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Hello all. I have a 1998 Eldorado that I purchased 3 years ago with only 23,500 miles on it. It was originally owned by an 80 year old woman in Sarasota Florida. (Yeah, I know that sounds like a used car salesman's pitch, but it's true & I have all the original papers). I've put about 4000 miles on it since. Replaced  the ignition coils, plugs, wires, cleaned out the throttle body, changed the thermostat, radiator hoses & other things & the car runs great. Also, changed the Dexcool 4 times & the oil 2 times. Read too many things regarding the cooling system & the head gaskets so I didn't care what I spent & did it myself. I know it was over kill but now I know the anti freeze is fresh. Here's the odd thing though. I've read that the Northstar will need a quart of oil every 1000 miles or so. With this car, I've never had to add a drop of oil & there isn't a leak anywhere. (Last oil change 3000 miles ago. An anomaly)?  Also (& here's a dumb question)...this car now has 27,500 miles on it & is 23 years old. Given the age & the extremely low mileage, what are the chances that the head bolts will fail literally down the road? I'm hoping that the head bolts again given the age of the car & the low mileage are "frozen" in place. So any comments from you experts out there? Thanks! 

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I think the '1000 mile quart' is just a rule of thumb or industry standard. 

Not just Northstars.....not just GM.......1000 miles per quart would be considered the normal oil comsumption for any engine.

Kind of a standard.....1000 miles per quart is ok.....500 miles per quart would require some investigation and start documenting date and mileage etc.


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Nice vehicle. Great buy.

As for the oil consumption, If you drive it like it was designed to be the consumption should be less.

I have 2 97s and I drive them spiritedly, I also only use non synthetic oil as much as possible. My consumption on both is little to none.

As for the headbolt failure, my theory is just drive it. Do not even think about it. Keep up on the coolant at least every 2 years.

Keep waterpump belt and tensioner free . (that tensioner tends to seize over time)

If you do those 2 I would not worry about it. If it does happen then worry about it then. 

Enjoy it and share a pic


Nice, clean, luxury= fine automobile

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Wow, that is identical to my 2001 Eldo.

How are the door panels?

Love that color. I actually sold mine mainly because I hated its oil consumption (newer gen N*), and was not a fan of the secondary air injection. 

Rode like a dream though


Nice, clean, luxury= fine automobile

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MY best tip to you is be gentle with the door panels. They are the only main weakness. And they are nearly impossible to find. I have had 3 Eldos and they were all broke. They start pulling away from the door as the retainer clips get broken. And someone not knowing how to remove them properly is a large factor


Nice, clean, luxury= fine automobile

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Just FYI about the Eldo door panel clips...

At one time there was a GM Kent Moore dealership repair kit for those years ago. Kit had maybe 20 clips.....maybe more....maybe less. 

You may see a kit show up on eBay once in a while. 




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Beautiful car you are lucky to find that with low mileage.

It has been said that the head gaskets blow because coolant goes acidic from not being changed, it eats the head gasket and coolant leeches into the headbolt threads and corrodes them via electrolysis weakening the threads and the bolts pull out of the block.  We had a Northstar powertrain here for a while and that was GMs finding on the matter.

And I am not doubting GMs prognosis, because I have seen aluminum block material turned to dust from electrolysis and acidic coolant would facilitate that.   

I have since blown 2 Northstar's and both times it happened at the redline, around 5,800 rpm.  I felt the head gasket let go and had a misfire at the next stop.

In both instances I was using regular fuel, when premium is recommended.  In both instances my foot was to the floor and hit about 85 to 90.  I am pretty sure I heard knocking before a stumble that I felt in the seat of my pants.

Now this is my opinion, I believe that my fuel delivery was compromised at either the pump or filter and fuel pressure dropped off causing a lean condition that led to destructive detonation ripping the bolts out of the block.  

A partially clogged filter can breeze along all day at 650 to 4000 rpm delivering adequate fuel only to fail to deliver additional fuel above 4000 rpm (arbitrary numbers but you get my drift) and even though the PCM calls for a rich mixture at full throttle inadequate fuel pressure is not capable of keeping up with demand and a lean condition arises.

So,  my advice is to change your fuel filter every couple of years for safety sake.  In addition, check your fuel pressure at idle and up the rpm range to be sure the pressure stays within spec.

Detonation causes huge pressure spikes in the cylinder and you want to avoid it.  There will be those who say, that's why there is a knock sensor, it will retard the ignition to eliminate the knock.  But, it has to actually knock for the knock sensor to act, and at 6,000 rpm, that might be too late.  I am also considering that this happens cumulatively, the first time the head lifts filling the headbolt wells with coolant and the cycle begins.   Destructive detonation could also push the headbolt outside of the elastic zone and into the plastic zone permanently lessening the clamping force, and so on and so on.

Be sure your cooling system is in perfect shape and that it holds rated pressure without leakdown.  High coolant temps invites detonation, so it is advisable to keep the cooling system in good shape.

Furthermore, I would never use regular fuel in a 93 to 99 NS again, low octane fuels detonate easier than high octane fuel. 93 octane!

A recipe for detonation, would be starving the engine for fuel at high RPM, with regular fuel, in an engine that is overheating.

If you watch engines on dynos or vehicles on a dyno you will notice that the tech tests to be sure the air-fuel ratio does not lean out at progressively higher rpms, they remedy that before going full power.

Good luck with that beauty

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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