engine oil question

[Guest DeSotoStan]

I just bought a 1949 DeSoto with (most likely) more than 100,000 miles on its tired engine.

The former owner said to use the heaviest weight engine oil possible - 30 weight, or 20-50.

Wouldn't the heavy oil take LONGER to get upinto the engine, thereby creating more wear?

Does any one have recommendations for brand of oil, synthetic or not, additives, etc?

THanks,

Stan

[NTX5467]

A thicker oil will take longer to initially get to all parts of the engine, upon an initial fire-up. It'll also take more power to run the oil pump at any temperature, which might cause the engine to seem a little "doggy" sometimes. Obviously, the heavier oil is needed to help compensate for bearing wear, I suspect.

BUT don't go too heavy! Many years ago, we got a call from a local mechanic shop for a crankshaft and bearing set for a Pontiac Firebird TransAm. Seems that the owner had done an oil change, with 20W-50 oil and had added two cans of STP to thicken things up. Only thing was that the lower end bearing knock he was trying to quieten down with the thickened oil became louder.

For a baseline, I'd get the engine fully hot from driving about 20 miles or so, noting the oil pressure (if there's a gauge) throughout. If the current oil is clean, then I'd just drive it until it might need a change, not disturbing what's already in there, or until it might need a quart added.

When you do change the oil, I'd start with a basic 30 viscosity oil, which is still available in many places. For good measure, you might look around for some with the higher zddp levels, but for right now, using the 30 oil would be for diagnostics to see how the engine acts with it in there, which probably shouldn't take very long to determine. IF there are no additional noises when the oil and engine is cold, then drive it about 20 miles (again) to get things fully heated and stabilized at that temperature, again noting the oil pressure throughout.

Now . . . in the genuine Plymouth service manual I have for 1950 Plymouths, it notes that as long as the oil pressure at hot idle is above "zero", and it rises with rpm, everything's fine. That was also when "summer oil" was 30 and "winter oil" could be 20W. This would be one reason to make sure the hot idle speed is "to specs"! If, perhaps, this is what the prior owner was seeing, rather than a more modern 20+psi at hot idle, then there's really no reason to use the heavier oil he mentioned. But if he was hearing a bearing knock with the 30 viscosity oil, that's another situation all together!

At this point, you can't completely disregard the prior owner's comments, but you can cautiously investigate why he might have had that orientation.

Most of the higher-zddp level oils I've seen advertised are usually multi-viscosity oils, as 10W-30, 10W-40, and 20W-50. An alternative could be Rotella T 15W-40 diesel-spec motor oil . . . which will work just fine in a gasoline motor, having gasoline rating approvals, too, PLUS having higher zddp levels. The Rotella T 15W-40 is readily available, too, at "normal prices". But I think I'd start with a 30 vicosity oil as that's what was available when the engine was designed , then progress from there. Even the most basic motor oil these days is far superior to the best oil "back then". You might even see if you can find some non-detergent motor oil in 30 viscosity, if desired.

If everything works out, you might want to change the oil filter pretty often if you use a more modern "high-detergent" motor oil. It might not hurt to get an extra valve cover gasket or two to see how gunky things might be under the valve covers . . . and then go from there.

There is also the ACCEL brand of motor oil which WalMart carries. It's claim to fame is that it is motor oil designed for earlier motors and their respective oil specs.

At this stage of the game, I don't know if synthetics should be considered. IF the synthetic is ester-based, then the esters will dissolve and liquify the sludge inside of the motor and clean things up. With the demands the engine will place upon the motor oil, synthetic would be vastly over-kill, with all due respect. Perhaps if you got the engine completely rebuilt AND could find oil seals which would be compatible with full synthetic motor oil, then it could be an option. At this stage, I'd say that normal motor oil would be a better choice.

Just some thoughts,

NTX5467

[Rusty_OToole]

How does it run? How is the oil pressure? Does it smoke? Have you done a compression test?

Suggest you use Rotella 15W40, or 10W30 of your favorite brand. If it raps and knocks, has no oil pressure, and no compression rebuild the engine.

Old flathead Chrysler products can be in an advanced state of wear and still run OK, reasonably quiet, with no alarming symptoms. They just get hard to start and down on power.

You seriously need to assess the engine's condition. It may have been rebuilt over the years, who knows? There are a lot of uninformed people who think all old cars have to use good ol' 30 weight non detergent oil. They are wrong. I have original owner's manuals for 1951 and 52 Chrysler products, they recommend light oil, 10W30 detergent oil was just coming on the market then, chances are your car never used anything else during the fifties, sixties and seventies.

Heavy oil will not cure an oil burner nor will it rebuild your motor. I saw some experiments many years ago by an owner with a worn out oil burning motor who tried various grades of oil. Lowest oil consumption was with 20W20 oil, any higher or lower and oil burning increased.

[Guest DeSotoStan]

Thanks very much, NTX 5467, and (once more) RustyOToole.

Seems as though engine "rebuild" means different things to different people. I believe my engine was taken apart, & the valve (seats?) changed so that it can run on regular octane unleaded gas.

I'll experiment with different viscosities.

The oil pressure needle is in the middle of the guage, which I suppose is normal.

However, IT DOES smoke! The oil filling tube has a vent cap WHICH SMOKES CONSIDERABLY.

I'll see about getting a compresson test.

Nice to hear the flathead engine is reliable. At first I was nervous about driving the car to work, but I've been taking it twice per week now, for the last couple of weeks (1/2 an hour ea. way, avg speed: 40mph.)

thnks again,

ss

[NTX5467]

Thanks for the update!

Oil from the breather tube is somewhat normal for an older engine "with miles on it". What you're seeing is leakage past the compression rings, which is more related to cylinder bore and ring wear than anything else. Oil from the tail pipe is due to wear on the oil rings, which aren't effectively scrapping oil from the cylinder walls, so it gets burnt with the fuel/air mixture on each power stroke. Tail pipe oil smoke can also come from valve guide wear, which probably has resulted in wear on the respective intake valves' stem oil seals, which can allow manifold vacuum to pull oil through the valve guide and around the valve stems and into the fuel/air mixture. There are various ways to determine if the oil is coming in through the valve guides or past the rings, but I suspect it could be a combination of both.

Doing a compression check will only be a test of the compression rings (in particular) and the rest of the pistons' ring packages (secondary). Key thing would be the variation between the cylinders rather than the compression test numbers per se.

Sounds like the car is in pretty useable condition! Getting the exterior oil smoke situation decreased would be good. What do the spark plugs look like?

Please keep us posted on your progress.

Thanks,

NTX5467

[ply33]

I believe my engine was taken apart, & the valve (seats?) changed so that it can run on regular octane unleaded gas.

Your car came from the factory with hardened exhaust valve seats. No need to add/change them for unleaded gas.

[Guest martylum]

Stan-I would think 10-30 oil would be a good choice-the multiweight oils were recommended even for early 40s cars in the mid 50s oil change charts.

I recently had a 49 Chrysler 6 cylinder in the shop for some mechanical work and found it too smoked enough that after 40-50 miles of driving the plugs on several cylinders were fouling with black carbon deposits to the point the engine had a miss. I added a quart of an engine restorative called Restore available from Car Quest and other auto parts.

Don't know whether it was coincidence or the Restore but in another 50-60 miles of driving the oil burning diminished and did not appreciably foul the plugs in another 200 miles of driving. The car had not been driven much for a number of years so actual driving might have freed up the rings with or without an additive.

My feeling is to try a restorative in oil burners to see what happens-the most you'll lose is the $8-10 cost of the additive.

Martin Lum

49 Chrysler

[Rusty_OToole]

Slight amount of smoke from the breather is normal when stopped, when moving the smoke disappears under the car.

Second the idea of trying the Restore additive. I have never used it but what have you got to lose?

So, how is your oil pressure? 45 PSI @ 45 MPH is factory spec for a new motor. How many miles to a quart of oil?

[Guest DeSotoStan]

Thank you RustyOToole & Martylum, I will definitely try Restore for the first time I change the oil. Next time I take the car out I'll check the pressure at 45 mph. I haven't had to add oil yet, but will soon.

I'll also check the spark plugs for fouling.

Thanks NTX5467 for all the info on the different types of wear on the seals & rings - I'm sure this baby has plenty of all that jazz.

In addition to the breather cap smoke, there must be smoke from the tailpipe, which I don't notice, BUT: WHEN THE CAR IS IDILING IN THE DRIVEWAY (while I'm opening the garage door to back in), the tailpipe LEAVES SOME VERY NOTICEABLE SOOTY DEPOSITS on the driveway. I also noticed these black blotches in a parking lot after I started the car up a couple of times to show some people the engine. ?Not too serious, I hope?

I guess I'm lucky from one standpoint: RustyOToole said the engines get "hard to start & down on power." The power IS lacking, BUT THE CAR STARTS EASILY (after just 6 pumps on the accelerator on a cold engine).

Next major project: welding on new metal for the entire length of the rocker panels, & welding new brackets in place - the original ones are rusted clear through.

THanks again for your responses,

Stan

[Rusty_OToole]

Black smoke and black sooty deposits mean it is running rich i.e. burning too much gas.

Could be automatic choke not releasing, carb out of adjustment, spark plugs not firing, carb worn out.

Or it could be the engine will stop smoking when it is warmed up.

Oil burning results in blue smoke. White smoke is water, normal on cold days before the motor warms up.

Probably due for a tuneup, a regular maintenance item once but now forgotten.

[Guest Al Brass]

Oil for a worn engine poses a problem. There is some advantage in going to a heavier oil to benefit worn bearings but this oil is more difficult for the rings to scrape from the cylinder bores. I would be thinking a straight 30 myself but I suppose the ultimate way is to try something and see how it works.

Regards

Al

[Guest]

I just bought a 1949 DeSoto with (most likely) more than 100,000 miles on its tired engine.

The former owner said to use the heaviest weight engine oil possible - 30 weight, or 20-50.

Wouldn't the heavy oil take LONGER to get upinto the engine, thereby creating more wear?

Does any one have recommendations for brand of oil, synthetic or not, additives, etc?

THanks,

Stan

_________________________________________________________________

Stan, ask any oil refiner, auto manufacturer, engine builder, owners manual, service manual etc. and they will ALL tell you to use the same brand of oil. So find out what brand of oil from the guy who sold you the car because that is what you should use, if that brand doesn't have the proper amount of zink and phosphorus you will have to add that. Check your service manual for the conditions required to measure proper oil pressure such as engine temp and what rpm for the test. I collect three brands of cars and the pressure requirements are all different and the rpm for checking is also different and my daily driver cars are different too.

I drive my collector cars about once a month so I oil prime the engines before starting them anyway so there is no problem having to get oil to all the places.

Don