Hey guys I have a 91 l98 auto

The other day I changed my oil to a thicker oil.

(I’m running 10-w40 I was previously using 10-w30)

When I was driving my vette I noticed a slight lifter tick and the engine was running slightly rough at idle not too rough to be concerning but still enough to check it out. I just think that with both of those happening at the same time I might have some oil lubrication issues? My oil pressure is good and I know my oil is at the right level. I don’t really think that changing the oil up to that thickness would cause it to run rough but I’m wondering what could be causing the issue or could it be completely unrelated to lubrication?

 

Why do you think it's a good idea to go to thicker oil?

 

Most likely, almost guarantee it, that it is NOT related to the oil. By the way, if you want to run a 40 weight, then switch over to 5W-40 instead.

Anyway, did you knock something loose? Break something while changing the oil?

It's possible a dirty engine with clogged passages may have a harder time moving the thicker oil, including through the lifters. On an otherwise healthy engine, the 40W will do just fine.

 

“Anyway, did you knock something loose? Break something while changing the oil?”

I don’t think I knocked something loose or broke something but if I did by chance and didn’t notice what in that area could’ve been knocked loose/break that could cause the running rough?

 

“Why do you think it's a good idea to go to thicker oil?”

I live in a hotter environment so when the oil gets hot it thins out too much causing the oil pressure to be lower than I’d want it to be so I upgraded to thicker oil to resolve that issue

 

Has the engine been well maintained? I've seen sbc engines that had infrequent oil changes that cause the groove on the distributor to build up gunk, thereby starving one of the banks of lifters of oil. Pull the distributor and have a look.

 

how many miles on the engine?
Perhaps the thicker oil is not reaching a lifter causing the tick.
Apply the what changed rule, and backout the recent change, put 30 back in see if that corrects it.
Anyway it seems there are issues there that need to be actually diagnosed and fixed, going to 40 is not the answer, nor the question.

 

If thicker oil is better then should you put grease in instead? Thinner oil flows better stick to recommended. That is my opinion.

 

Mine too. Thicker is usually for racing, not just because it's warm out.
It would also contribute to the new lifter tick OP has now

 

That's a pretty strong statement as opposed to "That's my opinion".

I have been tracking oil analysis and the effects of various oils and additives in engines for over 20 years. NOT as a professional, but rather as a hobbyist. During that time:

- I have seen many owners (including myself) run Mobil 1 15W-50, Valvoline VR1, and other thicker/race oils. Oil analysis from these users have demonstrated an equal amount of performance compared with thinner oils (5W30). That means, wear metals are the same...sometimes better with the thicker oil.
- I have NEVER seen an engine with increased wear purely as a result of thicker oils.

Personally, 10W-40 would NOT be my choice. I would rather use a synthetic 5W-40, Euro spec. Having said that, 10W-40 by itself will not harm an engine as long as oil change intervals are not abused. Another point, conventional 20W-50 will NOT do well in Alaska in the middle of winter. This is why owner's manuals included a chart (oil weight vs temperature) for you the owner to select the appropriate oil for your climate.

You may want to use thicker oils in certain conditions:
- Hotter climates
- Racing, of course
- During winter. Yes....winter! You should see what happens to the 0W-20 my 2018 Silverado calls for. The combination of winter, short trips and direct injection absolutely turns the oil to water. This is on an 8-quart pan...it is not unusual to find 2.5% fuel or more mixed in with the oil, which needless to say will diminish all lubricating, antiwear, and detergency properties of an oil. I actually run 5W-30 in the winter and 0W-20 in the summer (because water and fuel burn off happens a lot quicker).

If you think fuel dilution doesn't happen to your car because you don't have direct injection, then you'd be wrong. Winter affects all cars the same way. Leaky injectors can be as bad, if not worse than DI.

Last point, my Silverado calls for 0W-20 in the US market. However, the same engine calls for 5W-30 in the Mexican market. Why?

Ric