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Changing Northstar water pump


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I recently finished a two day water pump change on my 1995 STS with 125k miles. I figured I would share my experiences in case anyone else has to do it.

I got the pump impeller from my local parts shop along with (a cheap version of) the socket needed to remeve/replace. The job looked simple enough, remove the belt, the house cover with 10mm bolts and swap impellers.....wrong. It was apparent that the cooling system had ovbiously never been flushed out and the impeller's locking tabs had tons of lime and corrosion practically welding them to the inner pump housing. I tried to use the cheap tool (which looked like a cheap hole saw) with breaker bar and couldn't get it too budge. I tried again with a 2 ft pole over the breaker bar and the socket would slip off of the impeller as the little tabs just rounded off.

Anyway, to make a long story short, there was no way the thing was coming out with the cheap socket which was the only thing available anwhere in town except for Snappy or Mac which wan't $90 and $120 for the sucker! I found one on Ebay for about $25 which was still generic (Astro Pnumatic) but is still stout like any other impact socket. I sprayed some lime away on the impeller tabs and let it sit overnight, then used some break loose spray, PB Blaster on it. The thing still wouldn't budge with a breaker bar but at least wasn't stripping out. I finally ran an air hose from my neighbors garage and used his impact with the new socket. It finally broke loose after a about a of minute pounding with the impact.


1999 STS 65k

1995 STS 127k

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Great description.

I read (with interest) these type of posts as I still have my original pump.

Time is running out, I expect to be facing this job in the near future.

Thanks for taking the time to post your experience.


2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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On my 93 Eldo 4.6L I used the cheaper version of the tool. You are correct in stating that as you apply pressure the tool wants to pivot, and not make good contact with the pump. To counter this I did 3 things. 1) Had a friend position a 2X4 on the backside of the tool to keep it fully engaged with the pump. 2) Used a 2 foot pipe extension over the end of the breaker bar to gain more leverage. 3) Used a small sledge hammer as an impact on the end of the pipe to break it loose. The 1/2 inch breaker bar by itself was useless. It was somewhat difficult but none the less can be accomplished. For installation I used a little vacuum grease on the o-ring and it went back in fairly easy. I also used a vcuum grease on the pump cover. That was 15K ago and it's working just fine. More importantly change your coolant at least every 3 years and use 2 tubes BARS stop leak. WalMart carries it fairly cheap, around $1.50 per tube. Add this to the radiator hose and NOT the overflow holding tank. There is a real concern that if the coolant system isn't maintained properly the head gaskets will go and time serts will be required for reassembly. The choice is yours, either do the maintenance, or get prepared for a major repair bill.

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This is all very interesting reading. It seems to me that I have read before that the older (green coolant) pumps were harder to remove. Something to due with silicates and build up. Ofcourse lack of maintainence would play a big part. The interesting part is how the cheap (stamped) sockets don't really cut the mustard. In anticipation of having to do this job someday I made myself a socket a few months ago to the snap-on specs. http://www.geocities.com/grandolfo

I have not had to take it on a "test run" yet. I hope it holds up after reading all this.

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