V8 Experts! N62 Coolant Leak at Rear of Engine -

[93 525 Paul]

I have 130,000 miles on my 07 550i. I get an occasional spot or line of coolant in my driveway. Very small amounts. So I looked around the water pump and front block weep hole, nothing. I pulled the lower covers last night and see evidence of long term slow leak at rear of engine running down the back of the block and out the passages where the block and bellhousing meet.



Found this video https://www.youtube.com/watch?v=F_gjFZJbAoE
Great video, seems right on point, but it points to either the rear coolant passage cover 5 or the valley cover 1 or both. He says to pressure test the system, but with as inaccessible as the two are, I don't see how you can localize either leak without having the tranny off or the intake off. So, it doesn't seem to be the ubiquitous transfer tube, but looks like a ton of work either way, top end or back of block. Anyone do one or both of these?

[632 Regal]

I would certainly try this first before pulling an engine or trans. I know it's not proper but neither is green antifreeze

[632 Regal]

PS I can't get that video to load.

[Clarksonvalley]

If the 550 is like the 540, there are two aluminum tubes that run from the water pump to the rear of the engine. There are O-rings at each end of each tube - these O-rings are a bear to replace - you need to remove the intake manifold and the valley pan (the valley pan has a gasket). The tubes terminate at a plate at the rear of the engine - the plate also has a gasket.



You can see the rear termination in the picture at the lower right. This is what you see when you take off the valley pan. I have done this repair and it is a PITA. The valley pan gasket must be done perfectly or it will leak.

Tom

[Clarksonvalley]

You also need to remove the water pump before you remove the two tubes - this is a good time to install a new water pump - with 130,000 miles, you are due for a new pump if you have not already had it replaced. If you are really lucky, the rubber hose that connects to the 'coolant collector' is leaking and a new hose would be an easy fix. The hose is difficult to access, but it is possible.



Tom

[632 Regal]

I remember that tube. Mine was leaking where the hose attached, very hard to see. I was able to replace it after removing the expansion tank.

You also need to remove the water pump before you remove the two tubes - this is a good time to install a new water pump - with 130,000 miles, you are due for a new pump if you have not already had it replaced. If you are really lucky, the rubber hose that connects to the 'coolant collector' is leaking and a new hose would be an easy fix. The hose is difficult to access, but it is possible.



Tom

[93 525 Paul]

I would certainly try this first before pulling an engine or trans. I know it's not proper but neither is green antifreeze

It does look green on the bottom of the bell but it had blue BMW coolant when I bought it at 65k miles and it has blue BMW coolant in it now. When the fan motor died, it burst the reservoir so I flushed and filled with new BMW blue coolant.

[632 Regal]

Check the hoses that go to the heater valves (if this applies) I had a few small leaks that trailed down that were very hard to see. The one hose that attaches in the back had corrosion on the aluminum manifold. I had to sand it and paint it to stop the leak.

[genphreak]

Trouble with going in from the top is mostly how many new sealing parts you will need. I'd take the cover off and look at what will be necessary to buy to allow you to remove and inspect more carefully. All the V8s are sealed in the same stupid way (using too much plastic) and I suspect the N engine is far worse- I countenance a lot of care.

And you may find it is not a failed part, rather something that's been leaking a little since new. Though after 9 years of glory all the cooling system's plastics could well just be looking for an excuse to give way...

Wishing you loads of luck from down under!