[AaronV6]

Hello.

Recently, I had my oil changed from 5W-20 to 5W-40. This was done with the advice from the shop, since I seem to have issues with oil pressure (it's low). I live in a colder climate, and the mechanics emphasized that this would be a good idea to do, long-term - I have to admit, I know very little about oil, so I complied.

However, the switch to 5W-40 did not solve my oil pressure issues (the oil pressure light on my dash still keeps turning on, when the engine warms up, at random. It does sometimes turn off when I rev, though). Seeing as this is the case, I am now pondering - was the change really a good idea? I do not drive the car during Winter (a lot of snow), if that makes a difference.

Should I switch back to 5W-20, when I have the chance? Would performing such switches damage the engine? COuld I switch, say, at a much later date (having driven the car around for, say, 3-4k miles), and how would that impact the engine?

Thank you in advance, for any feedback on the matter.

 

[Cobrajet67]

Hello.

Recently, I had my oil changed from 5W-20 to 5W-40. This was done with the advice from the shop, since I seem to have issues with oil pressure (it's low). I live in a colder climate, and the mechanics emphasized that this would be a good idea to do, long-term - I have to admit, I know very little about oil, so I complied.

However, the switch to 5W-40 did not solve my oil pressure issues (the oil pressure light on my dash still keeps turning on, when the engine warms up, at random. It does sometimes turn off when I rev, though). Seeing as this is the case, I am now pondering - was the change really a good idea? I do not drive the car during Winter (a lot of snow), if that makes a difference.

Should I switch back to 5W-20, when I have the chance? Would performing such switches damage the engine? COuld I switch, say, at a much later date (having driven the car around for, say, 3-4k miles), and how would that impact the engine?

Thank you in advance, for any feedback on the matter.

Generally, you want thinner oil in the winter and thicker oil in the summer if you change the oil weight from what the factory recommends. It won't harm your engine but thicker oil in cold temps definitely means it will take longer for it to circulate around the engine after startup.
If you actually have an oil pressure issue then sometimes thicker oil can help out with it but since you still have the same problem as before with the thinner recommended oil the thicker oil didn't help you at all. You may just have a bad oil sensor. You might have a weak oil pump. A much more serious issue would be internal engine issues like bad bearings. You really just need to find out the actual oil pressure with a mechanical gauge to figure out if it's real or just an electrical issue.
I would change the oil back to the 5w20 when it's time for a new oil change.

 

[JBert]

no, changing oil grade (viscosity) by itself will not cause any problems; as long as you are not switching to the wrong grade

Increasing the oil weight (viscosity) does not seem like a good way to solve a low oil pressure problem at all, to me. That is just attempting to mask the problem, by making the reading on the gage go up. What you really want is enough oil pressure from the oil pump to push the oil to all the places it needs to go. Higher viscosity will make the pressure go up, because it is thicker and harder to push around, but it won't help the oil reach all the places it needs to go; rather it will probably make the underlying problem worse because the thicker oil won't go through all the little holes. I'd try to fix the underlying problem instead of hiding it by running the heavier oil.

I always run the oil grade that the manufacturer recommends, which is written on the oil filler cap (unless there is a very specific reason for running a different grade and I know what I am doing). I also like to use the higher end "synthetic" oils, which is not really needed but I like the "extra protection" and also they tend to work better in a multi-grade where you want good flow at low temperatures and at the same time you don't want it to thin out too much when hot.

I'd go back to the 5W-20 at the earliest convenient opportunity, and meanwhile diagnose the oil pressure problem.

 

[AaronV6]

Generally, you want thinner oil in the winter and thicker oil in the summer if you change the oil weight from what the factory recommends. It won't harm your engine but thicker oil in cold temps definitely means it will take longer for it to circulate around the engine after startup.
If you actually have an oil pressure issue then sometimes thicker oil can help out with it but since you still have the same problem as before with the thinner recommended oil the thicker oil didn't help you at all. You may just have a bad oil sensor. You might have a weak oil pump. A much more serious issue would be internal engine issues like bad bearings. You really just need to find out the actual oil pressure with a mechanical gauge to figure out if it's real or just an electrical issue.
I would change the oil back to the 5w20 when it's time for a new oil change.

Thank you!

I've changed three sensors, in total, and the problem persists.
I've also measured the pressure with a mechanical gauge. It was towards the lower end, and after the switch in oil, the pressure went back to normal. However, the indicator on the gauge still keeps coming on, regardless.

no, changing oil grade (viscosity) by itself will not cause any problems; as long as you are not switching to the wrong grade

Increasing the oil weight (viscosity) does not seem like a good way to solve a low oil pressure problem at all, to me. That is just attempting to mask the problem, by making the reading on the gage go up. What you really want is enough oil pressure from the oil pump to push the oil to all the places it needs to go. Higher viscosity will make the pressure go up, because it is thicker and harder to push around, but it won't help the oil reach all the places it needs to go; rather it will probably make the underlying problem worse because the thicker oil won't go through all the little holes. I'd try to fix the underlying problem instead of hiding it by running the heavier oil.

I always run the oil grade that the manufacturer recommends, which is written on the oil filler cap (unless there is a very specific reason for running a different grade and I know what I am doing). I also like to use the higher end "synthetic" oils, which is not really needed but I like the "extra protection" and also they tend to work better in a multi-grade where you want good flow at low temperatures and at the same time you don't want it to thin out too much when hot.

I'd go back to the 5W-20 at the earliest convenient opportunity, and meanwhile diagnose the oil pressure problem.

Wow, I didn't think about it that way, thanks so much! It makes sense, actually - the shop told me that the pressure went up after the change, and that "the problem should be fixed". It was measured with a mechanical gauge. But that explains a lot, damn!

I will do that. But if the light keeps coming up even after the change, and it's not the oil pressure sensor (changed three, in total), it's most likely the oil pump or the bearings? Are there any methods to check one or the other, before committing to a purchase / repair?

Thank you so much, once again - your comment was of huge help, sincerely.

 

[JBert]

I'm thinking the "root cause" might be the oil pump itself? Not sure, but I think I have seen some posts with comments about the oil pump being a potential weak spot and there are "upgrades" available, but not exactly sure . . . might be worth taking some time with the search tool for "oil pump" or "oil pressure" or "oil pump failure" and see what you find.

 

[AaronV6]

I'm thinking the "root cause" might be the oil pump itself? Not sure, but I think I have seen some posts with comments about the oil pump being a potential weak spot and there are "upgrades" available, but not exactly sure . . . might be worth taking some time with the search tool for "oil pump" or "oil pressure" or "oil pump failure" and see what you find.

I will do that, thank you!

One last question - I've heard that, since I've went with thicker (heavier?) oil (from 5W-20 to 5W-40), next time I want to swap back, I will need to do an "oil flush", and really clean the old oil out (wash it out, if you will). Is that true, or can I just swap the oils like normal, without performing any specific ceremonies?

I've been told that this needs to be done due to the fact that I would be going from higher viscosity to lower.

 

[JBert]

I definitely would not bother with any kind of "flush" when changing oil grades. I would change the filter though, like I always do every time I change my oil. The amount of old oil remaining in the system is so small that it will not make any significant difference to the viscosity of the oil after the change. Yes there will be a small amount of the old oil still in the system, but it will mix with the new stuff and you might end up with 5W-22 instead of 5W-20 but nobody will know the difference.

The idea that you need to flush the oil when changing to synthetic from non-synthetic is also a myth. If you look on the bottle of every synthetic oil I have ever seen, they all say "compatible with all other oils" or something like that. Again there will be a little of the old oil remaining, but it will mix in with no problem.

Viscosity, thicker, heavier all mean pretty much the same thing. "Viscosity" is the technical term for how easily a liquid flows; higher viscosity takes more pressure to get the same flow and also makes a tougher oil film, which is why you don't want to go TOO low on the viscosity. Basically, the numbers in the grade represent the viscosity; 40 is higher viscosity, also "thicker" or "heavier" than 20. I am not sure if it is proportional, meaning not sure if 40 is twice the viscosity of 20, I think it is on a non-linear scale. It does get more confusing though; because the first number "5W" means "acts like a normal 5 weight when it is cold" and the second number like 40 means "acts like a 40 weight when hot." This relates to the normal behavior of an old-fashioned non-synthetic oil, which gets a lot thicker when it is cold and a lot thinner when it is hot; compared to modern synthetics and synthetic blends which don't change as much when they go from cold to hot.

Well, that reply got a bit longer than I originally had in mind, but I hope it helps.

 

[AaronV6]

I definitely would not bother with any kind of "flush" when changing oil grades. I would change the filter though, like I always do every time I change my oil. The amount of old oil remaining in the system is so small that it will not make any significant difference to the viscosity of the oil after the change. Yes there will be a small amount of the old oil still in the system, but it will mix with the new stuff and you might end up with 5W-22 instead of 5W-20 but nobody will know the difference.

The idea that you need to flush the oil when changing to synthetic from non-synthetic is also a myth. If you look on the bottle of every synthetic oil I have ever seen, they all say "compatible with all other oils" or something like that. Again there will be a little of the old oil remaining, but it will mix in with no problem.

Viscosity, thicker, heavier all mean pretty much the same thing. "Viscosity" is the technical term for how easily a liquid flows; higher viscosity takes more pressure to get the same flow and also makes a tougher oil film, which is why you don't want to go TOO low on the viscosity. Basically, the numbers in the grade represent the viscosity; 40 is higher viscosity, also "thicker" or "heavier" than 20. I am not sure if it is proportional, meaning not sure if 40 is twice the viscosity of 20, I think it is on a non-linear scale. It does get more confusing though; because the first number "5W" means "acts like a normal 5 weight when it is cold" and the second number like 40 means "acts like a 40 weight when hot." This relates to the normal behavior of an old-fashioned non-synthetic oil, which gets a lot thicker when it is cold and a lot thinner when it is hot; compared to modern synthetics and synthetic blends which don't change as much when they go from cold to hot.

Well, that reply got a bit longer than I originally had in mind, but I hope it helps.

Haha, it definitely helps a lot, thank you so much for taking the time to educate me - I truly do appreciate it! This information will be super-useful when discussing further changes / repairs / oil pump swaps (haha) with the service shop I frequent.

Thank you, once again!

 

[eelstrebor]

I was always under the impression that when using multi-viscosity oil, the oil is always thinnest when cold. So it shouldn't make any difference using 5W20 or 5W40 when starting a cold engine?

 

[JBert]

Oil is always the thickest when cold, and thins out as it gets hotter. The difference between cold and hot is where the magic comes in.

Yes that is correct -- 5W20 and 5W40 are the same when cold. The difference is that the 5W40 thins out less when it gets hot. I guess the magic is in the base stock plus the additives, to make it do that.

I think the confusion comes from the "multi-viscosity" thing which is a bit confusing for me too. I am not sure if that is intended to mean that within the oil there is a portion that is low viscosity, which is the part that flows when cold; and high viscosity, which holds together when hot . . . that doesn't really make sense because I'm pretty sure that it all acts the same at any given temperature.

I think the term "multi-viscosity" comes from the fact that these new "multi-viscosity" oils can be used in place of several different viscosities of old fashioned dino oil. "Back in the day", you had to change the oil for winter and put in thinner oil, like a 10 weight, so it will flow on a cold start; then you had to change it again for the summer for something thicker, like 30 or 40 weight, so it wouldn't thin out too much when it gets good and hot. Now we have one can of oil called "10W-40" that takes the place of the 10 in the Winter (that's where the W comes from) and 40 in the summer. And I think the difference is in that magic where the viscosity doesn't change as much with changes of temperature.

Maybe a real oil expert will chime in and straighten this out; for now that's the way I understand it.