Engine Oil

[61 Silver]

I was at the engine machine shop today checking on the 340HP engine and dropping off the flywheel for dressing. The shop builds or will machine engines for any type of cars including race cars. The owner told me I should think about changing the type of oil that I use in my Corvettes. He stated that some changes in the modern oils are not protecting camshafts. He recommended that I use a diesel 15 W 40 oil. Does anyone have additional information on this subject?



He also thought that I would have problems with today’s gas, as I have chosen to rebuild the engine to stock specifications except for the head gaskets. Does anyone have a stock 340HP that is running 93 Octane gas and how is it running?



Thanks Ray

 

[ctjackster]

yeah, plenty of info on just that exisits here on even more so on the other forum. Duke convinced me a few years ago to use a diesel oil, like Chevron Deleo or Shell Rotella, given its higher additive package and the fact that our typical use of these cars (not piling on the serious miles) renders the benefits of syntheitic oil less important.

oh and I have a 65 L76 (365hp) and it runs just fine on todays premium - might be a little more succeptible to fuel perc / evaporation from the carb though, seems like my carb is often dry when I go to start it up (some cranking required). I am not starting it every day, however.

 

[BarryK]

Ray
I'm with Jack on this one.
Following Dukes (SWCDuke) advise I just used the API C1-4 15W-40 diesel oil when I had the oil changed last week.
The mechanic (who i'll never use again BTW) tried to convince me it was completely wrong but I insisted. I respect Dukes opinion more than this unknown mechanic (even more so now after he worked on my car and I saw the end result )

According to Duke, pretty much oil is oil as far as lubrication goes, but the main difference is in the additive packages mixed in and the diesel oil actually has a better additive package for our older motors for various reasons that I forget and honestly a lot was over my head in understanding but since duke knows a LOT more than I ever will I figured it sure wouldn't hurt to try his suggestions.

As Jack mentioned, if you do a search over on the other place you will come up with a lot of posts about this and probably here also.

the '63 L-76 340hp mptor had a stock compression of 11.25:1 didn't it? Sounds tough on todays gas unless you back the timing down I'd guess. Wouldn't putting slightly thicker gaskets on the heads lower the compression just a tad? maybe that would be enough to keep running good on todays gas and still give you good performance.
I can tell you that my '65 L76 365hp motor had a stock compression of 11.0:1 and on 93 octane gas I get no pinging or anything but since the motor was rebuilt before I got it I can't vouch for anything inside it or how it was actually rebuilt so don't know what the true compression is anymore. sorry

 

[JohnZ]

The key difference between modern passenger car oils and diesel oils is, as Duke has pointed out, the additive package; modern cars with fuel injection and computer control of fuel mixture have far less blow-by contaminants than the carbureted cars of old, and the additive packages have been reduced as a result. The traditional ZDDP anti-wear additive in particular has been reduced to almost nothing, as it contaminates catalytic converters and oxygen sensors in its historical concentration. Diesels don't have cats or oxygen sensors, and their oil additive packages have much higher concentrations of the detergent/dispersant/anti-foaming and, particularly, the ZDDP anti-wear additive, which makes them more suitable for our old carbureted cars.

It's not like we're piling up 100,000 miles on our old Corvettes, but given the choice between conventional and diesel oils, the CI-4 diesel oils are better-suited to our engines.

 

[srs244]

thank you all for this very valuable insite into what best suites carburated vettes in the way of oil.

for what it's worth, i have always been of the opinion that our older cars don't produce sufficiently high enough spark to properly burn today's fuels without HEI or something similar in the way of spark boost. i know that the buick bugle from the buick club of america (yeah, i have one of those too. a 1938 series 90L limosine) recently ran an article dealing with the subject and discussed methods of "spark boosting" to better burn today's gasoline. the older ignition systems were designed to produce enough spark to deal with the burn levels of older fuel specs.

steve

 

[TWINRAY]

Ok, what do I do now with the 2 cases of GTX 10w-30 that I just bought?I did make a switch last year from 10w-40 to 10w-30 based on some readings and use Rotella in my 1975 Honda 750 after previously running GTX 10W-40 based on discussions in their forum.

 

[JohnZ]

Ok, what do I do now with the 2 cases of GTX 10w-30 that I just bought?I did make a switch last year from 10w-40 to 10w-30 based on some readings and use Rotella in my 1975 Honda 750 after previously running GTX 10W-40 based on discussions in their forum.

Go ahead and use it - not a problem.

 

[JohnZ]

thank you all for this very valuable insite into what best suites carburated vettes in the way of oil.

for what it's worth, i have always been of the opinion that our older cars don't produce sufficiently high enough spark to properly burn today's fuels without HEI or something similar in the way of spark boost. i know that the buick bugle from the buick club of america (yeah, i have one of those too. a 1938 series 90L limosine) recently ran an article dealing with the subject and discussed methods of "spark boosting" to better burn today's gasoline. the older ignition systems were designed to produce enough spark to deal with the burn levels of older fuel specs.

steve

Today's fuels don't have any different burn rate than they used to - the difference is that modern fuel-injected cars run at much leaner average mixtures (due to precise real-time computer control of A/F ratio), and it's harder to start the burn with a lean mixture than it is with a richer mixture. Our old carbureted cars have nowhere near that level of A/F ratio metering capability under dynamic conditions, and most are calibrated to always run on the rich side of ideal for decent driveability; our old cars are much less demanding of the ignition system than modern cars are. Most modern engines now have no distributor at all, have computer-controlled coils for each cylinder, and the coils are either mounted directly on the plugs or have VERY short plug wires to maximize spark energy for ignition of lean mixtures with no misfires (misfires are monitored by the OBD-II system, and will set a code and light the MIL light above a given level).