2000 Buick Century 3.1 bad headgasket?

SaturdaysGS

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Jul 15, 2007
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My boss has the vehicle listed in the title, and at first he was adding coolant every week or so then the heat stopped working even if the car was at temperature. Pulled the dipstick and milky oil. The car has 140k on it, and I'm pretty positive no gaskets were ever replaced.

Am I right in assuming head gasket? He stopped driving the car, so idk how long it was running with coolant in the oil but it wasn't long, and no engine noises. He really doesn't want to put a TON of money into it, and would rather fix the car then buy a used vehicle.

Thoughts?
 

Dasfinc

Ready for the EVlution
Sep 28, 2007
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Wheaton, IL
My boss has the vehicle listed in the title, and at first he was adding coolant every week or so then the heat stopped working even if the car was at temperature. Pulled the dipstick and milky oil. The car has 140k on it, and I'm pretty positive no gaskets were ever replaced.

Am I right in assuming head gasket? He stopped driving the car, so idk how long it was running with coolant in the oil but it wasn't long, and no engine noises. He really doesn't want to put a TON of money into it, and would rather fix the car then buy a used vehicle.

Thoughts?

3.1's pop lower manifold gaskets super common also IIRC, just like the 3800's

HG's are alot more uncommon on those motors.
 

Dasfinc

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Sep 28, 2007
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Wheaton, IL
Sorry Dan, I meant headgasket job.

I still don't think its the headgasket if it was driving fine the whole time honestly....

Compression/leakdown test it.

Headgasket isn't TOO bad, took me and my bud the better part of a day *Maybe 6 hours?* on a 3.4 OHV in a Van *Being a van made it a bitch, back was a nightmare to get at*
 

Ron Vogel

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Jul 12, 2007
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Lower manifold gaskets are NOT a walk in the park on the 3.1/3.4 engines...there's just so much shit that has to come off to get to it.

Much easier on a 3.8!

Anyway, it's a real common problem on those motors. Ballpark repair costs are $400-$600. I can do it cheaper, but if he wants to bring it in to a shop that's a fair price.

Phatride has done a ton of these working at a dealer, I talked to him about it the first time I did one. He was doing that fix on a regular basis over there too. However, HG's are down the road too and not out of the question...but generally the lower manifold gasket goes first, and the HG's go in succession later down the road.
 

Theautoguy

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Nov 10, 2007
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Machesney Park, IL
LIM on a 3.1 is about 3 hours if you've done them before. The 3800 is easier but the 3.1 isn't hard. However, everyone is right in saying the HGs are soon behind so might as well change those but you must mill the heads before reinstallation; chances are they arped a little through the owners miss-maintenance. Further, you don't know how long the engine was ran with antifreeze in the oil; that motor may need bears too.

I suggest getting a good 3.4 and dropping it in there. We did that to my brother's 94 Grand Prix after his HG's blew for the 3rd time! The engines are vertually identicle plus there is a manual online that gives you the information on sensor relocation and rewiring. (There really isn't much.)

Three years later my brother's Grand Prix is still running better than new and no problems.
 

SaturdaysGS

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Jul 15, 2007
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Chicago (Southside)
He's going to have a shop he knows a good mechanic at do the work, I followed and drove it there and he followed with his other car. 478 and some change to do the LIM gaskets, upper and lower hoses, thermostat, oil change (obviously), and coolant D-A-F.

The mechanic did mention that since it was run with a DECENT amount of coolant in it he cant gurantee the engines bearings will not be damaged. Understandable. My boss would rather try to salvage this engine for $400-500 than go the route of an engine swap, or junking it (he's just not keen on throwing any more money in it) to buy a "beater" (to him) car. He already has a 09 Malibu that only has 2300 miles. :picard:

Thanks guys, I'll let you know how the engine fairs after this. The mechanic said hed have it done by 5 but my boss told him he'll pick it up in a few days so no rush.
 

bikrboy128

Some say.....
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Jul 15, 2007
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Wheaton
He's going to have a shop he knows a good mechanic at do the work, I followed and drove it there and he followed with his other car. 478 and some change to do the LIM gaskets, upper and lower hoses, thermostat, oil change (obviously), and coolant D-A-F.

The mechanic did mention that since it was run with a DECENT amount of coolant in it he cant gurantee the engines bearings will not be damaged. Understandable. My boss would rather try to salvage this engine for $400-500 than go the route of an engine swap, or junking it (he's just not keen on throwing any more money in it) to buy a "beater" (to him) car. He already has a 09 Malibu that only has 2300 miles. :picard:

thats a pretty good price for all that.
and yeah, you will wash out the bearings real quick driving with milkshake oil. hopefully he gets lucky
 

Alacran

GM fanatic
Jan 18, 2009
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Chicago
LIMs in a 3100 are harder to do than on a 3800. VC and pushrods have to come out and even then you have to be careful, the pushrods are different length.

On a 3100 HG all you do to get to them is undo the exhaust pipe and then change them out everything else is taken off for the LIM anyway. In this case you may need to cut the heads but checking for flatness will tell you. Also, the valve guides move up in the heads if the engine was over heated, which means you will need valve job or new heads and you have to pull eh. manifolds, so check the guides or valve stem seals too.

3 hours sounds fair.
 
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