hi guys,

my dad just gave me his old blazer 98 and he told me that he has been using 20w-50 oil for a long time, but the truck has had some over heating issues, and the heater core wasn't longer working, the a/c is not working either. (i don't know if it has any relation with the oil)

well, the manual says that according to my weather (41 to 77 F) i should use 15w-40 and it's time to do the filter and oil change.

what would you recommend me, stay with the 20w-50 that has been using for a long time (more than 50.000 miles) or change it to 15w-40?

thanks a lot!

pd: it usually runs at 40 psi or more with 20w-50.

 

The overheating issues and the heater core not working would make me suspect that the coolant system needs to definitely be flushed. Make sure after you flush you only use 50/50 solution of distilled water and DEXCOOL (the orange colored antifreeze). Don't use green antifreeze. It does make a difference. Both the Dexcool and the distilled water. The Dexcool is designed to work with the aluminum of your engine and distilled water mixed with anti-freeze prevents rust. I just saw a real cool demonstration last week. They tested two bolts (each in it's own sealed glass container). One was submerged in 50/50 tap water and antifreeze and the other was submerged in 50/50 distilled water and antifreeze. I don't know how many days/weeks/months they ran the test, but the one in the jar with the tap water mix was all rusted and corroded. The one in the distilled water mix look clean and as new as when it was first put in the mix. Pretty interesting.

 

oil pressure is always higher at start up(cold) and then drops when the oil warms. 20 psi is more than enough

 

thanks, i will do that.

what about the oil? should i continue using 20-50 or change it to the recommended 15-40? thanks!

 

I generally go with manufacturers recommendations. But are you sure it states 15W-40? At those temperatures I would think it would 10W-30. Matter of fact, I have a '98 and mine calls for 10W-30.

 

I don't know what manual you have, but I am looking at the official 1998 Blazer owner's manual and it says use 10W30. It also specifically says,
Do not use other viscosity oils, such as SAE 20W-50.

 

Yep 10-30 here also

 

thank you all!