be left with a thin film of oil still in the system. I had to perform a flush every few hundred miles to get that last bit of oil out (I added about 8-onze coolant flush additive during those to help emulsify and catch the oil). Lastly, after you get the bulk of the fluid flushed and cleaned, you'll be urged to change out your reservoir bottle (mine's see-through, so it's all browning badly) Even after I clear the fluid out, the brown is stained inside the reservoir bottle. I pretty much run about 5 flushes amongst 600 miles before I put a new bottle in, and from that point on, no more stain and no more oil to be found. Hope this helps.

Holy crap i just did the job yesterday and today. I’m like 24 hours in and after 5 distilled water containers full of flushes, I still have oil in the coolant system.

I tested dish soap vs laundry detergent and I am noticing that laundry detergent seem to get more oil out.
I only add 2-4 drops of each to the distilled water container from walmart.

Tomorrow, i will flush with a 25%-45% coolant mix while its hot. eventually, I use the liquimoly coolant flush nearing the end.
I have only been flushing from the right most bottom radiator hose which is easy to get to and pull off.

Maybe i should try the feed line to the expansion tank… hmm what your results with explansion tank feed line vs most bottom hose? Which got more oil out?

[yupetc]

I didn't get to do the bottom hose method because the return feed line actually does the trick very well as-is, for me, at least. Couldn't really shed some light on the bottom hose method, but as far as a choice being easier to flush the coolant, I had always resort to using the return feed line to the reservoir method. Even when I get the engine hot and driven a few miles, I only wait between 30-60 minutes to the temp to drop and I can use the return feed line to the reservoir without turning on the whole motor; just run the bleeding procedure and that'll get me some oil out.

My logic is that oil has lighter density, it'll tend to reside at the highest position, so at the end of the day, flushing it through the bleeder line makes sense to me as it comes from the top of the radiator, pretty much the highest position possible besides the reservoir itself. Hope my input helps.

[SlumsToMills]

Originally Posted by yupetc

I didn't get to do the bottom hose method because the return feed line actually does the trick very well as-is, for me, at least. Couldn't really shed some light on the bottom hose method, but as far as a choice being easier to flush the coolant, I had always resort to using the return feed line to the reservoir method. Even when I get the engine hot and driven a few miles, I only wait between 30-60 minutes to the temp to drop and I can use the return feed line to the reservoir without turning on the whole motor; just run the bleeding procedure and that'll get me some oil out.

My logic is that oil has lighter density, it'll tend to reside at the highest position, so at the end of the day, flushing it through the bleeder line makes sense to me as it comes from the top of the radiator, pretty much the highest position possible besides the reservoir itself. Hope my input helps.

I like that. I’ll try that next and see if more comes out.
Using some Preston coolant flush solution and running the engine hot 20-30 minutes idling and letting the coolant cool to 150°F, i was able to get even more gunk out. For those who may come upon this post in the future, pulling the hose or reservoir cap at 150° is fine as long as you have some nitrile gloves. I havent used the liquimoly coolant flush yet as im still waiting to use that last.

Good news is now my thermostat seems to be functioning again after all these flushes so im not going to install the new one i bought yet. Fault code for that is gone and my oil temp gauge is showing again. (This wasnt showing before, no one ever said that flushing oil from the coolant would fix this problem)