What causes the headgastkets to leak?

[serpentking]

I guess you know my question from the title but I want to know this because Im considering just getting a new engine to put in mines and I dont want to have that problem again. Someone told me that they just keep overheating from the first time they overheat. So I guess if I keep the engine cool all the time, then this should never happen, of am I being misinformed? Thanks in advance.

[Ranger]

You are misinformed. The biggest cause is lack of cooling system maintanence. Once the corrsion inbihitors get depleted (2 years for green & 5 years for Dex), the head gaskets can start to rot from the inside. In other cases the head bolt threads can sometimes pull. Not much you can do to prevent that except pray to the head gasket Gods.

[Cadillac Jim]

What causes most head gasket leaks in Northstars is failure to change the coolant before it becomes corrosive. There is always a very small amount of coolant in the head gasket, and once it becomes corrosive, it settles in the wells where the head bolt threads are. Eventually it will weaken the threads and a head bolt will pull out, and you will have head gasket leakage on the one or two cylinders nearest that head bolt. The most common bolts to pull out seem to be the one nearest the driver and the one just to the right of it, and all of the outside head bolts are more likely to pull out sooner than the ones nearest the intake manifold -- but it can happen to any of them. The red anti-freeze is advertised to last 150,000 miles, but few people drive their Cadillac 30,000 miles a year so the 5-year time limit comes up first -- and most people, including dealers, don't know about the danger of letting coolant go too long. I am a victim of this myself. I let my coolant go seven years because I was thinking 100,000 miles, not 5 years. That's why I have a remanufactured engine from Jasper instead of the original.

I recommend changing red coolant every three years or so, and green coolant every year or so. If you want to be more economical, get some radiator test strips and watch the condition of your coolant yourself and change it before it gets too close to losing its anti-corrosion capabilities.

When you do change your coolant, drain it through the lower radiator hose at the radiator. Have a couple of gallons of 50-50 mixture ready. Add three GM sealant pellets or the equivalent to the lower radiator hose, put it back on, and fill the surge tank with 50-50. Start the car and let it idle, adding more 50-50 until the bubbles stop, and the level is 2-3 inches below the filler neck. You should be able to see it with a flashlight, and the proper level is when the coolant is on the sloped ridge right below the center of the fill neck. Put a new AC/Delco radiator cap from the dealer on your car and you are good to go for another 2-3 years.

The idea that aluminum engines are ruined once they overheat once comes from the early Rambler straight six all-aluminum engines of the 1960's. These engines used conventional head bolts as used in cast-iron engines. Those head bolts are thick and have a free length of the thickness of the head, mayby 10 cm, and the threads start at the surface of the block. Modern aluminum engines, including the Northstar, use torque-and-twist head bolts. These bolts are thinner and have a long free area, often 20 cm or more, and the threads are deep in the block -- down around the main bearing cage. The thinner bolts and long free length, with use of steel approrpiate for this type of bolt, makes them a tension spring that will allow considerable expansion and contraction while keeping head clamping force within tolerances.

The Northstar is unique in that it has a limp-home mode. GM apparently noted during durability testing that the engine could be run without coolant for a considerable period without damage, and have a feature to the PCM that cuts off selected cylinders in a dance-around-the-motor pattern to avoid high temperatures at any given point in the engine. GM will allow the car to be run for 50 miles without coolant, without voiding the warranty, due to the limp-home mode. Car and Driver noted this, and ran 0-60 mph and quarter-mile times in the limp-home mode, and judged that the car had about 50 hp.

Summary: The Northstar is a brick of an engine. But, as with any engine with aluminum in the cooling system, keep the coolant changed, and don't push the time limits that the coolant manufacturer recommends. Corrosion by stale coolant will bring down any engine.

[Ranger]

The Northstar is unique in that it has a limp-home mode, starting in 1997

I believe that the Northstar was designed with this feature right from the start.

Modern aluminum engines, including the Northstar, use torque-and-twist head bolts. These bolts have a long free area, typically about a foot, and the threads are deep in the block -- down around the main bearing cage.

Are you saying that the head bolts are 12" long? I have never had one apart, but that seems rather lengthy to me.

[Cadillac Jim]

Ranger: Limp-home from 1993? I suppose. It was presented to me in 1997 as if it were a new thing. Fred -- does your 1994 STS have limp-home?

I really don't know how long they are. From the pictures I've seen, I would say that they are about ten inches total, so I was exaggerating to make the point. They could be a foot. Anyone with direct experience?

I edited the original post to soften the dates and head bolt length.

[Ed Hall]

My Northstar 1993 Allante has limp home mode.

[Cadillac Jim]

My Northstar 1993 Allante has limp home mode.

Excellent. I edited the original post to remove the date. Thank you.

[BodybyFisher]

Another feature of the Northstar engines is a "limp home" mode that allows the engine to continue running if all the coolant is lost. If the PCM senses an overheating condition, it temporarily disables up to half of the cylinders. This pumps enough air though the engine to keep temperatures from getting hot enough to cause any damage. Even so, GM says the vehicle should not be driven more than 50 miles in the limp-home mode.

http://www.babcox.com/editorial/us/us100232.htm

[WarrenJ]

GM will allow the car to be run for 50 miles without coolant, without voiding the warranty, due to the limp-home mode. Car and Driver noted this, and ran 0-60 mph and quarter-mile times in the limp-home mode, and judged that the car had about 50 hp.

Several years ago I sufferred a water pump failure and drove about a mile (IIRC) in limp home mode.

50hp sounds just about right!

Still, it was neat to have that confidence. I had 49 more miles available to me.

Regards,

Warren

[steve6]

I guess you know my question from the title but I want to know this because Im considering just getting a new engine to put in mines and I dont want to have that problem again. Someone told me that they just keep overheating from the first time they overheat. So I guess if I keep the engine cool all the time, then this should never happen, of am I being misinformed? Thanks in advance.

Its a GM, so mainly ***** design and cheap componants to start with.

[WarrenJ]

Its a GM, so mainly ***** design and cheap componants to start with.

Okay gentlemen and ladies, have at him . . . .

[Bruce Nunnally]

Also please use Search, as there have been some links to excellent articles in the past as well to this same question, but here are a couple of good articles:

http://www.babcox.com/editorial/us/us80222.htm

the most common causes of gasket failure, which are detonation, overheating and incorrect torque.

More general article on engine failure:

http://www.aa1car.com/library/us697.htm

The Northstar does not appear to have any *unique* causes of headgasket failure, just the normal ones high compression engines enjoy. The Northstar powertrain is a premium, DOHC all aluminum V8 produced by the largest manufacturer in the world for its flagship product. None of that syncs with 'cheap' in my book.

The real issue with the Northstar headgasket is that it is expensive to replace, and Cadillac Dealers seem to work to make it as expensive as possible.

[WarrenJ]

Bruce, EXCELLENT reading material. I particularly enjoyed the photo in the second article.

Regards,

Warren

[BodybyFisher]

Its a GM, so mainly ***** design and cheap componants to start with.

Okay gentlemen and ladies, have at him . . . .

[WarrenJ]

Its a GM, so mainly ***** design and cheap componants to start with.

Okay gentlemen and ladies, have at him . . . .

But you didn't "have at him . . . . "

Mike, you've disappointed me.

BTW as I type, the steed is being clayed and waxed. Can't wait to pick it up.

Regards,

Warren

[BodybyFisher]

Its a GM, so mainly ***** design and cheap componants to start with.

Okay gentlemen and ladies, have at him . . . .

But you didn't "have at him . . . . "

Mike, you've disappointed me.

BTW as I type, the steed is being clayed and waxed. Can't wait to pick it up.

Regards,

Warren

Watching our wonderful political election process over the last six months, I am realizing that half the population is brain dead and its useless to try to converse with them or change their opinion, you only get frustrated.

It's useless to wrestle with a pig, you get dirty, and the pig enjoys it...

[WarrenJ]

OINK!

[BodybyFisher]

OINK!

You are a pig?, I don't think so!

Can't wait to see how your car looks with the clay treatment

[WarrenJ]

Can't wait to see how your car looks with the clay treatment

I'll remind you.

Last year after Bobby clayed "Baby," I went to the gas station for a filling. I leaned against the rear fender and while gassing up nearly slid off the fender!

Coulda broke my neck! I told Bobby to "up" his insurance.

Regards,

Warren

EDIT: Was I OT there?

[epricedright]

Its a GM, so mainly ***** design and cheap componants to start with.

Okay gentlemen and ladies, have at him . . . .

But you didn't "have at him . . . . "

Mike, you've disappointed me.

BTW as I type, the steed is being clayed and waxed. Can't wait to pick it up.

Regards,

Warren

Watching our wonderful political election process over the last six months, I am realizing that half the population is brain dead and its useless to try to converse with them or change their opinion, you only get frustrated.

It's useless to wrestle with a pig, you get dirty, and the pig enjoys it...

You must be tired today.

[JohnnyG]

I do believe ALL of these gentelmen's remarks are correct, Steve6 excluded of course for obvious reasons. However, I do think one small thing may contribute to the head gasket issue that is not readily apparent. That is cold carbon rap. Yes, it is usually considered harmless, and annoying, but I think real damage can result if left unchecked. I feel that ANY unusual force against the head was not designed for and cannot be excluded from our analysis. Patricularly this force which is directed in such a way to allow the headbolts to pull or the headgaskets to seperate from there mating surfaces ever so briefly. Therefore, I recommend taking the Northstar engine to redline as described in the WOT procedure at the first sign of any unusual noise on startup, allowing the ****design and the cheap parts to do their thing up to about 6700 rpm in second gear. Hopefully with some rice burner with a 14" high wing and a fartpipe muffler next to you so you can blow his doors off in the process.

[BodybyFisher]

I do believe ALL of these gentelmen's remarks are correct, Steve6 excluded of course for obvious reasons. However, I do think one small thing may contribute to the head gasket issue that is not readily apparent. That is cold carbon rap. Yes, it is usually considered harmless, and annoying, but I think real damage can result if left unchecked. I feel that ANY unusual force against the head was not designed for and cannot be excluded from our analysis. Patricularly this force which is directed in such a way to allow the headbolts to pull or the headgaskets to seperate from there mating surfaces ever so briefly. Therefore, I recommend taking the Northstar engine to redline as described in the WOT procedure at the first sign of any unusual noise on startup, allowing the ****design and the cheap parts to do their thing up to about 6700 rpm in second gear. Hopefully with some rice burner with a 14" high wing and a fartpipe muffler next to you so you can blow his doors off in the process.

Johnny, I once raised this issue with the guru and he said that the knock can not cause a head bolt to be pushed out or pull.. I thought the same thing you just raised. I wish his posts were still on the board. But I agree that its important to keep the combustion chambers clean.

[WarrenJ]

I do believe ALL of these gentelmen's remarks are correct, Steve6 excluded of course for obvious reasons. However, I do think one small thing may contribute to the head gasket issue that is not readily apparent. That is cold carbon rap. Yes, it is usually considered harmless, and annoying, but I think real damage can result if left unchecked. I feel that ANY unusual force against the head was not designed for and cannot be excluded from our analysis. Patricularly this force which is directed in such a way to allow the headbolts to pull or the headgaskets to seperate from there mating surfaces ever so briefly. Therefore, I recommend taking the Northstar engine to redline as described in the WOT procedure at the first sign of any unusual noise on startup, allowing the ****design and the cheap parts to do their thing up to about 6700 rpm in second gear. Hopefully with some rice burner with a 14" high wing and a fartpipe muffler next to you so you can blow his doors off in the process.

Actually, it was "******," but otherwise I can't fault your conclusions.

Regards,

Warren

[Cadillac Jim]

I wonder what engine that photo in Bruce's second article came from? It looked like it might be from a high-performance SOHC big-bore two-valve-per-cylinder engine, like a Jaguar XK6, but I can't imagine what engine like that would have two big valves instead of four medium-sized valves per cylinder. Some writing on the side of the piston understructure is visible, and possibly legible. Looking at the valve thoroughly stuck into the piston crown, I would gather that we are looking at a siezed egine due to a timing belt failure, with the cylinder head effectively destroyed.

That kind of thing makes me grateful for the Northstar timing chain arrangement. I've never heard of one giving trouble. It looks to me like it may be inherited from the Quad 4, which also never gave valve train trouble. I drove my HO (180 hp) for seven years and shifted my 5-speed at 7,000+ RPM every day and the engine loved it.

[JohnnyG]

Johnny, I once raised this issue with the guru and he said that the knock can not cause a head bolt to be pushed out or pull.. I thought the same thing you just raised. I wish his posts were still on the board. But I agree that its important to keep the combustion chambers clean.

That's not EXACTLY what my post says. I meant to say that carbon rap could cause some kind of upward force on the head, maybe allowing the head gaskets to seperate just a little bit. Enough to break the "static seal" of any graphite or adhesive layer between the two major parts. We all know from other recent posts that the bolts act much like a very strong spring, so that idicates that they may just allow a little movement now and then. This thin seperation could allow coolant to get in and squish back out numerous times in the course of a cold start, and eventually (let's say) contribute to the failure. Example: Have there been known HG failures with cars under 5 years/150,000 miles? Sure there were. So since the coolant should be good until then at least, all failures can't be contributed to acidic coolant as the sole cause.

so mainly ***** design and cheap componants

Sorry Warren, but you had 6 *'s, so we both got it wrong. I also elected to pass on the misspelling of "componants" but I don't like to wage personal attacks. After all we are all adults here. I'll let the content of the post speak for itself.