So I'm buying a 2003 Trailblazer that has been lady driven, well maintained, and is reasonably priced. She's had the oil changed regularly at the local quick lube place, which I'm happy about.
However, assuming she's always used conventional oil, If I start using synthetic, will the old adage hold true that the engine will start leaking?
Depends on the condition of the gaskets. We switch cars too synthetic at work fairly often. The rear main in those seem too leak pretty often. If its leaking with dinosuar oil it may get worse with the addition of synthetic.
May not be the cause, but I bought a 2005 Highlander a ways back, and the last two oil changes, I've used synthetic oil. It now appears to have a small leak that is letting a bit of oil burn off on an exhaust manifold. May be the cam cover gaskets, haven't had a chance to diagnose it yet. I'll probably switch to a high mileage oil on the next change.
It'll only start leaking if there's already a bad seal and it's plugged up with gunk. In that case, if the gunk gets cleaned out, you'll have a leak. But if the seals are fine, then it won't leak.
No. Modern conventional oils are highly additized similar to synthetics. Unless she's been using some seriously old junk oil from the dollar store that was bought in 1984, you'll be fine. We analyze thousands of these "conversions" every month from a well know synthetic oil retailer. No issues with that. If there are leaks after the oil change, they were there before, just cleaned up ;) .
On my own junk, I've made the change as far in as 150k miles. My only word of caution on this is to monitor oil level closely for the first couple changes. It's not uncommon to burn a little off as many synths will clean up the old varnish and junk from the previous years of use and burn off during normal operation. I've personally seen this happen on all 4 of our vehicles. The Accent burned a quart and a half in 3500 miles on the first change, then would go 5k without burning a drop afterthat.
Is there any difference in high mileage oil and regular synthetic oils ? At what mileage do you switch over ?
"High Milage" oils have seal swellers in them. Once you start with High Mileage oils you can NEVER go back because the seals/gaskets will, from that point on, require the High Mileage swellers to keep from hardening and leaking.
scottdownsouth wrote: Is there any difference in high mileage oil and regular synthetic oils ? At what mileage do you switch over ?
You don't. Just use a quality oil that meets the manufacturers requirements. Anything that supposedly fixes your engine in bottle form is A.) temporary and 2.) a gimmick.
I've personally seen it happen on two cars. One a Nissan Sentra that was switched over at 185K and started leaking everywhere. The other was a Thunderbird that was switched over at 140K and started leaking worse at the rear main.
Anecdotal evidence for sure, but enough for me not to bother with it.
WildScotsRacing wrote: "High Milage" oils have seal swellers in them. Once you start with High Mileage oils you can NEVER go back because the seals/gaskets will, from that point on, require the High Mileage swellers to keep from hardening and leaking.
Huh didn't know this. I thought it was just a way of marketing higher viscosity oils to the average joe.
I made this mistake recently despite knowing better. 06 GMC Envoy with 135k but tight as a drum and never leaked. was lazy and had synthetic 5/30 in the garage instead of standard. It spit out an oil pressure sensor and now has a healthy drip. I changed it to conventional literally 1 day and 40miles later but the damage was done.
Friends don't let friends swap to syntehtic on high mile motors.
Supposedly very early on (like Mobil 1 in a cardboard can early) there was something up with the seal conditioners in synthetic oil that would make them shrink a little, then slowly swell back up again. I'd go with old wive's tale. I'd guess modern anecdotal reports are related to a full syn oil having better shear stability, so it's often blended on the lower end of the viscosity spec range. The thinner oil then leaks out faster.
I went from bulk 5w30 to M1 0w40 in my Prizm at like 130k miles and the motor is still dry. Switched my mom's Jeep from who knows what to Shell Rotella T6 5w40 somewhere well past the 100k mile mark and the 4.0 doesn't drip any more than it did before.
I switch every car i own to synthetic. Never had aa leak get worse or a new one start.
Switch the 4.7 dodge at 270k or somewhere around there. Oil pan gasket seepa, same as always.
Switched the lt1 at 80k, no leaks
Switched a honda f series at 120k, no leaks
I've only seen it happen once, and it was on my car. Went from not leaking at all between oil changes to four quarts heaving from every orifice in 2000mi.
OTOH, my Volvo was also subjected to a life on non-sythetic, and I exclusively run synthetic for the 30,000mi I've owned it, and it's still oil-tight.
If you guys have questions about oil----- and it's pretty obvious you do......we'll be conducting a Facebook Live broadcast on November 30th. We'll have a representative from Miller's Oil (Performance Racing Oil) tuning in to answer any questions you may have. It will be pretty informal--- but should also be informative.
as they say in show-biz......stay tuned!
too bad it's a weds I'd participate in that.
In reply to Joe Gearin:
Whenabouts on the 30th?
Bobzilla wrote: too bad it's a weds I'd participate in that.
It's work-related, surely your boss would understand. 
Joe Gearin wrote: If you guys have questions about oil----- and it's pretty obvious you do......we'll be conducting a Facebook Live broadcast on November 30th. We'll have a representative from Miller's Oil (Performance Racing Oil) tuning in to answer any questions you may have. It will be pretty informal--- but should also be informative. as they say in show-biz......stay tuned!
The GRM crowd will poop their pants when they see that stuff costs!
petegossett wrote:Bobzilla wrote: too bad it's a weds I'd participate in that.It's work-related, surely your boss would understand.
You know... now that you mention it I really should get work involved here....
Most of the leak issues were due to old-school cork or paper gaskets. As rslifkin pointed out, they would get cracked and plug up with gunk, then synthetic oil's solvency would clean out the gunk and let it leak. Gasket technology has come a long way in 20 years.
They are both the same basic oil molecule; its just that one comes from underground and one comes from a lab. The primary difference is the purity of the base stock. Conventional oil starts as crude oil with dirt, water, and a few hundred other things in it. Making it into motor oil requires stripping out everything that isn't oil. Synthetic oil starts as just oil, so its a purer thing with less stuff already dissolved in it.
Keep this in mind: The requirements for being labeled "synthetic" means that it has to pass a certain purity test, not necessarily that it actually started life as a synthetic oil. If a manufacturer takes a mineral oil base and cleans it enough to pass the synthetic test, they can label it synthetic. Some of the common brand names are like this. Anything Mobil 1 and up (royal purple, amsoil, redline, etc) are actual synthetic molecules.
Having said that, it doesn't really matter. They all lube the same, its just that conventional oil starts life with more stuff already dissolved in it so it can't suspend as much dissolved stuff as synthetic. That is the primary reason why synthetics last longer between changes.
curtis73 wrote: Having said that, it doesn't really matter. They all lube the same, its just that conventional oil starts life with more stuff already dissolved in it so it can't suspend as much dissolved stuff as synthetic. That is the primary reason why synthetics last longer between changes.
Yes and no. There are a lot of differences, and there are a lot of differences in the grade of the better synthetics. Some handle things like soot, dirt and fuel without degradation better than others. Some offer better thermal stability and can handle higher operating temps without degradation better than others etc. There's a lot to it.
true, bobzilla. I over-generalized
curtis73 wrote: Stuff
Halfway through that, I started reading it in a college professor's voice I had. He was was very good at breaking complex subjects down into the germane facts for his audience.
That's a compliment, btw.
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