Chevy G30: 350 V-8 5.7L recommended oil?

[Weblamer]

Last time I had my camper in the shop to replace the u-joints, the mechanic there told me to only use straight 40w oil in the engine.

I cant find any other info on the web as to why I would use 40w instead of what the manufacturer specified.

Any idea why he would tell me this? Because I live in Florida with more heat, or because it is an older engine? (1984)

[Froggy1936]

Hi, Oil viscosity (weight) Is subjective, Now that may just be his personal taste . Or he may know something about your engine we do not (as he heard it running ) The constant heat of Florida could be the only reason ? The manufacture,s have a lot more knowledge than any Technician and they have supplied tables for all heats and conditions . Heavier oils would only be needed for severly worn engines , I have opened up 2 5.7 engines recently 1@100K & 1v @ 250K Both had rod and main bearings that showed very little wear Though 1 had cam bearing #2 worn thru to the brass and the cam journal was severly worn ( this comes from cold starts without oil pressure ) Oil & filter not changed often enough .  But we do not know the mileage on your engine nor the service history , But if there are no unuseual noises and its not burning oil to the visible state of constant smoke i would stay with what you are currently useing . As long as being in Florida is not a recent occurance , Look in your owners manual and follow those reccomendations ! Frank

[Rickf1985]

15W-40 is the oil of choice for most flat tappet engines anymore since they have removed 90% of the zinc from regular oils. The zinc is what lubricates the lifter to cam interface. The 15W-40 is a diesel motor oil and still retains more zinc in it. The antique car crowd has also migrated to this oil. I use Rotella T but any brand name diesel motor oil should be good.

[TripleJ]

I would not run straight 40W oil in my RV, or any auto engine for that matter.

bobistheoilguy.com
and
themotoroilevaluator.com for more oil info than any human could possibly want to deal with

I use Rotella T6 5w40 in the RV, a 97 wrangler, 07 KLX dirtbike, and all my yard equipment.  Only the new Ford gets whatever the dealership puts in it, cos they still do the oil changes.