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Switching to synthetic oil?

18K views 67 replies 33 participants last post by  SLS TJ 
#1 ·
Just wondering if it's worth switching from regular oil to full synthetic. 2000 tj, 144k miles. I honestly don't know the history of the vehicle since i Just bought it just wondering if it's worth the switch. At this point, isn't everything in the engine really worked in with regular oil. Would anything actually be damaged by switching?
 
#3 ·
There is no HARM that can occur but real world benefits are highly debatable. Cost is higher. If you go to the various oil manufactuer's web sites, their FAQ sections and information pretty much state that change intervals are not really extended (the std 3000 mi most use is bordeline short) Synthentic may offer slighly better beneficial lubrication properties but the microscopic less wear is not something you are going to notice over the liftime of the vehicle (or the length of time you will have it)
 
#4 ·
In normal worlds/driving both oils are virtually the same. The biggest issue is the cost for synthetics. Past that, a good synthetic oil is far superior over conventional oils. Extended change intervals can easily be done with no ill effects to wear and tear. I became an Amsoil dealer just to save a little $$ and run it in everything I have. In my Denali I completely changed every ounce of fluid to synthetic. Once I did that I gained an average of about 2 mpg more per tankful. My supplier has a ford truck with 300k miles on it. He uses the top shelf of Amsoil and changes the oil every 25k with a filter change and oil topoff at 12k. The truck purrs like a kitten.
 
#5 ·
Honestly, if it's the 4.0, switch over to Rotella T5. It's a synthetic diesel oil and the 4.0 LOVES it. Ran it in an XJ I had and even with changes at 5k miles, it was coming out cleaner than regular synthetics were. Did all new seals and gaskets on that engine at 174k and there was literally zero build up in it. When I first switched to Rotella at 113k on it I ran T6 for 1000 miles then changed the oil and did T5 since. I saw little chunks of crud in the T6 when it drained and after that it's always been nice and clean.
 
#7 ·
Take it back and get the Mobil 1 10W-30 High Mileage.

J
 
#13 ·
Again, take it back and get the Mobil 1 10W-30 High Mileage. My Jeep is low mileage also but the seal conditioners and the higher zinc levels and fortified additive package are more suitable for our antique tractor engines.

You do not have a modern engine, it is a cross flow, push rod, solid tappet engine that dates back to I think the late 40s and certainly looks identical to the engine that was in the Rambler Classic I learned to drive in, 64 model I think it was.

My Jeep does not leak oil and it does not burn any either and it is so quiet people ask me if it is running.

J
 
#9 ·
I talked to the Jeep dealer and he affirmed that it is not worth the cost. Changing conventional oil at regular intervals will keep your Jeep running for longer than you will probably ever own it.
 
#10 ·
So are we saying that the synthetic stuff is somewhat more marketing than good. Doesn't seem synthetic does any harm and it might be better for the folks not really paying attention to their vehicles. For the people who are religious about changing their oil, the standard oil should be fine.
 
#11 ·
I noticed two thing when I switched to full Synthetic. Valve cover gasket started leaking next to the fire wall after the changed (thinner viscosity?). Fixed it. Then the other thing I notice was more "engine ticking" at start up until the fluids got pumping.

So my TJ seems to be happier and quieter with Conventional and Sythentic Blends (when on sale).
 
#18 ·
I noticed two thing when I switched to full Synthetic. Valve cover gasket started leaking next to the fire wall after the changed (thinner viscosity?). Fixed it. Then the other thing I notice was more "engine ticking" at start up until the fluids got pumping.

So my TJ seems to be happier and quieter with Conventional and Sythentic Blends (when on sale).
I highly doubt you sprung a leak switching to synthetic- sound's more like bad timing to me...there is no reason why it would leak - a 10W30 weight oil is a 10W30 weight oil at room temperature regardless of whether it is synthetic or conventional - the thickness doesn't change.

The ticking I can't explain- but synthetics have higher pour points than conventional, so your lifters should not be starved for oil on startup since synthetic would be much easier to pump through the system than conventional especially in cold weather.

Then again, it depends on the synthetic you are using...perfect example I can come up with right now since I just finished my research on comparing 10W30 synthetic oils

Take a look at Castrol GTX (conventional) vs Castrol Edge (synthetic) in the link above... The GTX is pretty damn comparable to its synthetic counterpart. Now I am not saying all synthetic oils are like this, actually quite the opposite since Castrol edge falls pretty short in the 10W30 category... what I am saying is, don't fall into the marketing gimmick of just because it is synthetic it is automatically better than the conventional you are currently using, because that may not necessarily be entirely true - in general it usually is, but that is not always the case.

So you may have spent extra money and bought something that was no better than your conventional oil and that tainted your outlook on synthetics (again, not sure what you used).

For those of you who want to stand by using conventional- I would definitely be looking at Castrol's stuff...They're really impressing me spec wise so far in my research (5W30 and 10W30)
 
#14 ·
Nothing is more important to maintaining the engine life than changing the oil and filter at regular intervals (3K miles). Using conventional versus synthetic will get you the same results in engine longevity but the difference is what you want to spend. I prefer to stick with conventional oil changed at every 3K miles. You will get those that swear by synthetic and their high mileage engines but ironically enough there's plenty of conventional oil users stating the same. It's all matter of preference.
 
#16 ·
Nothing is more important to maintaining the engine life than changing the oil and filter at regular intervals (3K miles).
Every 3K miles for typical driving is excessive and at least in my strongest possible opinion, of no benefit to the vehicle owner. That excessively short interval grew out of the quick lube places like Jiffy Lube pushing it trying to improve their bottom line. For the vast majority of us, every 5k miles is more than often enough.
 
#15 ·
I change at 5,000 to 7,500 mile intervals. J
 
#17 ·
I have been on both sides of this argument over the years....at first I felt it was "too costly".....with the "change" to a 5K mile oil change interval, I "switched" to MOBIL 1 a few years back. Yes to better mileage. Still no leaks. And Lastly with the -15° Temps last winter, and the "EASY Starts" in all my vehicles I am SOLD. Yeah it cost more, and I might be "wasting money", but my piece of mind is important as well. I run full synthetic in everything with a 5K mile full change.

FWIW the TJ has in excess of 170K on it and has been running the full synthetic for the last 100K
 
#19 ·
While I have no jeep experience with it, I do with my Saturn.

I ran synthetic in it, had to pull the valve cover for something, head was clean as a whistle. A while later I went through a "cheap phase" and switched to conventional. Pulled the cover 3 or so changes later, and the head was noticeably dirtier. Immediately switched back to synthetic. Pulled the cover again and the valve train was clean again. 192k miles later, and it hasn't seen anything but synthetic since. Usually Mobil 1. With synthetic I start to think about changing the oil at 6k miles. Have gone over 10k on occasion with both my vehicles on multiple occasions.

The jeep will also get synthetic. Sounds like rotella t5 is the stuff to go with.
 
#20 ·
I change between 3 and 5k miles. Usually have to add a qt if I go 5 and I use the cheapest oil I can buy at walmart. 155k and still running well. Most of the oil I loose is through gasket leaks and not burning.
 
#22 ·
NCtom,

On my '02 I just spin the filter on to finger-tip tight, then about another 2/3 turn. I can break the seal and spin it off by hand at the next oil change, it usually requires both hands. Don't forget to put a bead of fresh oil on the seal before installing the new filter.

YMMV, and invariably will...
 
#23 ·
Just to put the "I switched to synthetic and got leaks" issues to bed, synthetic doesn't cause leaks.

What happened when those of you that switched to synthetic and got leaks is that the synthetic cleaned out all the sludge and crusty crap that was plugging up existing holes and made those leaks evident.

Another reason why synthetic tends to get blamed for leaks is because the carbon chain for each oil molecule is shorter than the comparable conventional carbon chain. Think of these chains as cooked spaghetti noodles dumped into a strainer with holes the same diameter as the noodles. The shorter noodles are going to fall through easier than the longer ones. Same with synthetic oil going through leaky gaskets.

The 4.0L is a bullet-proof engine, seems they could run forever on just about any lubricant. :) Synthetic will definitely keep your engine clean, though.
 
#27 ·
Just to put the "I switched to synthetic and got leaks" issues to bed, synthetic doesn't cause leaks.
Brilliant Willys, but I fear that you've not put the issue to bed. Just because the oil used to be on the inside of the engine and is now on the outside of the engine doesn't mean the synthetic caused the leak. It more like just facilitated the leak. Both oil manufacturers and car manufacturers (e.g. Mercedes) have acknowledged that synthetics are more prone to leak - i.e. go from inside the engine to outside the engine - but hey who's worried about causation.
 
#25 ·
The biggest gain from switching to synthetic is that it doesn't boil off sludge like dino oil. It has a much higher tolerance to high temps. Better gas mileage 'cause its microscopicly cleaner and has much less friction. On the down side that same lack of friction/cohesion allows it to drain down faster which can leave your top end dry for a few seconds if you don't run the engine every few days. I haven't switched the Jeep over yet, but I use it in my Miata and Hyundai religiously with 10k intervals. I don't use it in the old Caddy... which burns a quart every 1k miles. I run maple syrup in that one.
 
#30 ·
I've seen T6 recommended a lot here as one of the better oils to run and I'm going to go with that. I've used it exclusively in my MS3 for 40k+ miles and everything is sparkly clean under the valve cover. I'm happy that I'll only have 1 type of oil to stock in my garage as well, keeps things simple.
 
#32 ·
For a diesel oil, T6 5w40 is hard to beat for the money and is what I also ran in an older Ford 302 because of the nice ZDDP package and the fact that I owned a diesel at the time so one oil for 2 vehicles was convenient. Otherwise I would've run Mobil 1 5w40 in the 302.
 
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