Oil additives in old engines

[Ximonatt]

I fully understand that the vast majority of oil additives are nearly or completely worthless in modern engines. But I've noticed that most of the discussions on this say something like ""no engine built in the last 25 years will see any benefit from <product X>""

A friend asked me to help him change the oil in his early '70s classic truck engine and brought up the subject, and both of us have heard the ""no engine built in the last 25 years will see any benefit from <product X>"" notices from consumer testing organizations. Both of us vaguely think we've heard claims that some of these things actually were useful in old low-tech engines. (Think no electronics beyond spark plugs and large cast iron blocks that have massive amounts of excess steel because they were made before weight savings mattered.)

I know there are several here with passionate knowledge on the subject, so I figured I'd ping the lounge: Are there any oil additives that would be beneficial for a 40ish year old engine? If so what? He's putting enough $$ into restoring the vehicle that a few buck for magic-motor-honey would be worthwhile if they actually helped the old engine.

FWIW, the engine starts great, puts out decent power, but has a few minor clicking sounds that might be valve noise. He hasn't torn into the engine, and wants to work on the interior before prioritizing the engine.

[AZgl1800]

I would avoid any of the 'honey' products, like STP.

I would instead, recommend the proven brands of oils that are labeled for "High Mileage" engines.

I am using Mobil-1 "High Mileage" Synthetic for "older engines" in my 2001 Suburban, it is a 5w40.
No leaks anywhere, I change it annually with about 4k to 5k miles on it.

the truck is used mostly to pull our Toy Hauler on summer vacation trips....

In my 2002 gl1800, I am using Rotella T6 in 5w40, it is a full synthetic.

Valvoline has a very popular High Mileage engine oil that I used for years in other vehicles.

[DaveO430]

No additives are needed with modern oils. The only thing you might want to use would be something to clean out the engine then change the oil.

[fcmusician]

I own a 2000 Freight liner (Detroit series 60). Bought it in 2003. Still drive it today with over a million three hundred thousand on it. Started using Lucas oil additive in 2005 with oil changes at every 12,000 to 14,000 miles. Still runs smooth as ever.

[RockportDave]

If it’s a 70s model engine with slight tapping under the valve covers, a quart of Marvel Mystery Oil will help quiet it down. Some of the old cast iron engines get a crust built up under the intake after many miles from old petroleum based oils and the heat they produce. The crust will find it’s way to the lifters and clog the very small oil holes in them. I have used Marvel Mystery Oil in a lot of old engines to clean out the oil passages and stop the tapping.
I would be carful using anything other than a good quality motor oil in any newer engines with computers or sensors.
Dave

[gamartin]

I can personally vouch for Lucas Oil Additive. Years ago my dad bought a 1970 F-100 with 390 engine in it. It had sat not started for 20 years. It had true dual exhaust and one we got it running the left bank always blue smoked out that exhaust run and it would use 1 quart of oil per 1000 miles. We stumbled upon Lucas and replaced 2 of the 5 quarts with it at each oil change. After a couple of cycles it quit smoking and using oil. Ended up being a super quiet engine.

I remember at the time some research had shown that you could use up to 80% of Lucas, instead of oil.

[redial]

I have a converted bus to a motorhome, and have lived in it when I was away working. The bus weighted about 10 tons in its registered configuration. It originally had a Perkins (English) diesel engine, that, when I contacted the manufacturers, they stated it was in specifications if it used 1 litre (about a quart) of oil per 100 litres of fuel! It would also travel at 73km/h (less than 50 mph), flat strap, no wind, on the flat. It took me a week traveling for 12 hours/day, to go from Darwin (Northern Territory capital) to Canberra (Australian Capital Territory - like Washtington DC). It was like traveling from Seattle to Washington DC. That was not acceptable!

I changed the engine, and put a Nissan UD 6 cylinder diesel, with a 6 speed gearbox, cruising at 100 km/h (60 mph) and using less fuel and no oil between oil changes. Modern oils are usually matched to the contemporary restrictions on diesel particulates, and, apart from the diesel bugs that live in the nether world between diesel and water, you do not have to add anything to the oil or fuel to keep them going.