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4.0 Durablility


 
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monkeyman3875
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Joined: 06 Jul 2005
Location: Charlotte, NC

PostPosted: Mon Jul 17, 2006 10:37 am    Post subject: 4.0 Durablility Reply with quote

How durable is the 4.0 straight 6?

How likely is it that the cast iron block or head could warp?

How likely is it to get a bad head gasket right out of the package?


Any help wanted...Thanks
_________________
-1997 Stock XJ
-4.0 L
-4-speed automatic
-130k Miles (and counting)-> let me know of any preventative maintenance you guys can think of. PM me.
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Mon Jul 17, 2006 12:55 pm    Post subject: Re: 4.0 Durablility Reply with quote

monkeyman3875 wrote:
How durable is the 4.0 straight 6?
Extremely durable with even basic preventive maintenence

How likely is it that the cast iron block or head could warp?
to some small degree most heads arent perfectly flat brand new out of the crate on any engine. Warping can happen, but it usualy takes something out of the ordinary to cause enough of a defect to surface

How likely is it to get a bad head gasket right out of the package?
Anything is possible. But had there been a problem with the head gasket early on, it would have surfaced fairly quick. Bad gaskets dont last very long.


Any help wanted...Thanks

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monkeyman3875
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Joined: 06 Jul 2005
Location: Charlotte, NC

PostPosted: Mon Jul 17, 2006 2:07 pm    Post subject: Reply with quote

Thanks, I ask because on my cherokee I'm losing compression in cylindars 2, 3, and 4. 2 is at 70psi, 3 is at 45psi, and 4 is at 100psi. 1, 5, and 6 all read within range.

I was led to these findings because one of the cylindars wasn't firing (could hear it missing and could smell unburnt gas). I checked the rockers/rods, the plugs and wires and was getting nothing (out of the ordinary). I checked the compression and found the loss.

And I just replaced the head gasket when I fixed the freeze plug (in the head).
Here's the story http://jeephorizons.com/phpbb/viewtopic.php?t=8724
_________________
-1997 Stock XJ
-4.0 L
-4-speed automatic
-130k Miles (and counting)-> let me know of any preventative maintenance you guys can think of. PM me.
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WhatWasIThinkin
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Joined: 02 Jan 2004
Location: Epping New Hampsha

PostPosted: Tue Jul 18, 2006 1:46 pm    Post subject: Reply with quote

If the head gasket is getting blow by, a couple other things usually happen. IF the head is warped enough to cause low compression, it will be pushing coolant out also.

Warped heads=low/no compression and severe coolant leak that you couldnt miss

This is what happens if the gasket blows from the cylinder into the water passages or if the cylinder as burnt a hole on the block deck.
1.You may get a small steam like vapor at the exhaust.
2.You will start using excessive coolant.
3.You will get a greyish greasy residue collecting at the end of the exhaust pipe.
4. Your engine oil will start turning the same greyish color, it will also get a foamy apperence.
5.You will see the same grey greasy residue on top of the coolant if you look into the radiator and may also see it in the overflow bottle.

If the gasket has failed or there is a groove burnt between the cylinders, you generally wont get a high compression reading at all as the cylinder trying to build compression just pumps the compressed air into the other cylinder. It would be doubtful that you could get more than a few pounds of pressure to build up.

Another thing that happens if you are pushing compressed air between cylinders, it ends up in the crank case as excess pressure. This shows in the form of severe oil leaks...blown pan gaskets, blown head cover gaskets etc.

Some things to think about.
Are the valves seating properly? did you check them? are the seats and valve seals in good shape? did you check them? These can cause low/erratic compression if thier a problem. Age/heat takes its toll on the valve train. Hammering on the engine also beats up valves. Cracked or loose exhaust manifold will cause excess heat at the valves as some air gets sucked in threw the crack. This is what causes burnt valves.
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monkeyman3875
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Joined: 06 Jul 2005
Location: Charlotte, NC

PostPosted: Tue Jul 18, 2006 6:10 pm    Post subject: Reply with quote

Thanks for the info. As for the valves, I'm not sure. When we tested we had just put the head back on and were'nt about to take it off again. While the head was off, I didn't notice anything out of the ordinary but who knows. The reason I'm not thinking it's the valves is because I'm seeing compression loss in 3 of the 6 cylindars. Also, I'm not seeing any coolant leaks, but we (my brother-in-law and I) haven't run the car for very long.

I gave up on it though. I didn't want to take the head off again so I'm having it towed to a garage that I trust. Hopefully they can pinpoint the problem.

Thanks for your help.
_________________
-1997 Stock XJ
-4.0 L
-4-speed automatic
-130k Miles (and counting)-> let me know of any preventative maintenance you guys can think of. PM me.
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View user's profile Send private message Send e-mail
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