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Please help. Northstar freeze plug.

97396 Views 389 Replies 26 Participants Last post by  Ranger
Hello guys. I have a 2001 Seville STS, a freeze plug (core plug, welch plug) fell out. The plug is (was) located on the rear of the left cylinder head, left front corner of the engine bay, behind the water pump housing. I can't upload pics because I'm posting this from my phone but even if i could it would be hard to see the hole, it is barely visible, it's somewhat blocked by the water pump belt as well as the housing (have to look very closely at a strange angle). I have already bought the new plug, but how do I access the hole to install? Does the entire housing have to be removed? If so, how involved is this going to be? I've already removed the air filter box/ducting, water pump belt shield and disconnected the hoses from the housing.

Any help would be greatly appreciated. Thank you.
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You are not the first one to have this occur. There are threads addressing this in the recent past. (last 3-4 months) I suggested using a rubber expansion plug & I think they were able to pull it off but I will have to find the thread to verify. If the coolant is removed it might gain you enough access to cinch up the bolt to expand & seal the plug. That part would look like this,

You don't want to get into removing the X-over manifold if it can be avoided, It a genuine PITA but not the end of the world. I'll see if I can find that old thread for you.

To replace the original type plug you would have to remove the X-over manifold.
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I found the thread but again there is no follow-up. I don't know if a rubber expansion plug would work. I would try it. Pull the coolant pump & see.
You should still take a look at whether the coolant pump removal will allow access for a expansion plug. You will save a bunch of labor if you pulled it off. here is a crossover link on a 96-there are better links out there and there will be some differences on a 2001 Seville including fuel rail removal.
I feel for you. You can see the freeze plug is right on top of the lower port.

DO GET new gaskets & 9" or more of silicone hose. Those are the biggies & don't kink the fuel line as I did.

I diconnected the grounds at the front of the block for more harness movement. Others have removed the ground below the coolant sensor It may be better to unfasten both harness grounds.

Which ever you do you will soon find out the harness being in the way is the main problem of this entire job.
Dry means dry. The only place you would seal is the thread sealer on the port bolts.

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The bolts will hold them in place but there is no guarantee they won't fall off.

I used some masking tape on the edge but it held no better than the bolts shifting the part around to line it up. There is a risk of the masking tape getting into the gasket surface & sticking, you would then have to pull it out again to clear the gasket surfaces. One did fall out of alignment but i was able to get it back into place & start the bolts.

This is the kind of crap that makes this a difficult task. The use of masking tape not very ideal.
All 8 bolts are held in place by the gaskets in this pic.

You will notice the upper ports are different on the later model N* along with how the TB mounts.

The later model N* x-over looks like this.
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Some of the original sealant remains in the bolt threads, I just used a brush on pipe joint sealant sparsely applied.
There are many thread sealers out there to choose from, you only need a tiny amount.

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The blue seals are OEM from Cadillac. Nothing special going on.

The blue or orange part of the seal isn't the problem, the black plastic laminate that the seal is supported by is what deteriorates. Once that breeches the silicone blows out. Other GM motors have the same problems only at the intake manifolds. Same gasket structure. This gasket design works excellent & is even reusable on the trans pan, front cover, But exposure with dexcool is slow death to the black plastic.

The Dexcool does impregnate the plastic over a long period of time, not long enough. The gaskets I changed lasted 13 yrs 10 months 104,000mi.

The coolant pump seal & cover is only a problem if you have excessive corrosion going on. Mine cleaned up well, no pits, not a problem. Just a fresh seal.
MRneatfreak-Teflon tape sucks, avoid it. You can get a small tube of thread sealer at any decent parts store for 2-3-$4.

Tape doesn't work very well on bolts, it's meant for pipe thread that wedges as you screw into a tapered thread.

Tape tends to want to bunch up & just peel off as you screw it in machine bolt thread. A paste or liquid will assure sealer stays in the minor thread diameter. You don't need very much.
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I know the lower bolts need to all be in place when the X-over is positioned into place.

It seems to me there may not be room to fit a plastic tie. Sounds like a good plan if they fit in the bolt holes with the bolts. The in board bolts are really hard to deal with(restricted) & may be difficult to snip remove the tie.
Lubing "o" rings is always a good idea, engine or transmission oil.
It's a very common GM part used on all GM brands its about $20 to replace.
3/8th's works for both lines. NAPA had a set of 5 release tools 5/16ths to 7/8ths for $6.

I'm sure the other chain stores have similar offering if not the same.
They should have a small tube of thread sealant.

This one is 0.20 oz. Thats 5 X more than you need.

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You can find Permatex at most hardware stores & Walmart.
It looks like there is a champher you want to clear on this N* head.

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Cylinder bank 1 or bank 2? I thought the leak was a frost plug that fell out.
If coolant is running out there is a good chance the gasket is misaligned or the bolt missed the hole or went through the center.
The red is where the gasket should be & the green is where the gasket is. The yellow X's are the bolt holes. This can happen easy. You cant see where the gasket actually is. The only other alternatives are bleek.

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OEM Northstar head gaskets very rarely fail. I'v never heard of one failing yet.

The Cometic gaskets, although very good have no advantage over conventional steel graphite sandwich type on N*'s.

The Cometic gaskets are known to have seepage issues because of the layered steel design.

The Cometic probably will hold up better in unusually extreme conditions as in a built-up engines
but the seepage(oil & coolant) is a reality and the OEM application doesn't warrant the special need.

They are better suited for 500+HP racecars where they are popular & rebuilds are scheduled by the number of passes or laps.
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