Mystery Oil Leak

[tajvelocity]

99 Mazduh B2500, 2.5L, 5spd., ~125k.

I was under my truck checking out where my exhaust was leaking from because it's loud and is running a bit badly. I found that and while I was under there I found something worse: oil has made it's way down the transmission as far back as the cross member. There are some drips on the ground as well. I'm not talking about a ton of oil but it's fresh and it's noticeable. I hadn't noticed anything until the temps outside dropped into the single digits, but there were no drips where I usually park prior to that.

I read up on possible causes. I haven't replaced the PCV valve yet as I heard if that doesn't function, too much pressure can build up and force oil out. I don't think it's coming from the oil pressure switch as it looks pretty dry around it. There seems to be oil on the other side of the bellhousing I think, on the block side where the trans and block meet, but I don't think it's coming from where they actually meet. It seems wet farther up than that on the engine (drivers) side. It's hard to see anything with the intake manifold in the way and I haven't found a place where I can see if it's coming from the valve cover. I haven't checked the plugs yet (PITA, it's super cold, other excuses...) and the oil on the dipstick looks like oil (no sludge).

So I guess my main question is: what does a rear mail seal leak look like? Will it come from where the trans joins the block? So far it's either looking like it's that or the valve cover gasket, neither of which are going to be cheap. I don't think I'm prepared to drop a transmission on my street in the hood and the valve cover job looks pretty crappy too. That would be especially annoying as I just finished changing the timing belt, water pump, t-stat and radiator about 1.5 months ago and all or most of that would have to be removed again. That job took me forever because I'm no mechanic. I mean I did it and it works (heat is still a little weak ever since but I can live with that) but still.

Sorry for the long post. Just trying to get it all out there so you know what I know.

 

[Mark_88]

If you can see oil on the bell housing and not directly under the front of the transmission then the oil can be coming from the valve cover or the dipstick tube. When it comes out the dipstick tube you have too much pressure and need to check and/or replace the PCV.

It can also be coming from the valve cover vent but not sure where that plugs in on the 2.5. The valve cover vent can get plugged too (with ice) if your oil is foaming. This results also in the oil coming from around the dipstick (or pcv canister or anywhere else it can find a way out).

Start with the PCV...I doubt you have a rear main seal problem if the oil is on top of the transmission...probably valve cover...

 

[tajvelocity]

Thanks Mark. I'll change the oil (or get it changed...it's freaking cold out!), replace the PCV valve and clean it up under there as best I can and report back.

 

[tajvelocity]

Well the PCV valve seemed fine (rattled when shaken). I wiped around toward the back of the motor and front bellhousing area and I'm seeing some more oil. I just noticed some seepage coming from the passenger side toward the top of the motor, possibly from the valve cover. I know this is all fairly vague and kind of pointless without pics, so as long as the rain holds off a bit I'll snap some tonight. Stay tuned for more excitement...

 

[Mikel89us]

The pcv valve isnt good just becuase it rattles.

 

[PetesPonies]

If you are looking for an oil leak get a can of brake clean and some paper towels. Spray the underside of the pan, the trans, the front of the engine etc. Brake clean dries quickly and with a wipe of a towel, should leave it clean enough to see if there is seepage over night. Then after the first short drive, check it again.

 

[tajvelocity]

Ah. Well I replaced it anyway because I bought it for $4 or whatever.

So here's what I saw tonight after work. Starting from the back of the engine on the passenger side, there seems to be some fluid coming from the valve cover:

Odd that underneath that area it's dry. The oil pan is wet from oil because it seems like it's dripping all down the drivers side and making it's way across the bottom of the oil pan:

I wiped away some oil from that flat part where the trans bellhousing (I guess) meets the engine. Sorry if my terminology is a bit off, I don't know my sh*t too well. It's hard to tell because the intake manifold is in the way but I think it's leaking equally or more on the drivers side. There was a drip forming under the oil filter that I just changed Sunday, and I know that thing is on there tight. Drivers side:

And the leaking exhaust that made me get under there and notice the oil in the first place! I guess I owe you a thanks. I mean I would have noticed it anyway but still. I think I can ghetto rig that with that Walker split flange kit and buy me another year, but the oil leak is obviously a bigger concern:

So. Does this pretty much confirm that I have a valve cover gasket leak? I drive mostly highway miles, with some long grades and crazy drivers. Plus I'm late a lot. There is some shifting into 4th at 55 or 60 on some hills and some pedal to the metal. I think higher RPM's could cause it to leak a little more right? I'm not an aggressive driver and I don't beat on it but this truck is slow anyway and the addition of 31's made it way worse so I'm WOT sometimes (btw, I'll trade anyone semi local to 41011 for stockish sized rubber...I should probably say that in the classifieds).

 

[Mark_88]

Could just be VC and it is a relatively simple fix.

Could also be a result of blow-by where the pressure in the crankcase is excessive and it will blow out the weakest point or find a weak point and exploit it.

You can check this somewhat with a simple test...idle your engine and remove the valve cover vent hose that goes into the throttle body then plug that vent hole with your finger or something else (it can be a bit hot there) and release it after a few seconds or longer...if you get a whoooosh sound (you probably won't now because your VC is leaking) then you may have excessive pressure...

Otherwise, changing the VC gasket might make it all work fine but keep checking your oil and watch the dipstick tube and the PCV canister for oil spillage after you change the gasket...once that is sealed properly the oil will look for the path of least resistance if there is excessive pressure.

 

[PetesPonies]

Yeah, change the VC gasket and go from there. Get a good blue one . . with a lip that goes over the sides.

 

[tajvelocity]

I wonder what could be causing excessive crankcase pressure. I performed that test when I changed the oil, at least I think it's the one you're referring to Mark: while changing the PCV I started the truck and put my thumb on the part of the tube that plugs into the PCV valve. There was a lot of vacuum. This is good right? I haven't looked in the intake tube or throttle body yet to see if there is oil residue in there, but I guess I will when I'm changing the VC gasket. I think one of the Felpro kits also comes with an intake manifold gasket (upper?) as well.

Maybe now would be a good time to do plugs and wires. I don't recall when they were done last but it was probably at least 40-50K ago, or maybe 6 years. My mom had the truck before me and had Goodyear do it and I remember spitting up my coffee when I saw the price tag. Anyway if I'm taking the intake manifold off maybe I should just do it. I'd tighten down the VC bolts a bit to see if that would help but you can't really even get to the ones in the back.

I wonder if I can do this in a day. The weather doesn't look promising though.

 

[PetesPonies]

Excessive crankcase pressure comes from one of two causes. If you are not evacuating the normal pressures, them pressure is built up and will causes problems somewhere. Secondly, if the rings are not holding pressure back from Combustion. But . why do you feel you have excessive pressure?

 

[alwaysFlOoReD]

Excessive crankcase pressure could be caused by worn rings, worn valve guides, cracked heads or block, head gasket issues.
You checked the wrong end....check the side opposite where you felt vacuum. If there is pressure pushing your thumb off then you may have excessive pressure.
A compression test along with a leakdown test would give you the answers, but the average joe wouldn't have the tools necessary.
I'd go with the advise given re: Mark_88 and PetesPonies.
I've never worked on a 4 cylinder so can't say if the intake needs to come off or not. Usually If you have enough room to lift the valve cover up 1.5" or 2" you have the room to change the gasket without removing other stuff.
I would change the plugs and maybe the wires and related ignition consumables.
You "should" be able to do this in a day. A second vehicle to do store runs could help.
Good luck,

Richard

 

[tajvelocity]

Ah that makes sense! I'll do that test tonight. I'm concerned about the crankcase pressure because of what people and the internet are/is telling me. I really hope I don't have to change the head gasket. I have neither the tools, the time, a decent place to work on it or the know how to tackle that one. The VC looks simple enough.

 

[Mark_88]

The vent I was referring to is on the top of the VC and you should feel pressure coming out of there in normal operation situations. There should also be vacuum to the intake from the PCV side of things so that is normal.

IIRC, you can remove the VC by just removing the throttle body and not the whole intake. Been a few months since I tore one down (got my current head from an 87 FI Mustang (dang, not the roller rockers but a good head over all) and didn't really watch what I was doing until I got to the head bolts.

Shouldn't take more than a few hours if you have everything you need handy and the weather is good...

LOL...I said that about my head swap but it ended up stretching over three days due to many unforeseen other fixes I had to do...and it was -20 or so even in the garage with a little ceramic heater blowing it's heart out...but it got done.

 

[tajvelocity]

Uh Canada is cold! It doesn't look too bad in Cincitucky this weekend (30 and 36F) but I'll be doing it outside. As long as it doesn't rain or snow I'll probably get cracking on it, assuming Advanced Auto or whoever has the gasket kit. I'll report back.

THX!