How much oil can leak from rear main seal? Without seeing it? (1 Viewer)

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I have a 96FZJ 80. With 143K miles. Going through may be a quart of oil every thousand miles or so. My mechanic says I have a rear main seal leak. But I never see drips on the driveway. I thought I might have a bad head gasket or leaking through the valves or something but I never see blue smoke.My mechanic doesn’t think the engine is burning oil, but if I don’t see drips under the car, could it really be all coming out the rear main seal?
 

HandForged

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a quart every thousand miles isn't much, as in maybe a few drops a day. That amount of oil would likely be concealed inside the bellhousing of the transmission. If he had seen oil around that area, rear main seal would be a good guess. Separating the two would be the only likely way to be positive. Get him to show you what he saw to make him believe it was the rear main. You can also have him add Dye to the oil, drive it around for a couple days and get under there with a black light. That will tell the tale definitively.
 

flintknapper

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Front main, rear main, pan arch, valve cover gasket, oil pump gasket...are all common leak points. Combined they tend to just cover/coat your undercarriage and not necessarily 'drip'. You are fairly low mileage...but I'd wager you are burning a small amount of oil as well. The valve guide seals will harden with age and allow small amounts of oil to enter the cylinders. It might not be enough to cause a puff of smoke upon start up...but I'd bet you have some loss there.

You don't really have enough to worry about.
 
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Front main, rear main, pan arch, valve cover gasket, oil pump gasket...are all common leak points. Combined they tend to just cover/coat your undercarriage and not necessarily 'drip'. You are fairly low mileage...but I'd wager you are burning a small amount of oil as well. The valve guide seals will harden with age and allow small amounts of oil to enter the cylinders. It might not be enough to cause a puff of smoke upon start up...but I'd bet you have some loss there.

You don't really have enough to worry about.

Thanks for this response. Is there any advantage to fixing the rear main seal other than to not needing to put in oil as frequently? Seems to me that I'll just continue to top off the oil, and when it starts burning too much, then worry about rear main seals, valves, even engine rebuild at that point. But not until i'm burning more oil?
 

flintknapper

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Thanks for this response. Is there any advantage to fixing the rear main seal other than to not needing to put in oil as frequently? Seems to me that I'll just continue to top off the oil, and when it starts burning too much, then worry about rear main seals, valves, even engine rebuild at that point. But not until i'm burning more oil?

Some of the better 'seal condioners' can help slow any leakage. Replacing the rear main seal means pulling the Transmission (or engine) take your pick. Typically they don't leak as much as a front main seal. You can have the entire engine and undercarriage steam cleaned and then monitor for leaks (to isolate where it/they are coming from), but if you don't have significant dripping, I wouldn't worry about it. Just top off as needed. Your's does not sound serious at all.
 
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if you were leaking 1qt/1k miles you would see it if it was coming from one source. yes the bellhousing can hold a surprising amount of oil but there will still be some that leaks out. you probably have multiple leaks and/or your burning oil, best course of action is to clean the engine and go from there. start working on leaks from the top down, valve cover gasket, dist o-ring, ect
 
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What weight oil are you running? My 80 uses and seeps drastically less oil when I went to heavier weight oil.
Ironically, (not sarcastically) mine leaked more when I went to heavier weight oil. I normally run 5W-30 and I accidentally poured in 10W-30. Within 1000 miles, mine was a quart down and it started leaking.

I changed the oil back to 5W-30 and it hasn't burned any in 5000 miles and has stopped leaking.

I seriously wonder how others do this when mine absolutely didn't like it.
 
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Not that it means anything but I’ve read a few times on here on links regarding the rear main seal leaking / seeping people suggest using 20w-50. I’ve been using to now and haven’t noticed any seepage since..... just my 0.0002.
 
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Some of the better 'seal condioners' can help slow any leakage. Replacing the rear main seal means pulling the Transmission (or engine) take your pick. Typically they don't leak as much as a front main seal. You can have the entire engine and undercarriage steam cleaned and then monitor for leaks (to isolate where it/they are coming from), but if you don't have significant dripping, I wouldn't worry about it. Just top off as needed. Your's does not sound serious at all.

Curious where does one take to have the undercarriage steam cleaned.....I need this.
 

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