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Repaired engine exhibiting the same symptoms after the repair

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here Repaired engine exhibiting the same symptoms after the repair

This topic contains 10 replies, has 3 voices, and was last updated by Jeff Jeff 9 months, 2 weeks ago.

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  • #895508
    Indi Singh
    Indi Singh
    Participant

    So, hello everyone, I’m new here! I’m in the UK so I expect there will be a delay communication between us!
    Right, so an into to me and what’s going on. I’m a self employed mechanic, just like Eric, yay! I’ve been at it for about 8 years and have done numerous repairs and builds, solving issues along the way.
    This one has be puzzled and I’m just looking for similar experiences with maybe a common solution that might be relevant to this problem.

    I have a Mercedes v8 engine (sl500, 1996) twin ohc on each bank so 32valve. The car came to me as a non runner, and I diagnosed a slipped timing chain due to a broken chain guide. Timed her up, new top guides fitted, leakdown pressure tested her, then compression tester her, and everything seemed ok. Started first time, and ran nice and smooth. But she smoked white smoke and drank coolant. After checking the oil, it was plain to see the coolant was getting into the pan somehow so…..We removed the cylinder heads to find both headgaskets failed and rusted to bits.
    Both heads were sent to the machine shop (a trusted tried and tested shop) and the heads were given 1 pass each on the skim. All pressure tested ok. Block was visually inspected on the deck and cleaned up. The bores and pistons were visually checked, and we left oil inside each bore to see if they leaked down – they didn’t. Long story short, everything was re-assemble using genuine mercedes parts (including replacing every chain guide, new chain, new valve stem seals, head gaskets, intake manifold gaskets, exhaust gaskets, cylinder head bolts, new sump gaskets -the works)
    She started up great! But she never stopped smoking! And the coolant is again dropping at a rate of 1 litre per 5 minutes, with no leaks disable anywhere. Coolant has become visible on the cam cases when we removed them. I look forward to replies!

Viewing 10 replies - 1 through 10 (of 10 total)
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  • #895510
    Nightflyr *
    Richard Kirshy
    Participant

    Possible that there is a crack in the block causing the coolant to leak into the oil galley.

    #895511
    Indi Singh
    Indi Singh
    Participant

    It’s possible. I have a surface crack detection kit I’m waiting to use if everything is pointing that way.

    #895516
    Nightflyr *
    Richard Kirshy
    Participant

    Just a shot in the dark ….
    Does this vehicle have a liquid oil cooler ???

    #895520
    Indi Singh
    Indi Singh
    Participant

    Hi. No, the oil cooler on this engine is air to oil type. It was something I thought about yesterday but quickly ruled it out.

    A little update – I did another compression leak down, at tdc , bdc , and mid travel. No bubbling through the coolant at all.

    #895522
    Nightflyr *
    Richard Kirshy
    Participant

    A little update – I did another compression leak down, at tdc , bdc , and mid travel. No bubbling through the coolant at all.

    Very interesting…..If this is true for all eight cylinders that would indicate some how an external to internal leak …
    At that point you would need a complete diagram of the coolant routing and passages for that specific engine.

    My only other thought,
    If after running the engine and having water vapor expelling out the exhaust, pull the plugs and inspect both the plug and cylinder for signs of coolant.
    Perhaps there is a coolant leak somewhere in the throttle body, sucking coolant in the intake.

    #895523
    Indi Singh
    Indi Singh
    Participant

    Some more updates – I’m still at the workshop, and after my leak down tests, she’s no longer consuming coolant???!!!??!! When I was going the leak down, initially there was compression leakage into the next piston, and into the intake manifold. This slowly disappeared as the air pressure slowly built up to 120psi. It did this on about 3 cylinders. All the water in the oil has now evaporated and coolant level is rock steady. Any idea on what people think is happening, or what happened?

    #895525
    Nightflyr *
    Richard Kirshy
    Participant

    When I was going the leak down, initially there was compression leakage into the next piston, and into the intake manifold. This slowly disappeared as the air pressure slowly built up to 120psi. It did this on about 3 cylinders.
    That ain’t right…
    You either have some sticky valves that are sealing under pressure , improper head gasket fitment, block deck or head have a low spot.

    #895526
    Indi Singh
    Indi Singh
    Participant

    3 things I can rule out are deck height and level, head gasket fitment, and level of head surfaces. The sticky valves, maybe on the left back which is making the lifter noise (heads both refurbished, but lifters may have been stuck open)

    #895527
    Indi Singh
    Indi Singh
    Participant

    Also, the leakdown test was run at different heights and the leak/ stop only happened once

    #895532
    Jeff
    Jeff
    Participant

    There could be some circumstances where issues can occur but it could be detected so can be resolved, but have to optimize accordingly.

Viewing 10 replies - 1 through 10 (of 10 total)

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