Got a 99 Yukon. Previous owner has always run 20w50 oil. Should I keep doing so?

[Rael]

Just got a 99 yukon with 178,000 miles. A friend purchased it for me about 6 months ago because I wasn't ready to buy it, and just sold it to me.
While he had it, he took it for an oil change at the same place the last owner always used. We have the service records, the last owner religiously had the oil changed every 3000 miles, but always had them add 20w50 conventional oil. The mechanic told my friend just to keep adding it because the last owner always had.

But why? I believe the manual calls for 10w30. And why not use synthetic? The truck doesn't leak oil and doesn't seem to be burning up oil. Is there any reason I should keep using this thick oil, contrary to what what the manual recommends?

 

[2door2wheel]

not if its really cold out. then i would opt for something in the 10w30 or 10w40 range. 20w50 is pretty thick stuff. it takes a while to reach the top of the engine. some people claim that synthetic finds smaller holes and leaks where conventional oil won't. personally i don't buy that but that is just my opinion. i made the swap to synthetic and it didn't miss a beat at all

 

[OR VietVet]

IMO you can use the 10-30 or 10-40 with no problems, especially since he did the lof every 3k miles. I would run synthetic if you want to but of course the mileage interval would change. I have heard pros and cons about the leaks but I have done the switch before myself with no problems but that is not to say you won't develop a leak but even that may just be because it is time and not changing the oil.

 

[SunlitComet]

Never use anything but 5w-30. Maybe 10w-40 IF weather permits and 5w-30 is not available.

 

[HoS]

I recommend following manufacturer suggestions.
As, they know their own equipment pretty well.

 

[SunlitComet]

Crap, that was 10w-30 that is permissible if needed not 10w-40. No other then those two can be used. Definitely not any 20w stuff.