1939 Dodge Inline Six Flathead Truck Oil

[RateNate]

Welp another old truck again, its a 1/2 ton dodge pickup and I have absolutely no clue what oil it should use but it probably needs a zinc additive for oil and fuel if im not mistaken. I can post a little more info about it later, and if I see anything on its dipstick regarding weight. For the most part its a project but we will put it on the road, just need to get title from ca dmv so that will be FUN

 

[blufeb95]

I think just about anything will work, remember oil in 1939 was probably not very good, any modern PCMO would probably be fine, but you could probably use 10w30 or 15w40 HDEO if it helps you sleep better with more zinc, I think higher Zinc really came later when you had big V8 muscle cars with aggressive cam profiles.

 

[Lubener]

I would run a 10w-40 or 15w-40 oil in your old Dodge In realty, any oil today is substantually better than what your engine used for most of its existance. I have a 1940 Ford tractor which is similiar in many ways to your inline six and this is what I have used.There is no need for any additional additives. That engine will not stress the oil due to its low compression and low stresses on the cam. Fuel dilution of the oil probably is your biggest issue depending how well your carb and engine are performing. If your engine has not been rebuilt or atleast recently, it had a steady diet of non detergent oil during its life. Don't get carried away with any engine flushes as that would loosen up a lot of sludge all at once.

 

[RTexasF]

I would run a 10w-40 or 15w-40 oil in your old Ford.

What? He is asking about a Dodge six cylinder engine

 

[jake wells]

You are in California so i would suggest Rotella T1 mono grade or Rotella in 15W40 or 10W30.

 

[Lubener]

What? He is asking about a Dodge six cylinder engine

Sorry, a short circuit took place in my cranium and has been repaired.

 

[Astro14]

Your Dodge will be fine on just about anything you out in it. Low compression, low cam lift, low RPM means you don’t need any special oil or extra ZDDP. Any modern oil will do. I would lean towards an oil related for diesel because of the extra additives for suspending soot and dirt.

If the history is unknown, I would run some short OCIs. Very short. 500 miles. Keep an eye on the oil condition.

Some of these old engines have a tremendous amount of sludge from running non-detergent oil in the past. A lot of old wives’ tales in the old car community about keeping them on a diet of non detergent oil means that it might be pretty dirty inside, and your modern oil will start cleaning it up.

If it were mine, I would drop the oil pan to clean it up and see how the engine looks inside. That would guide my oil change regimen. It may have had an informed owner, been run on modern oil for a while, and be nice and clean.

Or, it may not...

The only real issue with an old flat head in modern days is the lack of lead in the gasoline. The valve seats in these were soft. The lead in the gasoline “back in the day” helped prevent valve seat wear. No lead means that they can wear the valve seats pretty quickly under high speed/high load operation.

Don’t run it hard, or perhaps look for a “lead substitute” that was marketed to protect the valve seats.

Cool truck. Pics when you get a chance!

 

[Graham Piccinini]

This would be my "weapon of choice". As a matter of fact I actually run some STP 15w40 with this Rislone Zinc supplement additive in my 2000 Honda CR-V currently. Just happened to have some on hand from previous projects/cars, so that saved me a trip to the store. We'll see how she does when temp drops to 34F in couple days...

 

[jake wells]

I wouldn't run a additive there is plenty of anti wear additives in modern heavy duty oil. The only item i would run if it hasn't had a valve job or modern hardened valve seats installed is a lead substitute to keep from loosing a valve seat.

 

[demarpaint]

I'd be inclined to use a Delo 10W40 or something along those lines in it.

 

[Chris142]

Should be a 218. Does it have a filter? A filter was an option. Any sae 30,15w40 is fine and it does not need a zink additive.

 

[AutoMechanic]

15W-40 for diesel oil would be my suggestion or get some Valvoline VR1 Racing Oil they have it in a few different grades like 10W-30 and 20W-50 and I think SAE60 or something too. I’d run one of those. . Let’s see some pictures of it too.

 

[390pcode]

We have a 1939 Dodge 1 ton, 6 cyl, X-CDF (Cal Fire) brush truck. I have run 15w-40 in it since restoration, 21 years ago. Since it was state owned at one time, I assume it was well maintained for 10-15 years. Not sure after that, so went with short intervals.

 

[zrxkawboy]

Yeah, no zinc additive needed...very low valve spring pressure. I'm pretty sure they had hardened valve seats, too, but not 100% positive...check into that, as you may not need a lead substitute in the gas.

 

[krismoriah72]

There is a forum for your truck if you are interested. https://p15-d24.com/forum/6-mopar-flathead-truck-forum/

What oil to use in these flathead engines?

At our Plymouth Club meeting we had some discussion about what engine oil to use in our old cars. Well, it is obvious to us that you would not use a detergent oil in an old car that has many years of sludge build up inside the old flathead engine. Therefore, you would use a “straight weight” oil ...

p15-d24.com

What oil is everyone using?

What kind of oil is everyone using? This will vary with the age and condition of your engine of course. I'm using synthetic in my flathead that was rebuilt a few thousand miles ago. I used Pennzoil Platinum 10W50 just because it was on sale this week.

p15-d24.com

Interesting reads.. looks like the manufacturer spec'd 30wt non detergent. And it looks like just about any oil will work.

 

[bullwinkle]

Non detergent SAE 30 is available lots of places, it really depends how sludged the inside of the engine is. A modern HDEO in 15W40 or SAE 30 has a lot of detergents, so any dirt or sludge, or even old lead from leaded fuel, is going to break loose pretty quickly.

 

[Tim_S]

Your Dodge will be fine on just about anything you out in it. Low compression, low cam lift, low RPM means you don’t need any special oil or extra ZDDP. Any modern oil will do. I would lean towards an oil related for diesel because of the extra additives for suspending soot and dirt.

If the history is unknown, I would run some short OCIs. Very short. 500 miles. Keep an eye on the oil condition.

Some of these old engines have a tremendous amount of sludge from running non-detergent oil in the past. A lot of old wives’ tales in the old car community about keeping them on a diet of non detergent oil means that it might be pretty dirty inside, and your modern oil will start cleaning it up.

If it were mine, I would drop the oil pan to clean it up and see how the engine looks inside. That would guide my oil change regimen. It may have had an informed owner, been run on modern oil for a while, and be nice and clean.

Or, it may not...

The only real issue with an old flat head in modern days is the lack of lead in the gasoline. The valve seats in these were soft. The lead in the gasoline “back in the day” helped prevent valve seat wear. No lead means that they can wear the valve seats pretty quickly under high speed/high load operation.

Don’t run it hard, or perhaps look for a “lead substitute” that was marketed to protect the valve seats.

Cool truck. Pics when you get a chance!

Just a bit of gasoline history. Up until the mid to late 1930's ALL gasoline was unleaded in the US. The low compression flathead engines back in the day ran fairly well on the gasoline which was refined and distributed back then, albeit with some knocking periodically. Refining methods were nowhere as sophisticated as they are now, and gas was maybe 60 octane at best, if that. There was no additive available to reduce the relatively common engine knock the poor quality gas allowed. In the late 1920's, two GM engineers chanced upon tetraethyl lead to use as an additive to help control engine knock. Alcohol would do the same thing, but was't viewed as viable back then. So, to increase the effective octane of the poor quality gasoline, all of which was unleaded, available back then, tetraethyl lead began being added to commercially available gas. It became relatively common by the late 1930's. The only production facility for the compound was the Standard Oil refinery in NJ. As pointed out, an additional benefit of the tetraethyl lead was it tended to act as a "lubricant" for the engine valves. How long the engine valves and valve seats lasted prior to the lead being in the gas, I've no idea. Also TTE (tetraethyl lead) is such a dangerous chemical, that getting even a very little of it on your skin will result in lead poisoning. Several employees at the Standard Oil Refinery died each year from lead poisoning, but news of that wasn't made common.
The burgeoning aviation industry drove the requirement for higher and higher octane fuel, and that drove the development of better refining methods, as well as the addition of increasingly larger amounts of TTE in AV gas for the turbo-supercharged engines used during WW2. Better refining and the use of TTE to increase gas octane continued until the late 70's when TTE was finally phased out of commercially available gas.

 

[Astro14]

Very cool, Tim, thanks!

I didn’t know that TEL was introduced that late, thought it was earlier.

Perhaps I’m the one perpetuating old wives’ tales...

You’re spot on about compression. The Packard is 6:1. It can run on just about anything.

Guess I can stop worrying about the valve seats.

 

[Sberry]

If it's relatively clean would put a modern oil and new Wix filter in it and forget it, add some if it was needed.

 

[wpod]

Run a HDEO oilof choice oils back then were low levels of additives. the flat head engines are low pressure engines. .. Low RPM , low out put and low pressure valve springs.