everyone has their own opinions on that sort of thing... In the end it just comes to do personal preference and what you can afford...
personally I use Mobil1 10w-30 high mileage oil with the OEM filter (Mahle) - I really recommend you use synthetic oil..
and I use Bosch Iridium Fusion spark plugs. Honestly though, any of the Bosch plugs can do the job for the car, once it is the correct spec...

While you are doing the plugs, be sure to check your air filter and cabin air filter.. they may very well need changing.. and be sure to see if the fuel filter has been changed recently
Last thing, search the forum and you will find an answer to almost anything you can ask..

 

Mobil1 and Royal Purple are good brands for oil, and use fully synthetic oil, your motor will love you for it.I like NGK plugs, but Bosch and Autolite are also good.
Go with what suits your driving style and stay with it. Like nicolas said, "everyone has their own opions."

 

I was under the impression that synthetic oil is bad for higher mileage vehicles. My Volvo doesn't seem to burn much oil, but I don't want to gum up my valves if some of that synthetic stuff slips past the rings. Am I wrong?

I've been using conventional oil with Rislone to prevent sticky valves/lifters.

 

Alot of people run synthetic oil on higher milage Volvo engines with no problems at all.

 

Just dont put platinum plugs in, will cause overboost and check engine lights for it.

 

Considering that he has an NA engine I really dont think platinum plugs will be a problem.....

 

Why do you say that?
OEM plugs from the factory are platinum.
We use Bosch platinum in all the white motor cars and never have any problems with them.
I am running 14PSI boost in my 850 with them and it runs fine.

 

thought he had turbo model passed that one up. my bad

I put bosch platinums in my t6 and it caused overboost check engine lights they were all gapped correctly and what not reset the check engine light and it would come right back on.

did research and other people reported that problem with platinum plugs
.
put in regular spark plugs and the problem was gone.

 

my bad i obviously missed where he put that as i put overboost n/a isnt boosting oops

 

HMMM Maybe you had a bad batch.
But yes some people have had problems but I think that most that had them also had MODS done as well.

But I also have mods done and still fine. I think it is just if the car is picky or not.

 

not sure but i started replacing hoses that were cracked and what not and it takes some time to remove all tubing and what not to get to plugs didnt want anyone wasting that much time. My car is completely stock as far as I know. Wish i had a programmer or something tho , but then again it would prob just ruin the so called bad tranny of the 99' with harder shifts and what not

 

There is a few people on here that have modded S80's which I believe are 99's as well.