TD42 Excessive blow by and compression problem

[waseemkhsaad]

Hi gents,

New to the forum, just wanted to pick your brains on a problem I am facing with my GQ TD42. The engine has very high blow by from both engine filler cap and dipstick (when removed), we did a compression test and cylinder 2 came out very low (others were up to spec). Motor has about 200k kms.

Cylinder 1: 29.58 bar
Cylinder 2: 13.83 bar
Cylinder 3: 29.45 bar
Cylinder 4: 28.66 bar
Cylinder 5: 29.58 bar
Cylinder 6: 30.72 bar

No symptoms of head gasket failure/cold start issues/weird sounds. Wondering if there is any way to diagnose the problem without pulling the engine completely? Also, what happens if I simply keep driving it (drives just fine).

[mudnut]

Welcome to the forum. On a petrol engine, you remove a spark plug, test compression. Squirt a small bit of oil in and do another test, If the compression rises significantly, then worn rings are the problem. Not sure but maybe the same can be done to a diesel through the glow plug hole if the chamber and the shape of the top of the pistons allow that little squirt of oil to get to the rings. Not more than a teaspoon or so of oil should be used though as you don't want to hydrolock the engine.

Hopefully a diesel guru can shed light on a solution for you.

[mihit]

Rings seized in groove somehow?? Or valve guides/stems/adjustment worn... (odd that it would only be on one cylinder though) Easy enough to take the rocker cover off and have a nosey.

Rings though...worst case "if you keep driving it" it will oval up the cylinder, snap off the piston skirt and the rings will free themselves up spectacularly.
...Likely? I wouldn't think so. But possible...wiith those numbers I WOULD hunt down and fix whatever the issue is.
Chuck a leak-down test on it to give some more clues. (if done with rocker cover off will probably show up whether valves or rings)

Check PCV valve. Fix/delete EGR if you haven't already.
Unfortunately the only other thing I know would be a cracked block but that's highly unlikely on 2 since it's right up front and gets plenty of cooling. Unless it's taken a mighty impact to the chassis... that's about where the engine mounts are...

[waseemkhsaad]

Many thanks to both of you, PCV valve is fine and no accidents/chassis impact etc. I took a look at the valves and they seemed ok on first glance, unfortunately i did nt have the right socket to turn the engine over so will have to do that again.

Im guessing cylinder 2 rings are the key suspect. On that note, if its just rings/piston on cylinder 2, is it necessary to replace the rings/pistons etc on all 6 cylinders or can i just do cylinder 2?

[mihit]

Im guessing cylinder 2 rings are the key suspect. On that note, if its just rings/piston on cylinder 2, is it necessary to replace the rings/pistons etc on all 6 cylinders or can i just do cylinder 2?

Depends what you find when you get in there... If they've just somehow carboned up and got stuck in the groove then even taking it out and putting it back in might be enough to solve your problem.
But if they've snapped, cracked, scored the bore etc then you're in for replacement and probably honing.
It's not high mileage so pistons themselves should be OK (subject to inspection) and a set of rings isn't too expensive.

Rings I can't see any issue in doing just one cyl.
Pistons come as a balanced set, but I can't see the TDs being too fussy about that!

It's your time/ money so you have to make the call. but since you have the thing apart anyway personally I'd do em all and then you know can mentally reset the wear-clock to 0.

[waseemkhsaad]

Depends what you find when you get in there... If they've just somehow carboned up and got stuck in the groove then even taking it out and putting it back in might be enough to solve your problem.
But if they've snapped, cracked, scored the bore etc then you're in for replacement and probably honing.
It's not high mileage so pistons themselves should be OK (subject to inspection) and a set of rings isn't too expensive.

Rings I can't see any issue in doing just one cyl.
Pistons come as a balanced set, but I can't see the TDs being too fussy about that!

It's your time/ money so you have to make the call. but since you have the thing apart anyway personally I'd do em all and then you know can mentally reset the wear-clock to 0.

Got it, many thanks.