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Posted: 2/18/2024 5:33:46 PM EDT
[#1]
Isn't it a seal issue? Gaskets, seals all break down over time.
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Posted: 2/18/2024 5:37:08 PM EDT
[#2]
A very small maybe.
Don’t think there has been any straight conventional oil on the market for awhile. Think they are all to some degree synthetic blends. |
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Posted: 2/18/2024 5:38:00 PM EDT
[#3]
I think Synthethic gets into tighter places better so if there is a small leak the oil will find it.
Do you have a Napa near you? Their Brand oil is made by Valvoline and is good stuff, both convential and synthethic. |
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Posted: 2/18/2024 5:38:14 PM EDT
[#4]
you can get a semi syn. high mileage oil that will help with swollen seals/gaskets.
if the car is a flat tappett style you might need a zddp additive. |
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Posted: 2/18/2024 5:38:15 PM EDT
[#5]
Quoted: Anyway, is there any truth to synth causing oil leaks, or in my case, worse oil leaks? (old Dakota has always had a slight oil leak) No |
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Posted: 2/18/2024 5:40:21 PM EDT
[#6]
Quote HistoryQuoted: Isn't it a seal issue? Gaskets, seals all break down over time. 99% of them are just inconveniences you can live with. |
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Posted: 2/18/2024 5:41:19 PM EDT
[#7]
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Posted: 2/18/2024 5:42:42 PM EDT
[#8]
 Quoted: Quoted: Isn't it a seal issue? Gaskets, seals all break down over time. 99% of them are just inconveniences you can live with. That's where I was gonna go... My last truck, over 300K miles and had a rear main seal leak that I took to get fixed and they couldn't fix it (well, they were a shitty shop that I helped get shut down  )
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Posted: 2/18/2024 5:43:51 PM EDT
[#9]
Hi-mileage synthetic has an additive package that helps swell seals, ostensibly reducing or eliminating leaks.
I have 5 vehicles with over 100k miles, not a single one one drips oil on my garage/driveway. |
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Posted: 2/18/2024 5:44:09 PM EDT
[#10]
If you were worried about oil being hard to find, perhaps you should buy a whole bunch..
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Posted: 2/18/2024 5:44:38 PM EDT
[#11]
Mobil one makes synthetic high mileage oil thats supposed to help stop leaking seals.
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Posted: 2/18/2024 5:45:00 PM EDT
[#12]
My 23 year old Miata has zero leaks with 107K miles. Full syn last 16 years.
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Posted: 2/18/2024 5:45:22 PM EDT
[#13]
Usually a myth.
In a rare/exceptional case if your engine is significantly slugged inside and the sludge is the only thing plugging holes in already failed seals, then maybe a synthetic made from a PAO, Alkylated Naphthaline and Ester blend could result in cleaning the inside well enough to expose already failed gaskets and seals. If you've been changing the oil regularly, and are not experiencing leaks already, you’re good. |
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Posted: 2/18/2024 5:46:38 PM EDT
[#14]
If you had some barn-find AMC Javelin from the 60s maybe but otherwise there’s basically no concern. And that isn’t due to old seals it’s due to larger tolerances in manufacturing and less thermal efficiency in the materials used.
Just don’t mix synthetic and conventional. You can switch back and forth all you feel like just keep it all synth or dino in one fill. You could mix if you had to but it isn’t generally a good idea as they can have different shear points and such. |
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Posted: 2/18/2024 5:46:47 PM EDT
[#15]
I know this isn't what you asked exactly...
...the Castrol GTX 10w30 I've been getting from wally world is regular conventional oil. |
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Posted: 2/18/2024 5:48:18 PM EDT
[#16]
159K on my Tacoma, have used full synthetic from day 1, no leaks. Hyundai Elantra, 179K, but only about 30K on the reman engine. My fault, didn't replace the timing chain when I was supposed to. But the old engine never leaked, neither does this one. Full synthetic from day 1.
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Posted: 2/18/2024 5:50:00 PM EDT
[#17]
The way I understand is that synth flows easier than dino, so it might leak a tiny bit more thru an existing leak.
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Posted: 2/18/2024 5:53:03 PM EDT
[#18]
Had a 2006 Pilot that called for 5-30 conventional.
Moved it over to synthetic and it leaked a little. Moved it back to conventional and the leak was gone. Used full synthetic with 1/3qt of Lucas Engine Oil Stop leak per oil change. No leaks. My experience FWIW. |
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Posted: 2/18/2024 5:58:28 PM EDT
[#19]
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Posted: 2/18/2024 6:14:03 PM EDT
[#20]
Quote HistoryQuoted: Hi-mileage synthetic has an additive package that helps swell seals, ostensibly reducing or eliminating leaks. I have 5 vehicles with over 100k miles, not a single one one drips oil on my garage/driveway. (4) here, and same. Under my ownership (3) of the (4) have had rear crank/cover seals & oil pan gaskets replaced. (1) has had the front crank/cover seals replaced. (2) have had the valve cover gaskets replaced, the third will get done when the weather warms up... ...oh, and (1) of those^ + the fifth had a leaky transmission/ transfer case output shaft seal |
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Posted: 2/18/2024 6:16:32 PM EDT
[#21]
Quote HistoryQuoted: (4) here, and same. Under my ownership (3) of the (4) have had rear crank/cover seals & oil pan gaskets replaced. (1) has had the front crank/cover seals replaced. (2) have had the valve cover gaskets replaced, the third will get done when the weather warms up... ...oh, and (1) of those^ + the fifth had a leaky transmission/ transfer case output shaft seal Quote HistoryQuoted: Quoted: Hi-mileage synthetic has an additive package that helps swell seals, ostensibly reducing or eliminating leaks. I have 5 vehicles with over 100k miles, not a single one one drips oil on my garage/driveway. (4) here, and same. Under my ownership (3) of the (4) have had rear crank/cover seals & oil pan gaskets replaced. (1) has had the front crank/cover seals replaced. (2) have had the valve cover gaskets replaced, the third will get done when the weather warms up... ...oh, and (1) of those^ + the fifth had a leaky transmission/ transfer case output shaft seal ETA: Old rubbers leak... Real ETA: Whoops, meant to edit... |
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Posted: 2/18/2024 6:25:34 PM EDT
[#22]
Quote HistoryQuoted: ETA: Old rubbers leak... LoL. |
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Posted: 2/18/2024 6:30:51 PM EDT
[#23]
Supposedly, if you run conventional oil for long time and then switch to synthetic after high mileage you might have a leak
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Posted: 2/18/2024 6:37:16 PM EDT
[#24]
Yes
Edit to add. It was worse with the older cars. If it has a carburetor, don’t do it. Newer stuff with one piece main seals and non cork or paper gaskets, does a lot better. But I don’t recommend it if it’s high mileage. |
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Posted: 2/18/2024 6:44:25 PM EDT
[#25]
Don't overthink this, an oil LEAK is just an inexpensive, slow-motion OIL Change.
Top up the oil level as required, slap a new filter on every year or so, and drive on. |
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Posted: 2/18/2024 6:53:26 PM EDT
[#26]
Quote Historycame here to @ you. 
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Posted: 2/18/2024 6:55:29 PM EDT
[#27]
Quote HistoryQuoted: fuckin' a, dood. came here to @ you. Quote HistoryQuoted: fuckin' a, dood. came here to @ you. I gotta let the wrong answers go for a bit. |
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Posted: 2/18/2024 6:56:39 PM EDT
[#28]
Quote HistoryQuoted: I gotta let the wrong answers go for a bit. Quote HistoryQuoted: Quoted: fuckin' a, dood. came here to @ you. I gotta let the wrong answers go for a bit. 
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Posted: 2/18/2024 6:57:53 PM EDT
[#29]
No, that is some stupid internet Mechanic bullshit.
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Posted: 2/18/2024 6:58:37 PM EDT
[#30]
Quote HistoryQuoted: I gotta let the wrong answers go for a bit.  Attached FileGee Dee: where the dumbest motherfuckers in the world argue with the smartest people on the planet.  Attached File |
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Posted: 2/18/2024 6:59:37 PM EDT
[#31]
Don’t know about cars but this is 100% true with Harleys
I won’t use synthetic oil at my shop in any bike made before 2000 Evos, Shovelheads, Panheads, they all have fiber gaskets unless they’ve been upgraded Synthetic oil likes to creep out of those gaskets, once that happens you can’t stop it and switching back to conventional oil won’t help - once the seal has been compromised it will continue to leak The newer bikes have o-rings at the base of the cylinders and the rest of the gaskets are silicone coated metal Cometic gaskets, you can put synthetic in those bikes without any issues |
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Posted: 2/18/2024 7:01:59 PM EDT
[#32]
It turned me into a Newt!
I switched to all synthetic on my vehicles a while back. Any oil leaks can be attributed to age. For example, my 05 4Runner is starting to leak around the valve covers a bit. But it has 283,000 miles on it. I'll replace the gaskets this spring. |
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Posted: 2/18/2024 7:04:13 PM EDT
[#33]
I think it’s the high mileage blends in certain vehicles, synthetic itself not so much.
If you have leaks the high mileage blends can help, if you don’t, it can sometimes start them. They have seal swelling agents in them, but really it’s pretty rare to actually cause anything negative |
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Posted: 2/18/2024 7:07:25 PM EDT
[#34]
203,000 mikes, 38 year old Nissan Hardbody. I have run Castrol Edge full synthetic with zero issues for over a decade.
Lifters are starting to make noise but that's an issue with that motor. |
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Posted: 2/18/2024 7:09:24 PM EDT
[#35]
Quote HistoryQuoted: Mobil one makes synthetic high mileage oil thats supposed to help stop leaking seals. They make V-twin synthetic, too, in part to help bikers get over the common belief that synthetics caused bearings to slide, instead of spin. I read 797hp's comment, but I ran dino for the first six months, then switched to synthetic in my '95 Softail and it still wasn't leaking when I sold it 15 years later. Maybe luck...I knew lots of guys who absolutely refused to use it. |
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Posted: 2/18/2024 7:17:18 PM EDT
[#36]
Stores around me still have Castrol conventional oil.
 
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Posted: 2/18/2024 7:22:52 PM EDT
[#37]
I have had vehicles in the past that when I tried synthetic they did leak more.
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Posted: 2/18/2024 7:31:04 PM EDT
[#38]
No. I have over a million miles over several Toyotas with zero oil leaks. Power steering and shocks eventually seep but non have ever dripped. Not exactly what you asked but worthy of recognition.
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Posted: 2/18/2024 7:58:25 PM EDT
[#39]
Quote HistoryQuoted: They make V-twin synthetic, too, in part to help bikers get over the common belief that synthetics caused bearings to slide, instead of spin. I read 797hp's comment, but I ran dino for the first six months, then switched to synthetic in my '95 Softail and it still wasn't leaking when I sold it 15 years later. Maybe luck...I knew lots of guys who absolutely refused to use it. Doesn’t happen to all of them but I’ve seen it happen pretty often There’s an Amsoil rep that comes by my shop all the time, he claims Harley puts additives in their Syn3 oil that wash away deposits that prevent fiber gaskets from leaking, which will cause a leak Not sure if I believe him If your Evo ever does leak and you want to continue using synthetic, you can buy the new style gaskets from Cometic for the older bikes and they won’t leak |
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Posted: 2/18/2024 8:05:55 PM EDT
[#40]
Quoted: I ask because it seems as if dino oil is getting harder to find. Used Penzoil 10w-30 in the old truck since 1994, then last year I switched to Valvoline because I couldn't find non synth Penzoil. Today I bought Quaker State because I couldn't find Valvoline. Anyway, is there any truth to synth causing oil leaks, or in my case, worse oil leaks? (old Dakota has always had a slight oil leak) I had a transmission gasket leak on my 911. I spoke with the tech and he said that these are pretty common, over time, due to the newer transmission fluids. |
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Posted: 2/18/2024 8:06:37 PM EDT
[#41]
Quote HistoryQuoted: Doesn’t happen to all of them but I’ve seen it happen pretty often There’s an Amsoil rep that comes by my shop all the time, he claims Harley puts additives in their Syn3 oil that wash away deposits that prevent fiber gaskets from leaking, which will cause a leak Not sure if I believe him If your Evo ever does leak and you want to continue using synthetic, you can buy the new style gaskets from Cometic for the older bikes and they won’t leak Quote HistoryQuoted: Quoted: They make V-twin synthetic, too, in part to help bikers get over the common belief that synthetics caused bearings to slide, instead of spin. I read 797hp's comment, but I ran dino for the first six months, then switched to synthetic in my '95 Softail and it still wasn't leaking when I sold it 15 years later. Maybe luck...I knew lots of guys who absolutely refused to use it. Doesn’t happen to all of them but I’ve seen it happen pretty often There’s an Amsoil rep that comes by my shop all the time, he claims Harley puts additives in their Syn3 oil that wash away deposits that prevent fiber gaskets from leaking, which will cause a leak Not sure if I believe him If your Evo ever does leak and you want to continue using synthetic, you can buy the new style gaskets from Cometic for the older bikes and they won’t leak Avon rep? Sorry. Amsoil rep? |
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Posted: 2/18/2024 8:06:50 PM EDT
[#42]
When synthetic first hit the streets, way back when, it had the reputation of causing leaks and that may have had some truth to it. The problem has pretty much been corrected now. It could be the cleaning properties of the new synthetics that break away build up and allow leaks, that would be there if the crud wasn't wiped away, to begin.
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Posted: 2/18/2024 8:12:36 PM EDT
[#43]
Yes, but usually when oil type is switched and on pre 50s cars, same problem with a car not run in a long time and switching to a detergent oil
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Posted: 2/18/2024 8:16:53 PM EDT
[#44]
Quote HistoryQuoted: Doesn’t happen to all of them but I’ve seen it happen pretty often There’s an Amsoil rep that comes by my shop all the time, he claims Harley puts additives in their Syn3 oil that wash away deposits that prevent fiber gaskets from leaking, which will cause a leak Not sure if I believe him If your Evo ever does leak and you want to continue using synthetic, you can buy the new style gaskets from Cometic for the older bikes and they won’t leak I sold the Evo several years ago, but I'm thinking about a generator Shovel just for something to |
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Posted: 2/18/2024 8:17:27 PM EDT
[#45]
Quote HistoryQuoted: No, that is some stupid internet Mechanic bullshit. That theory predates the internet. If something is leaking bad enough to bother me it is not due to the oil. It is time for me to change the seal. |
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Posted: 2/18/2024 8:19:26 PM EDT
[#46]
Replace the seal when something is leaking bad enough.
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Posted: 2/18/2024 8:23:09 PM EDT
[#47]
The story used to be that is would clean the inside of the engine and wipe built up dirt and grime past the seals. Not sure if I buy it. There was push back in the truck business about converting diffs to synthetic because of the cost and supposedly causing seal leaks. What changed was manufacturer's extended the diff warranty if you ran synthetic and that made the swap easier to handle. Then everyone wanted it. That said even my old 70's tractor gets synthetic when I change fluids. I am a fan and have seen an engine saved with synthetic oil. Quick story car went off at Road Atlanta smashed the oil pan and broke the pick up tube. It ended up on the track and he cranked it up and drove it off the track with zero oil pressure. The bearings were all good and could have been reused. We rolled in new ones anyway.
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Posted: 2/18/2024 8:28:28 PM EDT
[#48]
Quote HistoryQuoted: When synthetic first hit the streets, way back when, it had the reputation of causing leaks and that may have had some truth to it. The problem has pretty much been corrected now. It could be the cleaning properties of the new synthetics that break away build up and allow leaks, that would be there if the crud wasn't wiped away, to begin. More like the snake oil sales tactic that synthetic would swell the seals and stop an engine that was leaking oil because seal softeners were known to do that. Right up until the seals failed completely and people blamed the synthetic in to turning their seals in to melted licorice. People bought in to the magic that synthetics would stop their already leaking engines, and some even claimed that the oil was too 'clean' and cleared out the sludge inside their engines that was holding them together and caused them to leak even more. People forgot that oil EATS rubber. Remember cork valve cover and timing cover gaskets ? How about graphite infused crankshaft seals? Even 2 piece rear main seals ? Don't forget the asbestos infused paper intake gaskets, paper water pump and thermostat gaskets. Pepperidge farm remembers. LOL |
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Posted: 2/18/2024 8:31:35 PM EDT
[#49]
What I was told is synthetic oil with high amounts of surfactant additives can dislodge or dissolve gunk that helped seal up certain spots where your seals and gaskets were already starting to fail. Is it the synthetic oil or additives causing it? No, technically it is a failing seal or gasket.
Is there any truth in what I was told? No clue, but I believe it. |
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Posted: 2/18/2024 8:32:18 PM EDT
[#50]
Quote HistoryQuoted: Usually a myth. In a rare/exceptional case if your engine is significantly slugged inside and the sludge is the only thing plugging holes in already failed seals, then maybe a synthetic made from a PAO, Alkylated Naphthaline and Ester blend could result in cleaning the inside well enough to expose already failed gaskets and seals. If you've been changing the oil regularly, and are not experiencing leaks already, you’re good. This makes possible sense to me but I don't know. In for the entertainment and eventual correct answer. |
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