Synthetic on a higher milage car...

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Jul 10, 2002
Memphis, TN
Hi everyone, I've been trying to talk my father-in-law into using Schaefer's oil in his '94 Corvette (5.7L engine (I think), 35th anniversary car). However, he doesn't want to because he "heard" that running a synthetic oil after using conventional oils will "hurt" his engine. The engine has ~115K miles on it and is not (noticably) burning or otherwise using oil between its 3K mile oil changes. I thought this was just rumor and heresay, but he it pretty adamant about it unless I can come up with some information that shows otherwise. I'm also waiting for him to get an oil change so he will use the oil analysis kit I bought him so we can see exactly what is going on inside the engine. Any help? [Smile] Scott PS. He also has a 4 cylinder Camry that Toyota replaced the engine on due to the oil sludge/gel problem they've got (~3K-4K oil changes, religiously) and I've been trying to suggest that a synthetic (namely Schaefer's) would also help with that car.
Simply put, running synthetic will not "hurt" the engine. The only issue that can arise from changing over to synthetics on a higher-mileage engine is the inherent cleaning ability of synthetic oils. If a lot of gunk is built up on seals, and the seals aren't sealing properly, the synthetic will clean away the "gunk" and you will get consumption issues. Alot of times though, after the synthetic cleans away the crud, the seal-swelling agents in the oil will cause the old, non-sealing seal the once again perform it's job properly.
Let him know that Schaeffer's is a blend of top quality petroleum oil plus about 20% synthetic (twice any other blend I know of). The fact that it is a blend tells that the components of the product are completely compatible. Let him know that using Schaeffer's in both engines will have little short term result--a couple of percent fuel savings and slightly less friction that he probably won't feel. The long term result will be cleaner engines with less wear. There is a chance of increased oil consumption for one, two, or three oil changes due to the improved detergents removing deposits in the engines and the new oil taking time to seal things again. After things get re-sealed, oil consumption will be equal or less than ever. A slow cleaning with Neutra or Auto-Rx will prevent this from happening. Ken
Thanks for the quick replies! I forgot to mention that I had told him that the car might seem to start burning a bit of oil due to the cleaning properties of modern synthetics, but I didn't mention that they will also help "refresh" the seals, "fixing" the problem. However, I seem to remember from another post awhile back in this forum that even synthetic oil will not really recondition the seals. They will a bit, but not nearly to the level that Auto-RX appears to. I bought him a bottle of Auto-RX just for that purpose, so I don't think that will be a problem, long-term. Since the Camry engine was replaced (essentially rebuilt), I thought now would be a good time to get started with Schaeffer's. Thanks for your help! Scott
syn.won't mess up anything ,but what would be the advantage of switching. If you are going to use Schaeffers why not use their petro oil ,there won,t be any less wear with syn oil. Just my opinion.
He shouldn't have problems switching with that engine, it's the LT1 engine, same as what's in my 95 Firebird (except in the Vette it's 300hp while mine came with 275 originally) By the way, if it's a dark red 40th anniversary edition (which I love!) it'll be a 93, not a 94, since 1953 was the first year of the Vette, so 93 was when they had the 40th ann. edition. 35th anniverary editions were white 88s. These LT1 engines like a slightly thicker oil, something on the high end of the 30wt to the low end of the 40wt range (something that's in the range of a viscosity of between 12-14cst at 100c) [ September 08, 2003, 03:28 PM: Message edited by: Patman ]
Patman, Ouch! You got me on that. I KNOW it is a 35th anniversary edition, so that would make it an '88 vette. It is white... Don't know why '94 stuck in my mind... DUH! Guess it just goes to show that I'm not a vette person. Personally, I prefer my wife's Infiniti G35 sedan. Go figure. Steve S, In response to your "why" question, he has been talking about doing various and sundry performance upgrades (it's a 245hp engine) to get more out of it and I have always believed that good oils won't hurt, but not so good oils can. Besides, an extra $10 per oil change is cheap insurance. 3 Mad Ponchos, Glad to hear that 115K isn't really that many miles these days (though I'd hate to see what my '99 Durango will be like then). I'll keep suggesting he take the plunge... on both cars. Thanks everyone for your responses! Scott [ September 08, 2003, 10:11 PM: Message edited by: Scott ]
I swapped my Grand Prix over at 104,000, with no ill side effects at all. Think about it this way: the oil is just a lubricant, and no matter if it's synthetic or conventional, it's still lubricating the engine. It's not going to deteriorate the bearings or something. As long as the engine is getting lubricated (which it is), you aren't going to damage it.
The 88 Vette uses the L98 350ci engine, which is one heck of an awesome torque monster! Almost 350ftlbs, and almost right off idle too. Nice! This engine can also benefit from slightly thicker oils, since it's clearances are very similar to the classic small block Chevy. I believe this engine is even "looser" than the LT1, so a 10w40 should work out well.
though I'd hate to see what my '99 Durango will be like then
It should be fine. I used to buy cars only if they had over 100,000 miles on them, because they'd be dirt cheap and still have another 100k of life left. Cheers, 3MP
115000 miles on dino, changed at 3000 miles, nothing wrong with that , proven receipe, car running flawlessly. Why changing ?? The car is not going to last 10 more years, and worth more, or take less time on 1/4 miles, I dont understand the logic behind ? If its just for fun then, go ahead ;-)
guitargeek, With respect, I think that oil does make a difference... otherwise, what is the purpose of this board? Especially in high stress areas. [Smile] Patman, I did think that the 245hp figure for this engine seemed surprisingly low. I hadn't seen any torque figures for it below, but after your comment I found that the engine produces 345lb-ft of torque at 3200rpm. Woof! The 1988 Callaways put out 382 hp and 562lb-ft of torque. Double-woof! With stresses like that, no way anyone can convince me that a better oil won't help! [Smile] 3 Mad Ponchos, Glad to see someone from Morgantown here. My wife's family is from there. As for the Durango, on there has been much written about this engine's sludging problems. Also, it is fairly "famous" for blowing intake manifold gaskets which can lead to sudden (and dangerous) consumption of oil. Already happened once, when my wife was on a trip with the kids to her parents. At ~46K miles, this engine (5.9L Magnum, 4x4, w/towing package, though not used off-road or for towing) is now consuming about 1-2 quarts of oil per 3K miles (we have been changing the oil every 3-3.5K miles since new and have records to prove it). We switched to Schaeffer's 7000 synthetic oil about 10K miles ago. The dealer is conducting an "oil consumption test" now so that they can tell that the engine is consuming oil... duh! They claim it is not another intake manifold because they looked inside the manifold and didn't see any oil. For some reason, the oil consumption seems to get worse when driven mostly on the highway. Personally, I think that anything over a couple ounces of oil consumption between changes on an engine with this few miles is very wrong. In fact, I don't think that it should be consuming any oil at all, based on the way we have taken care of it! Based on my experience with the Durango and my in-laws experience with their Camry, there is no way I'm going to not use synthetic oils from here on out. Saving the extra $10-15 just isn't worth it. ------------- Anyway, back to the '88 Corvette. I'm going to order him a case of the 10w30 (factory recommendation) Schaeffer's 7000 when I order some more oil this week, since he has finally said he will try it. Not forced to, just willing to do so now. I think it is especially important since he is now thinking about performance upgrades (chips, exhaust, etc.). However, he doesn't want to do anything MAJOR right now, because he is worried that with 115K miles, the engine won't handle anything more without being rebuilt first. I've suggested to him to get the oil analysis done so he can get an idea what is happening inside the engine. (I think it's in better condition than he does, especially since it isn't using oil.) Then if everything looks good (no significant signs of wear), I've suggested he try a Whipple twin-screw supercharger (~$4K installed, ~50% increase in hp/torque, w/o intercooler!) rather than spending ~$10-15K on a new, modified GM performance engine. [Cool] [Big Grin] If the supercharger blows the engine, then he is no worse off than if he had bought a rebuilt performance engine, financially. However, he just wants some occasional extra "oomph" (and the knowing the oomph is there, if he wants it), so I really doubt that the supercharger will do anything negative to the engine. Thanks for all of your help! Scott
Baveux, As mentioned previously and just above, he is thinking about doing some (minor now, more significant later) performance mods on the car and I just think that if dino is "good", then synthetic is better. Besides, extended oil change intervals are always a possibility, if an analysis says its ok... After spending money on performance mods, IMO, it would be a shame to have something go wrong because he wasn't willing to spend an extra $15 an oil change to put in a synthetic. He is WILLING to spend the money and the only reason he hasn't done so before now is because of an apparently unfounded belief that running a synthetic will "hurt" his car. We will know more about what is going on inside the engine when the oil analysis is done. [Smile] Scott [ September 09, 2003, 11:00 AM: Message edited by: Scott ]
The L98 engine takes pretty well to a mild supercharger (6psi), I'd definitely go that route if it were me. They run 9.7 to 1 compression ratios, which is more favorable to supercharging compared to the LT1 and LS1 which run 10.5 to 1 and 10.1 to 1 compression ratios respectively. Carroll Superchargers makes a nice 6psi kit for the L98 which makes 375hp and 425ftlbs of torque. Nice! You'd definitely want to run something like Amsoil 10w40 or Redline 10w40 in there once the supercharger is on though, as it'll be putting a lot more stress on the bearings. I had an 8psi Paxton supercharger on an 87 Mustang GT a few years ago and boy o boy was that car fun! Low 12s at 112mph in the quarter mile, but would still knock down 25MPG.
guitargeek, With respect, I think that oil does make a difference... otherwise, what is the purpose of this board? Especially in high stress areas.
I think you misunderstood me a little. OF COURSE the oil makes a difference, but I just don't see how switching to synthetic could hurt an engine... the synthetic is a better lubricant, right? So, by that reasoning, the engine should be better off, unless there's something I'm missing (which is always possible). If I didn't think the oil made a difference, I wouldn't be mail ordering Royal Purple right now [Big Grin]
If he's gonna shell out the money for a supercharger, why not shell out maybe a little bit more on a rebuild? He could rebuild the motor to stock specs and get the hot cam kit and put down right about where a stock C5 vette is assuming he has headers, cold air, and pcm tuning. Or he could rebuild it with forged pistons via a summit engine rebuild kit, recondition the rods, balance and turn the crank, decent porting of the heads, and a CC306 cam. He'd be putting down close to 350-370ish at the wheels with a motor that's basically new. just my 2 cents Jason
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