[jacob12521]

I’m going to DIY my oil filter housing gasket pretty soon and I just have a question about it. I’ve heard that you should do a coolant flush and change your engine oil after doing this job but is the coolant flush really necessary? I do plan to change my engine oil but I haven’t done a coolant flush on any car and would like to know if it is really necessary or if there is any way around this?

Thanks.

[Meeni]

You will loose some coolant during the procedure. Probably it it is leakimg you have over 60k miles so you are due for a coolant change anyway. As good a time to do it now as ever.

It is not completely necessary if you caught the OFHG before it completely turned to ruin and started mixing coolant and oil. The mixture will make an ugly mayonnaise in the oil passages.

[MartinWake]

Dude be careful changing the OFHG, when I did mine I did not flush the coolant.

[relative4]

Originally Posted by MartinWake

Dude be careful changing the OFHG, when I did mine I did not flush the coolant.

What was that supposed to mean?

[PortDover335xi]

I did mine two months ago in my garage, took me 4 hours from start to finish. You do lose about half a litre of oil and the same maybe a litre of coolant. When you detach the hoses and cooler lines have a catch tray underneath the car at the back of the protective shield. I managed to not spill any contents on the floor. I had an old towel as well that I tucked under the alternator to soak up some spillage. Just make sure to do the cooling system prime afterwards. I did it once and it turned out ok. I topped up the reservoir with pre mix I bought from bmw for under $20. I didn't do a flush as the coolant that I did lose was that perfect blue and the oil didn't look contaminated. I must say the job was a success! First job I did to my car, many more to follow.

[ckev70]

Just completed OFHG along with starter in Jan and did not drain coolant or oil. Only oil was leaking and not the oil/coolant mix.
Loosen OF Cap to let oil drain back into block.
Didn't remove any hoses for E90/N54 06' - 325i.

[TGTIW]

Originally Posted by relative4

What was that supposed to mean?

I think he's referencing the fact that a majority of N54s seize immediately after replacing the OFHG..

[dpaul]

Originally Posted by TGTIW

I think he's referencing the fact that a majority of N54s seize immediately after replacing the OFHG..

Perhaps you meant this as a joke in which case I apologize for my lack of humor. In any case this statement is completely untrue. Stop propagating this ridiculous myth around the internet.

OP-- as others have stated, you don't need a coolant flush unless you've got obvious signs of oil in the coolant.

Use a piece of tubing to siphon the coolant out of the reservoir before detaching the OFH. That way you won't spill any coolant on the block or your garage floor.

Follow the suggestion to loosen oil cap and let housing oil drain back to crankcase for a while - but even so, place plenty of paper towels around to catch oil spillage, which will inevitably occur.

[Efthreeoh]

I suggest you drain the coolant AND remove the hose from the OFH. Having the hose off the OFH makes it easier to properly reseat the new gasket. The most important step in the procedure is properly reseating the profile gasket because you want to seat it flat the first time as you torque the OFH old down bolts. Having the tension of the rubber cooling hose attached to the OFH gasket make it more difficult because you are fighting the tension of the hose to keep the housing from moving around. The BMW TIS procedure, 11 42 020Removing and installing/replacing full-flow oil filter (N52), calls for draining the coolant and removing the cooling system hose, just as a point of reference.

Now, the coolant drain and fill on an E90 is about the easiest thing do to on the car, and a lot easier than replacing the OFHG. The only extra work is removing the belly pan and lower radiator shroud, and opening the drain screw. Refilling and bleeding takes about 20 minutes tops. If you don't want to use fresh coolant and you think the coolant in the car is still good, then you can always reuse it if you drain it into a clean drain pan.

[dpaul]

Agreed you want to remove the hose for the reason you describe. But it is completely unnecessary to fully drain, which involves extra work and it is difficult to do without some spillage. The siphon neatly reduces the coolant level below the OFH and you lose zero coolant.

At least on an N54