Scottydawg

I need to change the oil on my GTA (350) What oil is everyone using? I'm in the UK so will only really be using the car in the summer months, when its relatively warm, but will also give it regular start ups/short runs in winter.

I've seen various answers for this from searching the web, so I thought I'd ask on here!

Go Blue

Everyone is going to be different. I generally use either Mobil 1 synthetic or Amsoil 5W30.

kaos420

vavoline vr1 racing oil but that only cause I have to run oil with zinc

OrangeBird

iTrader: (1)

Ok , so you've told us what kind of car you have , great , that's a good first step .

BUT !

The second most important bit of info required to make an informed decision is ; How many miles are on the engine ? The oil requirements for a 20K mile "creampuff" are gonna be VASTLY different than for a 175K mile "been there , done that" engine , and no recommendation can be made without that bit of crucial info ....

Scottydawg

Thanks for the pointer! It has 75k on it.

Boxtruck

What kind of Cam are you running in this Motor? Flat Tappers are going to need Zinc additive in their Oil for the cams, I've switched out to Hydraulic Rollers over the years, been sticking to Mobil 1 5w30(doesn't get over 75 degrees here often, 10w30 in my Vortec Swap TBI K1500 Toy Hauler, caramel color after 3500 miles.

Bow_Tied

iTrader: (1)

If it is stock with the roller valve train just run 5W30. You can decide if you think synthetic is worth it.

Scottydawg

Forgive me for being such a newby! But I would assume that the cams are stock, although one of the previous owners added a Hypertech chip and low temp thermostat. Air filter, ported the intake runners. air foil thing in the throttle body. Adjustable fuel pressure regulator. Flowmaster back boxes, (Thats copied from his message to me).

I'm slowly learning stuff about these fantastic U.S motors, so I 'll be asking all kinds of things that may seem obvious you you guys, but hey, I have to start somewhere!

Go Blue

We all started with very little knowledge of cars at some point. Sometimes when you ask a question on here, you will have to ignore some of the responses that are a little rude. They do and will happen at times. Try to do searches before asking questions as there is a ton of information on here but you may have to read several threads to get all of the answers that you want. We are all here to help you in the end though. Nobody on here knows everything but there are some really great members that have a ton of information are more than willing to share it, but, I still advise you to do a search first. I use synthetic on my car but the previous owner used synthetic for many years as well.

88IROCvertZ

iTrader: (1)

I had this question not so long ago.. I got a 30k mile car with all stock and unmodified engine that wasn’t rebuilt and didn’t leak anything. I didn’t want it to start leaking either.

After consulting this board, my mechanic, a big classic car dealer that does restorations and an ASE Parts guy I know I went with conventional Valvoline. I’ll do 10w30 in summer and change the oil to 5w30 right before I put it away for winter. That was the overall consensus from people that preserve stock original cars.

Many sources advised that although synthetic is superior, it may clean out deposits (not a terrible thing) and cause a weepy drip or two. I did have that happen in my 87 when I switched to Mobil 1, but they were tiny leaks that wouldn’t register on the dipstick. I used to go to the track with my 87 and it wasn’t bone stock, so I liked the performance of synthetic in that situation.

My parts guy said the engine was built to run conventional and he’d just keep running that if there are no problems. Mobil 1 wasn’t used in Corvettes until 1993.

It’s not that there’s anything wrong with synthetic, but kept getting the “If it’s not broke don’t fix it..” type response

T.L.

Use what the manufacturer recommends...

Scottydawg

That's why I'm asking! There's no owners manual! I'm sure you can tell me though?

vinny R

I am a Mobil 1 guy forever so my opinion is bias. I agree with 88 Iroc in that you have a low miles stock engine you stick with Dino oil as that is all it has had for 30 or so years. I use Mobil 1 high mileage 5-30. I also did a 250 or so mile flush before I started with the Mobil one as the bottom of my dipstick was black. That is the tell tale sign of oil not being changed when it should. My car had 81K when I got it.

T.L.

10w-30, or 5w-30 in cold climate...

88IROCvertZ

iTrader: (1)

I do 10w30 in spring-fall and 5w30 over the winter.. I start it up once/week and let it run 15 minutes in the winter.. we get below freezing and below 0 for at least 6-8 weeks of winter so I want a lighter weight oil to make it through those times.. I only drive 1000 miles/year (not a daily driver) so only do oil April and November.

Summer we get heat waves 80s-90s and occasionally hit 100 for 3-5 days in summer. I want heavier oil to coat moving parts during the hot months.. The car can run pretty hot in summer with the stock thermostat. Was thinking about switching that out.. used to run a 160 in my 87..

These cars came with 5w30 conventional oil but the manual does recommend using the correct weight oil based on temperature/region.

Might want to pick up a used manual, they’re fairly cheap and easy to get all over eBay.. Repair Manual can be useful if you’re gonna own one of these too..

midias

I have been using lucas hotrod oil for my flat tappet cam

dmccain

iTrader: (2)

All of it is good as long as you keeping it changed regular.

armos

When you mentioned air filter, do you just mean a standard replacement, or do you mean it was changed to a K&N style reusable filter with the thin layer of oil on it? If so, just be aware that those have a reputation of allowing some dirt into the engine, some of which can end up in the oil.
With the Hypertech chip and low temp thermostat, and maybe alterations to the fuel pressure, it sounds like the engine will see it's share of rich fuel conditions and maybe some short run times.
Given this, I'm supposing that this engine might have a higher than average exposure to fuel dilution and maybe water condensation in the oil. Depending on the air filter, maybe also some above average dirt contamination (shows up as silicon in an oil analysis).
If these are actually significant, then I think the counter move is to change oil a bit more often, and/or maybe choose a slightly higher viscosity. Try to give the engine some longer run times that get the oil up to full operating temperature at least periodically.

If you're concerned, you can take a used oil sample and send it off to be analyzed. In the US there are a few places that do that for something like $20, so you must have similar outfits in the UK. They can test for dilution, it's current viscosity, how much wear metals it contains and so forth.
You can find a lot of examples of those type of reports at bobistheoilguy.com. That forum also just generally talks a lot about oil.

Of course, this is a topic where it's really hard for anyone to prove that their opinion is correct, so there's a lot of guesswork and groupthink out there (including my own guessing and the popular views you'll see on that forum). The usual standard is "I used brand X for years and my engine didn't blow up". That doesn't mean it didn't wear a bit more than somebody else's engine did, but that's really hard to prove. Even if a difference in wear was established, there's always going to be other variables involved besides the oil.


Ignoring cost, my personal favorite for old pushrod engines like these is Valvoline VR1 10w30. No idea what it's availability or pricing is like in the UK. VR1 is basically a juiced up version of their mainstream conventional oil with more zinc/phosphorus content (which pushrods like). Due to the amount of phosphorus, this flavor of their oil violates modern API (US) standards so they sell it as "racing oil". It still has the same life span as their normal oil. So I view it as a tweaked version of street car oil that's optimized for old pushrods.

The downside is that phosphorus slowly contaminates catalytic converters and O2 sensors. That's why API imposed limits on it, but I don't think either of those are big concerns on these older cars. Cats are fairly cheap and single wire O2 sensors are very cheap.
But I wouldn't put it in a silly modern car with four $100 O2 sensors and a pair of $1000 catalysts.


I'm of the opinion that GM had an incentive to recommend thinner oil since it improved fuel mileage slightly and was adequate for the expected life of the car. I've also seen it argued that some engines in overseas markets tended to come with higher viscosity recommendations than when sold in the US market.
So based on my guesswork, I have no problem using 40 grade oil but I wouldn't go below the original 30 recommendation. Am I wrong? Probably.

Last thing I'll say is don't sweat it too much. It's easy to obsess over oil and it likely will make no perceptible difference what you use as long as it's remotely reasonable.

3rdgenparts

iTrader: (8)

+1 for Mobil 1

It gets HOT where I live, Been using Mobil 1 10W-40 in both my '82 trans am and '01 Suburban and made big difference in my Suburban runs quieter and more responsive in torque.


Dave

Scottydawg

Thanks for the detailed reply armos! I think I'm going to enjoy it on here!
This car is probably the most powerful I have ever owned, and as such, I'm just wanting to make sure that I'm treating the engine in the correct manner (I'm assuming because of the performance aspect of it, the tolerances will be different to cars that I have owned before).

I will probably stick with the recommended oil as per the filler cap.

And yes, the filter is a cone type sponge, so I'll try to keep it cleaned and oiled. The cats won't be a problem as the previous owner also had them removed.

Scott