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Oil weight

You have to determine what the “knocking” is.

Yes, it’s ok to switch to synthetic.

Synthetic more proven to leak?

Knocking is on the top end and Not always present

Im sorry i thought 98 jeep wrangler was in original question
4.0 liter 160,000 miles

:trollface:

You can use synthetic but I don’t think it is going to change anything with the knock.

The better cleansing effects of synthetic oil (if any), is best used as a preventive measure not after the problem surfaces.

I was not trying to fix the problem with synthetic

Thanks db4690 that was helpful…

prone…not proven

Have the knock looked before making any decision about oil first. If the engine is on it’s way out the type of oil won’t matter.

@badbearing

is the noise low-pitched or high-pitched?

high-pitched as in a ball point pen clicking

low-pitched as in a thud or clunk

The rule of thumb I always use is thus…Use the reccommended viscosity for the first 100K and then…maybe…start creeping up on the viscosity as the engine ages and more miles accrue. Though it may be just my old school mentality at play here…but my viscosity theory is based on normal engine tolerances opening up as it goes over 100K…tho…this theory may just be old school… In reality we may find the bearing tolerances to be just fine over 100K if we tore the engine down and Mic’d everything. It all depends on how the engine was treated and its oil change schedule. Since I basically and primarily own and operate used vehicles…I assume that the former owner knew nothing about proper engine maintenance or oil change intervals…and in that light…the higher viscosity as the engine ages holds water. All depends… My theory has never failed me…and an oil pressure gauge will tell you volumes about your engines internals.

Blackbird

My rule of thumb is keep using the original spec until you determine a thicker viscosity is needed. From olden days the higher viscosity oil will cause increased wear to the piston rings, so don’t use it till you need it.

“The rule of thumb I always use is thus…Use the reccommended viscosity for the first 100K and then…maybe…start creeping up on the viscosity as the engine ages and more miles accrue.”

“Since I basically and primarily own and operate used vehicles…I assume that the former owner knew nothing about proper engine maintenance or oil change intervals…and in that light…the higher viscosity as the engine ages holds water. All depends… My theory has never failed me…and an oil pressure gauge will tell you volumes about your engines internals.”

@HondaBlackbird
Mr. Blackbird, with all due respect… I appreciate your professional expertise and learn from your comments in community discussions, but not in this case. I too, lately, have been buying mostly used cars of unknown or sketchy maintenance histories. However, I use the oil specified by the manufacturer, the Synthetic version, always.

I bought my Bonneville 8 years ago. The onboard oil pressure gauge showed excellent oil pressure, cold and hot. Now, north of 175k, pressure is still excellent. It uses no oil. I have 3 cars with the 3800 GM engine and all use factory spec oil, no consumption, no problems, and I’ve had no reason not to continue using specified oil.

My Bonneville Owner’s Manual specs 5w30, except below -20F and then calls for lighter viscosity conventional OR 5w30 Synthetic. I get weather colder than -20F in winter and some hot summer weather, too. It would be a mistake, in my opinion, to use different oil.

I would say that if you’ve got an oil burner car that you are trying to wring the last few miles from then try higher vis or some “mechanic in a jar” additive, but otherwise, follow the book.
CSA

Maybe I’m missing something but if it has developed a knock, that would have to be a rod or crank bearing going bad, no? I don’t think putting in a heavier oil is going to help much.

Blackbird, you need not tear down the engine. Send an oil sample to the oil lab and the report will let you know the condition of various parts, because excess wear anywhere shows up as excess contamination for that type of metal. They do this all the time.

  1. “Engine knock occurred after i put lucas in and then drove to the high rockies where it was still freezing at night. Coincidence?” - OP

  2. "Ok lets try this… Is it ok to put synthetic in an engine that has had conventional its whole life? " - OP

  3. Lucas what? Lucas make a lot of different products and additives. Depending on what you added, it may not be a coincidence… but we have to know what you added.

  4. Yes, absolutely. And you can even switch back and forth without problems as long as the manufacturer doesn’t require synthetic (see the owner’s manual). But it must be the correct oil for the application.

So, what exactly did you put in the engine up there in the Rockies?

There is no additive or oil that will help an already knocking engine.

I think we are actually agreeing with each other @“common sense answer” we both agree to use the reccommended viscosity… I suppose I need to add some clarification… I dont automatically start creeping up in viscosity just because the mileage hits and goes above 100K miles… I would only go up in viscosity if other clues point to it being advantageous… Such as the oil pressure registering low or lower than usual. Otherwise I agree with you…use what is called for.

We all know those ugly little clues that tell us to use a thicker oil…and i think those clues still hold water as for why to go heavier in oil. Oil pressure is the primary clue I pay attention to… and I’m certain I’m not the only guy on here who would use thicker oil when we hear a bit more “Ticking” from our power plants than what is normal. Sometimes I go a bit thicker in the summer because of high temps outside…and in conjunction with any louder than normal audible engine emanations…lol

I would simply have to agree with you boys on sticking to the called for viscosity…as long as possible… Only when we get some good ole clues do I start playing with the oil viscosity. So no argument from me here… @“common sense answer” … I think we are much more in agreement than we are on diverging philosophies in viscosity…

Nope… I adhere to the called for weight as long as possible… I think I just stated things in a confusing manner by saying 100K miles… That certainly isn’t written in stone…I think I just start paying closer attention at that mile marker…thats all.

@irlandes …Oh yes I agree with you…no need for an engine tear down… I was just being silly. But do those Oil Analyses show you that much info? I know it can recognize specific metals and declare that is sees some main bearing dust or what have you… How accurate and specific do those oil test get? Ive never done one before…in fact I’ve never even looked into one of the reports generated… Hmm…Might be time to use the Ole Internet and have a looksie at one of those reports… I bet its pretty amazing what can be told from those reports.

Blackbird

Increasing the viscosity of the oil will just make wear worse since the most most wear occurs at start-up.

@Honda Blackbird
I get it, now. Then, we do agree. I would do what you have done. I could be wrong, but I believe one thing that happens when people use products like Lucas Oil Treatment to cut down consumption in an oil-burner is that the overall oil viscosity increases. I’m not saying that’s bad, but rather that it’s a good thing for an oil consuming engine.

I have used Blackstone Lab. It’s very interesting and worth trying out just to see what results.
There’s a space for comments about special concerns or questions on the form that you send in with your oil sample. I made comments and they were addressed with additional remarks in the analysis. I have felt my money was well spent. They are prompt, too.

It’s been a while since I’ve used them, but visit their site and you should be able to see a sample analysis report. Toward the bottom of the home page, look under “Customer Service” for
"My Reports" and choose one. Notice the “Comments” section.
http://www.blackstone-labs.com/
CSA