Cooling system diagram northstar engine - 1998 Cadillac DeVille

In 2007 the Buick Lucerne was equipped with 2 engine options. 3.8 Liter OHV V6 and the Northstar 4.6 Liter V8.

Was the cooling system recently opened? What was serviced?

The 3.8 has a 7mm bleeder screw on the top of the thermostat housing. A funnel in the radiator is helpful to bleed the air. You will notice the upper radiator hose curves to a higher elevation than the bleeder screw. Manipulation of the hose by hand may be needed to get the air out. I recommend and use a cooling system funnel to help. It minimizes mess as well. ( https://smile.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY/ref=sr_1_1?ie=UTF8&qid=1488855489&sr=8-1&keywords=lisle+cooling+system+funnel ) There are other brands available as well.

I do not recall if the Northstar V8 has a bleeder on all models, but some do have a similar bleeder screw. Be sure the system is filled initially and manipulate the hoses up and down as well as squeeze them to get air moving. The Northstar water pump is on the back side of the engine driven by the camshaft. The upper hose runs along the front of the engine bay and connects to the radiator at the top on the passenger side of the engine bay.

For both vehicles, fill as much as possible cold. Start and idle. As the temperature increases, I recommend occasionally revving the engine to between 1500 and 2000 RPM to fill heater core and move coolant with a little more force.

For my 1997 Cadillac Deville limousine with 4.6 L Northstar it should be 196 to 205 deg. And top out at no more than 230 deg. F. Check multispeed fans for high speed turning over and antifreeze fluid level in overflow tank. Also, check for head gasket leaks through tailpipe which will show up as steam when you start the engine.

You are going to have to use a pressure tester on the cooling system and follow the drip back to it's source.You may have to remove items to get a clear view of the leak source.Small mirrors can be helpful too,as is florescent dye added to the cooling system to help identify the leak.

When you say thermagasket kit,I assume you mean one of those silly DIY gasket sealant liquids that you put in the engine.

You should not use these type of products on ANY engine let alone the Northstar.

To cure a headgasket leak, replace the headgasket.....there is no miracle cure.

On the Northstar, you will damage the cooling system,plus you will continue to have issues as time goes on.

How do you know you have a blown head gasket?

Here is something to consider.......

The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.
If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.
The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.

The normal operating temperature for the Northstar engine is around 210 degrees.
The fans will not come on until the temp hits 225 degrees.

The thermostat in the northstar engine is located at the bottom radiator hose (unlike most conventional cooling systems).

The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.The hose goes in to the engine to a crossover and comes out the other side to near the thermostat housing,the blockage may be there.

If the other end of your purge line is not connected to anything then that is the problem......it must be reconnected otherwise the cooling system is not pressurized.

The thermostat in the Northstar is in the lower hose as you have stated.
The thermostat in the Northstar engine is a duel action device.
One end of the stem is the Thermostat(obviously) and at the other end is a spring loaded pressure valve(the thinner end).
Make sure the thermostat end is nearest the rubber hose and the pressure valve end is in towards the engine.
The cooling system in the Northstar does not work like the older,conventional systems, this is why most people are confused when they find the Thermostat in the lower hose.

There is no need to bleed air out of the system as the Northstar is self purging.

If you are having overheating problems the most common overheating problem with the Northstar engine is a blocked purge line. It's job is to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank(Not the cap!),this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.

Air locks in the Northstar engine shouldn't be a problem as the system is self purging, given that all hoses are clear.

need 1998 northstar engine diagram to change the head gasket thanks

I'm assuming your car has the Northstar engine?.

Strangely enough,if you remove the thermostat in the Northstar engine, it will overheat, this is because the stat is both a thermostat and a pressure valve.I can't be bothered to explain in detail how the whole cooling system works but please understand that you need to put the stat back in,(or preferably a new one).As for the cooling fans,what you described is normal for the Northstar.
Further to this, look at my profile,I have provided similar solutions for overheating problems.

I am assuming you have the Northstar engine.

Check for coolant flow at the Purge line,this is a common problem on the Northstar.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.

Are you running it without a thermostat? If so,then strangely enough,this will cause overheating as the Northstar cooling system is different to most conventional systems and therefore will not help you diagnose the problem.