how thick

[superman18]

i have a 2000 firebird with almost 1 hundered tousand miles on it. i am switching from regular 5w30 to synthetic. how thick should i get it.

[Publican]

Re: how thick

I think that's backwards - 5-30 if cold; 10-30 if hot. GM recommends 10-30.

[borispeed]

Re: how thick

I've heard that synthetic will damage your seals if you have more that 75,000 miles. Sometime ago I started using synthetic. After that the rear seal and gasket started dripping. Others say that is OK using synthetic if you add some extra-additive to protect your seals. Yesterday I changed the oil and I used High Mileage Castrol GTX (contains additives to protect seals) because I was not sure about synthetic. My desicion of not using synthetic for now came from the amount of money I spent for the dealer to change the rear seal and gaskets.

[cam98aro]

Re: how thick

do NOT switch to synthetic

[3.4 slow to go]

Re: how thick

synth won't damage seals, it just seeps through leaks that regular, thicker oil, caint.

[fast 3.4]

Re: how thick

Hmmmm, I always thought the thicker oil was for colder weather.

[cam98aro]

Re: how thick

Hmmmm, I always thought the thicker oil was for colder weather.

no, it is the opposite

[borispeed]

Re: how thick

How good is to use those additives sold separate that protect seals?

[terminaldegree]

Re: how thick

10w-30 is what I would use most of the time. Maybe 0-30 or 5-30 in winter.
I wouldn't bother switching to syn if your engine already leaks.

Keep away from 99% of the additives, especially if there isn't something wrong with the motor now!