Im working on a 2000 caddy deville 4.6 . Put in therm and w/p overheating when driving at any speed.does not overheat when parked. Please help.

Did it overheat before the changes? If not I'm guessing you have an air pocket in the cooling system that you need to bleed.

2004 Bonne SLE
1971 Chevelle SS

The 4.6 northstars are very bad about headgaskets and the headbolts like to pull the threads out of the block. While sitting at a idle remove the coolant jug cap and rev engine to around 2k rpms. for around 2 mins. If coolant has a sulfur smell and boils out, headgaskets are a good possibility. Have not seen a thermostat go bad on these. If headgaskets are the problem your better off selling the vehicle.

Although the aluminum block threads were a serious issue, there has been a valid long term repair for many years. If your issue does turn out to be a head gasket leak, check the link below for the repair kit that would allow you to rebuild it and not have to worry about repeat block thread failures in the future. Any machine shop worth their weight should be able to install the stud kit in the link below. The Northstar is a good engine really and this cures it'* Achilles Heal! Northstar Performance - SureGrip Cylinder Head Stud Kits

Said repair only has a 50/50 chance of success. Worked with several techs. who been in the business since the 80s. Their success rate is 50/50. I hate quoting a 5k engine job, and see them come back with pulled headbolts, anymore we price an engine job. Cya, you have to in this business.

In the beginning, it took almost 250 installs worldwide and 115+ in the Northstar Performance shop before ANY failure with the kit was actually documented and confirmed and actually, it was due to a defect in the head. The NP company repaired it under warranty since they had done the install. GM actually subs out their reman motors and they use this kit without hesitancy on warrantying the engines.

My continued searches with query strings of every possible combination have led to not one post about engines with these kits failing. Please back-up your statements of 50% failure possibility after a competent installation by reputable shop. I'm quite sure the Cadillac side of the internet would be buzzing if such numbers were factual instead bragging on their various forums about having trust in their now rebuilt engines. My old neighbor here in Vegas had this kit installed in his (how I learned about it) and the mechanic said it was amazingly simple and literally foolproof. As with any profession, the length of time as a mechanic actually is not always an indicator of how well one grasps new techniques and technologies and implements them. I anxiously await documentation to prove your statements of failures.

Hello - I am Jake Wiebe, inventor of the SureGrip Cylinder Head Stud Kit (US Patent #8,740,532) and owner of Northstar Performance.

Certain types of repairs on the Northstar only have a hit/miss chance of working. With our repair kit, success is guaranteed. The only car I managed to blow the head gaskets a second time on, was my 1997 Eldorado ETC. The composite head gaskets blew out from the repeated runs to 130MPH. That was our test car so it saw a LOT of abuse. none of the studs had failed and all were still tight, no thread fatigue or failure. So for racing applications I recommend multi-layer-steel (MLS gaskets) and our SureGrip studs on the Northstar. We sell the MLS gaskets as well from the Flat-Out Group. We did have one other failure, due to a head imperfection (a nick across the fire-ring sealing area, that I had missed) and due to that it slowly pressurized the cooling system).

Going with our kit I personally guarantee success or the money back on the kit (ask me the details). It works WAY too good for anyone to second guess it. I'm not saying that to brag- I'm saying that because I know the problems Northstar owners face and I've made it my life'* work to eliminate the chance of head gasket failure on these engines. We've fixed over 600 Northstars to date in our shop and our kits have been used by other technicians since 2009 with great success. GM Warranty had approved the use in one car, that I know of; and asked the dealer to keep a couple kits in stock.

That'* a beautiful SSEI there damadtech in your signature. I have a 2000 (recently had an accident with it) and now a 2004 GXP. Great cars!

I hope to be of help and potentially a site supporter/advertiser.

-Jake

Hey Jake, Thanks for accepting the invitation to drop in and join the forum today, especially this thread. Your experience and technical expertise with the Northstar engine is a valuable asset to any group of enthusiasts, especially in the GM family and you're a Bonnie owner to boot!!! I realize your business keeps you hopping but any time you can spare to drop in will be greatly appreciated by everyone involved. Thanks for the compliment on the car and welcome to the fold!!

Would be my hope that the OP returns with a little more information on his Northstar as to if he is approaching 100k on his motor, whether the overheating started before or after his water pump and thermostat change and whatever. I've seen these pissing contests before on Northstar fixes and it would be helpful if he would give us more information before everyone goes ballastic.

2004 Bonne SLE
1971 Chevelle SS

The one thing I can add to this thread is as a Cadillac tech back in the early 2000'* i do remember a northstar coming into the shop with the dreaded pulled head bolts and at the time the only fix was a kent more thread insert kit. The problem I remember with this particular engine was porasody was present around the threads I was trying to repair. Even with the jig set up on the deck as soon as the drill bit hit the aluminum block it just disintegrated and there wasn't enough good metal for the insert to hold and we winded up junking the block and getting a used motor for the customer.