Engine Difference between 97' & 99' STS?
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Northstar Engines and System Technical Discussion Discussion, Engine Difference between 97' & 99' STS? in Cadillac Engine Technical Discussion; I have a 99' STS that has recently had some major problems. My car went into the shop and was ...
  1. #1
    PWCadSTS is offline Cadillac Owners Member
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    Question Engine Difference between 97' & 99' STS?

    I have a 99' STS that has recently had some major problems. My car went into the shop and was diagnosed as having 3 head bolts stripped out so it was leaking coolant and overheating. The warranty company that I have for it decided to replace the entire engine instead of repairing the heads. Now here is my question. They ended up putting a 97' NS engine it my 99' STS. Is there ANY difference in performance or features that will be missing from the 99' NS engine? I know the design setup is a bit different, but past that is there a difference? My old engine had 114K miles and the one they put in only has 60K miles. Anyone have any answers? Thanks.

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  3. #2
    caddydaddy's Avatar
    caddydaddy is offline Cadillac Owners Connoisseur
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    Re: Engine Difference between 97' & 99' STS?

    They are the same engine! The '93-'95 and the 2000-up engines though, are different!

  4. #3
    chevelle is offline Cadillac Owners Enthusiast
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    Re: Engine Difference between 97' & 99' STS?

    Uh...not so fast.

    The 97 and the 99 are basically the same engine and same content but there were some detail differences in the engines that are important to an STS.

    The STS changed significantly starting with the 98 model year. Beginning with the 98 model year the STS was a "new" car completely with a new body and structure based on the GM "G" platform. That platform had a different engine mounting scheme that required a revised engine mounting bolt pattern on the engine block. So.....beginning in 1998 the Northstar engine had a slightly different front cover outline with some of the bolts in the bottom right hand corner moved slightly to make way for a new engine mounting bolt.

    Quite frankly, I do not see how a shop could have bolted a 97 Northstar engine into a 99 STS. The right front engine/trans mount shouldn't fit correctly. Either they modified the mount, cut off the corner of the mount, skipped installing one of the bolts or ????? I would ask them how they accomplished this. Take the right front wheel off, pull aside the inner splash panel and look at the front of the engine. You should be able to clearly see the engine/trans mount to the right side (rear side) of the engine at the very front and see if any thing looks funny or any bolts are missing.

    There is clearly a difference in the 1997 and earlier and 1998 and later Northstar blocks in that area as you cannot interchange the front covers or front cover gaskets.

  5. #4
    PWCadSTS is offline Cadillac Owners Member
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    Re: Engine Difference between 97' & 99' STS?

    Thanks for the reply. The shop did say they had to do a lot of modifications to get the engine to fit correctly. Thats why it took an extra week to finish once the dealer received the engine. They had to add and move a couple of motor mounts for it to fit correctly. I'm not so concerned about the set up and look of the motor, which is in great condition. I was just concerned about the motors having different specs as far as the performance end of it goes. Which to me seems to be just fine. In fact it seems to run better now than it did before it even started to have problems. I'm fairly happy with the results of all the work that was done. It was done by an actually Oldsmobile/Aurora dealer, not some common repair place. Plus, the car and engine is still under warranty for another 3 years. Thanks.

  6. #5
    caddydaddy's Avatar
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    Re: Engine Difference between 97' & 99' STS?

    I stand corrected! I didn't know they changed the engine again in 1998. But to answer the original question, they are the same performance wise.

  7. #6
    AlBundy's Avatar
    AlBundy is offline Cadillac Owners Connoisseur
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    Re: Engine Difference between 97' & 99' STS?

    Quote Originally Posted by chevelle
    Uh...not so fast.

    The 97 and the 99 are basically the same engine and same content but there were some detail differences in the engines that are important to an STS.

    The STS changed significantly starting with the 98 model year. Beginning with the 98 model year the STS was a "new" car completely with a new body and structure based on the GM "G" platform. That platform had a different engine mounting scheme that required a revised engine mounting bolt pattern on the engine block. So.....beginning in 1998 the Northstar engine had a slightly different front cover outline with some of the bolts in the bottom right hand corner moved slightly to make way for a new engine mounting bolt.

    Quite frankly, I do not see how a shop could have bolted a 97 Northstar engine into a 99 STS. The right front engine/trans mount shouldn't fit correctly. Either they modified the mount, cut off the corner of the mount, skipped installing one of the bolts or ????? I would ask them how they accomplished this. Take the right front wheel off, pull aside the inner splash panel and look at the front of the engine. You should be able to clearly see the engine/trans mount to the right side (rear side) of the engine at the very front and see if any thing looks funny or any bolts are missing.

    There is clearly a difference in the 1997 and earlier and 1998 and later Northstar blocks in that area as you cannot interchange the front covers or front cover gaskets.
    Chevelle I think we need to add you to the Guru list.

  8. #7
    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
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    Re: Engine Difference between 97' & 99' STS?

    Quote Originally Posted by PWCadSTS
    Thanks for the reply. The shop did say they had to do a lot of modifications to get the engine to fit correctly. Thats why it took an extra week to finish once the dealer received the engine. They had to add and move a couple of motor mounts for it to fit correctly. I'm not so concerned about the set up and look of the motor, which is in great condition. I was just concerned about the motors having different specs as far as the performance end of it goes. Which to me seems to be just fine. In fact it seems to run better now than it did before it even started to have problems. I'm fairly happy with the results of all the work that was done. It was done by an actually Oldsmobile/Aurora dealer, not some common repair place. Plus, the car and engine is still under warranty for another 3 years. Thanks.

    add and move a couple motor mounts?!?

  9. #8
    mmayer is offline Cadillac Owners Member
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    Re: Engine Difference between 97' & 99' STS?

    Beat it to fit and paint it to match!!!

  10. #9
    J.A.O. is offline Cadillac Owners Fanatic
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    Re: Engine Difference between 97' & 99' STS?

    What warranty company do you have? The fact that they try to put an engine other than the one that originally came with the car, let alone a used one sounds a little strange.

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