Ever a Case for Thicker Oil?

[Schredder]

Howdy,

Is there ever a case or situation where a thicker oil (when the engine is hot) is warranted? If so, what are these situations? Reason, I keep reading on where how the thinner oils can provide just as good wear protection while delivering better engine efficiencies.

I have ‘97 Chevy Z71 with the 5.7l vortec that has what a mechanic called a somewhat extreme case of piston slap. I know these engine are supposedly not know for this, but I guess I’m lucky.

So, I am thinking this engine may benefit from a thicker oil. Would Rotella T 5w40 be too thick?

Thanks,

Chris

 

[KW]

The Rotella 5W40 will not hurt your motor. You might notice a slight drop in fuel mileage is all.

 

[Jim 5]

I have observed that very knowledgeable people on this board recommend a thicker viscosity when higher lead shows up in UOA's. This would be the result of con-rod bearing or crank-journal bearing wear.

I had a 5.7L vortech (in the same truck as yours, except it was a '98) for 6 years and it had a little piston slap as well. There is no oil/viscosity that will correct piston slap, or so it has been said.

I have run a heavy 30wt (very close to a 40 wt) in my 5.7L vortech in the summer and it did OK. Nothing helped the piston slap though. However, it did bring the oil pressure into a range that I was more comfortable with in the summer.

 

[Quest]

Jim 5-

While higher lead in UOA may be an indication of wear metals coming from babbitt bearings, you have to realise that nowadays all production engines are using aluminium bearings so high Al can be read from UOA.

 

[Jim 5]

I didn't know that about aluminum bearings. My only experience inside engines has come from old small block ford, and an older Yamaha engine I rebuilt. The ford had copper faced lead bearings, and so did the yamaha.

I had thought aluminum bearings were exclusive to the cam journals in OHC engines, but I will admit to being totally out of date when it comes to bearing technology. I was mostly parrotting comments made by people like TeeDub, but will be the first to admit it if I have misunderstood their posts.

Also, I am not familiar with a babbitt bearing, or where it resides in a modern engine. Can you fill us in?

 

[Quest]

Jim 5-

Babbitt bearings been in use since the dawn of automotive engine (may backtrace it as far back as locomotive engine??! Not too sure) and it's an alloy comprised of tin, lead and antimony. This alloy possess all the properties necessary for a rotational bearing type (embeddability, "flow", etc.) but there are shortfalls as well, like low temperature flow characteristics may become a hindrance if you the bearings are exposed to high heat due to excessive bearing/oil load, and also difficulties in consistency( repeatence) during mass production phase for high precision applications.

It wasn't until approx. early 90s when major automotive manufacturers silently switch over to aluminium inlay bearings which bears the benefits such as high precision (and repeatence during mass production, mainly by using "sputtering" process) and high temperature, etc.

I notice this when Integra GSR in 1991 came out in the market and also my wifey's Camry Vee6 aftermarket replacement bearings are now all alu bearings (not the OE babbitt bearings).

So, alu readings in UOC can also be read as bearing materials as well....

 

[Schredder]

Thinking more about this cold start knock/ piston slap noise.. I may just try and decarbon the engine. Also thinking about trying some GC.

 

[Jim 5]

OK,

I didn't understand that Babbitt referred to the material the specific bearing was made out of. Got it. The bearings I have seen are Babbitt. Good to know.

 

[Jim 5]

Shredder -

I have never heard of an oil that will help with piston slap.

What is happening is that the aluminum piston is a little too small for the bore. When the piston is cold, it is even smaller. The size mismatch when cold is causing your piston to rock within the cylinder bore on the axis of the wrist pin. When you hear piston slap or CSK, you are hearing your piston skirts slapping against the cylinder bore when cold.

Once the piston warms up and expands a little, it is larger within the bore and is less able to rocker, and you don't hear it as much or at all.

I don't know, but I suspect that by the time any oil would get up in that space between the bore and the piston, the piston is likely warmed up enough so you don't hear it. In any case, I'm not sure if any oil would provide enough of a cushion to protect against piston slap

 

[Quest]

thicker oil can somewhat "cushion" the piston slapping effect but it will not eliminate that "rapping" (or sharp knocking sound) completely.

Also: if there's excessive piston slap in the engine, there would be a bit of piston skirt wear in the form of high alu readings in UOA.

Lastly, while it may be true that intentionally introducing additional "clearance" between cylinder and piston may helps in reduction of friction (which in turn converts to less energy/power loss), excessive piston slap may cause dramatic failures down the road, like breakage of the alu piston skirt, etc.

Also: it makes no sense whatsoever in hopes of salvaging that extra couple of % loss by introducing more piston to cylinder bore clearance and yet most domestic 3 keeps throwing in those 3 tonne chassis (did I hear denali?!), tranfer case and what-not (how many denali drivers are signel occupant and/or do offroading 80% of the time?)

I'm not critising any large vehicle owners but the truth is, the market is mentality is twisted somewhat....

My 2c's worth

 

[buster]

One other case too is long endurance racing. Higher viscosity in case of fuel dilution.

 

[427Z06]

Quote:

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I have observed that very knowledgeable people on this board recommend a thicker viscosity when higher lead shows up in UOA's. This would be the result of con-rod bearing or crank-journal bearing wear.

---

Not always a correct assumption as chemistry could also be a factor. Further, oil with too high of kinematic viscosity may reduce flow to the point that the oil and bearing overheat.

 

[Jim 5]

Quote:

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Jim 5-

While higher lead in UOA may be an indication of wear metals coming from babbitt bearings, you have to realise that nowadays all production engines are using aluminium bearings so high Al can be read from UOA.

---

I have been thinking about this a little more, and without in any way intending to sound lippy, I am wondering where lead comes from in UOA's if babbitt bearings are no longer used.

Or should I have read this statement to mean that all production engines use both babbitt bearings AND aluminum bearings....therefore you need to look at both lead and aluminum when evaluating bearing wear?

Am I interpreting this correctly?

 

[Von]

If you will search my posts, I am experimenting with the piston slap and different oils because my 6.0 Silverado has it.
The cause is not agreed upon. Most of us amateurs think it is the piston rocking in the bore. GM and Terry Dyson think it is carbon buildup.
Regardless, it has not changed for me with oil viscosity.
As far as UOA, the sweet spot seem to be a strong 30 weight for the lowest wear. I am about to test the last heavy oil I bought hoping that would help (Rotella 5-40). GC is up next and PP is on deck.
The truck has 90,000 and runs great. I wouldn't worry about piston slap too much. However, I am starting to see some tin. Got to figure that out, or pay Terry.
Von

 

[Schredder]

Ok.. what is the best way to get rid of carbon build-up? A cool tip a I just read is to use your vehicle's windshield washer system's pump to inject washer fluid while driving. Just disconnect the hose going to the nozzles and connect it somehow into the intake system.

 

[427Z06]

I like the water method (be careful of hydraulic lock), but there's also GM Top End Cleaner (Part#s 1052626 and 12345089). Some also have done a Lube Control piston soak, but I don't recall the efficacy of this method.

 

[Schredder]

Well.... tried de-carboning my engine last night using the windshield washer system trick. WARNING didn't go exactly as planned... scared the h%ll out of me.

I just disconnected the supply line to windshield washer nozzles, found a length of clear hose in the garage, connected this hose to the intake manifold via the PCV port.

Started the truck... the engine immediately began drawing in the washer fluid.. wanted to die, but I kept it running about 2000 RPM. Apparently, the fluid can be drawn through the pump without activating it.. I did not know this. In hindsight, I should have connected the hose before the throttle body to take advantage of injecting the fluid on demand.

The service engine light is now on, but I suspect an engine code got set because of rich condition created by the methanol in the washer fluid. I did also notice an oil burning odor and saw some bluish smoke. Don't know what happened to cause that (maybe I don't want to know), but it went away after a few minutes.

Then I decided to change the oil as I suspected some of the washer fluid probably ended up in the oil. Much to chagrin, when I removed the oil fill cap.. there was some sludge. I am hoping this was created from this harebrained experiment as I replaced my lower intake manifold gaskets a few months back... don't want to do this repair again anytime soon.

But, on good note, when I started the truck this morning, the cold start knock was greatly reduced.

Should I repeat this procedure...? LOL

Sorry for the long post.

Chris

 

[Von]

Ummm....doh!!!........I thought you were kidding.

 

[Merkava_4]

Quote:

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Well.... tried de-carboning my engine last night using the windshield washer system trick. WARNING didn't go exactly as planned... scared the h%ll out of me.

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Whoever gave you the idea of sucking windshield wiper fluid in through the intake manifold? And what does carbon build up have to do with piston slap?

 

[DINO_NO]

#@$%! #@$%!, run a fuel system cleaner! not washer fluid!