Best oil viscosity for an old 3.1 TBI engine

[Meridivs]

The car seems to like 0W-30 viscosity best, at the manufacturers recommended viscosity (5W-30) there's some tapper noise after a cold start.

I've heard that a higher viscosity oil could be better for worn engines than the thinner 0W-30 oil.

Is the 0W-40 oil any better for these engines at 100.000 miles?

[60dgrzbelow0]

The lifter noise you are hearing after a cold start may indicate the oil has not completely circulated through the block and not pressurized their hydraulic innards enough to quiet down the valve train. If it is very cold where you are and you are using higher viscosity motor oil...it will run as slow as molasses and the same problems will occur until the motor warms up enough to get the oil moving in, out and around the moving parts. Whatever you do...don't be tempted to race the engine while the oil is doing its best to make a complete circuit and plump up the lifters. Let it idle for a few minutes and listen for when the noise subsides. Note how long it took from the time the engine starts until things get smooth and quiet. If the engine tappets are still ticking after that, it might be time for a Marvel Mystery Oil Treatment.

http://www.expotv.com/videos/reviews/23/MarvelMysteryOil16oz/47984

[Joseph Upson]

0W is for your cold start, so going to 0W40 will not change what you experience on start up. If you don't have an oil pressure problem I would stick with what's recommended as oil pressure is a function of resistance and not a good indicator of lubrication if at all. Thanks to better understanding of oil fluid dynamics the O.E. oil recommendation is getting lighter and lighter, some are at 0W20. The 3900 runs about 45 psi tops so GM is showing that high oil pressure does not mean better lubrication. Still scary to have an oil pressure that low though.

[Meridivs]

Thank you for the replies.

It's clear that 0W grade is making a serious difference in lifter-noise comparing to any 5W or 10W grade oil.

Question: can 0W-40 synthetic oil provide better lubrication for TBI engines with over 100000 miles than manufacturer's recommender 5W-30 or should I stick to the "original" grade xW-30?

[Joseph Upson]

If you don't have an oil pressure problem I don't see a benefit by going to 40. It's when your operating temp oil pressure is starting to dip that you consider doing this. For example, say you go to a 50 wt oil and it makes your oil pressure go up by 10 psi. It doesn't mean you have better lubrication, it means you have more resistance to flow and possibly less lubrication as not as much oil is going past the bearings. on the other hand, if you loose 10 psi with 30 and go up to 40 and get it back you're doing good. Oil going past the bearings too fast or too slow can be bad, you want the happy medium. There's more wear on start up hince the 0w for the quickest time to the bearings on cold start then a gradual build to the 30 fluid dynamics for proper lubrication and oil film at operating temps.

[geoffinbc]

You need to understand that the 0W 5W and 10Wis not a viscosity rating. It is a cold crank rating. It is an number assigned to an oil based on dragging a specified object through a cold oil bath and measuring the resistance. So running a 0W30 versus a 15W30 is exactly the same when hot at 200*F. So like everyone is saying if your oil pressure is fine at hot idle, meaning you have at least 10 PSI, then run the 0W30 if it makes cold startup better. In cold weather all oils will be thicker than when hot so the only concern you need to have is if it is too thick which may be the case if your hearing audible noise with an oil that has a higher cold crank rating.

A heavier viscosity oil like a 0W40 or 5W40 will not help an old motor unless you require it to keep adequate oil pressure when hot. I had to do this on my Trooper because the oil pressure gauge would bounce off zero when at hot idle. But using a 5W40 versus 5W30 would keep it in an acceptable range

[bob442]

there is a difference on start up weight, or cold weight how ever, where the most wear is done on a motor. the last number is its operating tempature weight. so a 5w30 is better than a 10w30 for winter, because its "thinner" on start up, yet still remainds the same viscosity when its at operating tempature as the other oil. its also best for any motor with high tollerances and small moving parts like roller rockers and hydrolic lifters. If its to thick it wi;; mot lubercate anything properly till it warms up causing minor wear each time. It really helps keep down the piston slap on my monte
You might need that stuff they sell in alot of magazines for flat tap cams. hmmm what is it called.....

[Meridivs]

Thank you for the excellent replies. It made this issue a lot more clearer than it was so your 2c were very well spent.

Unfortunately my Pontiac Trans Sport SE doesn't have a real oil pressure gauge. It's more like an on/off switch and shows the same value no matter what oil pressure I have. It's designed to drop only if you have a serious oil pressure issue like zero pressure at idle...

I will ask around to see if I can measure the oil pressure in some other way and report back the values for cold and hot idle.

The best thing would be if I could find a sensor that would report the real oil pressure on the dash gauge...

[bszopi]

So wait... You have a dash oil pressure gauge, but it is either pegged or at 0? If so, then you just have the wrong oil pressure sender. There is a short on, that is basically just for an idiot light, and there is a long one which actually senses the pressure. If you have an actual gauge, then it sounds like you need to get the proper oil pressure sender.

[Meridivs]

The funny part is that our exact model ('92 Pontiac Trans Sport SE) is factory-built this way with a "dummy" gauge which shows either 2/3 or nil.

If it would be as easy as changing a sensor with one that can bring some life into the oil-pressure gauge it would be fantastic but I'm afraid it's a little more complicated than that (you'll probably have to change the dash as well, I'm not exactly sure how this goes).

[bob442]

doubt it, could just be the sensor, should be at the oil filter neck on the front of the block. or...where the hell is it on a 3400 now...

[Joseph Upson]

Yeah, the gauge should have variable capability regardless of the sensor. The switch is usually the on or off source, a needle gauge should have the ability to vary with resistance. For GM I believe 0 ohms or maybe 10 = 0 pressure, 80 ohms max and all else in between or just the opposite. The switch sensor basically does open or closed circuit representing 0 or 80 ohms resistance.