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Old 06-11-2021, 02:50 PM   #1
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Default rear main seal oil leak

Has anyone tried any of the products that are added to the oil to help condition the rear main seal and stop a leak? I have a very small oil leak where the transmission bolts to the engine (not really even enough to drip to the ground, just a small bit of oi there) which I assume is the seal. Any one have any success with these products? Any bad experiences?
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Old 06-11-2021, 03:06 PM   #2
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most of those products are a petroleum product which will soften an existing seal and temporarily perhaps allow it to be flexible enough to seal a seep. but they vastly shorten the life of every seal they come into contact with and could lead to more repair work than you want


a build up of pressure from a clogged PCV valve or a tranny vent tube can push fluid out past seals



on a vehicle any seep will run as blown by the wind and collect near the lowest point- you could have a seep 20 inches away- or even a slight spill aiming for the filler tube can create the appearance of a leak some time later



( I ride a '53 Harley, I know about seeps and leaks )


some fluids we use have a dye in them to help figure out what is what when there is a leak- which is why tranny fluid is red.


do you know if you have motor oil, tranny, power steering fluid or ?


you can buy a dye additive kit which with a blacklight can show the source of seeps



suggest you change your fluids to the correct type as spec'd as the additives will condition the seals- which often just dry out due to lack of use, once driven they tighten up again.
you can also try an oil rated a little heavier - the 0w and 5w are for MPG...nothing wrong with 20w-50, especially in the summer time



the time for a fix is when the dipstick levels show a drop or the driveway is splattered to the point of embarrassment
at which point you want to select a shop who works on your type of motor and tranny all day every day- not an RV shop



check BBB or your local Saturday morning am station car guy call in show


mike
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Old 06-11-2021, 03:22 PM   #3
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I assume this is on a small block Chrysler as a 318 or 360 CID.


They are prone to rear seal leaks, but as others have said make sure of where it is coming from as it could be from valve covers, oil pressure sender, intake manifold, or oil pan to name the most common ones.


Most of the time is in the joints between the two pieces on the main seal if it is the leak, so seal conditioners usually won't work if that is the case.


If it is the rear main but the real main bearing is worn it will be very hard to stop a leak.


The rear main seal and bearing can be replaced without pulling the engine or transmission, but it is an ugly job because you usually have to lift the engine some to get the pan off so the motor mounts have to be disconnected. It is also in a filthy area and what you are doing needs to be very clean.



Personally, I would check for all other leak points before doing much at all except to clean the engine areas around the drip to try to get a look at where it is showing up fresh. If you can get it up a bit you can remove the transmission inspection cover and see much more and it is only a few bolts to remove.


How many miles on it and how much oil pressure do you have at idle?
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Old 06-11-2021, 06:17 PM   #4
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The engine is the Chrysler 318 CID. I already cleaned it up and checked, and it seems to me the leak is coming from where the engine attaches to the transmission. The attached pic is not too good, but perhaps it will help. The oil pressure, warmed up at idle, is in the second pic (the mid-way mark is 40 psi). It has about 106,000 miles on it.
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File Type: jpg oil-leak-pic.jpg (136.3 KB, 25 views)
File Type: jpg oil-pressure.jpg (20.5 KB, 13 views)
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Old 06-11-2021, 06:23 PM   #5
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Quote:
Originally Posted by RT-NY View Post
The engine is the Chrysler 318 CID. I already cleaned it up and checked, and it seems to me the leak is coming from where the engine attaches to the transmission. The attached pic is not too good, but perhaps it will help. The oil pressure, warmed up at idle, is in the second pic (the mid-way mark is 40 psi). It has about 106,000 miles on it.


That area can show drips from pretty much all of places I mentioned, as well as the transmission so hard to tell. If you can see the areas above the transmission housing at the engine block and clean it a bit, you may be able to tell if any oil is coming down the back, top, of the engine to that point. If there is none there, then you down to pan gasket or rear main for the most part. There are oil gallery plugs up there also, but they are less commonly leaking.
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Old 06-11-2021, 07:08 PM   #6
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also...


synthetic oil is a seeper.


If the vehicle was run on conventional oil and you recently changed to synthetic that could be it


my rule of thumb is year 2000
much of the stuff built previous was designed for conventional oil and that's what has been used- there could be deposits of coke or sludge on the interior supplementing the seals


a switch to synth will loosen these deposits



post 2000 motors I use synth. and as mentioned above i alter the viscosity for wear or climate going a little heavier with more miles or AZ heat.


the "high mileage" Mobil 1 has additives which may be good for my high mileage gmc, so i use that


My van, chev 6.0 was run on synth for 1st part of it's life, the records show the PO started taking it to a dealer for changes with his "coupon"- which was for conventional oil.
over 10,000 miles I went through 3 changes of semi syn and am now on full syn again


mike
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Old 06-11-2021, 09:16 PM   #7
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I did change over to Valvoline full synthetic high mileage oil within the last two years, so maybe that's it. Maybe I'll try a heavier weight conventional oil. How about just an SAE 30?
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Old 06-11-2021, 09:41 PM   #8
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I did change over to Valvoline full synthetic high mileage oil within the last two years, so maybe that's it. Maybe I'll try a heavier weight conventional oil. How about just an SAE 30?

The high mileage oil should be good as it has the softeners in it, but you could try conventional. I would do a 15-40 or even a 20w50 in hot weather, but conventional won't do well in the thick grades as it turns cold. I would stay away from straight weight oils. Do get a high mileage oil, though, to see what happens.
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Old 06-13-2021, 11:16 PM   #9
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My 1998 dodge 360 leaked about 2 years ago after sitting all winter. Spring, I changed oil,Castrol synthetic 10w30. Drove a couple hundred miles,still leaked,couple hundred more,stopped leaking. 2 years and 2 oil changes later. All good,these older dodges just like to spit now and then.If it is not pouring out, just wash it off and monitor.
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Old 06-13-2021, 11:43 PM   #10
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Quote:
Originally Posted by Frumpster View Post
My 1998 dodge 360 leaked about 2 years ago after sitting all winter. Spring, I changed oil,Castrol synthetic 10w30. Drove a couple hundred miles,still leaked,couple hundred more,stopped leaking. 2 years and 2 oil changes later. All good,these older dodges just like to spit now and then.If it is not pouring out, just wash it off and monitor.
Thanks - that sounds like good advice. It isn't leaking very much at all, so I expect I will just keep an eye on it.
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Old 06-14-2021, 03:07 AM   #11
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Quote:
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How about just an SAE 30?

no, you want a multigrade


IF you NEVER use it in the winter you can go to a higher viscosity such as 20w-50


for winter you'd likely want a 10w 30

( consult your manual)



a multigrade "acts" like the lower number at low temperatures which will get oil flowing quickly to the lifters and the top end of the motor- very important- yet "acts" like the higher number when it's hot so the oil retains it's ability to form a cushiony layer between moving metal parts






with a synthetic, many will do 5000 between changes, conventional oil 3000


I have done oil changes on longer trips- usually in a pal's driveway using a dollar store turkey pan to catch the old stuff and recycling the used oil at the auto parts store.




Mike
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Old 06-14-2021, 01:51 PM   #12
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I would be hesitant to use a 20w50 oil. The 20 is to thick for cold start ups. The engine was designed for 10w30. For hotter summers, you could go to 10w40. Check your manual.20w50 is for purpose built engines with bigger clearance in the mains. Fyi, I use amsoil 75w140 in my 9 1/4 rear end. Now that is a high heat area!
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Old 06-17-2021, 07:34 PM   #13
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Brown color usually indicates engine oil, redish color transmission. Both can appear at the site indicated in your annotaed pic.
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