I understand everyone has a difference of opinion on synthetic vs. dino. I respect both sides, however my simple question is this: I have a 2000 SSEI w/ 71 k: do I put 5 w 30 in it as so many of you do or the recommended 10W 30 as I've always done. The reason I ask: the garage screwed up and put in 5/30 last month. Thought I'd just switch back to 10/30 next oil change. Suggestions?

In the summer 5w30 will be the same as 10w30. The first number is a winter viscosity, when the temp is below 30f The second number is the hot viscosity, above 100f. 5w30 is a far better oil all around because you want a thinner oil in cold weather.

To add to Dan'* post.....There is no difference with the viscosity rating for synthetics versus fossil fuels. There is a difference in price - synthetic usually a bit higher. There is a difference in longevity - synthetics last longer and you can go longer in between oil changes if you would like.

Thanks gents: you're the best............

And I will throw this in here...... If your engine states 10W30, never use 5w20. Period. Times 2 with older engines. 5w20 was created for engines made to closer tolerances than previous. In a cold older generation engine, you do not want a 5 weight oil in any condition. And I have read a bit info on the 'net showing high mileage engines, made for 10w30 folding up because the owner switched. Use what the manufacturer recommends. Why take chances.

Hey NEWLANDER, my 03'* oil filler cap shows 5W30 right on the cap. My opinion is that the shop put 5W30 in your car because that is what the factory recommends.

ALEX, as far as Synthetic or not, in my opinion synthetic oils have been proven to out perform regular oil but it has a huge cost difference. If you are changing your oils at the recommended intervals I feel you will give your engine long life. I am running synthetics in the Bonneville and 4 Runner but regular oil in my GMC'* 6.2 diesel because it recommends an oil change every 3000 miles and I am not ready to drop 5 times the cost for Synthetic oil for it yet. There'* my nickle of knowledge.
Mike

Just my 2 cent here, I found out once I was burning some tree limbs in my burn barrel and it didn't really want to burn good so like usual I'd pour a little oil on them to get them started, well I didn't have any regular oil so I used some my Dad gave me Synthetic Racing Oil he bought years ago real cheap. It wouldn't burn at all,it would put the fire out, I thought that was weird or the Synthetic was much better for being inside an engine rather than getting a fire going.

Life saver! Thanks Dan!

I use dino 5W-30 in my Bonneville. I change the oil when the car'* compute tells me to. 5k on a conventional oil is nothing, and is not harmful. If I were to run synthetic I'd be changing at 10k or so.