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Synthetic oil?


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Yup, That's the question! I purchased some at work the other day because I found some old closeout that we had to get rid of and sold for $1 per quart on some 10w-30 Kendall Synthetic Blend supposedly high performance oil. Grabbed an STP filter on top since it uses a much better design then that shitty Fram garbage.


My question is, after using the search feature (yes i did!) I found a little bit of relevant information, however it seems that everyone was recommending it not be used on old engines. Now, it seems as if it's on a full synthetic that was recommended not to be used. Would a part synthetic be okay to run? I've been wanting to try it out for a little while and came across this deal and HAD to jump on it. I just wanna see what you guys think before dumping it in.

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There's no guarantee it will or won't leak. By leak I mean a wetness around crank seals that are old and worn but otherwise working now. Valve cover gasket that are crappy to begin with. I used it in my tranny and the rear seal got wet. I changed it and it's fine. Happened on the upper input seal on my transfer case too. It's at the top and is the driest. Again I replaced it ($25 later) and fine. Same with the diff.


I would try it and if anything gets wet just change back next oil change. Should stop once it flushes out. Or replace what leaking... if it even does leak.

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I use 10w-40 full synthetic in my L20b. Motor was rebuild about 30k before i changed to synthetic, so seals were reasonably new. Valve cover started to seap a little, put a new seal in.

I like it a lot, top end of motor is still super clean when the cover is removed. And i noticed a very dramatic difference in the running temperature of the motor. Thinking of putting a warmer thermostat in to get better heat out of the heater, The motor runs that much cooler.


And i dont worry about the zinc content either. I would if i had anything but a stock cam.

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Switched to synthetic on two cars in the past honda and VW. Both started to have rear main seal, front cam and valve cover gasket leaks. The rear main on my 86 GLI was so brittle at 60k that it crumbled in my hand. I switched to synthetic when it had about 40k. Yes, you can see better performance, mileage, and cooler running temps. Just plan on seals getting brittle if you switch over on an old engine. For a buck a quart, I'd run it though.

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Here's the thing with synthetics:


They clean better than conventional oil. Consequently, if you have an older motor with older seals that have very slight leakage, or sludge blocking the leaky seal, then stick with conventional oil.


Because of the cleaning nature of synthetic oil, it will dissolve those sludgy deposits that are holding your crappy seal together. As a result, many people with older vehicles who switch to synthetic oil will find it "creates" leaks. In all actuality, it exacerbates the already compromised seal. If you have good seals, you won't have any problem.


As for the zinc, it's nice to have, but not completely necessary for L motors. They seem to be able to run whatever without problem. I've been running Royal Purple in the 510 for a while now, and no leak issues, but then I rebuilt the entire thing and it's still pretty new.

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The L series was designed in an age that made thing bigger and stronger than necessary to make them capable of lasting. Over engineered come to mind. Just look at the huge 5 main bearings used... no wonder it will support 8K revs and high hp numbers. When someone says they broke their crank or a rod, (a rarity in itself which proves my point) you just know it was either over heated or run low on oil or both. No way this can happen on a good motor with oil and water and reasonably good bearings. The J series has just 3 mains.


Today, motors rely on exotic metal alloys and processes and even more exotic lubricants to make them run and last.

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Thanks for the advice guys!



I'm thinking I may try it just to see if I have any issues. Although, 200K miles on the engine may prove to be a problem. Although, I've already priced rebuild parts and may be doing a full rebuild in the near future anyways, but I just wanted to check for the moment and see what you guys thought.

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guys dont laugh but sum older people i know always told me if u change oil type or brand even it might clean all the gook off of everywhere it needs to be and cause problems may be an ole wise tale but who knows


Thats only between conventional and synthetic. Essentially, the synthetic cleans out the engine. If the old seals are caked with sludge that is essentially, sealing the oil in and then you remove that crap, the old worn seal will most likely leak.

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  • 2 years later...

From my 15 years of kart racing experience(dad multiple grandnational wins engine builder).....hands down synthetics do a BETTER job of lubricating with less viscosity. Less viscosity leads to less/fewer dry starts...builds oil pressure faster. Synthetics also keep their lubrication properties at higher temps than conventionals can(LESS CARBON BUILD-UP in comb chambers too). If it starts leaking replace the seals.....If they leak they were not worth having anyway. Yes I have 2 block off half my radiator sometimes to get back the heat lost to the "reduced friction/windage"....
I think it is a good idea to epoxy a couple big strong magnets to the bottom of the oilpan 2 trap any ferrous particulates....put one on the filter too. Whether u go conv or synthetic it is foolhardy to put too heavy an oil in your engine (20-50) unless u are in a very hot climate.....use the viscosity chart in any chiltons.

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  • 2 weeks later...

My opinion: Use what you like, but add ZDDP. You can get it at most Autobones/Schmuck's. Oliver from ZSpecialties tells me that the cams need the phosphorus to last. Whether or not this is true, I cannot verify, but I trust the dude since he has been working on these things since they were new.


I run cheap synthetic with ZDDP. No leaks, no complaints.

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