looking for ideas on a stubborn oil leak (long)

[skeksis]

alright, I'll try to lay out the relevant details, and maybe y'all can help me out. I'm something of a newb at this, but I've been troubleshooting for a while and have ended up stuck.

'87 mr2 NA, 224k miles
runs very strong, no smoke.
I switched it over to mobil1 oil some 10 months ago (probably the ultimate cause of the problem?)
total leak ends up being somewhere in the ballpark maybe 1/2 quart or a little more per month, depending on how much I drive it (~800 miles)

leaks somewhere on the front of the motor, the resulting drip comes from the bottom right bolt of the A/C compressor bracket. it's a slow drip (maybe one drop every 20 seconds) , and only shows up when the motor is running, warm, and rev'd to moderately high rpm for several minutes. oil continues to drip off the engine when parked (small saucer-sized spot), but stops after a short while. I've tried a handful of things, which have slowed the leak somewhat, but not solved so far.

things I've already done:
tightened cam cover nuts (leak originates somewhere below this point)
oil filter adapter sandwich o-rings (needed doing, but wasn't the source of the problem)
oil cooler lines/crush washers (also needed doing, but not the source of the leak)
oil pressure sending unit (was actually leaking, so avoided a dramatic failure there, but didn't solve it)
distributer o-ring (also a small part of the problem)

things I haven't done:
internal distributer o-ring (I know this is leaking a very small amount from when I had the distributer off, but I don't think it's enough to account for the main problem?)
I haven't taken the timing belt cover off to see if there's any evidence of a front main seal leak, but from what I can see there's no oil coming from anywhere around the timing belt cover (except down by the A/C compressor, which is where the leak is most obvious).


SO, I think it's coming from the front of the motor, somewhere in the line from the distributer down past the oil cooler send line, pressure sending unit, and towards the right-front corner of the oil pan. I'm pretty certain it's above the oil pan and below the distributer/oil cooler line.

MY question(s): if the front seal were leaking, would I get these symptoms? are there other spots in the area (an oil pump gasket or somesuch) that might be the source? anything obvious I haven't thought of? Anyway, wondering if anyone's willing to help me brainstorm this? thx.

[LSG2007]

to me that sounds like the front seal. you should just take the seal out and check to see if its hard and has any cracks in it.

[tjmr2]

My two cents thinks that if the Mobile One finished off the front seal the rear main should be pouring oil too. Full Synthetics are notorious for exposing every weak seal in an older engine. Wonderful oils but they weep thru cracks petroleum oils never thought of.

I'd look first at replacing the valve cover gaskets and the nut washers on top. The valve cover gasket replacement isn't quite a no-brainer as you have to fill in some spaces in the front corners with RTV gasket material (I only use "Ultra Black", never had a leak). With an engine as old as yours is your valve cover gaskets may be cracked, or just hard and brittle.

Valve cover gaskets are a lot easier to replace than a front seal with the engine in the car.

While you have the valve cover off you might pull the distributor again and make sure you didn't nick or damage the O ring.

On that side of the engine (above the pan gasket) you have the valve cover gasket, distributor, oil pressure sender, oil filter assembly, oil cooler lines, oil pump and front seal.

Sounds like you have covered everything but the valve cover gaskets.

Pull the top cam belt cover, if it's covered with oil and your cam belt is soaked it's probably your front seal, but I'd bet that it's dry.

Try washing it really good with a degreaser, (up on blocks) then let it dry and start it up and run it for a few minutes, see if you can see the leak, if not shut it off, let it cool and feel for the leak, you should be able to trace it that way.

Good luck!

[skeksis]

thanks gents, here's an update: I pulled the top timing belt cover this morning before work... and it's dry. generally, I happy, 'cause I don't have time to take on the front seal right now. BUT, I still don't know where the leak is.

feeling around (more or less blindly) everything is dry around the cam cover and distributer, except for a couple drops worth on the bottom of the distributer cap heat sheild (I attribute this to the internal o-ring???). as I reach further down, I start noticing a more-fresh wetness underneath the A/C tensioner pulley. oil cooler line is dry, can't really reach the sending unit (behind the A/C bracket). that tensioner pulley is roughly on level with the oil pressure sending unit... but also due south of the distributer heat sheild. any chance that that internal o-ring might really be the issue here? seems to me, that much oil ought to really interfere with the functioning of the distributer? anyway, I'll pull the thing off again soon as I can, and have another look.

[NHinNC]

The 87 I purchased ran, had lotso' leaks in that sme area. The inside of the dizzy is dark brown from leaking a long time internally, so no, I don't think the oil leakin inside it will make make the dizzy function badly for some time

[skeksis]

hmmm.... well, so I put some work into this today. as my most-recent post hinted, I pretty much talked myself into thinking that the internal o-ring on the distributor was my problem. in a fit of desperation and idiocy, I pulled the dizzy, went out to the auto warehouse, and bought a rebuilt model ($160). installed it this afternoon. works marvelously, and is bone dry -- in the vicinity of the distributer. the main leak is pretty much unchanged. I spent a time under the car trying to source the drip - first, there's a pretty good flow off the timing-belt lower and mid cover bolts, in the vicinity of the A/C idler pulley. also... when I had the back end elevated (on ramps so I could get under the car), lying on the ground looking from the wheel well, I could see a drip falling from above the oil pressure sending unit and passing behind the A/C compressor. my guess is that this is the main leak, and when the car is flat on the ground that drip is travels along the block to the timing belt cover, and on down to the pan, where it drips off.

any reason I should still suspect the front crank seal? (despite a dry timing belt?)

given that the oil cooler line is dry... between the sending unit and the dizzy, there is, ummm, the head gasket? showing my inexperience here, but that doesn't really seem likely, does it? what should I try now? I'll try to get it cleaned up and have a better look, but visibility is so dang poor in there that I don't know how much it'll help. :-) thanks.

[LSG2007]

i dunno if this would work or not, but take some engine degreaser and spray where the front seal is then hose it off. and let the car warm up to to point of when it usually leaks and watch to see if you can see if coming from there.