Northstar Overheating Problem- Is it possible to live with or even avoid...?
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Northstar Engines and System Technical Discussion Discussion, Northstar Overheating Problem- Is it possible to live with or even avoid...? in Cadillac Engine Technical Discussion; I've read so many of the posts here, and after a LOT LOT LOT of research (and LOTS of years ...
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    Enjoytheroad is offline Cadillac Owners Member
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    Northstar Overheating Problem- Is it possible to live with or even avoid...?

    I've read so many of the posts here, and after a LOT LOT LOT of research (and LOTS of years enjoying the wonderful used Caddy market) I've never seen this directly addressed within the subject of overheated Northstars.... so here's my question in a new thread on an old subject for the techs here:

    If I should get a 100K mile DeVille with a Northstar, and supposing it's running fine as it is, is there anything I can do to prolong or avoid this problem by a decent amount? Every few years I usually drop into a really nice, well kept car for around $2K-$3K, so a major repair like that would ruin the bargain luxury deal I hope to enjoy.

    I would be going mostly long distances (2 hours and farther per drive) and would be HAPPY to upgrade something (fans, different temp sensor, etc...) or remove something (thermostat?) even if it meant no heat... just to enjoy the soft quiet ride of the DeVille. Is there a point or condition under which the problem is more apt to start? (Such as a granny idling at Shopmart, Livery sitting in traffic, teenager gunning it at every light, or some other situation where the car runs hot or harder than usual?) We all know that highway cruising is the easiest thing on a vehicle, it's the starting and stopping, heating up and cooling off, gaining momentum and stopping it that puts all the wear on a vehicle, so if I would stick to fall/winter long distance highway driving, keeping an eye on the temp, is it possible to mostly avoid that beginning stage of overheating/leaking/headgasket problems...?

    Thanks in advance for your input, I've always wondered about this and would love to have another Northstar instead of looking at the old 4.9's on Ebay.

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    neo126's Avatar
    neo126 is offline Cadillac Owners Fanatic
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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    From what I have seen on here for the past few years is pretty much, regular maintenace and coolant changes. If she is already having a overheating problem there are a few tests you can do. There are a few northstar experts on here that will chime in as well.

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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?



    Two things you can do. 1) Change the coolant every 2 years. 2) look for a 2000+, 2004+ is even better. Gm lengthened the head bolts in 2000, greatly reducing the HG failure rate. They went to a coarser thread pitch in '04 all but eliminating it.

    When and if it happens, there is nothing you can do. Some people have been able to baby it for a year until it became undriveable, but NO snake oil repairs in a bottle will help, despite what the manufacturer says.

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    Enjoytheroad is offline Cadillac Owners Member
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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    Quote Originally Posted by Ranger View Post


    Two things you can do. 1) Change the coolant every 2 years. .....................
    What does changing the coolant do? Prevent corrosion? Is there a specific thing that causes this? (Like the combination of corroded, weakened threads with getting a little hot) that causes this? Do you think there is any advantage at all to driving the car (before it has this problem) on the highway in situations where it has low operating temps?

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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    Boy are you opening a can of worms. The chicken or the egg theory has been discussed in great detail. Coolant looses it's anti corrosion additives over time. Neglecting the coolant can cause the Hg to fail. General consensus is that when that happens, coolant gets into the head bolt threads and acts as an electrolyte between the dissimilar metals causing corrosion of the threads. The threads pull and the heads loose their clamping force. You can figure out the rest. Some people think Dex is the problem. Either way, the best and only hedge is to change the coolant regularly and frequently, but there is no guarantees. Do some searching here and you'll find some lengthy discussions on it. No advantages to where or how you drive it. Don't even think of running a cooler thermostat or worse yet, removing it.

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    Enjoytheroad is offline Cadillac Owners Member
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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    What would running a cooler thermostat or even removing it do...?

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    Submariner409 is offline If it won't run, install a sound system
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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    No help - In a Northstar the thermostat is a necessary part of proper coolant circulation throughout the engine - and the stock thermostat begins opening at 188 and is fully open at 206 - way within safe, normal temperature limits for a 16 or 18 pound pressure cap....... and current engine operating temps are one reason that the engine oil "sludge" problem basically no longer exists in a properly maintained car. Cool engine temps create "sludge" - you can bank on that.

    Either repair the engine correctly - and don't dump in any magic snake oils or sealers - or sell the car as-is, with full disclosure.

    What makes you think that normal engine running temperatures have anything to do with overheating ??? Your first post - "If I buy this and if I do that will it prevent this or that .... ??" is the wrong approach. As posted, nothing you can do will guarantee the longevity of some mechanical apparatus - a wheel bearing fails, a transmission clutch pack blows up, a head bolt hole loses its threads and a gasket leaks. It's all mechanical and we should be ready to either fix it when (not if) it breaks/wears out or trade/sell it so frequently that we (almost) never experience wear or failure - regardless of just who built the thing.

    EDIT: As posted, you put the cart before the horse........ a failed head gasket (or any other cooling system gasket) causes coolant loss and subsequent overheating, not the other way around. An overheated engine does not cause a head gasket to fail - matter of fact, the engine would run better and more efficiently at 300 degrees than at 205. Why not run it at that temp ???? Because it would cost a LOT of money to maintain a cooling system designed and built to run at about 200 psi - and pressure is what raises the boiling point of our systems to about 265. Running a system at 300 degrees with a safety margin of 350 is a whole different physical can of worms. FWIW, in a naval propulsion nuclear reactor the "coolant" is pure water - pressurized to 1500psi+ and heated to 450 degrees +. That primary water, circulated to "boilers", is used to flash secondary water to steam for propulsion turbines.............. but you don't want to know the time and manpower it takes to safely maintain those pressurized systems. We can't do it in a car - yet.

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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    Quote Originally Posted by Ranger View Post
    Boy are you opening a can of worms. The chicken or the egg theory has been discussed in great detail. Coolant looses it's anti corrosion additives over time. Neglecting the coolant can cause the Hg to fail. General consensus is that when that happens, coolant gets into the head bolt threads and acts as an electrolyte between the dissimilar metals causing corrosion of the threads. The threads pull and the heads loose their clamping force. You can figure out the rest. Some people think Dex is the problem. Either way, the best and only hedge is to change the coolant regularly and frequently, but there is no guarantees. Do some searching here and you'll find some lengthy discussions on it. No advantages to where or how you drive it. Don't even think of running a cooler thermostat or worse yet, removing it.
    I agree with Ranger - first the head gasket fails - then coolant and combustion gases enter the head bolt hole. Not sure if it's the interaction between the steel bolt and the aluminum threads, or the coolant and combustion gases and the aluminum threads, but eventually, the aluminum threads dissolve into a silvery paste that looks like anti-seize compound. Once clamping force is lost, combustion gases enter the cooling system and over-pressurize the system, forcing the coolant out the overflow, and massive overheating ensues.

    I don't know if changing coolant more often than 5 years/150,000 miles would help...but it couldn't hurt.

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    rmac is offline Cadillac Owners Member
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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    Howdy,

    I'm new to this group, having bought my 96 Deville the week before Thanksgiving.

    The car has overheated several times once I bought it, and I've been forced to mix different types of coolant with water to get the car home.

    Today, I drained the coolant, and replaced it with Dex-Cool. I was expecting to have a lot of used coolant, but only got a little over a gallon. I performed the exhaust gas test before I changed the coolant, and the fluid did not change color, so apparently I do not have a head gasket problem. However, I am concerned about the amount of coolant that I drained from the car, and that the car ran hot when I test drove it afterwards.

    The traffic was stop and go, and the coolant got as hot as 239F. I also noticed that with the AC on, the coolant dropped as low as 208 while driving, but was usually around 217-222 when I'd restart the car. I made two stops, and left the car for 5-10 minutes each time.

    Now I'm wondering about what might be wrong...Fan? Thermostat? Water pump?

    Amy advice will be greatly appreciated

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    Re: Northstar Overheating Problem- Is it possible to live with or even avoid...?

    Ok, first off, you'll never get all the coolant out unless you can hold the car upside down and shake it. What you drained is about normal. You CAN get a bit more if you stick a shop vac nozzle in the surge tank, seal it with your hand or a rag and turn it on. Obviously you need to have the hose plugged into the exhaust (not vacuum) port on the shop vac.

    You may have to top it off once or twice afterwards until the coolant level stabilizes. Be sure that the purge line is clear and flows coolant. That's the 3/8" line that runs into the side of the surge tank near the top. It purges air from the system. Check it cold. Just pull it and stick it in the open surge tank neck. You should see some coolant flow. If not, it's clogged at hte hollow bolt it attaches to at the other end and WILL cause it to overheat.

    Define "overheating".

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