Can the 5w-20 or 0w-20 oils be used safely in a 5.7liter

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Jun 6, 2003
Petersburg, West Virginia
These new low viscosity oils have been laying down some real good UOA results recently. Would it be safe to attempt to try a interval in a high mileage 5.7 liter 350? Mobil 0w-20 is very close to the 5w-30ss at both 40 and 100 in relation to viscosity. Ford will recommend their 20 weight for older year models-so why not work in this motor? All of these brands seem to have great additive packages which seem to be the key and yes the moly. Maybe I am crazy but the continued quest for the best oil for your own use is really like a bad habit. Oh well [Big Grin]
It would probably be OK to use xW20 in the wintertime under light-duty operation, but I wouldn't recommend it otherwise. The 10w30 is the viscosity recommended for most all temperatures in the GM 5.7L. Some like to run 10w40 in the summertime, though. Pennzoil 10w30 works great for me in my '95 C2500 w/350, even when hauling a 2500# camper over the mountains.
Honestly, I don't even think a thinner 5w30 works very well in most high mileage domestic V8s, I honestly believe these engines need an oil that is a very thick 30wt to a thinner 40wt. The 5w20 and 0w20 might work very well in a new Honda engine with tight clearances, but these old small block Chevy motors, and even the new LS1 based Gen III V8s, all tend to like slightly thicker oils. That is my strong belief anyways, we'll soon see if I'm right or wrong when I switch my 5.7L LT1 engine over to the slightly thicker German Syntec (which is 12cst at 100c, versus the 10cst oil I've been using)
The pushrod V8s tend to do better with thicker oils. 10W-40 or 5W-40 synthetic is what I'd use. For OHC V8s I'd use a 5W-30 or 10W-30 depending on climate.
I agree with Patman on this one.I want to point out somthing alot of people do not pay attenion to. The clearance on the gears of the oil pump are just as important as crank bearing clearances. Dodges 4.7 liter V8 has close to the same clearances as the LA series engine in alot of respects. The tolerances are tighter but clearance did not tighten up that much. Their is one key area that was tightened though. They specificly tighten the oil pump gear clearances so it would be able to pump 5W30 as well as previous engines pumped 10W30,10W40,20W50. They even made a point in Mopar Power of pointing this out. They claimed that the only part of the engine specificly clearanced for the recomended 5W30 was the oil pump! This is significant!! If you have set of gears clearanced for say 50 wt oil and you try to use that gear set to pump 5W oil you are going to lose pressure and volume. Thighter clearance pump will still pump thick oils ok but a lose pump will not pump thin oils very well!! I just thought I would give everyone foood for thought!!
I've got the 5w20 in both of my Ford F150's right now. One has 162,000 miles on it, the other 87,000. Obviously, I'm not buying into talk that a 40 weight is best for my motors at higher mileages and I'm obviously not afraid of the lighter weight oils! That being said, I would be hesitant to use 5w20 in an engine where the manufacturer is not recommending it in any year of the motor, which is the case for the 350 (or an GM engine for that matter).
I'm with ya on that Gopher, but I think the oil runs cooler in big pick-up trucks that in small hi revin' 4s and V6s. Minnisota winter drivin'? I betcha' the oil never gets to operatin' temperature most of the time. Love that movie Fargo. Does everyone talk like a Cannuck there too?
When people argue against the 5w20 oils, generally the arguement falls into the camp of either "that high revving 4 cyl can't take it" or the "big V8 will trash that oil". I think this is one of the few times I've seen the arguement that it won't work the oil as hard! In any event, most people never realize that we have a climate of extremes in MN. Its called "humid continental". What does that mean? Friggin cold in the winter and hot and humid fairly often in the smmer. We're headed for the mid-90's today with a high dewpoint. Not my favorite kind of day! In the winter, getting the oil warm is generally at least a half hour drive to bring it up to temp, in my book anyways. Do we talk funny? People in most other places think we do, but the accent isn't nearly sa bad in the cities as it is in the rest of the state!
Gopher; I've watched your posts on the 5W20 subject. As I mentioned before, I've observed several vehicles experience very moderate oil consumption while using 5Wxx mineral engine oils. All of those engines stopped using oil between say 5000 mile average change intervals when switched to an xxW40 or single grade 30 or 40. I think the oil consumption comes from the volitile 5W portion of the multi-grade. I'm sure oil companies can taylor an oil to stay in grade by balancing the shear rate with the boil off rate. 5Wxx mineral multi-grades appear to have lower flash points than 10Wxx's, lower than 15Wx's and so on. I have found several SAE 20 engine oils with flash points around 230C (450F) while the same brand of 5W20 has a flash point of 190-200C. These single grades appear to have cold flow numbers that suggest a 15W20 and very likely just squeek into the 10W20 catagory if there was a 10w20 catagory to squeek into. Before the hot weather is gone, I'm going to buy a pail of SAE 20 CF and see what it does in a couple of vehicles that consume 5W30 at about 1/2 litre in 2500 miles, but do not use any oil between 5000 mile oil changes when xW40 or straight grades are in the pan.
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