Piston Slap: Help For The Rough Rocket? (Take 2)


Ron writes:

Hi Sajeev, I talked to you via email a year ago about my 1954 Oldsmobile Rocket 88. I too had a piston slap noise when I started the motor. You advised me to put diesel oil in place of my regular oil. I did it a few months back and it made a big difference. The engine is much smoother now and the piston noise is to a minimum when I start it. There is a little noise when cold but it dissipates after less than a minute when the engine is getting warmed up.

Thank you again for helping me. I have owned my car since 1983 when I bought it from a gentleman in Van Nuys, California.

Sajeev answers:

I am so glad my advice worked out for you! Bear with me for a second, as there might be a lesson to be learned for all classic vehicle owners.

Too often we get caught up in problems with our cars, and cannot see the forest for the trees. This is one of my (numerous problems) with Project Valentino, and I’ve been forced to listen to my internal project manager and his need to implement a “change management” plan. (Gotta listen to him because he’s got an MBA so he like totally knows what he’s talking about.)

It’s a slippery slope to introduce business concepts in places they don’t belong. But change management has validity in our complex world of automobiles. Otherwise, you’re just banging your head against a wall. The practice requires the user to recognize a problem, note any issue(s) surrounding it, gauge possible solutions, and approve/implement a solution. If your solution doesn’t work, you repeat the process. Simple as that.

In the case of Ron’s Oldsmobile, an engine rattle only has a few logical solutions: increase oil pressure via a change in oil type, tear apart the motor to fix an issue with the oil pump and piston rings, or a full rebuild before more engine damage occurs. The simplest, most logical solution for an armchair quarterback (like yours truly!) is to change the oil first, and diesel oil is generally the best for pre-1975 vehicles.

Luckily for me, the first step in my change management strategy worked for Ron. So if you think I can help YOU, read the next paragraph to make that happen. I could always use more questions to enlighten and possibly even entertain the Hagerty Community.

Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.comgive us as much detail as possible so we can help! Keep in mind this is a weekly column, so if you need an expedited answer, please tell me in your email.


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    I’m intrigued by the change management plan. It’s a shame companies don’t use it. At most places I’ve worked, when things go wrong they double down on what they’ve always done.

    Upper management types usually don’t use it, it’s the middle management types that are responsible for projects that inevitably need a tweak here and there.

    I’m always leery about using heavier oil to address engine chatter. Yes, the heavier oil will quiet things down, but it also takes the engine longer to pick up that heavier oil on a cold start, which tends to hasten degradation. Now for collectibles that aren’t started 2 times a day 5 days a week, it’s probably not a major problem

    Yes this is just a band aid to fix the real issue. But this is not a daily driver and this can go on for years with no major problems.

    Some older Chevy trucks and others have this same problem cold and to be honest they are driven till they are rusted away and never have it repaired. It is more annoying than damaging in many cases.

    This is a case you need to look at the car and decide are you keeping it for ever and plan to fully restore it or just keep it as a weekend play car and not invest much. If the latter the oil deal will work for a good while.

    Who knows the oil use or rings may give up and you will just fix it then. He never said how many miles and it may have many. These older engines need rings much sooner than modern engine. That would be a good time to repair it.

    Or this isn’t heavier oil, it’s the correct oil after years of modern thin oils being used on it. We may never know what weight was used previously, but odds are most places will recommend a modern oil for everything that pulls up in the driveway.

    Depends on what he was using to start. If he was using a 5w30 yes it was wrong.

    I know a 54 Chevy said 20 weight year round. I am sure some said 30 weight too.

    Most modern oils will work but if there is weak there is more play.

    It took me a minute to realize that the author of this article was not suggesting replacing the engine oil with diesel fuel. Some parts of the country call diesel fuel, diesel oil. Most people talented enough to know how to change their engine oil should know the difference, if not they will have no choice but fix the engine the right way with a complete overhaul

    Oil weight isn’t the only issue. ‘Diesel’ oils tend to have higher zinc and other good things for a harder duty cycle on new diesel engines or better for older engines that are missing the lead from the old days. So you can buy Rotella or the fancy vintage oils with an additive package.

    Oil rated for Diesel engines – at least Shell Rotella – is available in 10W-30 in quarts – the gallons I’ve seen & bought are all 15W-40. Diesel engines typically operate very differently than passenger vehicles, though. While I’ve had no problems using Rotella or Delo in older cars & trucks, for the valuable and/or performance cars, I use the oils from Lucas, Driven, etc that are formulated for what collector cars actually do.

    It would be nice to know what they were using before and what is being used now, but either way glad the car seems happier.

    In engines designed before tight tolerance, low tension rings, variable displacement valving, etc. the correct oil is the highest viscosity that will flow when cold. Multigrades, w their higher hot viscosity vs cold viscosity will be superior to single grades in any engine that doesn’t burn oil. So it is hard to do better than 20w-50 in southtexas in the summer or worse than a 50w in North Dakota in winter

    Diesel oil is commonly found in 15W-40, however there is also 10W-30 available for some engines, and I have also seen straight 40 weight used in older industrial applications. There is also a newer 5W-40 diesel oil available in synthetic.

    When zinc was first removed from conventional motor oil, it was common to recommend diesel oil for older engines with flat tappet cams, to get the zinc they needed. However, zinc was removed from diesel oils shortly thereafter, so people using diesel oil to get the zinc are not getting the benefit they think they are. On top of that, diesel engines typically run at lower RPMs, so the oils are not required to have the same anti-foaming agents that oils for gasoline engines must have. Foam isn’t good on your beer, and it doesn’t lubricate your engine well, either.

    For my older cars, I have two oils I use: for freshly overhauled engines, Mobil1 15W-50 is a great synthetic oil that actually has zinc in it. They get away with this because it’s a “racing” oil, not sold for or recommended for any new engines. The other good option is Castrol “Classic” 20W-50, which also contains zinc. There are a number of “boutique” oils out there with zinc in them as well, but they are all much more expensive. It’s cheaper to buy a bottle of zinc additive (about $10) and add it to your oil change, if you need an oil that doesn’t contain zinc in the desired viscosity.

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