Technical Can oil be too thick

I have a 57 235 in my 37 Chevy p/u that I had chased down a rattle and found that the crank and bearings were severely scored and the pressure had dropped a little so for the last few years have been using 20w50 and some oil stabilizer in it,I have another motor that was broken in on 15w40 and it seems to like only it so from now on I am buying 15w40 in bulk and everything is getting it including the lawn mowers. Changed the oil in the 37 today with the 15w40 and no oil stabilizer and that motor seemed to be more responsive,this is the first time I have noticed that the oil could have been too thick and will find out when it gets much hotter how the thinner oil in that motor will hold up. I do have a new motor ready to go in but not really wanting to change it so I am going to run the present motor until I can not then get off my behind and change it.

 

In a vintage motor (at least until the early 60s when multigrade came into more common use), back in the day your choices were generally 20W if you lived somewhere where it got below freezing regularly but didn't get above 60, and 30W if warmer. So a 20W50 would actually be the 'thinner' choice, and if it were me, the thinnest I'd use. My experience is thinner oil in these old motors tends to cause leaks and cause them to 'rattle' on start-up...

 

Oil can definitely be too thick. If you go too far, like using straight 30 in cold weather the car can be nearly impossible to start. And, you should know most engine wear occurs right after starting when the engine is cold. It takes time for the oil to circulate to all bearings and surfaces, until it does they are dry and scraping metal on metal. The thicker the oil the longer it takes to get around.

15 or 15W40 should be fine in anything but arctic conditions. It is the 15 that counts, that is the cold rating, the 40 is hot.

As you noticed thick oil also increases friction over thinner oil. This is the reason modern engines specify such thin oil and synthetic oil. Anything for a little better gas mileage rating.

 

I drove it about 15 miles and some on the highway to get it warmed up to change it and it still did not seem like the oil was very hot when I drained it and the motor has a 180 thermostat.

 

A friend gave me some quarts of new but 15 plus year old Mobil 1 oil so I used it in my lawn mowers this weekend and they seemed to start easier so I am now going to rethink about using too thick of oil,last year I started using that 15w40 in my other vehicles but never noticed any difference from the 10w40 I use during the warmer months but really noticed when that 20w50 was removed from the 37 today. I think my Harley is going to get synthetic again.

 

15w-40 Rotella would be fine and probably a better choice than anything not specialized.
I know all the stores have the 'offroad' 20W-50, but it is a bit too thick for something that is not going to see lots of load or heat. An oil too thick is just as bad as an oil that is too thin.

Ideally, if you really want to figure out what condition your oil is in, send a few samples of oil into a oil laboratory(such as Blackstone, Q&A is humorous) and they can analyze the oil, tell you if it needs to be changed more or less, and state what is in the oil(metals/contaminants) pretty handy if you are unsure if an engine needs to be pulled or just run it til it croaks.

As for the Mobil 1 oil, if that really is that old, that may be the TRUE full synthetic stuff. They changed the formula when they realized they could use a lesser grade of base stock oils and still get away with the 'full synthetic' branding. If that is the case I don't think you will ever need to change the oil in the lawnmower again

 

Went 6 seasons without changing the oil in my old Briggs&Stratton powered lawn mower because I switched over to Mobile 1 synthetic..... Dad bought the mower new in '79 and still runs like new...

 

We bought a fleet of Dodge police cars for police car training and we had been using Schaeffer's 15w40 semi synthetic in our Chevy and Ford cars with great results. The Dodge Charger's set an engine code that we had to take to the dealer to diagnose . They told us the oil was too thick and we had to buy 5w30 for the Dodges. After that no issues.
I put synthetic in a Briggs powered generator and it started to smoke. It smoked until I changed back to conventional oil. No other engines that I have converted ever did that .

 

The more I think about it the Mobil 1 is closer to or possibly older then 20,my friends dad died in 2000 or 2001. Usually oil after 15 or 20 miles is so hot it burns but would not burn when touched so that oil could be why that motor likes to drink gas and very hard to warm up,I will put some miles on it this weekend and see how it does.

 

I think many of today's Top Fuel dragsters and funny cars run between 50 and 60 weight motor oil for those 330 mph passes!!

Jimbo

 

Our Pontiac race cars would eat the distributor gears away if we ran thick oil, 10w40 was the norm. I have seem more then one engine sheer the distributor drive shaft with 70+ oil pressure.

 

Yes and people nowadays don't realize that shearing the pin is what it was designed to do, like in really cold weather. Because the engine wouldn't run with the sheared pin it saved it from running without oil. The old boys that designed things back then were pretty smart. I have seen people question why the oil pump was driven off of the distributor drive, that is exactly the reason for it, to be a safety factor.

 

I was skeptical of synthetic oil until I tried some in a little putt putt air compressor. This air compressor would not start from cold unless I disconnected the air hose and let it run for a minute. I thought it would break in and loosen up but after several years and oil changes it never did.

Then I changed to synthetic and from then on it started right up and seemed to run freer and faster. Now I use synthetic wherever possible, even in an oil can.

 

Among lubrication experts it is widely held that viscosity is the single most important characteristic of a lubricant. So the easy answer to your question is Yes, oil can be too "thick", though we don't really like to use the terms "thick" or "thin" with oil, they aren't really accurate terms, but that is what the public uses, so we all know what is meant. In any case, you have to understand how it is that oil builds a film between moving parts (it's actually a wedge of oil) to understand how important viscosity is; but if the viscosity is not correct the film won't form and contact between parts will occur. So, first thing is to get the viscosity correct.

As you noticed, the higher viscosity oil effects the cranking of the engine at start. That same effect is present after the engine starts, though you may not notice it, but energy consumed on pumping the oil is energy that cannot be used to move the car; that's why car OEM's have been pushing ever lower viscosity oils (Japan is now going with SAE16 grade oils, so 0W16 oils will be used in Japanese cars). As federal regulations on fuel mileage increase, OEM's look for anyplace they can pick up even the slightest increase in MPG, and lubricants are a low hanging fruit. But again, you have to have the right viscosity in order to form a protective film of oil, so too low of viscosity can lead to wear. But oil can also be too viscous, also leading to wear. For one thing, the increased demand on pumping also results in delayed delivery of oil to the extremeties in an engine, leading to wear until the oil makes the trek from the pan through the pump, filter and out through the galley's and through pushrods until it finally gets to the last points. The whole process is much quicker with lower viscosity oil.

So, in any case, getting the viscosity correct is very important. Either too little, or too much, viscosity will lead to wear, and can lead to hard starting.

I.e. those oil "stabilizers", don't use them. Those are long chain polymers that end up as deposits around the piston rings leading to stuck rings and polished cylinders, increased oil consumption and combustion blow-by.

 

A guy I know had a 283 that burned & leaked oil. so he put 90 weight gear oil in it. The first cold day in the fall on start up he twisted the oil pump drive apart. and ran it about a mile before it locked up. ive had engines that smoked and burned oil. and changed to synthetic oil and they stopped smoking. I believe the oil rings where gummed up. because they had no noticeable blow by even with the PCV unhooked. But Ive also had changing the oil make the oil burning worse. I mostly use 15W40 shell rotellat. synthetic oils are too expensive.

 

OK, so just to clarify things, the W after the number stands for "Winter", and is used to signify specific low temperature cranking viscosities. There is an SAE 20W specification, there is also an SAE 20 viscosity grade (without the W). Those are two different things. You can have 20W-20 engine oils, and they do exist. There is no 30W oil, that is not a viscosity grade. 30 is a grade (no W). And, 30 MAY only be heavier viscosity at low temperatures (that depends on the viscosity index of the oil), as soon as the oil is up to operating temperatures a straight 30 grade oil will be less viscous than a 20W-50 engine oil. 20W-50 will actually be much more viscous at 100C, the temperature where viscosities are measured and specified, 2 viscosity grades higher in fact. That is substantial.

Here is a link to SAE engine oil viscosity grades that will help:
https://wiki.anton-paar.com/en/sae-viscosity-grades/

 

That is a known phenomenon that does occur when changing oil brands. I'm not sure how or why it happens, but a change in brands can cause an increase in oil consumption, you are right about that. But that should normalize after a drain cycle or two.

Something else that changing oil brands will do, if you monitor your oils with used oil analysis, on a diesel engine with an engine oil cooler, you'll see a spike in copper shortly after changing brands. What happens is the new additive chemistry will come in and clean off a layer of film that forms on the copper tubes in the cooler. With the fresh copper exposed to the new oil copper sulfites form on the surface of the tubes due to a reaction with ZDDP in the oil. The sulfides slough off into the oil and get picked up in oil analysis as Copper. It's usually real high, into the hundreds of ppm. After a time a patina will reform on the surface of the copper tubes and seal it off from the oil, and the Copper readings in the oil analysis will return back to normal for the engine. This is a known phenomenon and there are papers written on it. I have a service bulletin from Cat that explains it.

I suspect it is some kind of chemical cleaning of piston deposits that causes the increase oil consumption, but I can't say for sure.

 

For those that don't know already, BLUES4U is a lubrcation engineer, and easily the most knowledgeable person on this site when it comes to oil.
I have no formal education in oil and it's applications, other than for over 60 years reading every tech article I could find on oil. And I agree with him on all he has written here and in countless other posts about oil. But I would like to elaborate a bit if I may.
When I build an engine, I know the clearances on the bearings and take it into consideration in choosing an oil's viscosity. IE: tight bearing clearances, I use a lower viscosity oil, such as the Amsoil 10W-40 "Premium Protection" in the SBC in my Hiboy, as it has clearances within the factory Specs with rods and mains at .0015-.002".
However, my '40 coupe I bought already built with a mildly modified SBF, and have no idea of bearing clearances and neither did the previous owner, who built the car except a professional motor shop in OH built that SBF However, the builder built it and told the car owner to run 20W-50 and I'm figuring that since both the pro builder and car owner lived in OH, then hopefully the builder put a little looser clearances in than I did. So when I changed that oil I put in Amsoil "Z Rod" 20W-50 synthetic.
As a full disclosure, I am an independent Amsoil Dealer and use their lubricants in everything I own with an internal combustion engine.

 

I once had a 56 Ford F100 6cylinder that burned oil really bad. I put 90/120 gear oil in it and it ran great with no burning oil. I didn't keep it long enough to run in the winter, but it didn't get too cold where I lived then anyway.

 

Blues4U, if you are still watching this thread, what is your opinion on SeaFoam or any other cleaners? Not the 'fix-it' goos.

 

I invite anyone who believes that multi-grade oil 'thickens' as temps go up to perform a simple test. Get a quart of 10W-40 and one of straight 40. With the oils at room temp, pour each one through a viscometer and note the results in the amount of time it takes to run through. Repeat this test, only put each quart in a pot of boiling water first to bring it up to 'operating' temp. You'll find the thinner oil will remain so. Hot 10W-40 oil will come out of a oil pan like water (far thinner than when cold), the 40 will thin too but will still be far thicker than the 10W-40.

I wouldn't use anything lower than 20W-40 in a vintage motor. If oil use, leaking, or cold-start noise occurs, I'd step up to 30W. And while I'm not a 'lubrication engineer', I was educated in proper oil selection by one from Chevron.

 

I don't like 'em. Engine oils are formulated with detergents and dispersants, a decent oil should provide the cleaning that's needed in an engine. If an engine is particularly dirty from over extended drains, I'd just change the oil on a more frequent basis for awhile. FYI, diesel engine oils are typically more loaded up with detergents, and will clean up a dirty engine faster. I've seen an engine with a lacquer build up so tough you couldn't scrape it off with a gasket scraper, and after a couple hundred hours with a good oil it was all cleaned off. I could dig through my files for photos and post them. So I don't see the need for these other cleaners, that may or may not play nicely with all the other additives in the oil.

 

Do you feel the cleaners strip out the additives or reduce the viscosity, dangerously, of the oil? Thanks.

 

No, they wouldn't strip the additives, but they may clash with some additives. Formulating an engine oil is a careful balance of chemistry. I don't like the idea of blindly adding chemicals into the stew not knowing how they will react.

 

I don't believe in additives. If you use good oil you shouldn't need to add anything too it. There is no such thing as a additive that will rebuild or restore a worn out engine. I did use lucas in a 4 cyl ford RANGER PK. I knew it was worn out but gas was $4 a gallon. It used as many dollars of oil as it did gasoline. The Lucas helped some but Bar and Chain oil would likely of worked the same.

 

Blues4U, thanks for all the good information!
I have always followed the manufacturers recommendations for oil and oil change intervals on my OT vehicles.
On the toys, which sit for longer periods I change the oil once a year along with a premium quality oil filter.
I have used 10W-40 for the most part and always avoid additives. When STP became popular in the mid 60's and old mechanic friend referred to it as "the racers sludge"! He told me to leave the "snake oil" on the shelf at the store. "Save your money kid"!
Listen to Blues4U he gets paid to know what he's talking about!
KK

 

I recently read the original specs for my 56 Ford y block 292. It stated SAE 20 detergent for normal use. I've been using 10-30 hoping to keep the oil passages feeding to rockers open (old known trouble spot) not knowing if the fixes for this on one of the cam bearings was done. I had considered 5-20 which wasn't available in the 50's. Any suggestions Blues4U?

 

The oil pressure gauge rises much quicker now but will have to see how the iffy bottom end of the motor holds up to the thinner oil. Motor has less then 15,000 on the rebuild and some how the crank got scored and the rod bearings were down to copper,did not check the mains and presume they are the same and it was prelubed before first fire up and break in. I know I am on borrowed time but that motor keeps hanging in.

 

We were forced to use re-refined oil in our Govt. pursuit training vehicles . So I put them off by getting them to agree to run 4 cars on that crap. I changed from Schaeffer's semi synthetic to the re-refined and monitored them carefully for one year. Analyzing the oil after each oil change.
The copper content went through the roof compared to the Schaffer's. We pulled the motor's at the end of one year and compared it to some other cars we ran with the test cars.
There was significant bearing and timing chain wear on the re-refined oiled engines . Where as the Schaeffer's oiled cars showed almost no wear . These were high speed police training vehicles. Chevrolet Impala's with 3.8 V-6 engines . Used to train students high speed pursuit. 8 hours a day 5 days a week.
The test convinced my bosses and we got to use the semi-synthetic for our use. They still put the re-refined oils in the motor pool sedans and trucks.

 

I run Kendall 20W-50 in my fresh 355 Chevy and it seems to be fine, I change it every 3000 miles. For the break in I went Valvoline 10W-30 VR1 at the advice of the engine builder. My 2nd oil change was Brad Penn 10W-40 semi-synthetic. Which I may go back to on my next change.

I had this old Chevy panel truck that burned, blew and spewed oil from every crevice and crack. I ran 60 weight Valvoline blower oil in that mess. That motor was so loose it cranked like normal even on colder days. Eventually I put used waste oil from work in it, strained through a shop rag. On a 20 mile trip (beach and back..) it would use 3 quarts.