Guy i bought 93 coupe from had 15w-40 synthetic oil in it. Not sure why. Since I've changed it to 5w-30, I've noticed a small leak. Could the 15w-40 have prevented that? And would 15w-40 damage it now?

1993. 89k miles. Stock

 

Nowadays oil is oil, as long as you’re using any type SAE oil it will be fine, doesn’t really matter what has been used before. Your leak isn’t caused from the oil you are using, you probably just have a bad gasket somewhere.

 

Some people run 15w40 in older engines to keep the flat tappet cam from going flat, this is caused by the lack of zinc in modern oils. Typically, 15w40 has more zinc in it as it's used in heavy duty service engines like diesels. Your 93 has a roller cam so that's not a wear concern. Chevy started using roller cams around 1987, Vettes got them but not all 350/305s did till later, mostly trucks.

 

I would try Mobil 1 5w-30 High Mileage. Supposedly it helps with leaks. The thinner oil maybe is causing the leak or it could be 32 years and 89K miles.

 

You bought an LT1. Get used to leaks. You can slow them down, but it will always leak from somewhere.

 

First thing I would do is fix the leak and use the Hi Mileage oil it's got extra ZZP ?? the good stuff. Whay not the heaviest oil I can buy ?? no ,the super thick oil when cold has a hard time getting under the bearings and maybe when hot as well, the 5 in 5x30 will allow the oil to get under the bearings and keep the old LT-1 on the road, back in the day people ran 50 weight ECT. Drag cars round track cars oil has come a long way from back in the day, The lt-1 was built for 5x30 oil or 5x40 in very hot areas of the country GM built the LT-1 for 5x30 oil ..

 

Yes, changing to a thinner oil or from conventional to synthetic will simply make a leak that was already there more apparent. The good news is that the new oil helped locate the leak location so it can be fixed.

 

True. A leak is a leak, and needs to be repaired. I honestly don’t think it really matters what weight of oil is used, any engine with good oil pressure will find the weakest gasket or sensor and start to leak lol

 

Most likely had 15w40 because it was cheaper.

 

Bwahahahahahah...so true! My 96 spots the garage every now and then. I'm not touching anything unless I see a half quart on the floor.

 

...or perhaps because the PO wanted the higher detergency/higher load capacity of a diesel oil. Diesel oils have to handle long intervals, need to maintain things clean, and handle a lot of soot until the oil is drained.

I am currently using Restore and Protect from Valvoline. I may switch to Castrol Euro 5W-40 in the near future.

 

not saying it's a bad choice or trying to argue... but I have 14 different engines to maintain. I try to keep it cheap and not have 7 different viscosity oils on hand. So I have 10w30, 15w40 (mostly for the diesels and the older engines that took heavier oils) and 5w30 for everything else. Keeps it simple and 15w-40 is both cheap (compared to most other oils) and possess good enough qualities to be used in most of my applications. (Except the boat. It shears to water in no time in that application for whatever reason and wears the worst by far compared to a normal 10w30) did I mention I'm cheap?

 

I understand. I simply added one more possibility as to why the PO may have used 15W-40.

 

I'm like you. Lots of different engines and requirements. Plus I work on boats and yachts, so I stock oil for them as well. Because I live in SoCal, my engines are almost never started at less than 40F. For many years, I ran Delo 400 straight 30W oil in everything, because it was suitable, I used lots of it in my client's boats so I was purchasing it in 6 gallon boxes, 5 boxes at a time. I expense oil in my business, so I saved 40% in income taxes on the oil going into personal vehicles.

Then I obtained the Cayenne. It uses a "European Spec" 0W-40 Mobil-1. Yeah, not putting diesel oil in that. I use what Porsche recommends (A40 spec Mobile-1), and in 13 years it has not developed the notorious Porsche 4.2L bore-scoring problem that costs 3 times what the car is worth to repair.

More recently, I've become cognizant of using high-zinc oils in cars with cat converters which are expensive, but necessary in California for emissions compliance. So I've gone back to using oil intended for gasoline applications which generally have cat-friendly zinc levels. But I still don't believe in 5W in anything of mine in SoCal. I don't even like 10W-30, because bearings in my personal engines looked like crap after using 10W-30. But, there aren't any cat-friendly choices of viscosity higher than 10W-30.

My 92 uses Mobil-1 10W30 High Mileage, The 85 uses Castrol GTX 10W-30 which is what has always gone in it except a couple of intervals with the 30W Delo. The 7.3 Powerstroke gets 15W-40 Delo like it has since new in 99. My ski boat uses either 20W-50 GTX or Delo 400 30W. I don't remember, I change it every 5 years, and it doesn't have cats. My daily POS S10 with 390k miles on it is to the point I don't care about it anymore. I put whatever odd oil I have on the shelf from client projects in it. (In the pic below there is a "Super Tech" 30 diesel oil. It cost $12 a gallon from Walmart Online. It is for the S10, because its cheap, and I don't care about this engine.)

I hear you on trying to minimize oil types. For myself, my cars are so seldom driven that change intervals are in years. So I just purchase the specific type/brand I need, when I need it. But I do keep some oil on the shelf. Cheers.




Oil filters, too. Some of these are for the marine diesels I service, but many are for my vehicles.

 

Tooo funny! Good to know. I feel lucky. I have one tiny leak, leaves a spot overnight about the size of a 50 cent piece. Replacing the valve cover gaskets made the difference!