Thread: 300Tdi Rear Main Oil leak.

Update - The plot thickens...

Tested yesterdays theory and ran engine until warm and then some to see if no cyclone = no leak (unlikely but thought i'd check) - the leak occurred about ~10min into running, just as the gauge arm began to tick up towards standard running temps.

As this dashed my (albeit small) hopes of just replacing the cyclone filter and calling it another job well done, I heated the engine up a bit longer and pulled the glowplugs from cylinders 2, 3 and 4. I left cylinder 1 in because the bloody AC compressor sits directly in front of it and I couldn't be fked to remove that entire apparatus. Some things I noted about the plugs:
- All plugs came out nice and easy, barely any force required to remove them (engine was warm so go figure)
- Plugs 3 and 4 looked nice and shiny down their shaft, although a bit of carbon build up on the tips.
- Plug 2 was absolutely cooked and needed pliers to pull out. Was absolutely caked in thick carbon, which had gammed up the entire bore in which the plug sits.

I then disconnected the fuel line and ran what I believe was two sets of dry tests (as I didn't add any additional oil to the bores through the plugs before conducting testing), my results were as follows:

Cylinder 2: T1 = ~325psi, T2 = ~310 psi
Cylinder 3: T1 = ~350 psi, T2 = ~340 psi
Cylinder 4: T1 = ~350 psi, T2 = ~340 psi

It seems clear to me that cylinder 2 is somewhat of a problem child in this engine, although since I haven't tested cylinder 1 I don't know if it has a partner in crime or not. Despite cylinder 2's crimes against the environment (in the form of unnecessary soot), the variance between these is less than 10%, which I heard is a good metric for telling if a cylinder has sht the bed or not. These values also apparently align with the manual's recommended values of 360 psi (I don't have the book so can't verify this).

Based on the above, it appears that despite me flogging the ole girl up and down the coast for the past 5 years, and my dad for the 10+ years before me, the OG cylinders are still holding their own (we don't actually flog it, revs stay below 3000 always).


In addition to the above, I found some VERY interesting relationships between engine RPM (when in neutral) and the leak flow rate. When idling at cold temps there are no leaks, however when idling at warm temps there is a drop every 3 seconds or so. I thought it would be interesting to see how much this leak increases when I rev the engine up, so i did so and had a geez - the leaks stopped... When the revs hit around 1500RPM and higher, the leaks cease to exist. What is even more interesting is that when I back off the revs to idle, a small but constant stream of oil emanates from breather hole for about 10 seconds, before the flow rate returns to its standard drop-per-3-seconds rate.

This just goes to show I have absolutely zero idea what is going on inside of this engine, because this make absolutely no sense to me. What on earth could be going on here? Is it just that the engine is cycling through enough oil when at high rpm that oil isn't bathing the rear of the crank, and then when you drop off the revs it dumps all this excess oil it now doesn't need, which then creates a temporarily increased leakage rate???

Let me know what you guys think!

your rings have lost tension

really loosly (pun may or may not be intended)

at low RPMS and load the cylinder pressure spike isnt abrupt and the slow stroke of the piston gives enough time for leakage to occur. Once the revs come up the pressure rises faster and the pistons moving faster so the pressure spike itself seals the gap by putting more pressure on the rings and helping sealing by acting like a fluid barrier (same sort of principle as an air curtain door keeps AC in and hot air out) and theres less time on the stroke to let the air escape.

and if the crank case vent is doing its job properly it scavanges the vapor out of the cylinder head but not the crank case. at idle theres not enough airflow through the intake trunk to get that scavaging working properly so the crank case pressure can be higher.

Originally Posted by Blknight.aus

your rings have lost tension

really loosly (pun may or may not be intended)

at low RPMS and load the cylinder pressure spike isnt abrupt and the slow stroke of the piston gives enough time for leakage to occur. Once the revs come up the pressure rises faster and the pistons moving faster so the pressure spike itself seals the gap by putting more pressure on the rings and helping sealing by acting like a fluid barrier (same sort of principle as an air curtain door keeps AC in and hot air out) and theres less time on the stroke to let the air escape.

and if the crank case vent is doing its job properly it scavanges the vapor out of the cylinder head but not the crank case. at idle theres not enough airflow through the intake trunk to get that scavaging working properly so the crank case pressure can be higher.

Ok I think I understand the problem you are outlining. Perhaps the rings on cylinder 2 have been semi perma-compressed by the carbon buildup in that cylinder, or perhaps it's just from old age.

What I don't understand is how this problem would result in the observed sudden increase in oil flow rate, to be followed by a decrease in flow to a steady, slow rate?

Is the fix for this problem a full rebuild of the pistons (new rings, rebore, etc?) or could I get away with an easier fix.

In the meantime as well, would it be viable to install a small vacuum motor to relieve crank pressure? I may instead just do a quick botch job and install a catch can at the bottom of the bell housing so I can at least stop the oil loss.

Cheers

if its a ring sticking from carbon build up you can try putting a flushing agent in then giving it an italian tune before dumping the oil.

if its rings and that doesnt work the only proper fix is a rework of the bores and pistons.

putting a vac pump on the engines probably not going to be great for the vac pump.

good luck

Originally Posted by Blknight.aus

if its a ring sticking from carbon build up you can try putting a flushing agent in then giving it an italian tune before dumping the oil.

if its rings and that doesnt work the only proper fix is a rework of the bores and pistons.

putting a vac pump on the engines probably not going to be great for the vac pump.

good luck

Ok ok,

I actually have access to a borescope which can take photos and provide a live feed, so I'm gonna pop that into the cylinders as well and have geez at the condition of the bores and pistons. Will post photos here after.

Do you have a recommended flushing agent for this? I was looking around and found a product called BG EPR which acclaims that you can add it without having to worry about lubrication impacts or draining the oil??

Looking forward to doing this Italian tune as well lol

Cheers.

I've never used it, but people on have said good things about it.

Engine Blowby Kit - Cost Effective Maintenance

Tony

Originally Posted by BlueRunning

Ok ok,

I actually have access to a borescope which can take photos and provide a live feed, so I'm gonna pop that into the cylinders as well and have geez at the condition of the bores and pistons. Will post photos here after.

Do you have a recommended flushing agent for this? I was looking around and found a product called BG EPR which acclaims that you can add it without having to worry about lubrication impacts or draining the oil??

Looking forward to doing this Italian tune as well lol

Cheers.

Theres a lot out there, I generally use the supercheap one, the nulon one or whatever the customer provides for me because its the flavor of snake oil marketing they like best.

There are some that you must dump, there are some you dont and there are some that are a 3 bottle package.

1 you add before an oil change, the next is an oil stabilizer additive and the last is a seal saver that you only use if the seals are still leaking once youve run the second bottle for a few hours.

Originally Posted by Blknight.aus

Theres a lot out there, I generally use the supercheap one, the nulon one or whatever the customer provides for me because its the flavor of snake oil marketing they like best.

There are some that you must dump, there are some you dont and there are some that are a 3 bottle package.

1 you add before an oil change, the next is an oil stabilizer additive and the last is a seal saver that you only use if the seals are still leaking once youve run the second bottle for a few hours.

Haven't had time to flush engine yet, probably will have a peek around with the borescope tonight then run it hard and see if there's a difference.

Do you have any suggestions for what I should be looking for in the cylinders to indicate health status? (I.e. shiny, dull, cross hatching, etc?)

Also, I'm thinking that it might be a viable idea to open up the little cover plate on the front side of the bell housing-engine interface (the one used to connect the flywheel and flex plate) and see if I can have a look at the rear main seal. If it's clearly leaking out of the seal-crank interface, would that suggest high pressure blowout, but if it's leaking from the aluminium frame-engine interface, perhaps the seal is just warped?

Cheers.