My first Post!! My dad and I operate a 90-95 ZR-1 performance and repair shop in Addison, Il. I bought my first Cadi, a '96 Deville when I was in College back in '05 for $3000 with 125,000. Of course it ran great in the city, but as soon as I got about 30 miles down I-55 it started overheating any time I drove over 70 mph. It was also blowing coolant out the vent hose at WOT. So I sniffed the coolant tank with our exhaust analyzer and it spiked over 500 ppm HC within seconds, a passing tailpipe reading would be under 10 ppm. So I time-serted it over Christmas break, it ran perfect and was a great car after that. My dad bought a '99 Eldo ETC in '03 with 40,000 miles, he changed the coolant to conventional green coolant as soon as he bought it. The car now has 130,000 miles and doesn't overheat or use coolant. I believe using DEX-COOL to be one of the root causes of head gasket failure. A year and a half ago I needed a daily driver so I bought a 2000 Seville SLS with 110,000 miles, which I test drove extensively on the highway, and was fine the first few months. However, 8000 miles later it was overheating on the highway, and same thing, 500+ HC in the coolant tank. My advice is DO NOT BUY A NORTHSTAR CADDILAC WITH OVER 75,000 MILES!!!! NO MATTER HOW GOOD A DEAL YOU THINK IT IS!!! The gas analyzer in the coolant tank test will tell you within 10 seconds if you have blown head gaskets. Don't waste your money on a water pump, radiator, or thermostat, it's not going to fix an overheating on the highway problem. I also had an '05 CTS with the 3.6L which uses a MLS head gasket from the factory. I never had any trouble with that engine.

 

Buying a caddy with pulled head bolts isnt a bad thing. Just because it happens it is still very fixable.
I have had 3 90s eras with blown headgaskets. My 96 ETC did exactly as you mentioned. I could drive all day in the city but just out of the city and I was overheated rapidly.
The Dexcool Debate is a hard one.
I run dexcool in both of my cadillacs with no problem with proper maintnence. My Deville has 197000 miles completely original. No major engine work. Runs flawless
My 97 Seville, blew at 99000 miles. 4 headbolts had pulled purging coolant everywhere including the oil. but the funny thing is no external leak was present. got engine timeserted. I maintain meticulously. I bought the car because of the problem it had but it was worth every penny.
I absolutely agree on the water pump, thermostat... Dont waste your money. Get your coolant tested for exhaust gases first thing. It gets right to the point and saves time, money, and headaches

 

I can't say for sure that Dex-Cool causes a problem on Northstars. The Northstar and LT-5 both were originally designed to use Conventional silicate based (green) coolant. We measured a failed head gasket from an LT-5 using an organic corrosion inhibitor (Dex-Cool) for a year and it swelled significantly compared to a head gasket from a factory assembled engine with 10k miles using a silicate based corrosion inhibitor. There is a detailed article about this on our website, zr1specialist.com.

 

Ok so I did a block test revved it up and ran it a while no color change took it to gm and was advised it was not a headgasket problem I drive 45 min to and from wrk daily and it doeant overheat unless I go over 50 mph excessively or if its hotter than 70 outside I owe a lot on this car and i adore it but Wats my problem with it

 

What year is the car? Have you been changing the coolant regularly? It can be confusing in the early stages of failure. The root cause of overheating is the threads being pulled out of the block, once this happens the head gasket cannot seal. Sometimes only one or two bolts pull out, and only one cylinder is affected. Next the exhaust gasses enter the cooling system and aerates the coolant, this is what causes the overheating. Driving around town at low speeds doesn't put much load on the engine, but high speed highway driving does. Constant high load driving aggravates the problem. I confirmed the problem on my 2000 Seville by going WOT a few times after the engine is warmed up and then measuring the HC level in the coolant tank. A typical passing exhaust reading is 8 or less. So if there's more HC in your coolant than in your exhaust, you've got a problem. In my opinion this is the only true test.

 

I absolutely agree on the water pump, thermostat... Dont waste your money. Get your coolant tested for exhaust gases first thing. It gets right to the point and saves time, money, and headaches




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Light Brilliance of DVDs --- Grey's Anatomy Season 8 DVD，Live in the moment, live with it!

 

we have been beating this dead horse for years and one would think everyone understood the issues .. BUT .. I am responding because this thread does offer something NEW! its logical that sniffing the coolant tank would work, so I side with that idea, not only on Cadillacs over 75,000 miles, but on any car with an aluminum head being GM or Ford or whatever .. however, its even more important the AGE of the coolant is determined!

Did you see our FAQ thread ?


please read the thread on the subject in our FAQ .. specially aging coolant.

 

I wanted to share my experience with my 97 Deville head gasket problem that was resolved beautifully recently. After much careful research and extensive testing, all signs indicated head gasket failure at 142,000 miles. Oil changes every 3,000 matters not on a Northstar. Considered scrapping the car but she's a real cherry Deville and everything I looked at to replace it was much higher than the repair but now the real test. In upstate NY, where do I find anybody that knows about and will touch timeserts or studs? Right in Rochester I found a 20 year Cadillac man with his own shop doing just that - timeserts for the Northstar !!! Scott Spade of ROC City Auto Service in Rochester answers his own phone almost every time and returns the call right away if he misses you. He took very careful care of my baby and got it back to me in a few days with new oil, new coolant, new power steering fluid and new cam cover gaskets too. I opted for a water pump while the cradle was down and the old one already off the car. Scott installed it for the cost of the pump. The only minor issue experienced was the AC did not work when I picked it up. Scott and his high-end scanner found a high-resistance connection within 5 minutes and had the AC back up in a flash. I can tell you it's priceless to find a real quality Cadillac man in his own shop at small shop prices and not Cadillac dealer prices. I now have a bit over 1,000 miles on the new build and am feeling like I'm driving a brand new Cadillac. If you happen to read this Scott, thank you so much for my new 97.

 

Good to hear you kept your Deville on the road! My '96 Deville made the spring break trip from Normal, Il. to Sarasota, Fl. and back with 6, yea 6 people, a full trunk, and never had any trouble. I time-serted the block 3 months prior to the trip. It powered through the mountains effortlessly. Only thing I had to watch was oil consumption, which was a quart every 500-700 miles. This is pretty typical for a high mileage Northstar, though. Just keep up on trans fluid and filter changes. My dad's been changing the fluid on his '99 ETC every 40,000 and even with 136,000 miles it still shifts perfectly smooth, and still chirps the tires on the 1-2 shift at WOT if you shift it manually.

 

failed head gasket from an LT-5 using an organic corrosion inhibitor (Dex-Cool) for a year and it swelled significantly compared to a head gasket from a factory assembled engine with 10k miles using a silicate based corrosion inhibitor. There is a detailed article about this on our website, zr1specialist.com.