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'93 STS
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4 Posts
Discussion Starter #1
Hello one and all! It's my first time posting here and I'm new to Cadillac ownership, so please bear with me :eek:

Recently I bought a cheap 1993 Cadillac Seville 'hooptie' with the notorious 4.6 Northstar engine. I find it absolutely love it when it actually works and doesn't overheat - that rumble and torque is intoxicating! However, ever since I drove it off the dealer lot I have been struggling with this, and the 2 hour drive home was certainly interesting! After hearing this most of you will conclude that it's the dreaded head gasket issue, but I have reasons to believe that it's not.

Basically the car overheats quite quickly from when it's cold - I can typically only drive 10 miles or so. The 'Check Coolant Level' warning text comes on periodically, and there is an apparent loss of coolant in the system. I noticed that there was dripping from the radiator and tried to resolve the issue by adding Bar's Leaks coolant sealant (not ideal, I know) into the radiator hose. It appeared to be successful as I didn't see any leak anymore, but the overheating issues still persisted. I also tried to bleed potential air out of the cooling system by having the car idling without the expansion tank cap on and giving it revs to 3.6K RPM.

The strange part about all of this is that 1) the car cools down rapidly when I turn the engine off and 2) on my first drive home after the car had already overheated multiple times, I could all of a sudden drive it without any issues for hours after adding a small amount of coolant. They returned again the next day.

After bleeding the air out of the cooling system (or at least trying to) in combination with the coolant leak sealant, the car would overheat again. I removed the cap once more and added some coolant, and after that it ran reliably without overheating for at least 30 miles during my test drive. I've yet to test if this was merely a moment of luck or if it's been permanently fixed, however.

Have any of you guys experienced a similar scenario, where the car periodically doesn't overheat and runs just fine, and sometimes overheats almost immediately? What could be the cause for this, and what would you recommend I try next if my problems persist? Any insight would be much appreciated! :eek:

Thanks in advance!
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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71,046 Posts
Welcome Aboard !!! What "notorious" Northstar ?

We don't like "repairs" using radiator sealants. Find the leak and repair IT correctly. Hope that the sealant has not clogged small cooling passages or the heater core.

Correct coolant level is about 1/2 - 2/3 in the surge tank, checked cold only.

Do some research on the "purge line". It runs from the water crossover hollow bolt/nipple over to the upper side of the surge tank. That line must flow a small steady stream of coolant at idle - it removes air and gases from the coolant so the water pump sees "solid" coolant - it's a centrifugal pump so any bubbles interrupt flow in the pump. The engine overheats quickly.

Read the stickies in the Engines; Northstar forums. Lots of cooling system info there.

For more info, Google "cadillac forums northstar engine cooling purge line" or something close.

Study up on the water pump drive assembly belt tensioner pulley.

Subscribe the car to www.alldatadiy.com - it's the online GM/Cadillac service manuals plus a lot more.

Study all this - written about your engine by one of the Cadillac Powertrain engineers...... https://www.cadillacforums.com/cadillac-tech.html
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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20,222 Posts
most of you will conclude that it's the dreaded head gasket issue, but I have reasons to believe that it's not.
that is where I stopped reading -
THREE things to do -
check coolant level -
check the PURGE LINE -
do a BLOCK TEST -

--------------------

tried to resolve the issue by adding Bar's Leaks coolant sealant
BIG mistake - causes more problems than it solves -

I also tried to bleed potential air out of the cooling system by having the car idling without the expansion tank cap on
that won't help -
the PURGE LINE is the ONLY way to eliminate trapped air from the cooling system -
physically check the PURGE LINE for coolant flow FROM the thermostat housing TO the serge tank -
 

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Registered
'93 STS
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4 Posts
Discussion Starter #5
Wow, thank you for the overwhelming amount of information and resources - I'll look into everything that you suggested and hopefully I'll be able to pinpoint the cause and fix it! The purge line definitely sounds promising, so that's my next step forward assuming that I'll actually be able to reach it with my limited (or complete lack of) mechanical knowledge.

Also, based on your remarks, it is safe to say that I indeed messed up with my "repairs" so far. While I'm also highly skeptical of these sealants, I figured it was worth the try to remedy the leak this way as I didn't want to invest potentially copious amounts of money on a car in such molested condition, even if it's special. Lesson learned, in hindsight it would have been better for me to consult with you guys first. Your expertise is impressive to say the least!

I'll keep you updated what happens, cheers everyone!
 

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Registered
'93 STS
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4 Posts
Discussion Starter #6
Update: I took the car out on a long test drive (at least 40 miles) and didn't experience any overheating issues whatsoever today apart from the 'Check Coolant Level' warning text, even when idling for extended periods of time in traffic. It appears that the car is running fine... for now, and I have absolutely no idea why it's working so well all of a sudden. Perhaps the coolant leak sealant did the trick after all? There isn't any temperature gauge in this car either, making it even more difficult to assess the cooling ability. I'll keep you guys posted if something unexpected happens! :eek:
 

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Registered
1999 STS - diamond white
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5,229 Posts
Sounds like you are headed down the path we were led down. i didn't use any sealer though. Your heater core will probably plug up from it. Don't be surprised when the engine fails completely. I hope you aren't far from home when it does. Our STS is now on Craiglslist, basically for parts.
 

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Registered
'93 STS
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4 Posts
Discussion Starter #8
Sounds like you are headed down the path we were led down. i didn't use any sealer though. Your heater core will probably plug up from it. Don't be surprised when the engine fails completely. I hope you aren't far from home when it does. Our STS is now on Craiglslist, basically for parts.
Oh, I'm prepared for the worst - this car has seen better days and I'm doing my best to enjoy it while I still can. It's a ticking time bomb, but I'm nonetheless impressed with it considering it's 25 years old with 150K+ miles on the clock and a shady owner history. That sucks, I'm sorry to hear about yours. Mine is bound to follow the same fate soon.
 

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1999 ESC
99' Eldo
Joined
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48 Posts
Hello one and all! It's my first time posting here and I'm new to Cadillac ownership, so please bear with me :eek:

Recently I bought a cheap 1993 Cadillac Seville 'hooptie' with the notorious 4.6 Northstar engine. I find it absolutely love it when it actually works and doesn't overheat - that rumble and torque is intoxicating! However, ever since I drove it off the dealer lot I have been struggling with this, and the 2 hour drive home was certainly interesting! After hearing this most of you will conclude that it's the dreaded head gasket issue, but I have reasons to believe that it's not.

Basically the car overheats quite quickly from when it's cold - I can typically only drive 10 miles or so. The 'Check Coolant Level' warning text comes on periodically, and there is an apparent loss of coolant in the system. I noticed that there was dripping from the radiator and tried to resolve the issue by adding Bar's Leaks coolant sealant (not ideal, I know) into the radiator hose. It appeared to be successful as I didn't see any leak anymore, but the overheating issues still persisted. I also tried to bleed potential air out of the cooling system by having the car idling without the expansion tank cap on and giving it revs to 3.6K RPM.

The strange part about all of this is that 1) the car cools down rapidly when I turn the engine off and 2) on my first drive home after the car had already overheated multiple times, I could all of a sudden drive it without any issues for hours after adding a small amount of coolant. They returned again the next day.

After bleeding the air out of the cooling system (or at least trying to) in combination with the coolant leak sealant, the car would overheat again. I removed the cap once more and added some coolant, and after that it ran reliably without overheating for at least 30 miles during my test drive. I've yet to test if this was merely a moment of luck or if it's been permanently fixed, however.

Have any of you guys experienced a similar scenario, where the car periodically doesn't overheat and runs just fine, and sometimes overheats almost immediately? What could be the cause for this, and what would you recommend I try next if my problems persist? Any insight would be much appreciated! :eek:

Thanks in advance!
In August 2019 my Northstar in my 1999 Eldorado was overheating and was losing coolant - I did a block test and it confirmed I had exhaust gas in my coolant. I installed Thermalweld - THERMALWELD - LANDING PAGE - Head Gasket Repair | Thermalweld in August with 82000 miles on my 1999 Eldorado – I’ve now driven over 1600 miles and have no loss of coolant. When you call Thermalweld you should have the opportunity to talk with the owner – Mr. Robert Hooper for any technical advice regarding the conversion. He is also the chemist who created the product over 20 years ago. He has helped hundreds of Northstar owners fix their overheating problems. Despite all the naysayers I saved over $6000 and my Eldo is still on the road and not overheating any more
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
Joined
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71,046 Posts
Chelly, please go back over the first several threads in here.

Be very careful when pouring magic potions into your cooling system. The posted "fix" contains sodium silicate which renders the engine useless for further repair or overhaul.

Personally, as an experienced Northstar hobbyist mechanic, I would strongly recommend against temporary "fixes" and repair the engine correctly. Yes, the right way is more costly - but not so for the long run.

However, if you intend to patch up the car and drive it as a beater, junking it when it blows up, then go ahead and take the cheap way out.
 
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