Help Needed Diagnosing Coolant and Oil Leak

[6MTGirl]

Hi everyone! I'm trying to investigate a couple of leaks and would appreciate some help with figuring out where to look and what to replace. Car has 50K miles, cooling system all original, valve cover gasket and oil filter housing gasket replaced with OE BMW less than 10K ago, CPV o-ring replaced as well. Car sat for a few months and after being started and warmed up, I noticed dripping fluid from the belly pan, so I removed the belly pan to take a look.

1) There appears to be a lower rad hose leak, and maybe a leak at the coolant temp sensor. Should I replace the two hoses with OE BMW or are silicone hoses a better option? Should I replace the expansion tank as well? Anything else to look into? I will change the temp sensor o-ring.

2) While the belly pan was off, I noticed an oil leak as well on the passenger side between the high pressure power steering hose and the steering rack. It appears to be coming from above the oil pan. The part of the oil pan behind the steering rack is black with oil grime. What could the culprit be?

3) Does it look like the power steering pressure hose is leaking too?

Thank you in advance.

[bigjae46]

Might be the chain tensioner, VCG, VANOS sealing plate or VANOS gasket.

At least those are places I’ve had oil leaks from.


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[sapote]

50K miles, but what year?

I would think the temp sensor O-ring might leak but not the hose. The OEM hoses are very good.

Re oil leak, I think it starts at the front right of the head. Could be VANOS to head bolts need to be torqued again, or the VANOS solenoid bolts to be torqued again. I'm surprised that the OFHG had been replaced due to leaking, as for some reason the M3 don't have the same leaking OFHG as the non-M E46 cars. When the valve cover gasket replaced, did the mechanic add some sealant to the seams between the VANOS and the head? I would remove the VCG and check at the seams. I doubt the chain tensioner cap is loose, but check with a big socket, 32 or 36mm.

[Arith2]

Chain tensioners like to leak. So do valve covers when RTV isn't used. Start at the top with a clean glove and just work your way around everything. Oil usually moves down and back.

[6MTGirl]

50K miles, but what year?

I would think the temp sensor O-ring might leak but not the hose. The OEM hoses are very good.

Re oil leak, I think it starts at the front right of the head. Could be VANOS to head bolts need to be torqued again, or the VANOS solenoid bolts to be torqued again. I'm surprised that the OFHG had been replaced due to leaking, as for some reason the M3 don't have the same leaking OFHG as the non-M E46 cars. When the valve cover gasket replaced, did the mechanic add some sealant to the seams between the VANOS and the head? I would remove the VCG and check at the seams. I doubt the chain tensioner cap is loose, but check with a big socket, 32 or 36mm.

It's a late '04.

You were right about the temp sensor. I took another look at it from the other side of the air duct and you can clearly see coolant has been trickling down from the temp sensor. Fingers crossed this will fix it and at the same time I'm pretty amazed by how much coolant has leaked out through there!

I don't remember if the OFHG was leaking when I had it replaced, or if that was just my scope creep - that was 6 years ago, even though it's only been 9K miles since then. I am not sure if sealant was used when the VCG was replaced. It was done at an experienced BMW specialty shop, so I can only hope so but can't assume.

I will take another look tomorrow as Arith2 suggested, the timing chain tensioner should be easy to inspect. I assume it's the washer that leaks on it, and I wouldn't have to replace the entire chain tensioner? Thanks for your help!

[heinzboehmer]

I will take another look tomorrow as Arith2 suggested, the timing chain tensioner should be easy to inspect. I assume it's the washer that leaks on it, and I wouldn't have to replace the entire chain tensioner? Thanks for your help!

Yeah just the washer. However, the chain tensioner also likes to collect oil that's leaking from somewhere higher up (VANOS, VCG, etc.). I've even had oil make its way from the bolt behind the thermostat that holds the driver's side timing chain guide to the tensioner.
Point is you should make sure that something else is not the culprit even if you do find oil on the tensioner. Otherwise you might go crazy needlessly replacing the washer multiple times thinking that maybe you didn't torque it properly last time (ask me how I know).

[6MTGirl]

Yeah just the washer. However, the chain tensioner also likes to collect oil that's leaking from somewhere higher up (VANOS, VCG, etc.). I've even had oil make its way from the bolt behind the thermostat that holds the driver's side timing chain guide to the tensioner.
Point is you should make sure that something else is not the culprit even if you do find oil on the tensioner. Otherwise you might go crazy needlessly replacing the washer multiple times thinking that maybe you didn't torque it properly last time (ask me how I know).

Good info! I definitely want to get in there and overhaul the VANOS soon as I haven't done that yet (I might be the only one on this forum ). At that point I may as well replace the VCG too and know everything has been done right.

What *is* the correct torque for the chain tensioner, and can you even get a torque wrench on it? I've found 39ft-lbs in the stickied torque spec doc, and 52ft-lbs in the Buildjournal doc for the primary timing chain tensioner (I'm assuming that's what the leaky one is). I would love to cross-check, but my google-fu yielded "refer to Technical Data 11 31 8AZ", which I haven't been able to find.

[heinzboehmer]

Good info! I definitely want to get in there and overhaul the VANOS soon as I haven't done that yet (I might be the only one on this forum ). At that point I may as well replace the VCG too and know everything has been done right.

What *is* the correct torque for the chain tensioner, and can you even get a torque wrench on it? I've found 39ft-lbs in the stickied torque spec doc, and 52ft-lbs in the Buildjournal doc for the primary timing chain tensioner (I'm assuming that's what the leaky one is). I would love to cross-check, but my google-fu yielded "refer to Technical Data 11 31 8AZ", which I haven't been able to find.

Hmm, looked it up on TIS (that's where 11 31 8AZ is) and the S54 is missing?



50 Nm lines up with what the torque spec doc says, but there's no mention of the S54. Maybe I just don't know how to read that table. Regardless, I haven't been able to fit a torque wrench in there so I've just torqued it by feel.

[sapote]

Chain tensioner cap torque: I snug the cap until it bottoms, then add 1/8 turns. Make sure to clean all sealing surfaces. Personally I wouldn’t remove it to replace the washer; just retorque it.

[Chas3n]

Subscribed.

I’m in the same situation. Replaced chain tensioner (part and washer, very snug) replaced CPV, still leaking, looks like I have a leak from the front and the rear passenger side still.

Checked the bolt under the thermostat housing, was dry. Don’t see any VANOS line leaks, either. Might pull everything apart, again.

[bigjae46]

Subscribed.

I’m in the same situation. Replaced chain tensioner (part and washer, very snug) replaced CPV, still leaking, looks like I have a leak from the front and the rear passenger side still.

Checked the bolt under the thermostat housing, was dry. Don’t see any VANOS line leaks, either. Might pull everything apart, again.

I’d put money on the VANOS sealing plate.


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[Ramps]

The high pressure vanos line to the accumulator can also cause oil leakage that is hard to track down. The oil ends up seeping around the front of the block under the vanos, and down to the steering rack. Yet much of the block is dry. I replaced mine with the updated OE one and cleaned up all the oil and haven’t had any more oil. Took a while to figure out, i had replaced various crush washers and o-rings before i realized it was the line in my case.

[BlAikenstein]

I would recommend covering the electrical components and carefully cleaning the engine bay and undercarriage with a pressure washer, dawn and paint brushes. It’ll be easier to track down fresh oil.

I’m with bigjae on the vanos sealing plate.

[sapote]

Hmm, looked it up on TIS (that's where 11 31 8AZ is) and the S54 is missing?

50 Nm lines up with what the torque spec doc says, but there's no mention of the S54. Maybe I just don't know how to read that table. Regardless, I haven't been able to fit a torque wrench in there so I've just torqued it by feel.

S54 should be same as M50, M52, M52TU, M54 with 70NM = 52 ft lbs.

[2004LSB]

The VANOS high pressure oil line is usually the culprit - - the insulated section that is slightly bendable usually develops a small fracture (I'm assuming through repeated heat cycles) and spews oil all over the headers, exhaust side of the block, and even chain tensioner when the car is running. Replaced it and no more pesky leaks!

The stuff on the belly pan though...that looks almost coolant-like. When was the last time the car had its coolant drained out? With age and repeated heat cycles, the O ring on the lower radiator hose temp sensor usually flattens out and causes a leak once the system becomes pressurized.