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Bryan
Hagerty Employee

Piston Slap: Diesel engine oil for classics?

Edwin writes:

Is there an advantage to using synthetic oil in the older engines from the ’40s and ’50s? Please mention both rebuilt and original engines. I have a ’53 Olds Super 88 

 

Andy writes:

I have a ’41 (or ’42?) Ford Flathead V-8, and I have heard different things about what oil to run in it. The Flathead has been bored 0.30 over with a ¾ Isky cam, Edelbrock 65cc heads, and intake 2 super 7 carbs. What oil do you recommend?

 

Sajeev answers:

It’s a bit ironic that not only did we speak to Shell’s petroleum gurus about this, but their advice applies to both vehicles. Read the full article on Hagerty.com:

 

https://www.hagerty.com/media/maintenance-and-tech/piston-slap-diesel-engine-oil-for-classics/

24 REPLIES 24
Pepperalls
Detailer

Engine shop that did my 69 Mustang 302 rebuild 7 years ago insisted it run a 20W-40 diesel oil.

 

I have had older mechanics note this and say "yep" while younger ones question it.

 

Interesting.

CaptainCardigan
Intermediate Driver

Our default motor oil is Rotella T6 5w-40. We've run it in everything from a 2014 WRX to a 1941 Oldsmobile Straight 8 (and even in a diesel truck).  I went back to Mobil 1 on the WRX when T6 got 'de-rated' for petrol cars, just as a wait and see, and my old Triumph I'm using a 20w-50 specifically recommended for that motor; but those are exceptions. 

Sajeev
Community Manager

No wonder that Olds did so well at the Lemons race!  

Ztstefsn249
Passenger

I’ve got a ‘58 TRIUMPH TR3. The engine was rebuilt and believe it or not for first time I have oil leak from rear of engine. Any oil suggestions or fix ideas appreciated. vfs

hearsedriver
Intermediate Driver

another oil to consider which contains the zinc necessary for the older engines with flat tappets, is Lucas "hot rod and classic car" oil. comes in several SAE grades

Sajeev
Community Manager

I had no idea Lucas made an engine oil for these applications, that's great to hear!  Thank you for sharing. 

ThatGuy
New Driver

I have an all original 1967 Dodge Dart with a 225 Slant Six that has 98,000ish original miles. I use the 20w50 flavor of Lucas Hot Rod and Classic oil in it and have never had a problem. The Slant Six runs better, smoother and quieter than it did when I used “regular” oil in it.

MoparJeff
Pit Crew

Any comment on my current practice, which is 'regular' motor oil, then adding (usually Lucas) zinc additive?  Would that be the same effect as the Rotella T4 with zinc?

Sajeev
Community Manager

Probably the same (depending on the zinc content between Lucas and Rotella T4, which I do not know offhand) except I suspect what you are doing is a lot more expensive, considering Rotella is $14 a gallon on Walmart.com right now which kinda blew me away (just checked via Google Shopping). 

ThatGuy
New Driver

MoparJeff, I have an all original 1967 Dodge Dart with a 225 Slant Six that has 98,000ish original miles. I use the 20w50 flavor of Lucas Hot Rod and Classic oil in it and have never had a problem. The Slant Six runs better, smoother and quieter than it did when I used “regular” oil in it.

slammin
Pit Crew

Many restored Model A Ford drivers swear by Rotella T, sighting the increased zinc content to protect the cam. While I had my 29 Tudor, I felt that the low rpm flathead 4 didn't benefit from increased zinc,  and used a good multi-grade detergent dyno oil instead.

60Caddy
Pit Crew

I have to agree with Tony T. VR1 Valvoline is the way to go. I run a 60 Caddy and a 1951 Chrysler Crown Imperial with the first 331 Hemi in it.

 no issues, no leaks, no noisy lifters. I tore the caddy engine down as we need to reduce the compression ratio from 10.5 to 9.5 and the cam and lifters were mint. over 100,000 miles on the old girl and time was time

MoparJeff
Pit Crew

What do you recommend for older engines that I had understood needed the zinc for lubrication, but that are new enough to have catalytic converters (ie. 1970s-early 1980s)?  Thanks again for the great information.

 

Sajeev
Community Manager

Because of the cats, odds are running a conventional gasoline engine oil is still best.  If its an older rebuild or all original, stick with non-synthetic oil and get it in the right weight as per factory recommendations.  If you can run synthetic (gas engine oil) without it leaking everywhere, that will likely get you the added protection we all would like. 

Greg_I
Advanced Driver

I use a conventional oil of my preference in my 69 Grand Prix and add Lucas TB Zinc-Plus to the oil. My local NAPA carries it on the shelf, and since it is a Lucas product, it is likely very easy to come by at any average parts store, so it may be a more accessible option for some.

 

https://lucasoil.com/products/engine-builder-lubricants/engine-break-in-oil-additive-tb-zinc-plus

 

For anyone curious, here is a table of Zinc content that they post for average oils and what mix ratios will get you.

 

https://lucasoil.com/pdf/Zinc_Values_MotorcycleOil.pdf

 

 

59SilverHawk
New Driver

We've been using 15w40 Diesel in "older" engines such as Ford & Chrysler flat-heads along with Gen 1 Chevy engines for decades with excellent results. I highly recommend it!

TonyT
Instructor

My experience with using diesel oil in a gasoline engine was less than satisfying. A 402-inch big block Chevy with a solid lifter cam (nothing radical) with a little over 70,000 miles on it, sparingly driven and treated with respect. When zinc started disappearing from the name-brand oil that I always use, I tried a refill using a name-brand diesel 15W40. After about six months, I noticed that the oil pressure was dropping a bit when it was idling. A preemptive yank was in order, and  we found some pretty gnarly pitting in both the cam and main bearings, particularly on the bottom of both. We deduced that when the engine sat for a few days or weeks, the acid byproducts from combustion were aggravated by something in the oil. We freshened it up and used Valvoline VR 1. A sample sent in for analysis after 1,000 miles in six months showed no bearing material in the oil. Your results may vary from ours. 

DennisTheROACH
New Driver

I have had quite a few pre-1980 vehicles and I use MoS2 Anti-Friction Engine Treatment from LIQUI MOLY instead of a zinc additive. As directed by their tech staff, I add it at 15% by volume to either conventional or synthetic oil. I only use it with synthetic oils after a fresh rebuild as, everybody knows, an older engine will leak through seals and gaskets with synthetic.

As for using VR-1 or any other racing oil be advised that they are formulated to be run hard and changed often. They do not contain many of the additives for cleaning and anti-sludge buildup that most oils do. Not good for seasonal cruising.

LIQUI MOLY also sells jugs of 10W-40 semi-synthetic oil premixed with the proper amount of MoS2 Anti-Friction Engine Treatment

DennisTheROACH
New Driver

OOOPS! The proper ratio is 5% by volume, not 15%.

MrJoshua
Passenger

All cj-4 and ck-4 diesel oils have a high level of detergent. I recently ran into an issue where a customer started using Rotella T-4 and after 500 miles lost oil pressure. This is a 60 year old original flathead. When I pulled the pan I found the oil pick up packed full of small chunks of sludge. It's not definitive that the oil is at fault but I'm sure it didn't help. So just be careful with original engines, it really depends on how well it was maintained.

rabbit123
New Driver

The 4.6 Ford oil filter adapter leak was common enough on any oil. That is happened after you changed to synthetic may be coincidence. Coincidence is not causation.

Sajeev
Community Manager

Except it was very common on the Mark VIII forums when second/third owners would buy one and switch to synthetic.  It was not just me, that's for sure. 

OldRoad
Instructor

30HD and a jug of STP is the best combination for a tired but good performing old engine hands down.

spoom
Technician

My '64 Avanti R1 (stock 240HP 289, 10¼:1 Comp.) Factory shop manual called for SAE 30 for use above 32° but lists SAE 10-30 & 20-40 as "acceptable alternatives". Since it only comes out in the warm months and doesn't go too far per trip, I use conventional SAE 30 with original STP additive, just like it came from the factory. Snake oil to add the STP, despite the valve cover sticker to do so? Possibly, since Studebaker owned STP at the time, but it's inexpensive for one oil change every late Fall when it goes to hibernate. It's got just over 100K on it, so it seems to be a good plan.