Synthetic oil changeover in high mileage engine

[AceRock]

Hello everyone! My names John and I am new to this forum. I recently purchased a used '97 Tahoe with a 5.7L from a friend of mine who owns an auto repair shop. This vehicle belonged to a friend of his who bought it brand new. It is exceptionally clean and original. It has 98k miles on it and I was wondering if changing over to Mobil 1 oil this late in its life would cause more harm then good. Any suggestions? I have purchased most of my vehicles brand spankin new and have always used Mobil 1 in all of them and have been quite pleased.

 

[Vicious95]

I dont see why it would hurt. I had a 98 f150 with 140k and switched it over to syn. oil keept it for two years wit no problems.

 

[Biggwaukegan]

go with royal purple

 

[drumrpunk]

The main difference between regular and synthetic is that synthetic does not break down as quickly and easily as conventional motor oil. So there is no reason that synthetic would do any damage to your motor. So fill er up!

 

[AceRock]

Thanks for the feedback guys. I will be doing the oil change this weekend.

 

[peterey2]

you can always switch to synthetic. most people also ask if they can switch back if they needed to, and that answer is yes as well. as long as your keeping the viscosity the same.

 

[strd27]

syn or reg oil

Let me tell you a story. I have been a diesel tech for 33 years and I bought my wife a brand new 1996 tahoe I did the brake in then I switched to Val syn motor oil with what they said sould be 5000 mile oil change. Well I put the val syn motor oil in and I change the motor oil every 3000 miles NEVER went over if I was taking a trip and it would put me over my 3000 miles I would change it before I went. Now let me tell you syn every 3000 mile is very costly but what the heck. I did the oil changes and I kept my sales ticket on evey oil change. I was driving down I-80 Just pass Kamas andI heard a knocking sound I had it towed on a flat bed back home it had rolled a rod bearing at 97000. miles no big deal I called val told them my delama sent copies of my sales tickets and I was told that they could not help me. So I have put a new crate motor in and I have ran reg motor oil ever since with NO problems. You could not pay me enough to run syn. What I tell people when asked is would you rather have a blow up doll or the real thing??

 

[peterey2]

ya. i havent heard any stories of how great the shyt is. ive personally found it leaks and burns up more than anything. i know of an old time mechanic who would never change is oil, only the filter every 3000. he always said oil never gets bad, it just gets dirty, and he had cars srun forever by just changing the oil filter and topping off the oil every 3000.
who knows. hah

 

[newmarketEOD]

Synthetic may leak more. It can make its way through old seals more so then conventional motor oil.
In the bad cases of it damaging the engine I am going to say user error on that part or actual part failure. Both I and my father also a mechanic of 30 some odd years run nothing but full synthetic in all our vehicles, motor oil and other internal fluids throughout. Not an issue, I love it.

My recommendation if you are going to use synthetic buy the real good stuff. I personally run AMSOIL in everything.

 

[drumrpunk]

Let me tell you a story. I have been a diesel tech for 33 years and I bought my wife a brand new 1996 tahoe I did the brake in then I switched to Val syn motor oil with what they said sould be 5000 mile oil change. Well I put the val syn motor oil in and I change the motor oil every 3000 miles NEVER went over if I was taking a trip and it would put me over my 3000 miles I would change it before I went. Now let me tell you syn every 3000 mile is very costly but what the heck. I did the oil changes and I kept my sales ticket on evey oil change. I was driving down I-80 Just pass Kamas andI heard a knocking sound I had it towed on a flat bed back home it had rolled a rod bearing at 97000. miles no big deal I called val told them my delama sent copies of my sales tickets and I was told that they could not help me. So I have put a new crate motor in and I have ran reg motor oil ever since with NO problems. You could not pay me enough to run syn. What I tell people when asked is would you rather have a blow up doll or the real thing??

I am not doubting your mechanical knowledge or experience but I highly doubt the motor grenade based soley on running on synthetic oil. I am an X ASE cert mechanic myself and stay pretty up to date on most technology. Everything I have read (popular mechanics and Consumer info) have said that Synthetic is better on almost every field. Because synthetic is made in a lab it only has what they say is in it. Crude oil although processed still has MANY contaminates in it. It breaks down at lower temps and has less viscosity on cold starts. Google it for yourself. Synthetic has been around since the 60's and has had a bad rap waaaay back in the day on older cars (and I mean WAY back). It still comes up every now and then but the facts in the testing. Almost all new cars even come with it now and I would think that if you have the money it would be smart to go synthetic. HOWEVER, is it bad to use conventional? No. To say either is bad is just not correct. There both fine for most cars now. Blaming oil for grenading you motor (syn or conventional) is a highly unlikely situation and when it comes down to it you would find that somewhere down the line a part failed or other human error caused it.

 

[bigskybassguy]

I'd say, save the $$ you'd spend on synth oil, and use those savings toward your new transmission. Yours should be going out in a few thousand miles. After all, it IS a 4L60E.

 

[peterey2]

ive heard all good about that amsoil.
any opinions on Rotella T?? good? bad?

 

[qlc1964]

i did read some where that syn oil shouldn't be use in high miles motors .

 

[Exec]

This is my first post on these forums, so firstly I would like to say Hello World

Now to the question. I have 1997 Tahoe 5.7 with 290.000 km on it, which is more or less 190.000 miles. I have just bought it and I'm planning to change every fluid that runs through it.

At the moment the engine oil is some unknown brand 10W-40. Would you suggest to change it to recommended by GM 5W-30? Or alternatively 10W-30?

I am not very fond of this idea, firstly because I am not sure about upgrading oil type from semi to full synthetic - I've heard it may wash out all the dirt from the inside, which will end with engine leak. Secondly, I believe the xxW-30 type is meant to run below 30 C degrees, which might not be enough for Polish summer.

Is there anything that might go wrong with the engine because of semi-synthetic 10W-40 oil?

Thanks!

 

[J4Landberg]

new to the forum but long in manufacturing environments that use many different lubrications in rotating equipment...
You may run into some seeping around valve covers, front/rear mains, timing chain cover, etc. A good synthetic, as mentioned above, acts like a solvent (runs very clean on the internals) and can break down the the buildup left by long usage of conventional lubricants. Witnesses this first hand on an old BB Ford FE motor. Buddy picked up almost 500 rpm on idle after switching to synthetics but started seepage (everywhere) after 2 weeks...
good luck

 

[Exec]

Ok then, I will stick to the 10W-40 which at the moment keeps the engine tight and clean. Any producer you would recommend? I saw many are satisfied with Royal Purple, but it's very hard to get in Poland, and if you are lucky to find one the price is a killer.

Any positive feedback about Motul or Liqui Moly?

 

[J4Landberg]

Consistency

Not familiar with either brand you mentioned, Exec, but I believe that Mobil 1 is some of the more consistant synthetic as the base stock all comes from a single source in the gulf. Either way, once you find a product that you like, or have been running for awhile, consistency will go a long way.
I know that many people in the states don't like Pennzoil for the high parafin content, but I have seen a BB GM motor go almost 400k on Pennzoil 10w-30 and ONLY Pennz 10w-30 at regular intervals, no matter the driving condition.
Welcome to the forum.
JL

 

[79powerwagon]

Synthetic oils do not hurt anything (unless used right after a rebuild. You won't be able to set your rings).

You can run synthetic oils in older engines without any issue.

If your engine starts to leak oil, it was already leaking oil and you didn't notice.

If you throw a rod after you change to synthetic, it was broken already, or you just then broke it. It has nothing to do with the synthetic oil OTHER than it will clean out your engine better than conventional oils.

 

[79powerwagon]

Synthetic oils do not hurt anything (unless used right after a rebuild. You won't be able to set your rings).

You can run synthetic oils in older engines without any issue.

If your engine starts to leak oil, it was already leaking oil and you didn't notice.

If you throw a rod after you change to synthetic, it was broken already, or you just then broke it. It has nothing to do with the synthetic oil OTHER than it will clean out your engine better than conventional oils.

 

[footinSD]

I switched over to synthetic at about 105,000 on my '99. It seemed to be more viscous (i dont know all the facts) but it sure found any worn out seal to leak from, and burned off quickly. At first, I was adding a quart every week, and thought it would catch up and seal itself off, but after 3 months of spending too much money on synthetic i decided to call it quits and switched back to standard motor oil.

My mechanic recommends synthetic blend for high mileage instead of synthetic due to the burn off situation, but that is just what i experienced.