Northstar headgaskets...

[manowar77]

There are all lot of posts on this forum regarding Northstars bad headgaskets due to a bad coolant service, but have anyone seen with their own eyes how the gasket have been after opening an Northstar?

If the gasket have been corroded around the coolant channels,then u can blame the coolant,other people means that its the headbolts that pulls, not the gasket that have corroded and started to leak.

Have anyone done a headgasket change and noticed corroded areas on the gasket? Or is it all to blame on pulled bolts?

Anyone maybe taken a pic of a used headgasket? If u did,can you post it here?

I havent had this problem so far...i change my coolant every 24 months with 50% "green stuff" and 50% distilled water!

[Bruce Nunnally]

This seems a reasonable approach, although I think the objective evidence is that you still can't tell which came first -- a bolt pulled and allowed coolant past the gasket or the gasket failed. But I agree let's see some gaskets!

[Jan Olsson]

It is important to know that the one (and only) thing you can do to keep your head gaskets happy is regular changes of coolant.

I know that there are people who maintain their cooling systems and still get head gasket leaks.

The guru never said it was "a magic cure" just that it was the best way to prevent gasket failure.

I might also add that he never saw a pulled head bolt. Many times the "evidence" is pictures of bolts with aluminium in the threads and that proves nothing to me.

The head bolts on my -93 STS (with no overheating issues) looked just the same after 130000 miles when I fixed some burned exhaust valves on the no. 1 cylinder.

Time-serts are a much stronger connection than the original one. You might also have read about pulled inserts. No way they pull if they are done properly! Just if the block itself got crystallized.

There is also a lot of talk about studs instead of bolts. I personally wouldn’t use them. Not just because they are not approved by GM but because of this:

Many feel that they should be stronger because you only turn the studs down (with a slight torque). The real torqueing is done with the nut, therefore the threads in the block don’t see galling when torqueing the heads.

In theory it is a superior technique (because you avoid galling), but when using Time-serts (made as a solid hardened insert) the galling/sticking would develop between the bolts/ inserts. Not in the block.

Gasket and bolts are calculated together to work as a unit. Changing dimensions etc would be some sort of trial and error. A larger stud for instance would make the dynamic load variations on the head gaskets larger than with a smaller one for instance. A stiffer gasket would on the contrary lessen the variations.

Just my 2 cents.

[32v_dohc]

What I found when I took mine apart is that neither poor coolant maintenance nor head bolt thread pull-out was the problem. When you open the Northstar you find the deck is an open deck with the bores unsupported at the top. This allows the bore to move slightly with respect to the head as the cylinder fires and the piston generates a side load. In order to ensure the gasket stays centered on the bore at all times the northstar incorporates a raised lip around the top of the bore. When the head is torqued the raised bead clamps into the gasket at the fire ring and prevents relative movement between the gasket and the bore. This would be fine except that the steel sleeves are held in place by a siamesed aluminum casting between the sleeves. The expansion between the sleeves expands greater then the gasket because the block is aluminum and the gasket is a steel composite. This puts the thin steel part of the gasket in tension and causes micro cracks in the ceramic part of the gasket. Another feature of the gasket is that the fire ring is made as one piece for all bores. On the bottom of the gasket the where the raised ring crimps the fire ring the gasket is continous thin steel that is strained by the aluminum between the bores expanding with the heat of the engine. The puts a tensile stress in the material between the crimps that is greatest at the crimp because it is bent. Over many cycle fatigue cracks form and propagate radially around the bore. This causes a leak where high pressure gas is blown from the crack through the micro cracks into the coolant jackets. The additional momentary pressure provides the push to force coolant through the micro cracks. It also provides additional impurities that deplete the coolant and foster corrosion of the gaskets. The gaskets I have seen have cracks on the bottom surface in the area between the bores. The gasket also rusted locally near the cracks. However there was no other sign of corrosion anywhere except locally near the failure. Also all of my bolts released with a snap. They did show signs of intrusion but they were all tight. The largest crack in the fire ring was 1.5 inches long and at that point the cylinder spit coolant drops with the plug out. My opinion is that this was purely a design error and that these failures have nothing to do with the bolts or coolant service. The "fix would be to add a slot in the stainless piece that connects the fire rings between the cylinders. Breaking the tension path in the stainless part of the gasket would eliminate the cracking and reduce failures to instances of true corrosion. Think about it, these engines lose water by the gallon but the gaskets are always firmly glued to both head and block and have to be painstakingly removed. This only makes sense when the water travel through the gasket.

HTH

John

[Bruce Nunnally]

Good info and thanks for posting Jan and John.

[Bruce Nunnally]

jcobz28 posted an image here: http://caddyinfo.ipbhost.com/index.php?showtopic=16154#

of bolt and head:

[Jan Olsson]

What I found when I took mine apart is that neither poor coolant maintenance nor head bolt thread pull-out was the problem. When you open the Northstar you find the deck is an open deck with the bores unsupported at the top. This allows the bore to move slightly with respect to the head as the cylinder fires and the piston generates a side load. In order to ensure the gasket stays centered on the bore at all times the northstar incorporates a raised lip around the top of the bore. When the head is torqued the raised bead clamps into the gasket at the fire ring and prevents relative movement between the gasket and the bore. This would be fine except that the steel sleeves are held in place by a siamesed aluminum casting between the sleeves. The expansion between the sleeves expands greater then the gasket because the block is aluminum and the gasket is a steel composite. This puts the thin steel part of the gasket in tension and causes micro cracks in the ceramic part of the gasket. Another feature of the gasket is that the fire ring is made as one piece for all bores. On the bottom of the gasket the where the raised ring crimps the fire ring the gasket is continous thin steel that is strained by the aluminum between the bores expanding with the heat of the engine. The puts a tensile stress in the material between the crimps that is greatest at the crimp because it is bent. Over many cycle fatigue cracks form and propagate radially around the bore. This causes a leak where high pressure gas is blown from the crack through the micro cracks into the coolant jackets. The additional momentary pressure provides the push to force coolant through the micro cracks. It also provides additional impurities that deplete the coolant and foster corrosion of the gaskets. The gaskets I have seen have cracks on the bottom surface in the area between the bores. The gasket also rusted locally near the cracks. However there was no other sign of corrosion anywhere except locally near the failure. Also all of my bolts released with a snap. They did show signs of intrusion but they were all tight. The largest crack in the fire ring was 1.5 inches long and at that point the cylinder spit coolant drops with the plug out. My opinion is that this was purely a design error and that these failures have nothing to do with the bolts or coolant service. The "fix would be to add a slot in the stainless piece that connects the fire rings between the cylinders. Breaking the tension path in the stainless part of the gasket would eliminate the cracking and reduce failures to instances of true corrosion. Think about it, these engines lose water by the gallon but the gaskets are always firmly glued to both head and block and have to be painstakingly removed. This only makes sense when the water travel through the gasket.

HTH

John

That explanation is a good one! The casting technique (die-casting versus conventional sand core casting) excercises the gaskets. The greatest amount of work is seen when heating the engine to normal temperature and of course when it cools down again.

Thanks Bruce

[manowar77]

That was a detailed answer, John! Is it the same construction on the 4,9? It does not seems like it is the same problem on the 4,9l engines...

with leaking gaskets!

Question:

Does anyone ever had a Northstar from it came out of GMs factory,shift coolant often with the right antifreeze and water, and never had a headgasket failure??

[Jan Olsson]

jcobz28 posted an image here: http://caddyinfo.ipbhost.com/index.php?showtopic=16154#

of bolt and head:

As you can see aluminium is in the threads. Prooves nothing to me...I'm not saying that he didn't experience loose bolts. Just saying that a picture don't proove it to me. As I said. I also had the threads strip when loosing the head bolts on my -93. Because of the high tension in that joint the bolts comes loose really easy.

Compare that joint to any other joint on the engine. The bolts don't look like that when you clean your EGR for instance. Just because they are not that tight!

[Ranger]

I know that there are people who maintain their cooling systems and still get head gasket leaks.

That is why I've always felt that the threads pull first.

Does anyone ever had a Northstar from it came out of GMs factory,shift coolant often with the right antifreeze and water, and never had a headgasket failure??

Many people have NOT had a head gasket failure. It is not a given.

I HAVE seen pictures of both pulled threads as well as deteriorated gaskets. I think Jake has posted some over at CF.

[manowar77]

What about the 4,9l engine...is it common on this engine also? Doesnt seem like it in this forum..

[Bruce Nunnally]

No, the 4.9L dont' get as much discussion about head gaskets as the 4.6L's do. As Ranger says, it is not "common" in either engine, as most engines go their entire service life without a headgasket issue.

Thanks to the goodness that is the Internet Wayback Machine I have recovered Ian's photo journal here: http://www.caddyinfo.com/nsrepair.htm of doing a Timesert.

[Ranger]

No, the 4.9 is very reliable and not known for head gasket failures. The 4.1 on the other hand is. It also is open deck, but if I remember correctly, it had an aluminum block and cast iron heads (different expansion rates).

[KHE]

No, the 4.9 is very reliable and not known for head gasket failures. The 4.1 on the other hand is. It also is open deck, but if I remember correctly, it had an aluminum block and cast iron heads (different expansion rates).

Actually, the 4.1 (HT-4100) is better known for intake manifold gasket leaks vs. head gasket problems.

[Ranger]

I seem to recall that, but I had 2 and replaced the HG's on one. It was actually spraying out the side between the head and the block.

[bigtone]

There are all lot of posts on this forum regarding Northstars bad headgaskets due to a bad coolant service, but have anyone seen with their own eyes how the gasket have been after opening an Northstar?

If the gasket have been corroded around the coolant channels,then u can blame the coolant,other people means that its the headbolts that pulls, not the gasket that have corroded and started to leak.

Have anyone done a headgasket change and noticed corroded areas on the gasket? Or is it all to blame on pulled bolts?

Anyone maybe taken a pic of a used headgasket? If u did,can you post it here?

I havent had this problem so far...i change my coolant every 24 months with 50% "green stuff" and 50% distilled water!

When I tested mine, I only had a leak from number 1 cylinder to the coolant passages. I noticed that the bolts were much looser on the back head. All I could see on the gasket was a very thin shiny line between #1 and the coolant jacket, pointing towards the front of the engine. It looked like the gasket was actually cut buy the combustion gas.

[MrEldo97]

I blew all of the headbolts out of the rear head on my '97 Eldorado three years ago. When I took the motor apart to Timesert it I found absolutely no evidence of leaking headgaskets ( front head was fine). IMO, the problem with pulled head bolts has more to do with a lack of cooling airflow around the rear head than anything else. The Northstar creates too much underhood heat which leads to a breakdown in the aluminum of the block and so on and so forth.

[BodybyFisher]

I blew all of the headbolts out of the rear head on my '97 Eldorado three years ago. When I took the motor apart to Timesert it I found absolutely no evidence of leaking headgaskets ( front head was fine). IMO, the problem with pulled head bolts has more to do with a lack of cooling airflow around the rear head than anything else. The Northstar creates too much underhood heat which leads to a breakdown in the aluminum of the block and so on and so forth.

Are you saying that when you removed each of the ten bolts in the rear head that none of them released with a SNAP?, they were all loose?, that would be the first time I ever heard that, usually 3 or 4 adjacent bolts fail and usually at the end of a head

[MrEldo97]

Yes. The six headbolts in the middle were finger tight - I just turned them out with my fingers and the four on the ends all just turned out - no snap, no release they just came out. The front head was fine; those headbolts all released with that snap. I would bet that a survey would find that the rear head is the troublesome head in terms of head gaskets/bolts. Many aluminum engines in "restricted" (lack of a better term...) engine bays have heat problems at the rear of the motor whether it's transverse or longitudinally installed regardless of make. The headgaskets all fail between rear cylinders. All manufacturers need to find better ways to remove that heat.

[BodybyFisher]

Well I will say that it appears that I have problems with the two cylinders in the rear bank toward the passenger side.

I wonder if this is the reason we are beginning to see functional vents on the fenders?, maybe this is more than a stylistic accent

[MrEldo97]

"I wonder if this is the reason we are beginning to see functional vents on the fenders?, maybe this is more than a stylistic accent "

Could be... Vents that allow for flow through ventilation to get that heat out would certainly help and I would bet cut down on head gasket failures.

[Bruce Nunnally]

In that case, I'll stop making fun of them. I'm all about functional. The new vents on the CTS Coupe prototype actually looked very good; hopefully that style will continue in production.

[JimD]

Well I will say that it appears that I have problems with the two cylinders in the rear bank toward the passenger side.

I wonder if this is the reason we are beginning to see functional vents on the fenders?, maybe this is more than a stylistic accent

I can see where underhood temperature would be a concern for an air cooled engine.

The chicken/egg question with head gasket failure versus head bolt thread failure was discussed many times by you-know-who. The threaded holes in the block suffer no damage until the gasket allows coolant to wash away the protective coating on the bolt threads which leads to accelerated galvanic corrosion with the coolant as an electrolyte.

[Cadillac Jim]

Hood vents were once the way that air flowed through the radiator. They were found on most cars until WW II. My first car, a 1941 Chevrolet, had functional hood vents. That's what the Buick "portholes" originally were. But after WW II they started routing hot air under the car instead, probably to keep the car cooler inside in the summer. My 1966 Corvette also had functional side vents; the gill-looking openings in front of the doors in the C2-C3 Corvettes was where the radiator air went. My big-block hood bump had side louvers in chrome that were functional. Mine came with rain baffles bolted in, sealing them; I took those out, so that, at any speed faster than a crawl, air pressure on the hood supplied cold air to the exposed air cleaner element that protruded into the hood bump.

There was something about that 1966 Corvette that has always intrigued me: it's traction in rain. The radiator was tipped forward (and mine had an air conditioner condenser in front of it). The air came in the grille, the water separated out and went down through a baffle while the air went up through the radiator. A heavily shrouded clutch-driven puller fan then took the air back and it exited through the fender vents and under the car. I found that the engine stayed dry even when driving 30 mph in four inches of water and throwing speedboat wakes on both sides. That's a good thing, what with an exposed air cleaner element.

Once, while driving toward Atlanta on my way to NC form Texas, a highway patrolman started shadowing me, mile after mile. I had out-of-state plates, Texas! Common sense said that it was just a matter of time before I met the man no matter what I did. But, we had a downpour that got worse and worse, and traffic on IH 20 slowed. We moved into town and the water started puddling on the highway and people slowed drastically. I found that hydroplaning kept everybody on the road below 40 mph but me. I could do 50 mph with sold traction. Traffic was driving 35 mph. The cop was pushing 40 mph, hydroplaning again and again, trying to stay up. Eventually, on IH 85 North, I lost him in the rear view mirror and never saw him again.

[MrEldo97]

This has always been GM's pos. I think there's more to the head bolt issue than the coolant story. I'm anal about maintenance and my head bolts pulled in spite of my efforts.