A compression check will not always verify a leaky head gasket on a Northstar engine. Most of the time these head gaskets fail due to faulty head bolts. The threading on the bolts slowly pulls out of the engine block, creating a gap between the head and the block, allowing combustion fumes, oil, and coolant to mix together. One thing you can do is check your oil. A leaky head gasket will make your oil look like foamy chocolate. Also, you can take the cap of your coolant reservoir, start your car, and look for bubbling or "false boiling". Excess pressure in the cooling system caused by combustion fumes leaking into it causes this, which would also signify a leaking head gasket.
how can you tell if you need a radiator in a 99 cadillac northstar engine
Where is the radiator drain plug for a 1995 Cadillac Seville 32valve northstar 4.6litre V8
waterpump or radiator hose
The easiest way to drain the coolant on a Northstar is to pull the lower radiator hose off. There is a petcock on the lower left (driver side) of the radiator but it's almost impossible to get to without a special tool.
when overheating occurs at highway speeds the cause is usually. a radiator or coolant circulation problem, Check for a restricted or clogged radiator.
follow the top radiator hose to intake
try a radiator cap......or you have a head gasket leak.
the thermostat is usually located were the top radiator hose connects to the eng
Check coolant level Replace radiator cap Radiator may be clogged Make sure air flow through radiator is not resitricted
On the 2.7L it is under the housing where the lower radiator hose attaches. On the 2.4L it is under the housing where the upper radiator hose attaches.
Should be in a removable housing at the engine end of the upper radiator hose
I have a '98 STS with the Northstar and was recently on Cadillacforums.com and the same question was asked about the northstar and alternator. From what I remember, You have to take the right radiator fan out, take passenger side tire off, I think remove the black plastic (might be in the way) and you should be able to get at it from there. word of caution though, watch you dont bash the radiator in when you turn it to get it out.