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Registered
2004 Deville DHS
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20 Posts
Discussion Starter #1
I am the second owner of a late 2004 DHS with 85,000 miles on it. The car is in excellent condition and runs great except for a slightly rough idle on hot restarts
after which the idle clears out shortly and car runs great.

She gets 28 mpg on the highway and generally runs great

The car was driven by my 80-year old uncle who babied the car. 3,000 mile oil changes, coolant flush at 61,000 miles, etc.

Before I bought it, (at 74,444 miles) the dealer looked at it for the check engine light coming on and rough running. They pressure tested the cooling system and
scanned the codes. They found P0171 and P0174 fuel system lean and p)300 engine misfire. They removed spark plugs from front of engine (note: not the back)
and let vehicle rest to check for coolant entering cylinders. None found. Reset codes and ran and no further problem found.

I have not seen any signs of eating coolant, overheating, etc.

Yet, I am concerned about the possibility of head gasket failure and am wondering if anyone can give me feedback on how concerned I need to be.

I am considering replacing this car when another becomes available.

Thank you in advance!
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,250 Posts
3,000 mile oil changes
that's a waste of time - money and oil -
follow the OLM - Oil Life Monitor -

coolant flush at 61,000 miles
coolant should be changed every 2 to 3 years -

dealer looked at it for the check engine light coming on and rough running.
They found P0171 and P0174 fuel system lean and p)300 engine misfire.
99.99% of the time -
the plenum gasket between the throttle body and intake is split -
causing a vacuum leak -

Yet, I am concerned about the possibility of head gasket failure
long story short -
pre 2000 Northstar motors used short - fine-thread head bolts -
some developed head gasket failure -

in 2000 - several improvements were made to the engine -
including longer head bolts -
this reduced the head gasket problem DRAMATICALLY -
but didn't solve the problem -

mid production year 2004 the head bolts were changed to a coarse thread -
this virtually solved the problem -

bottom line - don't lose any sleep over the head gaskets -
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
We drove my daughters '04 SLS from CHI to PDX last Jan. with around 160K on it. Probably near 165 now with no HG problems yet. Relax and enjoy the car.
 

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Registered
2004 Deville DHS
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20 Posts
Discussion Starter #5
Thanks for the interesting replies. No paranoia here, just planning ahead to avoid being caught with a car with a useless engine. Will purchase a friend's Lexus LS soon when available, since there's someone in line waiting for this car.

In the meantime, I'm enjoying the great highway mileage and cooled seats....only 5,000 miles put on it in the last year and a half since the car sits 8 months per year while I travel.

New Dexcool coming next month.
 
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