: What Spark Plugs for a 1999 DeVille Northstar?



bighank
12-11-07, 12:58 PM
What plugs should I use in a 1999 Northstar engine. Owners manual says Delco 900. Haynes manual says Delco 950. Think both of these are platinum.
My LS1 NOW USES IRIDIUM plugs in place of the old platinum plugs originally installed. Old plugs had hockey pucks on the electrode which would "fall off" and get ground up by the pistons. How much hassle is it to change them?:hmm:BIGHANK

EcSTSatic
12-11-07, 03:38 PM
I would have said go with the Caddy manual but the AC Delco site agrees with Haynes for your car.

http://198.208.187.182/internet/VehiclePartDescription.jsp?selectedfld=&application=Car%2FLight+Duty+Truck&year=1999&make=CADILLAC&model=DEVILLE&engine=V8+4.6L+281cid+GAS+FI+N+Engine+VIN+%3D+Y+++ +++&productline=25&part=7212

CadillacSTS42005
12-11-07, 04:35 PM
ac delco PERIOD

Submariner409
12-11-07, 05:44 PM
The new series "Professional" ACDelco double platinum plug listed for your car is #41-987, $5.05 or so from www.rockauto.com (http://www.rockauto.com).

There are a skrillion words in here on spark plugs, and if you read them all you'll stick with the Delco.

Gap .050, torque cold to 11-13 ft/lb.

TexasCadillac
12-16-07, 04:14 AM
What plugs should I use in a 1999 Northstar engine. Owners manual says Delco 900. Haynes manual says Delco 950. Think both of these are platinum.
My LS1 NOW USES IRIDIUM plugs in place of the old platinum plugs originally installed. Old plugs had hockey pucks on the electrode which would "fall off" and get ground up by the pistons. How much hassle is it to change them?:hmm:BIGHANK
I was wondering why my 98 Deville manual says to use Delco 900 spark plugs and the ones I just changed were Delco 950 plugs and the ones I took out were 950 also. Which one is the hotter plug and which is best to use? The 950 seem to work fine. TexasCadillac

Ranger
12-16-07, 05:50 PM
I am not positive, but I would guess that the 950's superceed the 900's. I think I used 950's in my '97.

Zorb750
12-22-07, 01:53 AM
41-950 is what mine had.

I use Denso plugs, I find them to do quite well, 40K so far. NGK will be fine too. The only non ACDelco plugs that really cause problems unless you buy junk (Champion basic, Autolite (even platinum), or any copper plug), are Bosch's platinum plugs which seem to be thermally incompatible with a lot of GM engines.