I have owned my 91 Firebird (305 TBI) for about a month now. Since I purchased it I have added about 5000km to the odometer, and have added 1.5L of 10W30. I noticed today that the manual calls for 5W30, not 10W. The weather isn't especially cold here, so I doubt this is a problem. Is there any danger in running the heavier oil in my engine, or should I change the oil to 5W immediately? The engine seems slightly less responsive, I'm not sure if this is related or not.

Thanks

 

you should be absolutely fine with 10w30.

 

Changing to 10w30 is no problem. A lot of people switch between the two for summer and winter driving (I don't remember which to use when). It shouldn't change how your motor performs, though, I don't think.

 

10w30 is fine, if your gunna switch on and off use the 5w30 in cooler and cold months...cuz its less thick in start up when cold so it starts easier and builds oil pressure quick. Use the 10w30 in warm months because it protects more on those warmer 80-90*+ days.....in near zero degre days it takes alot more time to get oil pressure with the 10w30 in mine

 

i use the 15w50 synthetic in my modified engine, is that bad? what about the winter?

 

wouldnt run that in the winter way to thick....15 thickness when cold....not to good for oil pressure build up, since its synthetic it might be a little better but i still wouldnt use it....being the weight is 50 when hot its really viscous and u could prolly get away with it. I'd run maybe a 10w40 instead.

 

Nope, it's fine. If you look at the pour point of even 15-50 syn oil it's better than parrafin based 5-30. With 7 motor vehicles, cars, motorcycles I use 10-30 in everything. 15wt base stock will prevent excessive consumption related to thinner base stocks. With a high performance engine 15wt base will also prevent the thinning of a lighter stock increasing pressure. Synthetics are overall the best choice for any engine when you consider pour point, viscosity index and anti-dispersant agents.