synthetic in a high mileage YJ

[sicnik]

I'm sure this has been brought up before, i remember reading it but I cant find the thread. I hav a 93 YJ with 130,000 miles been using Penzoil high mileage oil for 5 yrs, was thinking about switching to Mobil 1 Syn. Will this help or hurt my 4 banger?

Nick

 

[Laph]

only thing it could do is help, I have been running mobil 1 for 5 years on my wj, now has 160+k miles on it and still runs as good as when I brought it home.

 

[TWDJ]

I started runing synthetic in my 1993 4.0L YJ at 153,000 miles ... it now has almost 157,000. Emmissions improved, gas mileage went up (1/2MPG) and engine runs about 10*F cooler.

And it doesn't leak any more on any less!

I also went to the synthetic ATF. Shifts smoother but firmer ... if that makes any sense.

Still debating the Xfer case and diffs. I don't do water crossings as a rule.

 

[jfrabat]

I started using synthetic oil also since I got my 2.5L 94 YJ (it came with 109K miles already on it, and it is not even corrected for the 31" tires, so it is actually even more), and even though I dont know for sure, I believe it is one of the causes that I am getting 20 mpg (yesterday I topped off, and it came out to 19.68 mpg) on my 4 banger.

Just make sure you use the weight that you need for the temperature range you will most likely see on your neck of the woods. For me, it is 20W-40 or 20W-50 (the coldest temp in Miami is the high 50's), but your case could be different. I have seen people use 10W-30 with good results as well (ussually in colder temps, though).

Felipe

 

[jps4jeep]

I would agree, but also disagree, I have found in high milage motors, synthetic blend oils work best for oil pressure as well as durability. I believe that if you use synthetic from mile 1, then that is a diferent issue.

 

[TwistedCU]

This is probably going to spur debate, but many say it will cause oil leaks because of the gaskets breaking down if you put synthetic oil in a high mileage motor that has always been run on organic (regular) oil. I'm not sure of the hows and whys but I tried it in my 92 YJ, and it was only a synthetic blend. I figured the people claiming it causes leaks were just exaggerating. After the first 3K mi oil change I noticed 2 small leaks, one at the head gasket and the other the valve cover. I switched back to organic oil and I kid you not the head gasket stopped leaking. The valve cover still leaked but not as badly.

That said, I am seriously considering converting everything in my '05 LJ to synthetic. The mileage is still low on it. There's no way I would even consider it on my 91 YJ with well over 180K miles.

 

[jfrabat]

This is probably going to spur debate, but many say it will cause oil leaks because of the gaskets breaking down if you put synthetic oil in a high mileage motor that has always been run on synthetic oil. I'm not sure of the hows and whys but I tried it in my 92 YJ, and it was only a synthetic blend. I figured the people claiming it causes leaks were just exaggerating. After the first 3K mi oil change I noticed 2 small leaks, one at the head gasket and the other the valve cover. I switched back to organic oil and I kid you not the head gasket stopped leaking. The valve cover still leaked but not as badly. /QUOTE]

Twisted,

I used to work for Exxon in Panama some years back selling lubricants, and if I remember correctly, it is not the synthetic vs mineral that will cause problems; it is the weight of the oil. What a synthetic oil allows (among other things) is that the viscosity does not degrade as fast as other oils (so a 20W-40 will be as viscous as a 20 weight oil when cold, but will also retain the viscosity of a 40W oil at operating temperature). Because of this, there are many (if not most) synthetic oils that have very thin viscosities when cold

The reason for this is that when you park your car at night, gravity pulls all the oil out of the engine. When you cold start your engine the next day, for a couple of revolutions, the engine will in fact be runing without any lubricant in the system. How long it takes the lubricant to reach the engine depends on the length of the oil lines, the power of the pump, and the thickness of the oil. Thinner oil reaches the engine faster on startup, but becomes even less viscous with temperature (reducing its lubricating potential). But multigrade oils can have less degradation than single grade oils, which means that they can be thinner when cold, but still lubricate like a thicker oil at operating temperatures.

Both blended and fully synthetic oils allow for multigrade ratings. The thinner the oil, the faster it moves through the engine, but also, the easier it is for it to leak. You just have to be careful not to use a synthetic oil that is too thin (there are even 0W-30, which will be VERY thin at room temperatures, and could cause problems on cars with high mileage); this is why I chose the 20W-50 for my synthetic oil (it is a bit thicker, so it will take a little longer to reach the engine when starting from a cold start than a thinner oil - where most damage is done typically - but it should also keep leaks at bay. I have yet to have a leak on mine, and I have been running it with synthetic oils for almost 6 months...

My point is that the debate about leaks should center not on the KIND of oil (synthetic, blend, or mineral), but on the WEIGHT of the oil (viscosity).

Synthetic oils also have other advantages, such as better lubrication, better cleaning, etc... So I prefer to use an oil that is a bit more viscous, but fully synthetic.

Anyway, that is what I remember, and I could be wrong...

Felipe

 

[droopey]

This is probably going to spur debate, but many say it will cause oil leaks because of the gaskets breaking down if you put synthetic oil in a high mileage motor that has always been run on synthetic oil.

TC, Do you mean if you use synthetic after using conventional oil.

 

[TwistedCU]

TC, Do you mean if you use synthetic after using conventional oil.

Yeah... that's what I meant.


Good info jfrabat! There was a several page long thread on this a few years ago here on Jeepz, and no one brought that up.

That makes sense, but the part I do not understand is why would it cause leaks after high mileage but not when used on a low mileage or newer engine? Possibly because the gaskets have been partially worn and permeated with the the old oil? Also, if you have a 10W30 oil how would that be heavier or lighter than 10W30 oil that is synthetic? Isn't the weight the same? I know I used the same weight blended oil on the 92...

Sorry for all the ??? but I'd love to figure this stuff out.

I would not want to put anything other than the recommended viscosity in my '05, for warranty reasons.

 

[sicnik]

I am currently running 5w30 with the dino, should I go to 10w30 with the synthetic? I live in kansas it's -0 one day and 110 the next Tornados and blizzards all in the same day.

 

[jfrabat]

TwistecCopper,

The reason (I think) is that generally speaking, people tend to move to lighter (at cold temps) synthetics than they would with mineral oils, and because the gaskets get worn out (by time, temperature, and all the dirt that gets trapped in your oil - which is what makes it go dark), the oil can start to leak with the lighter oils. So if you get leaks from a 10W-30 synthetic, you will also most likely leak with a 10W-30 blended (or, should it exist, a 10W-30 mineral oil).

When I used to work for Exxon (I quit in 97!), all multi grade oils were either blended or fully synthetic. But then again, the top oils were SJ, and now they are SM, so the technology has certainly changed (and I have not kept up with it), meaning that most likely there are now mineral multi-grade oils...

Sicnic,

The oil you should choose depends on the most common temperature you will likely face. Since oil changes ussually happen at least 2 times a year, you should use the lower end of the recommended weights for the winter, and the higher ends for the summer.

According to the Haynes manual, the range is 5W-30 for a max temp of 32 degrees, and 10W-30 for temps above 0. According to the Chilton Manual, 5W-30 ca be used up to a max temp of 60 degrees, 10W-30 or 10W-40 can be used from 0 degrees and up, and 20W-40 or 20W-50 can be used for temps of 30 degrees or more. Based on my experience, I likes the Chilton numbers better, and since in Miami we almost NEVER go under 50, but often go over 100, I went with 20W-50. Keep in mind what usage you will be doing, as the more you are pushing your engine, the more protection your engine will need. So, what i am getting at is, it depends on your average temps, and intended use.

I know it does not help much, but there you go!

Felipe

 

[TwistedCU]

if you get leaks from a 10W-30 synthetic, you will also most likely leak with a 10W-30 blended (or, should it exist, a 10W-30 mineral oil).

Here's the thing... I had no leaks with regular old Pennzoil, switched to a synthetic blend of the same exact weight and 2 leaks appeared. Switched back to regular old Pennzoil and one leak actually stopped, and the other lessened.

My theory is that the synthetic oil must permeate smaller openings than the mineral oil, which might not be a problem with a new or newer gasket, but an older gasket that has seen years of exposure to mineral oil cant contain the synthetic or breaks down when exposed to it.

I'm no molecular scientist but it seems to be the only reasonable explanation (at least when exact oil grades/weights are being used).

 

[jfrabat]

Well, the synthetic oil is better at lubricating, so I guess that would imply that it can squeeze into tighter spots than the mineral oil (which is why it is better at lubricating than mineral oil), which in turn causes the leak. Again, the technology has changed since I learned all this stuff, so I could be wrong...

Felipe

 

[1989hog]

I would agree, but also disagree, I have found in high milage motors, synthetic blend oils work best for oil pressure as well as durability. I believe that if you use synthetic from mile 1, then that is a diferent issue.

I agree and do use blends in all my motors