Engine block failure

Discussion in 'Gen 3 Prius Technical Discussion' started by donzoh1, Apr 18, 2019.

  1. donzoh1

    donzoh1 Junior Member

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    I replaced the head gasket on a gen 3 about 2K miles ago. Yesterday, the block developed a serious crack...Maybe an inch wide near the water pump. Is there something that I might have gotten wrong during cylinder head installation to cause this. I'm pretty sure the bolt torque values and sequence was correct. The engine code originally was for cylinder 1 misfire although the problem only happened on early morning startups. Cylinder 1 also had some polishing on opposite sides while the 2, 3, and 4 had uniform cross hatching from the factory. I believe the original misfire was from coolant collecting in that cylinder. I'm wondering whether the coolant in the cylinder could cause an over pressure situation that would create a small crack...although I didn't notice any visible ones. Curiously, cylinder 1 had the best compression numbers.
     
  2. FnRedPrius

    FnRedPrius Member

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    Oh man that's bad.. Is there any way to get pics?
     
  3. TMR-JWAP

    TMR-JWAP Senior Member

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    A one inch wide crack? A photo would be great.

    Water in a cylinder will frequently cause a bent connecting rod. Bent connecting rods lead to weird things, like pistons not staying true in the cylinder bore, not to mention eventual rod failure. The force it takes to bend a rod usually does some damage to the rod bearing.

    Does the engine still run normally?

    A one inch wide crack/opening is usually indicative of a connecting rod letting go and poking a hole in a block. An engine in this condition will definitely not be running normally.
     
  4. donzoh1

    donzoh1 Junior Member

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    There were no DTCs and it seemed to run normally. But, it did have pronounced polishing on opposite sides of the number 1 cylinder wall. I would think a bent connecting rod would cause that as well. Also, that cylinder had better compression than 2, 3, and 4. I will try to get pics. My belief is that the coolant was leaking into the cylinder during engine cool down. The amount of coolant deposited would vary depending on piston position after shut down.
     
  5. cnc97

    cnc97 Senior Member

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    Sounds like head bolt failure. Didn’t you reuse the old head bolts when you put it back together?
     
  6. donzoh1

    donzoh1 Junior Member

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    The bolts last used were new from Felpro...installed and torqued only once. The engine block failed in the lower area near cylinder 1, between the dipstick and water pump. I don't see how previously torqued bolts or even overtorqued bolts would cause this. The idea of a bent rod from continued use after gasket failure...with the high pressure created on startup by coolant in a cylinder...seems much more likely. No coolant was lost in the several housand miles between head gasket replacement and block failure.

    Bottom line is if I knew the vertical polishing in cylinder 1 was an indication of a bent rod, there's no way I would have put the engine back together without replacing the connecting rod. The bent rod theory also explains the increased compression in that cylinder before and after repair. Nothing related to the head can explain the two symptoms known before complete failure.
     
  7. donzoh1

    donzoh1 Junior Member

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    This is the front of the block looking down between dipstick and water pump. Dipstick is yellow out of focus near top.
     

    Attached Files:

  8. Raytheeagle

    Raytheeagle Senior Member

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    Did you put a new water pump into service?

    If so, did you use FIPG on the 2 studs that penetrate the block?
     
  9. cnc97

    cnc97 Senior Member

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    Ok, I thought you had reused the bolts.

    But, when my head gasket let go, the rod came out just above the upper oil pan, at the lower portion of the cylinder wall. So if the gasket failed, and filled the cylinder with coolant, that would cause a failure in the lower portion of the block.

    Did the engine sound change to be any different at all before the failure?
     
  10. donzoh1

    donzoh1 Junior Member

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    I see where the confusion is. I did re-use one set of bolts on the advice of the Felpro tack people. The coolant accumulation was prior to my work on the car. Coolant lost after I worked on it went into the crankcase, not the cylinders. I didn't feel good about having reused the bolts but another issue came up when I failed to seal the coolant passage in the timing chain cover. Anyway, I installed a new bolt set after that. There was no coolant loss after I fixed the RTV problem in the timing cover and put the last new set of bolts in. However, I believe the connectingcylinder. Was present from start to finish based on the issues I mentioned earlier.
     
  11. donzoh1

    donzoh1 Junior Member

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    I used RTV Ultra Black on the water pump flange. The existing pump was reused. I might have put antiseize on the bolts but not sure on that.
     
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  12. The Critic

    The Critic Resident Critic

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    Wow, that is bizarre. So you're telling us that the engine continues to run fine, but a 1" wide crack just suddenly developed?

    The only cause I can think of is overheating. Was this engine severely overheated at any point?
     
  13. donzoh1

    donzoh1 Junior Member

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    It's not mine but I've been told that never happened. The failure was apparently quite sudden and it sounded like things were bouncing between the engine and the road surface.

    I would imagine that the hydraulic pressure developed when coolant accumulated in an engine cylinder is compressed through the exhaust valves into the manifold is quite high. High enough to bend a rod and maybe even fatigue or crack the block. But, if that's what happened, there were no symptoms except for the increased compression in that cylinder and the vertical polishing on opposite sides of the cylinder walls.

    This is the only motor I've seen with uniform compression across 3 cylinders and dramatically higher compression in 1 cylinder.
     
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