98 chevy malibu:engine wont turn

Sounds like an electronic pressure switch or electronic governor. Your engine check light should be on or intermittent and it should have a code. A lot of parts stores or transmission repair shop should be able to tell you with a code reader.

Check the ignition fuse. And if that is could u need a new ignition switch not the key mecanisum but the electronic switch it goes into

Inspect the old ignition cycle which is out.Is there any problem noticed of Ignition cylinder getting worn out.
Because when issue of ignition not turning off,its faulty ignition lock cylinder or faulty ignition switch.I suggest re-inspect the new ignition cylinder.
For more help,click the help link mentioned below:----

Ignition Switch Will Not Turn Off?
http://schematicsdiagram.blogspot.in/2012/04/ignition-switch-will-not-turn-off.html
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1995 Ford Taurus: Ignition switch not turning OFF?

http://repairhelpcenter.blogspot.in/2012/06/1995-ford-taurus-ignition-switch-not.html

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Ignition Problem Troubleshooting

http://whoisbyme.blogspot.in/2012/07/ignition-problem-troubleshooting.html

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These will help.

Thanks.

replace thermostat did bleed coolant system check coolant level.because if not engine could have overheated and blowed headgaskets warp or cracked the heads check engine compression.sound like engine got too hot.

If the engine was overheated, you most likely have a cracked cylinder head and/or a blown head gasket. The reason it won't start is because there is angine coolant getting in the combution chambers. (You cannot run the engine on antifreeze)

Carefully pry it off. Use a plastic knife so you wont hurt anything.

99 chevy malibu v6 3.1 engine, head bolt torque is-- 98 through 2001 is step1- 37 foot lbs, step 2- rotate an additional 90 degrees (1/4 turn). the rocker arm bolts are 168-in. lbs.

You probably have a large vacuum leak. With the engine running, listen under the hood for a hissing sound. Check all of the rubber lines running from the intake.

if you are mostly having trouble with cold weather,i would check the engine temp sensor,it tells the computer how cold your engine is so in the morning the computer will increase fuel like an old carb with a choke

Sounds like you need to have a new ignition switch installed. Copy & paste this link into your browzer: http://www.autozone.com/autozone/catalog/parts/partsShelf.jsp?displayName=Ignition+Switch&currentPage=1&categoryDisplayName=&navValue=16200189&itemId=189-0&parentId=62-0