[Brian86]

Radiator shops used to offer a flush service. I was never really comfortable with the idea, but then I've never had 'sludge' in my cooling system.

If it was me:

-Fill with water
-Burb/bleed
-Run the engine to operating temp
-Perhaps cycle the pump to 100% for a few minutes while hot
-Immediately drain the coolant hot
-Let the engine cool down
-Repeat.

Of course if the 'sludge' is so bad it could damage the pump..... I'm at a loss.

At some level the stuff never comes out short of *complete* disassembly. My e36 sloshed oil into the coolant about 5 years ago. I bet I've drained and refilled the system half a dozen times fixing things since then, the expansion tank still gets dirty oil floating to the top. Doesn't really cause any long-term problems.

[sonofsun]

OP is breaking new ground here. Hopefully he can remove all oil from his system and post a good DIY guide for anyone else in the future.

[jojojijijojo]

Hey guys,

A quick follow up update:

I had the radiator upper return hose ( that little hose that connected to the expansion tank) clogged somewhere, which was restricting coolant flow and ended up blowing up coolant from the expansion tank cap.

So I bought one of those oil transfer hand pumps, and I pumped water into the return pipe, this solved the clogging issue and I got all the junk raising up from the expansion tank.

So far I have done a dozen flushes. Before every flush I let the car warm up for 5 minutes, then take it on a spin around the block for 30 minutes.

I also used 3 bottles of liqui moly, and that stuff works! It helped liquify all that thick oil and made it easier to flush it along the water.

I still have one final flush to do after going for a little longer ride, but judging from the current situation, I think its safe to say that most of the oil is out.

Anyone knows where I can get a replacement of that small rubber seal that fits the radiator return hose? It is all swollen up and cracked by the oil. Thanks.

[jojojijijojo]

Ok so I have a problem here.

I have been flushing the system regularly and I got to a point where the coolant system was super clean. Been taking many long trips and still the coolant was crystal clear, I was very happy but not for long...

I have a valve cover leak for a while now so my engine oil tends to go low over time. I got the low engine oil warning and I topped up 1 L. I took the car to it's final trip before I completely call it a day and fill the system with BMW coolant, but to my surprise, the expansion tank was all sludgy again like day 1

Apparently as soon as I topped up engine oil, it leaked heavily into the coolant system AGAIN.

I had both oil filter and cooler gaskets changed and torqued to specs, so im at a loss here

[gster109]

I think The gaskets pinched or something, I'd recheck those gaskets. No where else other than the head gasket where the oil & coolant will meet on the n52.

[jojojijijojo]

Originally Posted by gster109

I think The gaskets pinched or something, I'd recheck those gaskets. No where else other than the head gasket where the oil & coolant will meet on the n52.

Thanks for your reply, I have removed both cooler and oil filter gaskets, visually they look fine, but I suspect they are trash quality, I'm going to get original bmw replacements, anything else is a complete waste of time.

[jojojijijojo]

I got this where the Oil filter housing meets with the aluminum head, seems like the previous owners didn't keep up with regular maintenance and I ended up with this. How can I improve this to the point where I can safely put the gasket back on and not have oil leaking back in? It looks like the aluminum all around the coolant intake is all eaten up with tiny holes.

[RayLivingston]

Flushing with coolant is a waste of time. Buy one of the Prestone back-flushing kits, and flush with soapy water (like Dawn dishwashing detergent) until it comes out clean and clear. Then flush with lots of clear water until you're sure all the detergent is flushed out. You'll have to flush the block, the heater, the radiator and the reservoir(s).

[jojojijijojo]

Originally Posted by RayLivingston

Flushing with coolant is a waste of time. Buy one of the Prestone back-flushing kits, and flush with soapy water (like Dawn dishwashing detergent) until it comes out clean and clear. Then flush with lots of clear water until you're sure all the detergent is flushed out. You'll have to flush the block, the heater, the radiator and the reservoir(s).

I already did all of that if you read a couple posts above, flushing is not the issue, the aluminum area where the gasket sits is all rusted and fresh oil keeps leaking back into the coolant system.

Im looking for advice on how to remedy this and fix the uneven part on the aluminum block shown in the picture.

[RayLivingston]

Not rust, corrosion. Nothing to be done for that other than get another oil filter block. If you're really ambitious, you could sand it, with a sheet of wet-or-dry paper on a sheet of glass or other dead-flat surface. But it'll take forever. You could have a machine shop fly cut the surface, but not sure if moving that surface down will cause problems with other parts - I don't recall the parts stack-up in that area.

Best solution, by far, is get another filter block.

[jojojijijojo]

Originally Posted by RayLivingston

Not rust, corrosion. Nothing to be done for that other than get another oil filter block. If you're really ambitious, you could sand it, with a sheet of wet-or-dry paper on a sheet of glass or other dead-flat surface. But it'll take forever. You could have a machine shop fly cut the surface, but not sure if moving that surface down will cause problems with other parts - I don't recall the parts stack-up in that area.

Best solution, by far, is get another filter block.

I'm tempted to go the wet sanding over flat glass route, but still looking for easier options. The corroded side is on the engine block, not the oil filter housing, I don't see how I can get another filter block since its basically one piece with the rest of the upper engine block.

[RayLivingston]

Originally Posted by jojojijijojo

The corroded side is on the engine block, not the oil filter housing

Oops! Of course, you are right. That is MUCH worse. I would try this:

Use a very flat metal or glass plate and plate, and wet-or-dry paper to remove any high spots. Fill any pits with JBWeld. Cut a fairly thick rubber-impregnated PAPER gasket, instead of the stock rubber one. Not an ideal solution, but done properly should hold up fine. Only other viable option I see is strip the block and have that surface machined.

[jojojijijojo]

Originally Posted by RayLivingston

Fill any pits with JBWeld.

Thanks for this! That's actually a pretty good solution. I have searched around and I found many folks fixing their engine blocks corrosion pits with JBWeld and it works great for this stuff.

My plan is to fill all the holes and use a razor to even up the surface, leave it until it cures and lightly sand that area for final touches, then put things back on together and hope for the best.

[jojojijijojo]

Would an RTV like JB weld High Temperature RTV Silicone Gasket Maker work in this case? Im thinking about replacing the OFH gasket with RTV red silicon. normal gasket does not hold anything as if it's not even there.

[charlie_m]

You mean that you filled the pits, cured it, then sanded and it still leaked? Can you confirm what gasket you are using? Augmenting (not replacing) with RTV may be your only choice at this point. I personally have better luck with a filled RTV, like Hondabond HT or permatex ultra grey. Be sure both surfaces are cleaned well with a solvent like acetone or non-chlorinated brake cleaner, then dried.

[RayLivingston]

I would NEVER use any kind of gasket maker on that part. One small silicone "worm" downstream of the filter, and it's goodbye engine.

[PichaDis11]

Originally Posted by RayLivingston

I would NEVER use any kind of gasket maker on that part. One small silicone "worm" downstream of the filter, and it's goodbye engine.

Isn't that why it's recommended to use small beads and allowing it to cure before final torque of the screws?

[RayLivingston]

Originally Posted by PichaDis11

Isn't that why it's recommended to use small beads and allowing it to cure before final torque of the screws?

Look at the actual sealing surfaces on the OFB. They are VERY narrow in places. There is no way to use gasket maker on that and be certain you got enough for a good seal, with no worms created. It's a VERY risky move.

[charlie_m]

Looking at the pic in post #29, it looks to me that corrosion has eaten away the aluminum below the original surface. That has to be filled somehow and then brought back to flush. Best way of course was mentioned earlier, machining it down to fresh material. Filling with a thick (mineral-filled) epoxy, then carefully filing & sanding flat, may be the only in-car option.

[jojojijijojo]

Yes I cleaned up the area then filled pits with JB weld, here are before and after photos, not the best craftsman job but I think its better than what it was.

I can still see and feel there are some areas under-filled, but those are mainly away from the gasket seal and not affecting anything.

Its clear that JB weld filled areas have been stained by oil, except for the lower left corner, which makes me think that the gasket did almost nothing. I still have not put an OEM gasket in there because I was under the impression that it wouldn't solve this problem. I can't get an original BMW gasket where Im located now, I only have access to MAHLE brand, anyone knows if its as good as OEM?

[PichaDis11]

That's pretty good work you did. Hope you'll be able to fill in some more, Mahle is an OE supplier so you should be good. to g