1998 Pathfinder-How to Remove/Replace Downstream O2 Sensors?

[Alibireason]

I had recently posted asking how to get the downstream O2 sensors snaked up thru the engine bay to where they plug in.

I was just under the vehicle with the O2 socket and noticed there is no room at all to get it connected to the wrench to loosen it. Passenger side I was not even able to slip the socket around the sensor...driver side I could fit the socket over the sensor but no room at all for the wrench either. The small section of CAT heat shield seems in the way as well.

My question is what is the trick and what tools do I use to get these sensors removed? My only thought is an open ended wrench (?size of wrench?), but with the heat shield in the way it doesn't seem like I'd have much room. Should I be spraying it occasionally with PB Blaster to help as well?

Thank you.

[AZhitman]

Definitely PB Blaster (or an ATF/brake cleaner mix).

I'm not able to picture the issue, but if you're using an 02 sensor socket and still can't get at it, it might be easier just to drop the downpipe and do the R&R on the bench.

[Alibireason]

I was able to loosen both sensors very easily after I realized I was using the wrong O2 socket. I had initially used the longer one, but then I realized I also had a shorter, stubbier one that has the place you insert the wrench into off to the side as opposed to on top, giving me all the room I needed to remove the sensors.

I'd like your opinion on ordering the right pair.
On Rockauto I found: BOSCH 13264 Downstream Right; Automatic trans. & BOSCH 13257 Downstream Left for 24$ a piece.
My local shop has on their website a variety of Bosch sensors some with different product numbers that seem to be the same part at 55$ a piece.
Will the Rockauto pair work just fine?

[AZhitman]

My guess is the local store has the same ones, just marked up. I've always had good luck with RA.

Nicely done!

[Alibireason]

I got the O2 sensors installed. Using the 3 ft long string worked perfectly. With the passenger side it was seemingly hooked into a spot that I couldn't get it out til I figured out there is a tiny gap and the cable came through. Pulling it up took some time. The driver side I didn't notice til I was installing it that the tip of the sensor was different than the one I took off. Instead of holes it was lines.
The code hasn't come back and it runs great with new O2s, Starter, and Alternator.

I do have a a concern I noticed as I was sticking my arm up into the engine on the left (driver) side to unclip the O2 sensor. I took a pic of it while I was under the car. I noticed coolant coming out of what seemed to be a bolt. Any idea why and where (I'm not sure exactly what the wet area is) it could be coming from?

[mdmellott]

I noticed coolant coming out of what seemed to be a bolt. Any idea why and where (I'm not sure exactly what the wet area is) it could be coming from?

That's a mounting bolt for something I can't quite make out, but that's not the source of the leak. Clean up the area with brake cleaner so it's good and dry, then run the engine for a bit and see if you can spot where the leak is coming from.

[Alibireason]

[/img]Ok sorry for the delay it seemed to rain every time I had a moment to check it out. I was able to wipe off most of the moisture, but it was tricky getting my arm up there to reach all the nooks and crannies. I then warmed the car up for about 7 minutes and checked again. It seemed as if a bit of moisture was forming around the washer that the bolt holds on, as well as the nook just to the right of it. It did not come back as bad as before I wiped it off. I will be driving it around town today and then will check again tonight.
I hope this pic gives better perspective of it's location. I took it before I wiped it off. I slid under the car from the front driver's side, and you can see on the left side of the pic the wires coming from the O2 sensor. It doesn't seem to be leaking onto the ground, it's just wet with what looks like coolant.

[Alibireason]

I also have an slight oil leak coming from just behind the starter. The lower starter bolt also had oil on it. I have only driven about 20 miles since I've gotten the car running and the leak has returned to the same spot since initially cleaning it. I'm just wondering what could be causing oil to leak in this location (from view of pic, oil pan and starter would be just below this angle). The black dot and far bottom right of the pic is also a drip of oil.

Oh and of course the ABS light has turned on and off twice in the 20 miles I've driven. It is currently off. The brake fluid was about a quarter inch low so I topped it off. I checked for continuity on the 40a ABS fuse in the fuse box of the left side of the engine and it sung like a soprano. If topping off the fluid and checking the fuse doesn't solve this could it be the ABS module, brake pads (I replaced in 2021 and they have about 25k on them), or something else? Thank you in advance.

[Alibireason]

I drove it about 30 miles today. The ABS light has NOT come back on. After it cooled down I went underneath and saw that there is moisture coming from the area I drew lines on in the pic.

[mdmellott]

... It seemed as if a bit of moisture was forming around the washer that the bolt holds on, as well as the nook just to the right of it.

That looks like your exhaust manifold and one of its mounting nuts. The gasket area you see the coolant seepage coming from is your head gasket. A blown head gasket requires is a major engine dismantling to replace it. You can try some snake oil head gasket leak stopper but it's only a matter of time before the small leak becomes a wrecked engine.

[mdmellott]

I also have an slight oil leak coming from just behind the starter. The lower starter bolt also had oil on it. I have only driven about 20 miles since I've gotten the car running and the leak has returned to the same spot since initially cleaning it. I'm just wondering what could be causing oil to leak in this location (from view of pic, oil pan and starter would be just below this angle). The black dot and far bottom right of the pic is also a drip of oil.

Oh and of course the ABS light has turned on and off twice in the 20 miles I've driven. It is currently off. The brake fluid was about a quarter inch low so I topped it off. I checked for continuity on the 40a ABS fuse in the fuse box of the left side of the engine and it sung like a soprano. If topping off the fluid and checking the fuse doesn't solve this could it be the ABS module, brake pads (I replaced in 2021 and they have about 25k on them), or something else? Thank you in advance.

Leaky rocker cover gasket or a leaky rear engine crank shaft seal are the likely suspects of this oil leak. I don't know what to make of the ABS light turning on and off. The leaking head gasket is a critical issue.

[Alibireason]

Thank you very much mdmellott! Boy these problems are cascading! Weighing value-to-me of vehicle vs cost to repair I'm really losing hope in the longevity of this car to me. I paid $1000 for it in 2019 and have put about 35k miles on it (It now has 247k miles). It has helped me move residences a couple times, as well as just moving large items and not having to rent a truck. Besides transportation, it's biggest value to me has come from you and the other knowledgeable people on this website that have helped tackle problems along the way, saving me thousands in repair costs. I have replaced brakes/rotors, front wheel bearings, starter, alternator, 4 O2 sensors, upper/lower/front/rear control arms, ball joints, tie rod ends/boots, all fluid changes, transmission fluid/filter, EGR codes, and more that are not coming to mind. Before this I had only ever changed oil. I now feel armed with basic skills (and tools) that should save me thousands of $$ in the future as well as being able to help friends and family. For this I am EXTREMELY grateful for you and the people that took the time to help guide me through these situation. THANK YOU!

With that said, going forward I would like to ride this out to the end without investing in major repairs. It now starts superbly and drives extremely well (except for humming, has lots of power). The fluids leaking do not leave puddles at all. The big ? I am facing now is do you have an idea of what to expect as these problems get worse? Will the leaks gradually get worse? Will I start to hear and feel things get worse? Could these issues cause it to break down today, hypothetically?

[mdmellott]

Could these issues cause it to break down today, hypothetically?

The head gasket will continue to leak and only get worse. If it is only leaking to the outside, a head gasket stop leak product like BlueDevil Head Gasket Sealer might stop it up. I have personally never used this type of product. A friend of mine, back in the '80s had an old Mercedes with leaking head gaskets. He used Bar's Leak, or maybe some other brand, to try and stop the leaks but it ended up getting into the crankcase and seized the engine. Towed it away and never saw it again. I had an old beat-up Honda Civic back in the early '90s with leaking head gaskets that eventually leaked catastrophically into the engine, turning the oil in the engine into a chocolate milkshake as it died while I was driving. Towed it home. Rebuilt the entire engine. It ran beautifully afterwards, then my niece totaled it in a wreck.

Whether you use a gasket sealer or not, there is a risk of wrecking the engine. It all depends on how far gone the gasket is. If you do use a sealer/stop leak product, be prepared for the worst and hope for the best. You might get lucky.

[mdmellott]

If that oil leak is coming from your rear crankshaft seal, Lucas Oil Stop Leak might help to swell the seal so it slows the leak or stops it completely, at least temporarily. I have used this product several times on my Pathfinder and I can attest to its effective work on dried out seals that leak a little. I use it just to slow down the inevitable.