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I'm looking at a 07 DTS with 70k miles and am iffy on it because of previous north star issues with head gaskets/bolts. Did they fix the issue by then or is it still going to have problems? Are these cars reliable? I'd like to get 150k out of it.
 

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The 2007 falls in the last generation of Northstar FWD engines. Throughout the engine production run it was modified on an almost-yearly basis, so you would have the latest and greatest.

Our non-scientific poll in Engines; Northstar shows precious little info for the 2007 but, just like any other internal combustion engine on earth, it would still be subject to wear, tear, and maintenance.

Your call.
 

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I was one of the unfortunate...developed head gasket problems at 115,000 miles on my 2006 DTS Any vehicle can have head gasket failure. I usually go to car sites like "cars.com" for a particular model to see how many miles previous models have. Lots of DTS's are way over the 150,000 mile mark...not scientific by any means not knowing the history of the vehicle. Its a crap shoot. I'm still in a DTS, fixed my head gasket problems in an unorthodox way. Heres the link if your interested.

http://www.cadillacforums.com/forum...012/857666-better-body-man-then-mechanic.html
 

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the problem with the head gasket on earlier northstar engines is that the bolts can't be reused to bolt the head down. A Failing head gasket at 115K miles is not a problem on the 2007 northstar engines because by 2007 Cadillac switched to better head bolts that allow the head to be removed and replaced.
 

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"better head bolts" is not the answer. Northstar head bolts are torque-to-yield pieces - the action of torque plus degrees of additional tightening stretches the bolts and loads the cylinder head with clamping pressure. You cannot reuse Northstar head bolts - you install new ones any time the head is removed. Even in the newer engines, you have head gasket failure, you install either cylinder block bolt hole inserts (for new head bolts) or you stud the block. The main Northstar problem is failure of the (aluminum) cylinder block head bolt hole threads - one or more holes have threads fail, you insert all 20 holes.

Head bolts have changed, yes. Bolt total thread length was changed several times. Bolt/hole thread size and pitch were changed several times. You need to know which engine series you're repairing because the head bolts (among many other specs) were changed several times over the engine production run.

Get into www.rockauto.com. Compare the cylinder head bolt pictures for 2007, 2004, and 2002. (Click the little thumbnails for a zoom, simply close the zoom in your browser.) You should be able to see the thread length and pitch differences. 2004 saw the length/pitch change and that's easy to spot. The earlier ones are more subtle but part number comparisons show the differences.
 

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"better head bolts" is not the answer. Northstar head bolts are torque-to-yield pieces - the action of torque plus degrees of additional tightening stretches the bolts and loads the cylinder head with clamping pressure. You cannot reuse Northstar head bolts - you install new ones any time the head is removed. Even in the newer engines, you have head gasket failure, you install either cylinder block bolt hole inserts (for new head bolts) or you stud the block. The main Northstar problem is failure of the (aluminum) cylinder block head bolt hole threads - one or more holes have threads fail, you insert all 20 holes.

Head bolts have changed, yes. Bolt total thread length was changed several times. Bolt/hole thread size and pitch were changed several times. You need to know which engine series you're repairing because the head bolts (among many other specs) were changed several times over the engine production run.

Get into www.rockauto.com. Compare the cylinder head bolt pictures for 2007, 2004, and 2002. (Click the little thumbnails for a zoom, simply close the zoom in your browser.) You should be able to see the thread length and pitch differences. 2004 saw the length/pitch change and that's easy to spot. The earlier ones are more subtle but part number comparisons show the differences.
According to the old guru, the bolts are torque to stretch not torque to yield. The reason they cannot be reused is that they come new with a proprietary sealing compound already applied that is not multi-use.
 

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According to the old guru, the bolts are torque to stretch not torque to yield. The reason they cannot be reused is that they come new with a proprietary sealing compound already applied that is not multi-use.

Caution: Ensure the cylinder head bolts that are being used are the proper pitch or engine damage will occur. The thread pitch on the M11 cylinder head bolts and the engine block cylinder head bolt holes have been revised. In order to prevent engine damage it is important to identify which thread pitch is being used. Cylinder head bolts with a pitch of 1.5 mm have a thread length of about 48 mm (1.890 in) long. Cylinder head bolts with a pitch of 2.0 mm have a thread length of about 67 mm (2.638 in) long

Every fastener has an elastic limit, commonly referred to as its yield point, or more properly, "the threshold of yield." Up to this point, if the load on a fastener is released, the fastener will spring back to its original length. When a fastener is stretched into the yield zone, some of the elasticity is permanently lost. Once the bolt is stretched it cannot be used again. Sealing compound has nothing to do with it.
 

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Caution: Ensure the cylinder head bolts that are being used are the proper pitch or engine damage will occur. The thread pitch on the M11 cylinder head bolts and the engine block cylinder head bolt holes have been revised. In order to prevent engine damage it is important to identify which thread pitch is being used. Cylinder head bolts with a pitch of 1.5 mm have a thread length of about 48 mm (1.890 in) long. Cylinder head bolts with a pitch of 2.0 mm have a thread length of about 67 mm (2.638 in) long

Every fastener has an elastic limit, commonly referred to as its yield point, or more properly, "the threshold of yield." Up to this point, if the load on a fastener is released, the fastener will spring back to its original length. When a fastener is stretched into the yield zone, some of the elasticity is permanently lost. Once the bolt is stretched it cannot be used again. Sealing compound has nothing to do with it.
My source is a Cadillac engineer that was an original designer of the Northstar that used to frequent this site but got himself in trouble by truthfully answering sensitive questions. He said the head bolts are not torqued beyond the yield point but are torqued to a stretch length and are safe to reuse except for the proprietary locking/sealing compound that is applied during manufacture.


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The engineers name was Allen Cline and he was on the original design /developement team for Northstar/Aurora. He was also involved with the team that set a bunch of 24hr speed records with the Olds Aurora which was a 3.0L Northstar.
 

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The next time you do a head gasket job on a northstar measure the old bolts to the new ones. The locking/ sealant is available in 8 oz. bottles. It took GM from 1993 to around 2004 to fix the head bolt problem. There first fix was to increase the length of the insert and kept the thread pitch the same. Most of the time the insert would pull out. I think in 96 some independent company’s came out with course thread inserts with new bolts or studs and they would hold. It took GM about 11 to fix the problem when it was solved years earlier. GM has spent a lot of money fixing the Northstar, Head bolts, oil leaks, oil consumption, chain tensioners , half case bolts and ect.
 

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The next time you do a head gasket job on a northstar measure the old bolts to the new ones. The locking/ sealant is available in 8 oz. bottles. It took GM from 1993 to around 2004 to fix the head bolt problem. There first fix was to increase the length of the insert and kept the thread pitch the same. Most of the time the insert would pull out. I think in 96 some independent company’s came out with course thread inserts with new bolts or studs and they would hold. It took GM about 11 to fix the problem when it was solved years earlier. GM has spent a lot of money fixing the Northstar, Head bolts, oil leaks, oil consumption, chain tensioners , half case bolts and ect.
The problem was never the bolts, it was the threads in the block. GM never installed any inserts from the factory. Timeserts were an authorized dealer repair, and Norms inserts and probably others by now came along later. The jury is still out as to whether the lastest northstars are actually fixed or not. I feel that they may be improved.
 

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The problem was never the bolts, it was the threads in the block. GM never installed any inserts from the factory. Timeserts were an authorized dealer repair, and Norms inserts and probably others by now came along later. The jury is still out as to whether the lastest northstars are actually fixed or not. I feel that they may be improved.
Your right the bolts are not the problem. It was the fine threads in the block. When we used the factory inserts there was an 8 to 10 comeback ratio. Then there great idea was to make the inserts longer and fine thread. Same ratio. Then they tried again with fine thread same problem. Then Norms came out with coarse inserts and bolts and if done right it never came back for head gaskets. I can’t tell how many times we had to do inserts on motor that we were replacing piston and rings for oil consumption, the threads would just pull out.

I guess you never taken apart a Northstar service engine (GM remanufactured)
 

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Awhile back, when it seems alot more people had failed threads on the Northstar forum, it was pointed out that when drilling the block if you saw the "black dust of death", the timeserts would probably fail. I did 2 h/g replacements, one with timeserts and one with Norm's. When I drilled, all I saw was shiny virgin aluminum. I think that is the key as to whether the fine thread inserts will last. Last I heard both cars are holding up well.

No, I never disassembled a GM reman engine.
 

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If you go to Engines; Northstar and dig way, way back in the head bolt/head gasket sticky threads you'll find a series of pictures (by AJxtcman) of cylinder block head bolt holes - some with obvious slag and gas pockets in the walls of the threaded holes. That was about the time that GM changed the aluminum formula for the block for the second or third time - after the 1999 manufacturing run. 1998 - 1999 are the "worst" years for failures in the non-scientific poll in the same forum.

IIRC one of those pictures actually showed coolant weeping into a bolt hole through a porosity that extended to a water passage.
 

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Discussion Starter #14
So I should avoid it or not? I now understand what the problem was that caused failures but was it fixed before 07
 

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The engine was redesigned and groomed throughout its production run. The 2007 should have the latest and greatest Northstar updates. Northstar reliability is in the same boat as any other engine on earth - something can happen (go wrong) at any time - or the engine could go 250,000 miles with only normal maintenance.

No one can predict what can/will/might go wrong with a used car - or even a new one, for that matter.
 

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It's very hard to control the cooling rate of an entire aluminum engine block during the casting process. One characteristic of some aluminum alloys is that if it is improperly heat treated they are very susceptible to intergranular corrosion. Such aluminum can assume the consistency of wet cardboard under the right conditions. While Cadillac was working the bugs out of the casting process there were some engines produced that had been improperly cooled and eventually developed this form of corrosion in key areas. In addition, there were problems with the head gasket design that caused it to gradually deteriorate if the engine coolant was not properly serviced. The gasket would seep coolant into the area of the head bolts and the aluminum would degrade into mush. The threads would pull, the head would lift, and the head gasket would leak. The casting and cooling process was massaged, the bolts went through a series of changes, and the head gasket was improved. At about the time this developement was completed it was decided to abandon the engine as being to expensive to produce.
 
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