When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I did a search and saw some threads and posts on this subject, but I have something to add to this question..
So if you have an original, bone stock 80s car that originally called for 5w30 conventional oil, 30 years later what should you run?
The car doesn’t seem to leak at all.. Even the guy who did the paint had it for a long time and said he was shocked it didn’t drip a drop of anything in his shop or showroom..
The P.O. casually said.. “I probably put 5w30 or 10w30 Valvoline or something..”
I’m fine with that.. but some people have suggested running Mobil 1..
I remember when I switched my 87 back in the day to Mobil 1 it started having leaks that needed addressing.. It could have been due to racing, driving hard and storing winters.. Could have been coincidence..
People had mentioned that switching to synthetic will make older cars leak because they “weren’t designed for synthetic oil”, but then when you learn about the superiority of synthetic oil, you would want to switch..right?
Gonna change the oil soon and thinking of putting 5w30 Valvoline back in it but wondering if I should do Mobil 1..
Personally, I've run Mobil 1 5w30 synthetic in all of my cars, forever. My black '89 has had it since the factory fill was drained after break in.
I think my yellow '85 started to leak more when I went to Mobil 1, but who knows. BTW, my '85 is a flat tappet so I've added a zinc additive, just to be safe.
People had mentioned that switching to synthetic will make older cars leak because they “weren’t designed for synthetic oil”, but then when you learn about the superiority of synthetic oil, you would want to switch..right?
I don't run synthetic oil because I'm frugal {cough}CHEAP!{/cough} but I run Mobil 1 in any rear differential I service. Not that it's necessarily applicable, but all the rears I've serviced seep gear oil. Some worse than others. Since I did the Iroc the 9-bolt now leaks on the garage floor. The Mustang has a completely rebuilt 8.8 with a few hundred miles on it, leaks like a sonuvabitch. The Formula leaks too, when it never did before the synthetic. Hadn't really thought about it until now, but I think the next time I'm in a differential it's going to get dino gear oil.
I don't run synthetic oil because I'm frugal {cough}CHEAP!{/cough} but I run Mobil 1 in any rear differential I service. Not that it's necessarily applicable, but all the rears I've serviced seep gear oil. Some worse than others. Since I did the Iroc the 9-bolt now leaks on the garage floor. The Mustang has a completely rebuilt 8.8 with a few hundred miles on it, leaks like a sonuvabitch. The Formula leaks too, when it never did before the synthetic. Hadn't really thought about it until now, but I think the next time I'm in a differential it's going to get dino gear oil.
That’s what I’m saying.. I feel like my 87 started getting little leaks when I switched to Mobil 1 5w30.. bought the car with 26k and switched around 40k.. Might be coincidence, but always remember people warning me if I switched I’d get leaks..
Doesn’t make sense.. in theory synthetic oil should be the same “weight” but better and doesn’t break down as easily with heat and friction.. in theory it should help keeping seals from drying up..
A guy I used to work with said just get a synthetic premium filter.. said the filter is the weak point and breaks down before the oil does..
Another guy I worked with that hated American cars just said all those greasy V8s leak because they’re made like crap and slapped together with crappy seals and gaskets.. (obviously a Porsche/Audi/BMW mechanic)..
Back then I figured, it’s gonna leak anyway, put good oil in it..
I never heard of leaks occurring because of using synthetic oil but why not run an oil additive to help stop the leaks. There are plenty of oil additives for that. As far as being frugal remember synthetic oil can stay in the crankcase a lot longer then conventional oil at 3,000 miles. I usually change mine at 5,000 miles. My wife's Audi recommends changing the mobil 1 at 10,000 miles.
Mobil 1 in everything for me. I do use the high mileage version in the Z. It says it has conditioners for the seals but who knows if that is true. I have no Idea what the 7 previous owners used but ever since I got the car 3 yrs ago, and started using Mobil One, it does not leak any more than it did. I get 2 small seeps from the front and rear main.
I used Mobil 1 in my 03 Silverado from the 1st oil change, 187,000 later no leaks at all. My buddy bought the same truck 2 months after me and he put Mobil 1 in his after the break in also, 150,000 later his leaks like a sive. IMHO I don't think the oil matters when it comes to leaks and I would much rather have the proven advantages of synthetics.
Synthetic in my diesel just because it makes it easier to start when it's cold outside. Synthetic in my race car to reduce friction.
Dyno oil in my Harley and daily driver pickup truck.
Oil needs to be replaced on a regular basis. Dyno oil is typically around 3000 miles. Synthetic oil can go a lot longer as it doesn't break down like dyno oil does. It costs more to put synthetic oil into an engine but an inexpensive oil sample can tell you if you should be changing it or not. Automotive diesel engines can easily go 15,000 - 25,000 km on an oil change with synthetic oil. So when you look at the increased cost of the oil, you're also doing less oil changes so it balances out.
If you still want to do an oil change every 3000 miles then just keep using dyno oil. Put a good filter on like WIX. I wouldn't use a Fram filter if they were free.
This is one of those questions that really has no right or wrong answer , kinda like the whole "Ginger or Mary Ann" conundrum . Pick whichever floats yer boat , keep the ol dipstick clean , and you'll do just fine ......
I run synthetic in my car and my daily driver pickups because when I change oil it is still golden colored and not burnt out. What got me started on the late 90s i bought a Z28 around 140k mi and the P.O. had used synthetic. Upon changing valve cover gaskets i noticed the cylinder heads were clean as new! Car never smoked i ran it over 200k. That sold me. I use Pennzoil in my car but for my 2 trucks for years now i just use Wal-Mart's house brand which Quacker State.
I changed my Jimmy and Envoy to Mobil 1 and had been wondering about the '87 if I should change it too. But I never thought about the high mileage synthetic, I should look into that more.
FWIW. my '86 TA has had Mobil 1 since the early 1990s. It doesn't leak a drop of anything.
Further, look in your owner's manual, and NOT the oil filler cap. The "5W-30" on the dap is a guide. Correct viscosity is in the manual. Unless you are driving when it's 0° F outside, use 10W-30. Follow the manual.
I started using Mobil 1 10w30 in my 87 back in the day when it hit about 80k.. After I had all the leaks and valve seals addressed and it never gave me problems..
It always made more sense to run 10w30 but I know a lot of guys that would only run 5w30.. especially those vette guys..
I think my yellow '85 started to leak more when I went to Mobil 1, but who knows. BTW, my '85 is a flat tappet so I've added a zinc additive, just to be safe.
Originally Posted by Eightyninef
3rd gens leak with synthetic oil. I went back to dino oil, and it's a little better.
When Mobil 1 was first released it was actually documented that it caused seals to leak. There were a few different explanations but it was well documented. Mobile 1 has been continually reformulated since and shouldn't cause the same problems (this was fixed in the 70's, not something recent).
Other synthetics are made differently (there are at least 3 different basic processes), but it's doubtful that any modern synthetics will make the same mistakes that Mobil did in the 70's.
If you put synthetic in a car recently (last 20 or more years at least) and it leaked you most likely would have gotten the same leak with conventional, but there is a small chance that the synthetic cleaned out some crud that was sealing the leak to start with, not so much a problem with going to synthetic as it is a lack of maintenance before going to synth.
Originally Posted by Drew
I don't run synthetic oil because I'm frugal {cough}CHEAP!{/cough} but I run Mobil 1 in any rear differential I service. Not that it's necessarily applicable, but all the rears I've serviced seep gear oil. Some worse than others. Since I did the Iroc the 9-bolt now leaks on the garage floor. The Mustang has a completely rebuilt 8.8 with a few hundred miles on it, leaks like a sonuvabitch. The Formula leaks too when it never did before the synthetic. Hadn't really thought about it until now, but I think the next time I'm in a differential it's going to get dino gear oil.
I think rear axles are just prone to leaking. Honestly, if I saw a completely dry/spotless rear axle I would wonder if it's empty.
Interestingly I don't know of any gear, axle or carrier manufacturers that actually recommend synthetic, and there are multiple ones that recommend against it, that recommend conventional (If you talk to them you typically get a story about better film strength or that it clings to the gears better, works better under high-pressure conditions...). OTOH, Synth manufacturers swear that their stuff is better, I honestly don't know. The oil manufacturers have the incentive to sell their oil, the gear/hardware manufacturers want to protect their parts.
I know that the only manufacturers that recommend synth in axles are OEMs, and their lube recommendations are largely driven by fuel economy requirements.
If you talk to synthetic company's engineers about "I have a race car and I don't care about anything but going faster," if you get to someone that actually tries to answer your question you'll be surprised that their answer isn't any of their synthetic gear lubes.
Originally Posted by AlkyIROC
Synthetic in my diesel just because it makes it easier to start when it's cold outside. Synthetic in my race car to reduce friction.
Dyno oil in my Harley and daily driver pickup truck.
Oil needs to be replaced on a regular basis. Dyno oil is typically around 3000 miles. Synthetic oil can go a lot longer as it doesn't break down like dyno oil does. It costs more to put synthetic oil into an engine but an inexpensive oil sample can tell you if you should be changing it or not. Automotive diesel engines can easily go 15,000 - 25,000 km on an oil change with synthetic oil. So when you look at the increased cost of the oil, you're also doing less oil changes so it balances out.
If you still want to do an oil change every 3000 miles then just keep using dyno oil. Put a good filter on like WIX. I wouldn't use a Fram filter if they were free.
Really for most people, the extra time between changes is the biggest reason to go synthetic. On my DDs and even my Cummins I feel totally OK going 5000 on a synthetic blend that I trust and 7-10,000miles on a good synthetic.
I'm kind of curious why you go conventional in the HD?
Conventional- For the amount of time I drive mine during the season it does not pay to use synthetic. Change every fall before putting her away for the winter.
Synthetic just leaks worse from holes you already had (it flows easier), and keeps the engine cleaner so there's no sludge to stop up the gasket leaks. If you address the gasket leaks before you switch it's not an issue. Fresh gaskets and seals are maintenance just like changing your oil - asking what the best oil is and then not wanting to fix gasket leaks makes little sense.
The best oil is CLEARLY synthetic. All the OEM's require it on EVERY new car.
I use Amsoil 10w40 premium protection. It's still based on the one of the old high zinc formulations from the 60's.
And I don't have any leaks on my '86 LB9. It sat in a field for 11 years. I resealed it. It runs phenomenally with the 10w40. Oil pressure is 35+ psi at hot idle.
I'm not completely sold on the idea that engines filled with synthetic oil are more likely to leak.
I've got a '93 LT1 Corvette...Chevrolet filled the crankcase with Mobil 1 when the car was built, and specifically warned in the owner's manual, and also on a sticker on the valve cover to continue using it.
My Corvette now has 88,000 miles on it, and no sign of an oil leak anywhere that I can see.
I'm not completely sold on the idea that engines filled with synthetic oil are more likely to leak.
I've got a '93 LT1 Corvette...Chevrolet filled the crankcase with Mobil 1 when the car was built, and specifically warned in the owner's manual, and also on a sticker on the valve cover to continue using it.
My Corvette now has 88,000 miles on it, and no sign of an oil leak anywhere that I can see.
My '94 Corvette leaks oil in a few spots, as most LT1s. I have two low mile LT1's on the stand and both have leaks.
I'm not completely sold on the idea that engines filled with synthetic oil are more likely to leak.
I've got a '93 LT1 Corvette...Chevrolet filled the crankcase with Mobil 1 when the car was built, and specifically warned in the owner's manual, and also on a sticker on the valve cover to continue using it.
My Corvette now has 88,000 miles on it, and no sign of an oil leak anywhere that I can see.
Partly because as an engine designed for synthetic oil, it's given seals for the same?
I know GM did this for axles. I suspect the same would be true for engines.
04-06-2018, 10:12 PM
This is one of those questions that really has no right or wrong answer , kinda like the whole "Ginger or Mary Ann" conundrum . Pick whichever floats yer boat , keep the ol dipstick clean , and you'll do just fine ...... 
