Oil is leaking slowly from the oil filler cap on my '88 744 w/ 225k miles. I replaced the rubber gasket on the filler cap and cleaned the PCV but it still seeps enough that oil drips on the valve cover and down the engine.
Does anyone have any troubleshooting ideas?

Thank You...

Mine was doing this, turns out the small vacuum hose going from the flame trap to the intake manifold was clogged with crud. Replaced it and cleared out the nipple and it stopped doing it.
--
'91 Volvo 740 wagon. A big comfy box.... and a '90 Mazda 626 GT turbo. Heavily modded, really fast.

Forget the posts about messing with the cap... it's only a symptom of teh problem and shouldn't be happening. You mention you have cleaned the PCV and breather box... you're sure, right? Since you don't mention a flame trap I'm assuming this is a turbo, right?

I had a similar problem on my brick, and it turned out to be symptomatic of a lean condition. Basically a mixture problem generated a slight lean condition that was only really apparent and a problem under boost. The more boost I gave it, the worse it would run. If I boosted while this was happening the result (aside form retarded running) was a wet spot arond the filler cap as the higher pressures would push oil past the rings, etc.

If this is the same as your problem I would suggest examining the following:

1) Inspect all pressure side turbo hoses... in fact, just inspect all the hoses closely for any leaks. Look at the AMM to turbo, turbo to int., and int to int. man. hoses, paying particular attention to the low spots where oil can pool and rot the hose.

2) Check that it isn't a bad sensor connection. Disconnect the AMM and KS harnesses frm the sensors, examine them for damage or problems, and then reconnect very deliberately making sur ethey click in place.

3) Check the CBV and make sure it is attached to the holding p,ate firmly wit the allen screws. Soemtimes they can back out and allow teh unit to leak. the CBV is that silver bell looking thing at the front left of the engine with a small hose off the top running over to the intake manifold (across teh valve cover). You might also check to see if teh CBV is bad by seeing if it holds pressure when you suck at the hose from the top.

4) Check that it isn't a bad sensor related to mixture. ECT, KS, AMM, and o2 are the ones to check for proper resistance, etc.

It could also be something big like a broken ring or something, but as long as it runs well otherwise I would look for a sensor or hose problem. BTW, if you run crappy gas that could cause the same problem... lower octane fuel doesn't burn evenly under compression (i.e., boost) and would trigger pre-detonation which would trigger the knock sensor which would retard teh timing which means your engine would be running lean.

good luck,
rt

I have both symptoms also. Seeping cap with new seal and a leann condition. I sorry, but don't understand how they could be related. I've already fixed the leak in the hose running through the firewall to the overboost switch and guage. I've also replaced the vacumn hose on the FPR.

I haven't done the oil filler cap "jiggle" test yet. Where you unscrew it with the engine runnning and see if it wants to float over the cover.
--
Erwin in Memphis, '88 745t 183,000 miles, '95 855t For Sale

Think about it: you boost on an engine with a known lean condition, forcing even MORE air (lean = less fuel, more air) into the engine, increasing compression, etc. A lean engine is a hot engine, hot air expands, you have more air than normal, the air has to go somewhere, you are exceeding the pressure capabilities of the cylinders, etc. The excess pressures force oil past the rings, which increases the crankcase pressure. The oil filler cap isn't made to handle any serious pressures, although it does manage most of it. The result? Some air pushes out the seal, and oil comes with it. The end result is a wet oil spot around the filler cap.

As I said, this is a SYMPTOM of another problem, and it is ONLY APPLICABLE if you have a turbo engine and see the wet oil spot after trying to boost under said condition. If you want to test it clean the oil spot and go take a drive. Do one drive without any boost at all, check it, and than do another with boost.

The jiggle test is absolutely worthless, so I don't know why you are even bothering. If you have an oil stain around the filler cap its pretty obvious you have excess crankcase pressure, so why would you bother confirming the obvious? What you need to analyze is WHEN you have excess crankcase pressure and then trace it back to a single cause.

In my case this was a bad AMM or Knock sensor connection (I reseated both when the it became fixed), though I favor the AMM.

good luck,
rt

erwin,

be carefull of the jigle test...it only works with the older metal caps AND (i think) if yout mounts are ok....if not (or you have a plastic cap) it gets messy...

however...modified jiggle test...

run car at idle, unscrew cap keeping fingure on top to hold in place....now rev to say 2000 rpm..cap should NOW be sucked down HARD...it if it isnt then you have presure if it is...you dont...

on my 940 I know i have negative presure (presure meters are wonderfull things...) but it still fails the jiggle test due to plastic cap and possibly dodgy mounts...

as to the stuff about the seal round the cap...what can I say I have to keep mine oil free or it seaps slightly (very fine film over head..)

One thing I found was the big hose over the head gets cruded up..still flows air etc but internal diameter and 'suck' reduced...had to spend a while cleaning mine with degreaser and platic covered wire rodding it thru...made a whole lot of diference....

interesteing thought for u...put a presure gauge on your manafold...find out what your pulling at idle...

i get -20 to -21 "

take the filler seal off the filler and remove any oil you can see on the cap, seal and engine top....then replace...

of course this is predicated by the fact that you have already:-

replace breather box and flame trap
cleaned nipple on manafold and ALL the PCV hoses
checked all hoses for tightness...

checked oil is not over filled

If you are sure the system is clear and not building pressure then I would bend the tabs on the oil filler cap slightly to increase their ability to pull the cap tighter.

Did you remove the plastic oil separator box on the side of the block and clear out the passages in it? I recently had a rear main seal blow out on one of our cars because of a restriction in the oil separator.

Randy

Clean the flametrap.