What are your thoughts on changing the oil viscosity to a higher grade as an engine wears more?

If anything It’ll just reduce your estimated MPG by a fractional amount. HOWEVER, upon further research, it might not be too GOOD for an engine. Because if it’s consuming a lot of oil, it could be signs of a deeper problem.

You could try one of those “high mileage” oils.

Actually, you may well get better service and less oil-burning by running a lower weight oil in an engine toward the end of it’s wear cycle. Heavier oil sticks to the cylinder walls, can’t be scraped off as efficiently by the worn piston rings, and gets burned partially in the next combustion cycle. Lots of smoke and carbon buildup in the valve seats. The heavier oil doesn’t really provide a better “float” on worn bearings, contrary to myth. Only reboring, new rings, valve seat renewal and new bearings will restore the engine to it’s proper functionality.

There is no reason to use a heavier grade of oil. The only thing you’ll get from that is harder starting and a slight reduction in power and fuel economy. If you’ve lost oil pressure due to engine wear, you’re looking at either a teardown or the last rites at some point.

100K miles isn’t what it used to be. Newer engines are built to closer tolerances and thus don’t tear themselves apart as readily as they used to. If an engine is well-maintained, it can go to more than twice that.

I just bought a modern pickup last month and the manual does recommend 10/30 as does most other modern cars I’ve seen. A 2001 Dodge 1500 with 111,000 mi just seems a little used compared to my old truck which is a 1965 F-100 with about 340,000 mi original. 10 yrs ago we replaced its engine with a Ford blueprinted rebuilt and it has maybe 60,000 mi. Here in the Southwest its brutal hot for 5 months a year so I use 10/40 then it gets 10/30 the rest of the year. I can’t tell yet if the Dodge is using oil I haven’t driven it that much but given the mileage it probably is using some. it sounds good and drives good but whenever it’s a used vehicle you really can’t tell how well its previous owners took care of it, or what the dealer has done in regards to any make ready “repairs”

The heavier the grade of the oil, the less likely it is to seep past worn piston rings, engine seals and bearings. The amount a heavier grade of oil would reduce your average fuel consumption is nothing to worry about compared to how much you will increase the life span of the engine and reduce the amount of oil it consumes. Keep in mind if you go too heavy you’ll run into problems like Stranger said. Hence why there is a manufacturer recommended min/max for oil viscosity for all engines. This is also why companies like Bardhal and Wynn’s make oil thickener additives.
I have a Mazda Protege that has had all it’s seals and bearings eaten by gasoline flowing past the piston rings thanks to a faulty fuel pressure regulator, so to offset this it now runs 10w40 all year long as opposed to the recommended 5w30 to keep it from leaking out the rear main and destroying the clutch again. On the other hand my Jeep TJ with a good ol’ straight 6 has 280,000 on it, and is still running it’s standard 10w30 without burning a drop.
It comes down to engine design, quality of the oil, how frequently you do your maintenance and whether or not you want a stop-gap fix like my Mazda since it’s been a pain in the ass or if you plan on doing a rebuild when the time comes like the Jeep.

@ApolloX64 .. So how big of a viscosity jump is it between 10w30 to 10w40? On really hot days the oil pressure gauges will show a drop especially when using 10w30. I’m trying to get a feeling of what kind of oil is too heavy. or has anyone mixed 2 different viscosity(of the same brand) to get a tuned hybrid oil.

@woodcutter mixing viscosity and type of oil is generally not recommended as you usually degrade the performance and life of it. I once had a customer who told me he liked to mix semi-synthetic and full synthetic because “his vehicle performed better.” Never mind that he had to change his oil three times more often lol. The jump between 10w30 and 10w40 isn’t a huge one, but a jump from 5w30 up to 10w40 is quite a haul. If your engine uses 10w30 as standard, then a good jump is up to 15w40 but anything higher like 20w50 could potentially cause some issues like hard starting depending on the strength of the engine. My freshly rebuilt Pontiac 400 can use it easily as slinging around oil like that is like a flyweight, but if I were to use 15w40 or 20w50 in the Jeep’s straight six I’m pretty sure she’d be groaning after a week.
Another thing that people often ignore is brand. AutoLab, Motomaster, Pennzoil and Quaker State are all well known brands, but they are also the lowest of the low. I know I might get some flak for saying Pennzoil is a “low grade” brand, but it is. There is a reason Mobil, Valvoline and Castrol are used by companies like Ferrari, Lambo, Porsche, Nissan, GM, Ford and others as “stock” oil.
The cheaper the oil the more chances you will end up with foaming and oil break down at high temperature operation. Quaker State is the most notorious for having issues with foaming and forming a gummy varnish on engine components and yet people still use it because it is often a very cheap alternative to a quality oil like Mobil Super or Synthetic and Castrol GTX (my personal fav for non-synthetic).
If you’re worried about oil pressure going down but are not sure if you should go up a notch in viscosity then try an oil additive first like Bardhal or Wynn’s to thicken it up. If you notice that your pressure no longer drops with that, then you may have found your stop-gap fix for now. Also for an engine that you’re unsure of whether or not it’s been taken care of properly, avoid using a synthetic right off the bat. Synthetics are great and it’s probably what saved my Mazda from blowing up before I discovered her fuel issue but if the engine had worn any further it would have seeped out a lot faster than it did.

Here is my take, and bear in mind that the average vehicle I have owned was ~12 years old with 140K-200K on the odometer when I got it.

Older engine need thicker oil. Simple as that.

I tried running the thickest recommended oil in an 11-year-old car with 168K and it bled out like a stuck pig. It would not hold oil pressure, and I wound up with a quart of gasoline in my oil pan within a week (~300 miles). I went up one grade to 10W40 and it was fine until the weather warmed up to >50F, then I had to switch to 20W50. I ran it for the next year and a half with 20W50 in the warm weather and 10W40 in the cold and never had any issues again.

With another car (12 years old, 152K) I would lose a quart a week of 10W30 but could go a month before losing a quart of 10W40 and never lost 20W50.

My current car (age 25, 212K miles) had all sorts of issues after I did the first oil change and used 10W30, didn’t like 10W40 much once the snow melted, and runs like a top on 20W50. And since going to 20W50, I went from ~23MPG to ~27.5MPG with no other changes (same plugs, ignition timing, driving style and route, weather…).

That said, every engine is different. I had a few (though not many) that ran fine on the recommended viscosity, so I think it depends a bit on how the car was treated before the odometer got that high.

@stranger_in_a_strange_land I guess the Toyota 4A-LC is an odd engine then since my last emissions test was cleaner than many new cars. Actually, having torn one apart before, I know they are a little odd (though not the strangest engine I’ve pulled the head on). I almost think that they like to be abused!

@jerv Toyota makes engines like that on purpose lol. One of the things I respect about them. Their cars aren’t the most exciting, or often pleasing to drive but at least they keep going even after you drop a piano on them.

@ApolloX64 My first Corolla was given to my father-in-law who honestly believes that oil changes are (and I quote) ”... a conspiracy by the fucking ragheads to suck money out of American’s pockets.” It was also lightly tuned and thus required premium gasoline to avoid sounding like a tin can full of BBs. Well, after five months and 7.000 miles of running on 87 octane without an oil change, he broke a piston rod.

He still drove the car for another month in that condition, all the while complaining that it wasn’t as quick as it used to be and how, “Those damn Japs can’t build a car worth shit!”, before it gave up. Every other car he has owned blew up without warning, but that Corolla kept going for quite a while despite him!

@jerv well, I too often wonder about the hard and fast 3k rule for oil change intervals. I’m guessing that it could wait a lot longer at least 5k depending on the engine. We had a ‘97 Neon that burned so much oil we gave up changing it as we were adding so much it didn’t have much time to get really dirty. The filter still needed it though. Switching to 10w40 did make the oil last longer. At our mech advise we got rid of it because he said the car was like a hand grenade with the pin pulled. That said, I thought it was a decent car (before the engine wore out).

@jerv My experience has been mostly with diesel and large, low-compession gasoline engines. It could well be that your Japanese engine responds differently. We should distinguish between the type of wear the engine has experienced. Worn bearings may well benefit from higher viscosity oil, for a while. In an engine with worn rings, the higher viscosity oil will stick to the cylinder walls and not be scraped down well, being incompletely burned in the next combustion cycle.

As an aside, the best thing you can do for any engine is install a prelube system that brings up the oil pressure before the engine is cranked. All of my road vehicles, except for J’s S400 have this, hers will get one as soon as the warranty expires. My 1961 190D has had the prelube system since I got it; now has 720K, no rebuilds, still tight, plenty of oil pressure, 38 mpg and 1500 miles to a quart of oil. Odd that M-B offers the prelube system on all of their engines except automotive yet won’t honor a warranty if you install one.

@woodcutter My owners manual says 5K under “severe use” and 10K otherwise.

@stranger_in_a_strange_land Most of my vehicles were four-bangers no larger than 2.2 liters (many of them were 1.6L), and with a compression of < 10:1.
I have to say that the American engines are the worst as far as engineering goes; too heavy yet still fragile, and things don’t fit right. Germans design for keeps (at least they used to) which is why they tend to last long enough for you grandkids to inherit them. And the Japanese stuff varies, but I honestly think that the 4A-LC was made for small trucks; tough and torquey.