I have a 1995 cadillac concours deville with a northstar engine and I replaced my serpentine belt, after I replaced it, it was still loose and I tightened it as tight as I could. The belt was the right size, so I figured it was slipping because I didn't clean the pulleys. So I scrubbed the pulleys,bought a new belt, put the new belt on and it was still loose. Do u think I need to replace my tensioner? Or is there a way I can adjust my tensioner?

A hunt and count question. core/freezed plug.
NO VIN told no RPO code for engine told.
8th digit of VIN is ENGINE CODE VIN :"Y" below.
or vin=9 (8TH)
well even the service manual does not do the count.
it shows some, block and heads.
what you can learn to do is google it.
here is how to do that
I google new rebuilt raw engine blocks for sale.
watch out engine can evolve and even be swapped a newer GEN engine, 279 cu in (4.6 L)
but I will post for DAY new,1996 only
1996, the Northstar engine
RPO code LD8 or L37
lets to LD8
the DeVille Concours was available with the new 270 hp (201 kW) LD8 Northstar V8, and later, the high-output L37 Northstar generating 300 hp (220 kW).
LD8
first hit shows VIN-=Y shows 4 in the 2 heads 2x2.=4
left and right heads outside ends. and 1 rear and front of head for 6 total,

https://www.npdengines.com/product-page/96-99-cadillac-deville-4-6-northstar-engine-vin-y

found with google
die-cast aluminum block!!! SORRY NOT SAND CAST.

A GOOD TECH FINDS THE ACTUAL LEAK FIRST
SEEMS YOU ARE GUESSING,
THE 1995 BACK IS ALL DIFFERENT.

LOTS OF VIEW HERE, ALL FOUND VIA GOOGLING FOR YOU.

https://www.hpmotors.com/cadillac-northstar-v8.html

FIND THE LEAK FIRST, THEN WORRY CORE PLUGS IF AT ALL.

I found this picture, it didn't say northstar. The tensioner in picture has a half-inch cut-out. Use a 1/2 rachet or break-over in cut-out, usually the longer the handle, the better. You pull the tensioner one way or the other to get slack in the belt, then remove belt from accessory pulley.

There are two belts. One is long and one is really short. See the diagram attached:

Hello: All Cadillac Devilles had a Northstar starting in 1996. It will not make any difference if it is a SLS (275 HP) or a STS (300 HP)

You'll need to locate the tensioner pulley and rotate it toward the center of the engine with either a 3/8 or 1/2 inch ratchet or breaker bar. This will allow you to pull the old belt off and install the new one. There should be a sticker near the radiator that shows the belt routing, if not there will also be a diagram in the owner's manual. This is a fairly easy job so good luck.

Hello: The Concours has the Northstar engine and the starter is UNDER the plastic intake manifold. Remove intake to replace starter.

No it won't, The 1995 has OBD I diagnostics, 1996 and up have OBD II.

Assuming you have the Northstar engine

usally tearing belts is the ac compressor not turning or poorly. your tension could be going bad also alllowing the belt to flex and contact another object. you will need to block your wheels.open the hood. have a freind rev the engine in cycles for you to watch and see if the belt flexes or the ac commperssor is the cause

replace fuel filter first. cheapest and easiest.