85-86 DeVille Deaths
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 85-86 DeVille Deaths in Past Cadillac Vehicle Discussion; What necessarily was the reason for the deaths of the 85-86 DeVilles' engines? My girlfriend's 86 Sedan, my friend's 85 ...
  1. #1
    DopeStar 156's Avatar
    DopeStar 156 is offline Cadillac Owners Master
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    85-86 DeVille Deaths

    What necessarily was the reason for the deaths of the 85-86 DeVilles' engines? My girlfriend's 86 Sedan, my friend's 85 Coupe, they all died because of some kind of engine failure and I've always heard that they had "bad engines." I'm curious as to what the problem was with the 4.9's from those two years? Was there some kind of defect or design flaw?

    Also I have another question. In 1985 did Cadillac make an '85 DeVille with the old 80-84 body with a RWD drivetrain and then switch their design to the FWD DeVille somewhere in 1985? I've heard of half year models of certain cars and I'm wondering if the same thing happened here. Thanks, I just wanna know for my own personal knowledge.

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    AElayyat's Avatar
    AElayyat is offline Cadillac Owners Connoisseur
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    Re: 85-86 DeVille Deaths

    Quote Originally Posted by DopeStar 156
    What necessarily was the reason for the deaths of the 85-86 DeVilles' engines? My girlfriend's 86 Sedan, my friend's 85 Coupe, they all died because of some kind of engine failure and I've always heard that they had "bad engines." I'm curious as to what the problem was with the 4.9's from those two years? Was there some kind of defect or design flaw?

    Also I have another question. In 1985 did Cadillac make an '85 DeVille with the old 80-84 body with a RWD drivetrain and then switch their design to the FWD DeVille somewhere in 1985? I've heard of half year models of certain cars and I'm wondering if the same thing happened here. Thanks, I just wanna know for my own personal knowledge.
    1) re: 85-87 coupe/sedan devilles and fwd fleetwoods, eldorados/sevilles--The defect was called a 4.1 aka ht4100.

    2) As far as I know the only RWD caddy in '85 was the fleewood brougham (A real caddy), everything else was FWD (even factory limos).

    Just be glad that you dont have a 4.1 man.

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    DopeStar 156's Avatar
    DopeStar 156 is offline Cadillac Owners Master
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    Re: 85-86 DeVille Deaths

    Quote Originally Posted by AElayyat
    The defect was called a 4.1 aka ht4100.
    Can you explain what the defect was, what went wrong?

  5. #4
    AElayyat's Avatar
    AElayyat is offline Cadillac Owners Connoisseur
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    Re: 85-86 DeVille Deaths

    Quote Originally Posted by DopeStar 156
    Can you explain what the defect was, what went wrong?
    When I said the defect was the 4.1 I meant it as a joke.

    Those engines are not Cadillacs best (nothing beats a 425/472/500) as they had the overheating problems. Members here on the board suggest that the high rate of head gasket failures are do to coolent not being changed every 12/12 and people not using that cooling supplement stuff. What I know though is that when you throw a 252 cu. in. motor to move a 4000+ lbs car (ie RWD devilles and broughams) that will wear it out early and cause problems. And on top of everything the 4.1 has an alumminum block and iron heads so you aint gotta be a scientist to know that the two metals heat up at different rates and bam, there goes a headgasket.

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    BeelzeBob's Avatar
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    Re: 85-86 DeVille Deaths

    The 85/86 engines were 4.1 liter engines, not the 4.9.

    There is the chance with the 4.1/4.5/4.9 engine family that coolant can leak internally into the oil and go undetected. This would deplete the oil of the antiwear additives as the oil was degraded by the coolant intrusion.

    That is why those engines were all specified to run with a cooling system sealer in the system. The GM coolant supplement pellets are mandatory in that engine to prevent a leak or seepage at the head gasket to block interface or the intake manifold coolant crossover to the head connection at the intake gasket seal.

    Typically the engines were protected for 5-10 years by the original dose of the coolant supplement/sealer that was installed at the factory. Lack of cooling system maintenance (drain and replace the coolant every 2-3 years/24-35K miles) caused the coolant to fail and the corrosion inhibitors depleted and allowed internal corrosion to weaken the gaskets causing the coolant intrusion. In addition to the coolant corrosion inhibitor failure the coolant sealer would also fail after several years and thousands of miles of use. It needs to be replenished occasionally , also. This obviously would not happen if the owner was not even changing the coolant itself.

    The motors were actually fairly robust and would run virtually forever if the coolant system was maintained and the oil changed regularily. I still see an awful lot of the driving around certain areas of Detroit. They are getting to be real beaters but they are still running.....

    The internal coolant seepage had nothing to do with the dissimilar metal construction...i.e...the iron heads and aluminum block and wet cylinder liner construction. The fact that the engine was made of dissimilar materials was not missed by the development team that designed it...so the gasketing and sealing was done accordingly. That is also why the coolant supplement was added to the system as a redundant protection against seepage internally. If it was not maintained then it could not protect the engine.

  7. #6
    DopeStar 156's Avatar
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    Re: 85-86 DeVille Deaths

    Damn, so that's what did it. Thanks guys, you've just filled a hole in my Caddy knowledge.

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