Here’s a weird one, I changed the oil in my ej251 vanagon conversion to 20W50 to see if the oil consumption is getting better. Engine ran fine before no unusual noises etc., earlier today I stopped at a street light when all of the sudden the engine started making a loud knocking noise, pulled over to check if anything came lose.. all tight, knocking sounded like rod knock.. I decided to baby the car home. After two minutes the knocking disappeared. Car stuttered two three times and was running as before… WTF?!? Can a rod knock be intermittent, did I lose the oil film for a moment? Is it the oils fault? I had 10w30 before, maybe I should go back to that?!? Head gaskets, timing belt, idler, tensioner and water pump are new. Any ideas here? I will drain the oil and replace it with 10W30 again, and see if there are any metal shavings in there. I will also check the timing belt tensioner, although it was new just 400mls back.

Did you use a genuine tensioner or an aftermarket one?

It’s odd that it came and went. Got any codes? That could point you in the right direction.

If you did a big end you’ll be sure to hear it on start up when cold. It shouldn’t come and go when driving, but knocking on start up is a definite sign of an impending issue.

I hope it’s a tensioner issue!

Cheers

Bennie

33 minutes ago, el_freddo said:

Did you use a genuine tensioner or an aftermarket one?

It’s odd that it came and went. Got any codes? That could point you in the right direction.

If you did a big end you’ll be sure to hear it on start up when cold. It shouldn’t come and go when driving, but knocking on start up is a definite sign of an impending issue.

I hope it’s a tensioner issue!

Cheers

Bennie

i did'nt check the codes yet, thats a good idea! i have used a continental water pump and belt kit.. fingers crossed it's just that.

Okay, so went back to the car, no error codes in the ECU, started the engine up, no knocking noise which is reassuring, however the engine stared to blow an impressive cloud of smoke, which it never did before.. i am wondering if this is still remnants of the sea foam treatment, but that's more than 100miles and an oil change ago..well compression test and oil change back to 10w30 next and then some more oraceling...

 

 

I’d do a compression check first up. You could have an issue with a cracked piston or something random like that.

Do you know the history of this engine? I’m wondering if it was overheated previously and has caused some issue with the piston or cylinder liner. Rare if it is either of those.

If one cylinder is clearly down on compression compared to the rest of them, get a bore scope down the spark plug hole and see if you can see any ring landing damage/chipped piston.

Cheers 

Bennie

drain the oil, swirl a magnet around and see if you get metal? or send oil in to Blackstone labs?

3 hours ago, 1 Lucky Texan said:

drain the oil, swirl a magnet around and see if you get metal? or send oil in to Blackstone labs?

yeah, if i cant find anything obvious by eye/magnet/filter i might send it out for testing..

Edited June 8, 20214 yr by pvfahrer

16 hours ago, el_freddo said:

I’d do a compression check first up. You could have an issue with a cracked piston or something random like that.

Do you know the history of this engine? I’m wondering if it was overheated previously and has caused some issue with the piston or cylinder liner. Rare if it is either of those.

If one cylinder is clearly down on compression compared to the rest of them, get a bore scope down the spark plug hole and see if you can see any ring landing damage/chipped piston.

Cheers 

Bennie

Compression test shows 225+\-5 psi over all four cylinders.. car smoked heavily during warm up. Oil change tomorrow..

smoke smell fuel-ish or oil-ish or sweet like coolant?

if you suspect fuel is getting in the oil, don't neglect oil changes.

maybe PCV valve is stuck open?

fume is white/blue, smells like oil i would say, not sweet and not black/fuel. I think its oil.. replaced the PCV valve 200mls ago.  

Do you have a low pressure light or oil pressure gauge installed?

Rod knock is easy to diagnose on subarus.  With engine warmed up to normal temps, rev it up really quick and snap the throttle shut with your hand.  You might hear light tapping on a worn engine, which is okay.  You'll definitely know if it's knocking.

If that test seems ok it's likely the tensioner or something wrong with oil pump/pickup tube.

triple check breather  and PCV hose routing I guess.

 

in the 'old days', oil smoke at startup, and on the highway after  -  an abrupt foot off accel. , wait a few yards, then foot on the accel.  induced smoke puff  -  often was a sign of bad valve seals I think?