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Hi All,

Was talking to a Caddy mechanic about HG failure....he said his "database program" (don't know which one he has) showed that the vast majority of N* HG failures occur between 120-130K miles. He says it's really a function of mileage, not age.

....and the % of N* engines that do fail from model years '97-'00 was very very high....like around 80-85%

As always, I appreciate everyone's thoughts and comments...:)

Thanks!
 

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I'd probably agree on the miles not age thing IF regular cooling system maintenance has been done. That said, we've seen MANY fail at much earlier miles than 120K.

In 2000 GM lengthened the head bolts and the failure rate fell dramatically, so I say he's pretty close it he is not including the 2000's. Check the HG Sticky poll in the Northstar forum.
 

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Yep ^^^ - You can always look through the non-scientific Engines; Northstar sticky poll on head bolt hole thread>gasket failures. It supports the pre-2000 failure rate.
 

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I'd say the information your were given is mostly false. Not sure what database he's talking about. None of the major players collect data like that and if they did they aren't sharing with their competitors. So how do they get enough data to say 80-85%. Sounds like some seat of the pants statistics to me. Unless he has his own database. In which case I'll offer this up. Vehicles with less than 100,000 miles are much more likely to be dealer serviced. Vehicles with much more miles might not be considered "worth fixing". And if your job is to fix Northstar headgaskets the percentage of customers you see with headgasket failures will be much larger than the population at large. Anytime statistics are used be on the lookout for possible sampling bias.

I'll share my personal experience having repaired these cars for a long time now. The majority of failures are 99 and earlier with the year 2001 being a close second. That is just what happens in my shop. I've talked with other Cadillac specialists and they seem to confirm the 2001 phenomenon, and always cylinder #1 on those years.

As to the failure percentages. Over a long enough time frame the failure rate is always 100%. These cars were mostly built with a 4 year/50,000 mile warranty. Many auto manufacturers feel that the effective lifespan of the cars they design is 100,000 miles for consumer automobiles. So anything past that is the product of good engineering and good maintenance. I have seen more than a few 200,000 mile Northstars that have never had any engine mechanical repairs including the head gasket. Invariably these were well maintained cars. I have seen poorly maintained Northstars easily cruise past 150,000 miles and with oil leak repairs and head gasket repairs I've seen Northstars top 300,000 miles. The point is that the life and maintenance of any engine has a huge effect and by the time you pass 100,000 miles the variance can be huge.

I reject the idea that the failure is mileage based. The failure is of the threads and corrosion is the cause. Everytime I pull stripped head bolts they come out as powdered aluminum oxide. The blocks are porous and coolant works its way into the threads. If the coolant is in good shape the corrosion is greatly delayed. If its corrosion inhibitors are depleted or it has been exposed to oxygen while hot, the corrosion will be accelerated. GM was fixing these under warranty so the idea that 120-130k is the magic number doesn't fit that detail. I've also had to do head gaskets on cars with under 50k miles that were rarely driven but the coolant was never changed for 20 yrs.

I'd say maintenance, time, and casting variations are the biggest factors. Some of it is luck of the draw. If the casting was exceptionally good you might never have an issue even with mediocre maintenance. If the casting was poor all maintenance in the world might only slow the issue down. The best you can do is stay on top of the coolant and hope for the best.
 

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Discussion Starter #5
Hi Russell,

Thanks for that in depth, articulate post! I so appreciate it....especially in an era where folks tend not to communicate very well.

But maybe we're kindred spirits because we have the same first name.....(with 2 LL's, no less.....:)

It was a difficult decision, and I ALREADY miss the car, but I sold it yesterday. Put it on Craigslist for $3900 and a fellow loved it and gave me $3500. Was that fair?

She only has 70K miles, and I hope he has many happy, no HG years, but the thought of when the HG goes, it's $3-$5K+ not to mention the 1/5 century old electronics going just scared me.....guess I'm a wus....:)

The shop that the N* performance fellow sent me to in Ca. said AT LEAST $5,500 to install studs...... Whew...

Don't shoot me for saying this, I know it's sacrilegious, but they shoulda done a recall (of course too expensive, think Pinto) or just put in the old reliable 327/350 Chevy engine. They are bulletproof. I've had one in my boat since 1979, using raw (salt) water cooling!! (No Dexcool....:) It's still runs great!

OH...just FYI, the N* Performance guy was adamant......NO DEXCOOL.....EVER. He says if someone uses it in an engine they've repaired IT VOIDS THE WARRANTEE.....wow, that speaks volumes.

Well, I wanna thank all you folks who have been so generous with your time and expertise.

I expect I'll have another Caddy soon.....so.....another question:

What year do you think is the best bet?

Cheers,
Russ
 

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Really any of the RWD Northstars are pretty bulletproof for the head gaskets. They still have the oil leaks though. The DTS years of the FWD Northstars were solid too. $5500 is a high price for stud install unless he's going through the engine pretty thoroughly or there are local economic differences. I'm in a major metropolitan area, but out of the city center and in the Southeast US. So everything costs less here. Our price for studs is one of the higher on the East Coast, we do a more complete job than most also. But, we aren't at that price. For that price we could do the head gaskets with lower end reseal and bearings and rings, pre-tax.

I'm always amused at the Dexcool hate. I've seen failures with every type of coolant in Northstars. But, there are two important things to consider about Dexcool. 1, it doesn't break down linearly like older green coolants and some of the aftermarket long life coolants. As an HOAT coolant it is really good for 5 years or more and then it degrades rapidly. The indications are that while Dexcool requires less maintenance, missed or delayed maintenance is much more detrimental. 2, it does not react well with oxygen, especially when it is hot. In GM training and service manuals for early Dexcool cars it was often recommended that if there was a breach in the cooling system while the vehicle was at operating temperature that all of the coolant should be flushed no matter how new it is. This was also at the heart of a settled class action lawsuit by GM. Some early Dexcool vehicles had overflow bottles instead of pressurized surge tanks and this allowed hot coolant to contact oxygen. Some gaskets while being coolant tight were not air tight and allowed oxygen intrusion every time the vehicle cooled. The result was rapid breakdown of the coolant into a corrosive substance.

Northstars have always had air tight gaskets and surge tanks so with proper maintenance and repair it should be no issue. But, how many Northstar owners are driving around with bad surge tank caps negating their benefit? How many have slight coolant manifold leaks that they are putting off due to the cost of repair? How many low mileage cars are well past the 5 year change date? The problem isn't the coolant. Its a lack of knowledge at dealerships and repair shops and a lack of using that knowledge to educate their consumers and customers so they can make the best decision for them. The block porosity of the Northstar makes coolant maintenance that much more paramount.

I don't have anything against other coolants. But, some aftermarket coolants are just HOAT coolants with a different color dye. So you have all the same risks. Another risk is mixing. OAT, HOAT, IAT coolants all operate at different PHs and achieve corrosion protection differently. Mixing them will neutralize their chemical effectiveness. So any change in coolant formulation must be a complete and thorough changeover. Otherwise you are much worse off than when you started. This risk is more pronounced on some engines like the Northstar because they have no block drain for the coolant. This means a change of type requires a very thorough water flush that produces a lot of regulated hazardous waste followed by a very thorough flush with the new coolant which will produce more waste.

So for me it is just easier to stick with Dexcool and educate my customers.

To put the Northstar in its proper place in history. We have to look at its contemporaries. The only other GM engine producing the power of the Northstar was the LT1 in the Corvette and some other models. That was it. The Northstar did it with almost a full less liter of displacement, similar MPGs despite being in larger vehicles and an idle that was glass smooth. The engine also previewed many of the features that would be found on the Gen III small block (LS engines), thermoplastic intake, dry valley, crank driven oil pump in the timing cover, etc. The engine lasted 17 years through many fuel economy crackdowns and only succumbed to the High Feature V6 engine family (3.6, etc) that itself is enjoying a 14 year run and still going strong.

There are far worse engines than the Northstar. But, most of those are in cars that are far worse themselves and many that are less labor intensive to work on. The Northstar gets its reputation in part due to the amount of labor required to perform these repairs due to the construction and in part due to the fact that these cars are actually worth keeping. If this was a 97 Mitsubishi with a blown head gasket no one would bat an eye. Its 21 years old and well past its appointment with the scrap yard. A Cadillac on the other hand? Well the Cadillacs makes you at least consider spending the money which I think says a lot about these cars.
 

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I'm always amused at the Dexcool hate.
I've heard the same about Dexcool… Mainly "highly corrosive". I've been using Dexcool for the V changing out no more than two years on. Recently it's been more frequently than that because of leaky radiators being replaced. At repair shops I've heard a variety of opinions... The Chevy dealer where I get service highly recommends Dexcool. The only reason they claim to come across for customers not using it is cost. Actually their "bulk" coolant is Dexcool and they have to order out for different coolant which could increase the price. On occasion I will go to Firestone as I purchased my tires there and I get the related tire services for free. Concerning all fluids and lubricants they recommend whatever is recommended by the manufacturer. The "cost" issue is much more prevalent here compared to the dealer and they do find many customers requesting the "cheaper" services. They actually seemed surprised when I request "full synthetic", "Dexcool" (or compatible) or whatever is recommended for my car. I even use premium fuel every fill up because it is "recommended" even though it isn't "required". idk maybe I fit into that "well maintained" category...

I have to agree with Rainbowbridge… Your posts are very well written and informative. If I have a question about my car I'll be looking to see what you have to say.
 

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Well I have a 1997 N* here with 236k miles (380k km) on it, supposedly having its (supposedly) first headgasket failure :) Will keep you updated after the engine is out and disassembled if it is really first HG job on it :)
 

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After reading so many varying opinions on this topic. I’d have to also agree that the measure of “when” wouldn’t be the mileage or the age of, but rather a measure of how many heat cycles, expansion and contraction, the engine has had. IMO it would explain how some fail at much lower mileages than others, if frequent short trips are the norm. Would be nice if there was some way to measure this variable, make it semi permanent like the odometer but resettable like a trip meter after an engine has been replaced or had a full set of threads repaired.
 

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Has nothing to do with how many times the engine is started, stopped, heated, cooled. The block and heads are the same aluminum alloy so they expand and contract at the same rates. The machined cast iron cylinders are cast into the aluminum block. Why don't they work loose and leak? The hardened iron valve seats are pressed into the cylinder head reliefs - they don't fall out. Many, many steel bolts tapped into holes into and near coolant passages. Very few leaks there, too.

DEX-COOL, properly maintained and exchanged, is not the cause, either.

ANY internal combustion engine can have a head gasket failure at 100, 100,000, or 250,000 miles. It's the luck of the draw.

As posted much earlier, study the non-scientific head bolt thread failure sticky poll in Engines; Northstar. ALL these discussions have been posted so many times that it's almost laughable. All documented in the stickies in Engines; Northstar.

Here's 2 quarts of DEX-COOL out of my STS at about 4 years. See anything to worry about ? Looks the same yesterday - but two exchanges later.

2 quarts coolant 3.jpg
 

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Okay, luck of the draw, got it. All variables, scientific or not hence forth be invalid. No need to argue what components might be under various material stresses during normal operation. ‘97 thru ‘00 were just really unlucky years. Good thing they didn’t blow their wad on lottery tickets back then.
 

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No one's saying "can the past data" but - in some cases - it may well be the luck of the draw. There are many, many 97, 98, 99 Northstars still running around in the world with no problems.

You might want to get into the several sticky threads in Engines; Northstar that get pretty deep into the head bolt problem. In particular, the one that gets into the different metallurgy changes in the block for 1987, 1998, and 1999, then the total redesign for 2000 and later........ and how some of those earlier blocks seemed to have severe ash pockets in the head bolt threaded holes. There are borescope photos in there, too.
 
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