the rear main leak

[brucecooner]

I understand that a rear main leak is a common issue with 4.0's around 200K.

 

Mine is nearing the 200K mark and she's got a pretty good drip going under there.

 

I also understand a leak from the oil filter can sometimes mimic these, but based on its location, coming from the front of the bell housing, I don't think this would be the filter.

 

 

So be honest with me doc, how long does it got?

 

Is this something that drips for a long while?

Or is it a sign of imminent danger that had better be addressed sooner rather than later?

 

I don't have the know how nor tools (nor a shop) to tackle this.

How hard is it to find a shop that can fix this issue?

I did talk to a local shop that specializes in classic and older wheels. The fella there said is was an engine out job, but I just said it was a 4.0, I don't think he knew what vehicle it's in.

Is that the case? Does a rear main repair require extraction of the entire drivetrain?

 

 

 

[Pete M]

double check the back of the valve cover first.  it's common to have a leak there that appears to be an RMS because they drip to the same place.   

 

and no, you don't need to drop the engine or the trans.  I think there's a link about it in the list in my signature. 

[cruiser54]

CRUISER'S MOSTLY RENIX TIPS

REAR MAIN SEAL DIAGNOSIS

OCTOBER 31, 2015 SALAD 3 COMMENTS EDIT

 

I’d be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn’t own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking. Many mechanics, friends, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don’t jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons:

First off, the engine sits nose-up and any oil will run back to the RMS area.

Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber’s adage apply here: “Crap flows downhill”.

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.  A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly. 

 

[brucecooner]

14 hours ago, Pete M said:

double check the back of the valve cover first.  it's common to have a leak there that appears to be an RMS because they drip to the same place.   

 

and no, you don't need to drop the engine or the trans.  I think there's a link about it in the list in my signature. 

 

I've looked up top, but not closely enough to rule it out.

I read the rear main project page linked from your signature.

( http://gojeep.willyshotrod.com/HowtoRearMain.htm )

That's beyond anything I've done to an engine, and I have read it's easy to do it wrong, but that's not as involved as I would have thought.

 

Thanks for the info!

 

 

3 hours ago, cruiser54 said:

CRUISER'S MOSTLY RENIX TIPS

REAR MAIN SEAL DIAGNOSIS

OCTOBER 31, 2015 SALAD 3 COMMENTS EDIT

 

I’d be looking up ABOVE first, and VERIFYING the source of the oil leak YOURSELF.

Everybody, who doesn’t own or have to pay for or perform your vehicle repairs, loves to poke their noggin UNDER the Jeep and come out bearing the false bad news that your RMS is leaking. Many mechanics, friends, and good old Uncle Bob seem to enjoy telling you it’s the rear main seal. Has a catastrophic ring to it, doesn’t it?

A simple leak at the back of the valve cover or other source could produce the same symptoms. You don’t need to be a mechanic to figure this out. If you have good eyesight and a dim flashlight, you’re good to go on your own. Don’t jump on the RMS/oil pan gasket bandwagon right off the bat.

Almost any oil leak on your 4.0 is gonna drip from the RMS area for two simple reasons:

First off, the engine sits nose-up and any oil will run back to the RMS area.

Secondly, the RMS area is also the lowest point on the engine. Simple physics and the old plumber’s adage apply here: “Crap flows downhill”.

Valve cover gasket, oil pressure sending unit, oil filter adapter seals and distributor gasket, in that order, have to be eliminated as possibilities first.  A little tip here. Rather than use a dizzy gasket, use an o ring instead. NAPA #727-2024. Tips 12 and 13 will help you get your distributor back in place correctly. 

 

My non-mechanic brain only contains a map of the major and generally expensive parts of the engine, so it's likely for me to jump to the most catastrophic conclusion.

My eyesight's not what it used to be but I have a pair of glasses and a flashlight.  I'll have to give the forward parts a closer look.

 

Thanks cruiser!

 

 

[Pete M]

wipe you finger across the back of the head right under the valve cover.  check for fresh oil.  if RMS it'll likely leak a bit more at higher RPM, so maybe have someone rev the engine a little to see if it at all increases the drip rate.  or I guess you could place a small cup where the drips fall and rev it yourself.

 

little oil leaks are super common on Jeeps and rarely catastrophic.   

[howeitsdone]

If you're interested in learning the RMS repair yourself it's pretty simple. The hardest part is scraping off an original or cork gasket. Didn't you say the seal was replaced recently? If so, it may not be so bad of a job. It's just a little messy. We don't have a girdle which helps speed things up a bit.

[brucecooner]

I just haven't had a lot of time lately to roll around under my Jeep (which I understand is one of the primary reasons people buy an old Jeep).

 

I did take a closer look at the parts known to leak, and while this guy has all the popular seeps, I wasn't seeing anything like a stream that would lead to the steady drip drip dripping in my driveway.

 

Homing in on the oil sender... (I think that's what this is)

 

Yep, definitely got a leak there.

 

Moving on to the oil adapter... (I think that's what this is)

It's hard to tell from the photo in which everything is black, but there is a layer of grime to the left of the what I think is the adapter seam just above the oil pan.

Don't see any gushers here though.

 

What strikes me is that it appears the bolt holding the adapter in place is a hex head and NOT a T60 torx.

Were some engines given a normal bolt on the adapter instead of a T60? 

The paint on the bolt corners looks touched, could somebody have gone after the adapter at some point and replaced the original piece?

Or am I completely misreading what I'm looking at? (don't put it past me)

 

Also note the bright blue squinches of a recently changed oil pan gasket. 

The mechanic who sold it to me said he had recently replaced the rear main seal and I believe him.

He clearly specialized in XJ's, but whether he changed it right might be up for debate.

 

Anyway, it's hard for me to say whether this particular layer of grime is from the adapter or the sending unit above it. 

I think I'd change the sending unit first, clean everything up, and see what happens in this neighborhood. Take a top down approach I guess.

 

And on to the back of the head...

 

Driver's side, near the back. There's something a bit moist there, not that dark looking but the lighting is not great here.

 

Raking my hand over the backside...

The flash didn't capture it, but that is a bit shiny and fresh, so yep some is sloshing out back there.

 

However, none of these culprits seem to be outputting enough lubricant to form a cascade of drips.

 

I crawled back underneath and looked a bit more closely at the bell housing area.

Looks dry up around the oil pan on the starter side at least.

 

Everything ahead of the bell housing looks dry. 

That...plate (the name of which escapes me) that covers the front part of the transmission is dry as a bone, and I couldn't find any streaks anywhere coming from higher up.

 

Everything running down the engine is dark and grimy, while the drip coming off the bell housing is as clean as the dipstick oil.

 

So I still think it does have a rear main leak, but I've learned some important stuff.

I've learned it actually has several leaks.

 

I don't see anything that's going to keep me up at night though.

Now that I've seen what a rear main seal actually looks like (thanks for the links) I don't think there's any imminent danger of anything turning loose there.

I'm okay dripping on parking spaces while keeping an eye on the dipstick, and working on the higher up leaks first.

 

I do have another question though...

The leaks I found have formed a rich thick coating of grime on top of the starter, which probably ain't good long term.

And I'd just like to get it clean on the sides of the motor down low so I can get a better look at what's really going on.

So, if I took it to the car wash, shot it with some simple green and spritzed at it in that area, how many electrical problems would I generate?

 

 

As a consolation prize for anyone who's stuck with me this far, I took a picture with the hood up.

This is what I saw when I first raised the hood.

Yeah I know this is probably just the result of a power wash and some new hoses before I showed up, but I thought it was rather fresh looking under the hood to be 30 plus years old.  Note all the stickers, and the still visible chalk date on the right of the radiator support "2-17-88".   Part of me feels bad about having to park this in my driveway in the Arizona sun.  But somebody's got to enjoy this thing and that might as well be me.

 

Occasionally I get in a more rational mindset though.

I told my wife the other day part of me thinks I should have bought something I could get straight out on the trails, a lightly used JK, or one of the literally millions of Tacomas roaming the roads.

Then I said, "Man, if I had just spent three or four times as much money I could have had a really nice rig."

And that made me laugh. One payment and it's mine, can't complain about that. And I get to drive something that I love to look at.

 

 

 

 

[cruiser54]

Renix 4.0s used the hex head bolt on the oil filter adapter. 

 

See if the valve cover bolts are loose. Very common. 

If you decide to replace the gasket, us only FelPro blue.

Starters with oil on them indicate oil sender and/or distributor leaking. 

[howeitsdone]

Something to note: Rear main leaks can easily get into the bellhousing and get on the clutch. I just replaced my clutch this week and oil was everywhere from a long-term RMS leak. Not an immediate problem. But when you do find time to roll around under there, it'll be a good idea to replace. The ONLY benefit of driving it like that is the oil covers and protects everything underneath 

 

Like Cruiser said, Fel-Pro blue rubber gaskets.

[AZJeff]

That is a VERY nice old engine compartment that looks pretty close to original production in appearance.   

 

You can wash all the grime off the engine with engine cleaner and some hot water.  A pressure washer works better, but keep it away from anything fragile, like the underhood labels and the like.

 

Once the engine compartment is free of the grime, the source of leaks will be MUCH easier to find.   And added bonus is that fasteners that are not covered in oil soaked grit won't grind up your tools when you work on the vehicle.

[cruiser54]

Rear main seal leaks are not common on the 4.0.

MISDIAGNOSED rear main seal oil leaks ARE!

[brucecooner]

Thanks everyone!

 

I intended to put a wrench on the valve cover bolts and test them for tightness this evening, but family and other required chores got in the way.

I haven't driven it in a week, and when I looked under it this afternoon there weren't any fresh drips in the pan I put beneath it.

But I think that just means I needed to drive to push some more oil through the leak.

 

I think the sending unit is working fine. The gauge shows 20-ish at idle and around 40 cruising warm, which my research indicates is within normal ranges.

If that's the case, would it be okay to pull the unit, clean the threads really well, and re-apply some sort of thread lock to fix the leak?

Or is a replacement unit a better bet?  I'm not confident I could clean one up well enough to reuse anyway.

 

As far as the valve cover, I found this video on youtube with a few pointers, and it looks like these guys are using the Fel Pro Blue others have mentioned.

(I do wish the video had gone into more detail about removing the old gasket from the head surface.)

 

Anyway I've always avoided any mechanical work that called for a pulling gasket, but doing that has been on my bucket list for a long time.

If the blue jobs make it as straightforward as this video indicates, I think I can tackle that.
 

 

 

 

 

 

 

[cruiser54]

Reuse the sender. It's better than the chinese knock off crap available new. Use Permatex #2 on the threads. 

 

While the valve cover is off, do this:  http://cruiser54.com/?p=131

[gogmorgo]

The sender is pipe thread, it seals because it’s tapered. I would just try snugging it up before putting anything on the threads. The threads are also the ground for the sender, so you don’t want to block the path to ground by putting something on the threads if you don’t need to. 

[cruiser54]

That^^ scares me a bit. I'm afraid it might snap off. 

[brucecooner]

I was doing some more sniffing around the sending unit.  I can't detect that it's losing anything where the unit itself screws in.

It seems really dry around those bright colored threads.

 

 

There IS a pretty good coating on the adapter below, but the way it is spread out would seem to indicate it's coming from the part that sticks up which the sending unit screws into, or even farther up.  The picture doesn't show it well but the side of the block is all wet there, and you can see the buildup on that length of wire loom.

 

Going up from there....

 

It looks like a pretty good film all across the block head seam, front to back, so maybe got a seeping head gasket.

I'm not saying the other accoutrements aren't leaking, but this looks like another culprit.

 

If this is the case, should I be worried about imminent blowout, or oil and coolant mixing?

Or is this another of the famously longstanding standard Jeep oil seeps?

 

I did gingerly put a wrench to the valve cover bolts.  I only went with low medium force on the wrench, and only a couple budged , and only slightly at that.

 

 

 

 

 

[cruiser54]

That head gasket seep won't pose any future issues. Look real close at the bottom of the distributor while you're at it.

 

As suggested, it would be good to degrease the engine at some point and monitor any leaks after that. 

Do not get the TPS wet!!

[brucecooner]

Yeah I think the next most logical step is CLEAN IT, so I know what's coming from where exactly, and not just guessing from bad photos.

 

After watching a couple of videos my understanding is that the TPS is part of the throttle body assembly, and the throttle business is all over on the driver's side.

 

Unfortunately I live on a nice street and can't just dump grease into the gutter, so I have to go to a car wash.

For sure high pressure sprayers on the old engine with all of its delicate electrical connections makes me nervous.

I'm thinking "stand way back" and don't get the nozzle up in there.

But my plan is to just NOT spray any water on the driver's side of the engine, at all.

 

And while I do like to know the various sources of oil on the old guy, my impression is that these things at 200K are just going to seep some oil, and it's not something I have to freak out about, right now.

 

There are other more pressing things I should probably be focusing on, notably that irregular idle.

 

 

 

[rokinn]

I've been washing my engines at the car wash for years and never had a problem.  The top side of the engine I never pull the trigger, just what comes naturally from the sprayer when it comes on.  I try to not spray directly on sensitive parts.  Only on the under side do I pull the trigger.  My MJ when I got it took several attemps to do a thorough job.  I started with the most obvious first.  Oil pan gasket & rear main were last.

[Tex06]

My comanche has gotten full blast hose pressure with a Nozzle (not a pressure washer) and engine degreaser many times over the years. Undo the battery, let dry for a few hours in the sun, then hook back up. 

[brucecooner]

Well it weren't the rear main seal.

 

When the clutch started going I suspected that rear main leak might be clutch fluid.

Let me rephrase that, I WANTED the leak to be from the clutch.

But I couldn't see any indication of a leak in the clutch system.

 

Anyway, took it in, told them the rear main might be the source of that leak, but it wasn't.

They called me up to come in and look at it after the transmission was out and the rear main was dry as a bone.

The last clutch service was not well done however, and the mechanic pointed out some issues with it.

So that was good to find, and she shifts nice and smooth again.

 

And cruiser was right, of course.

Misdiagnosed rear main leaks apparently are a common thing.

 

The question for me then is, how could I have correctly diagnosed this?

How does someone figure out that it's their clutch that is leaking?

 

The fluid coming from the bell housing was thick, like oil. Drops of it clung to the housing, and it did not flow like brake fluid.

I think this might have been because it was flowing through the bell housing and picking up enough grime to thicken it, so maybe you can't use the quality of the fluid to determine this.  I should have sat a cup under there and caught some more of it, that might have helped.

 

The master cylinder remained nice and full, and the level didn't change when I pumped the clutch.

The clutch pedal did not feel limp, not even when it was failing to disengage.  It might have gotten a little limper and I didn't notice though.

 

But yeah, apart from total disassembly and inspection, is there a reliable way to debug this issue?

Was removing the dust cover on the bell housing an option that might have lead to any insights?
 

 

[Pete M]

generally speaking, they smell different.   and they feel different between your fingers.  but I'm not sure if that's something that an owner can determine from a couple drops. 

 

the important thing is that the leak is fixed.  

[cruiser54]

this^^. 

and we're glad you got it fixed!!

[cruiser54]

A guy could compare smell of fluid coming from the suspect area with the fluid in the clutch master and engine dipstick. Side by side. 

[gogmorgo]

A rear main leak is typically going to be puking from between the engine and trans, oiling down both the back of the oil pan and trans dust cover. You might get a little inside the bellhousing but it'll be coming off the engine side of the flywheel if it is, probably just about coating the whole thing or leaving a radial drip pattern. It'll also leak whenever the engine is running. The slave cylinder will generally be coming from the middle or back of the bellhousing, and if your clutch is still working it's unlikely to be a huge amount, but if it is, it's mostly just going to leak when you're pushing the clutch pedal, whether the engine is running or not. It's not likely to run up the outside of the dust shield at all, and almost definitely won't be getting on the oil pan. If it's dripping off the oil pan, it'll be engine, if it's dripping off the bellhousing, just about guaranteed to be clutch or trans.

Old brake fluid tends to get pretty dark and scuzzy, but it will almost always rinse away with water. Engine oil won't mix with the water, isn't likely to get flushed away easily.