[N54Society]

I did a coolant flush (DIY) and noticed a little oil in the reservoir tank. I know I had a OFHG leak before but that was repaired. Is it safe to say that some oil remained even after my flush? I'm thinking of flush it again because I only used BMW coolant and distilled water mixed 50/50 (point being it was cheap).

My real question is, how can I effectively remove the remnants of oil? Any chemicals? Will pouring distilled water through the reservoir/radiator clean it out a bit more?

Thanks!

[N54Society]

Does the oil just rise to the top? Can I just skim the top layer from the reservoir? Thanks

[N54Society]

Bump

[paintballdude05]

Skim what you can see off the top, and see if more comes back. The next step after that if you're still getting some and you're concerned would be to empty out the cooling system again, flush it with distilled water and maybe a cleaner, and refill once again once cleaned.

[TheBigYahi]

If you're just flushing you should be able to use distilled water as many times as you want then the 50/50 for the final fill.

[N54Society]

Originally Posted by paintballdude05

Skim what you can see off the top, and see if more comes back. The next step after that if you're still getting some and you're concerned would be to empty out the cooling system again, flush it with distilled water and maybe a cleaner, and refill once again once cleaned.

You mentioned a cleaner. Which cleaner are you referring to? Thanks

Originally Posted by TheBigYahi

If you're just flushing you should be able to use distilled water as many times as you want then the 50/50 for the final fill.

Cool, so prime the water pump with just distilled water and drain until it's clean?

Thanks!

[Efthreeoh]

Oil and water do not mix, so just trying to flush the system with water will not remove the oil. If there is oil in the cooling system you need to use a detergent in the system with water. The detergent breaks down the surface tension of the water molecule and allows the oil to combine with it and that will rid the system of oil contamination.

[paintballdude05]

There are a few cooling system or radiator cleaners out there that you can use, Prestone makes one. I haven't used a cleaner made for that specifically, but I have used dishwasher soap in the past on my winter beater with some success. I'd suggest using the stuff specifically made for cooling systems though, especially since what you're trying to get out is fairly fresh and just oil (not caked on everything). You can use household water for the flush a few times over, then follow that up with at least one fill and drain of distilled, maybe two if you want to be sure that any water left behind is as close as possible to the quality of distilled water. Once the distilled is out of the system fill it back up with new BMW coolant and you should be good to go.

As far as mixing up coolant, I usually try not to waste the distilled (because I'm cheap like that). It depends I guess how much coolant you have and the capacity of your distilled water bottles. Here in Canada I get 4L distilled water bottles and coolant usually comes in 4L jugs. I would poor half of the distilled bottle in the car followed by half of the coolant. What's left gets mixed together in the bottles. You can shake it up a bit if you want, but it usually blends itself pretty good. The stuff that went into the car unmixed will mix itself fairly quickly with one heat cycle. This method ensures you end up with a 50/50 mix.

[N54Society]

Originally Posted by Efthreeoh

Oil and water do not mix, so just trying to flush the system with water will not remove the oil. If there is oil in the cooling system you need to use a detergent in the system with water. The detergent breaks down the surface tension of the water molecule and allows the oil to combine with it and that will rid the system of oil contamination.

I tried to skim some more off today but I couldn't find any more oil. I think that's good thing though. Either way, it doesn't hurt to do another flush so I may go with that.

Originally Posted by paintballdude05

There are a few cooling system or radiator cleaners out there that you can use, Prestone makes one. I haven't used a cleaner made for that specifically, but I have used dishwasher soap in the past on my winter beater with some success. I'd suggest using the stuff specifically made for cooling systems though, especially since what you're trying to get out is fairly fresh and just oil (not caked on everything). You can use household water for the flush a few times over, then follow that up with at least one fill and drain of distilled, maybe two if you want to be sure that any water left behind is as close as possible to the quality of distilled water. Once the distilled is out of the system fill it back up with new BMW coolant and you should be good to go.

As far as mixing up coolant, I usually try not to waste the distilled (because I'm cheap like that). It depends I guess how much coolant you have and the capacity of your distilled water bottles. Here in Canada I get 4L distilled water bottles and coolant usually comes in 4L jugs. I would poor half of the distilled bottle in the car followed by half of the coolant. What's left gets mixed together in the bottles. You can shake it up a bit if you want, but it usually blends itself pretty good. The stuff that went into the car unmixed will mix itself fairly quickly with one heat cycle. This method ensures you end up with a 50/50 mix.

Great explanation! Thank you. I'm going to do exactly what you recommended.

[atikovi]

How will having such a small amount of oil left in the cooling system cause any harm?

[N54Society]

Originally Posted by atikovi

How will having such a small amount of oil left in the cooling system cause any harm?

It likely won't harm anything in the short term but it could contribute to plastic parts wearing out faster. At least, that's what I've read on E90post.