How to tell the difference between oil pan gasket & rear main seal

[k20]

Title says it all, is there a way to tell a rear main seal leak from an oil pan gasket leak. Noticed it today, right after I added some oil, dont know how much it leaks or anything, just trying to figure out which it is. I cleaned off the back of the pan, where its leakin, to see if it leaks overnight, or only if its runnin. Ive heard that if its just when its running, its teh rear main, any truth to this? Almost time for an oil change so might be a good time to take care of it.

 

[kevin's87]

/forums/images/graemlins/ears.gif Anybody? I have the same problem. I rebuilt the motor and noticed a leak. I have tightened the pan bolts with no improvement. I am coming up on an oil change and plan to remove the dust cover off the bell housing and see if I can isolate the leak. Supposedly the one piece rear main seals rarely leak. Maybe I have a loose pipe plug on the back of the motor. We'll see. /forums/images/graemlins/confused.gif

 

[diesel4me]

Be sure its not leaking from the valve covers,oil sending unit,distributor base,or the rear of the intake manifold first.Its really hard to get a good look in there behind the motor unless you have a body lift--then you can peek from behind the transfer case and get a better look at it.You will probably have to clean the oilpan and rear of the engine real good at the car wash,or pressure washer if you have acsess to one,then you can use talcum powder to dust the block and oilpan areas to help show up the leaks better.Dealers and repair shops use a dye in the oil and a blacklight to pinpoint leaks--its pricey but it works very well.If it does turn out to be the rear main seal /forums/images/graemlins/frown.gif and its a one peice one,the tranny or motor needs to come out far enough to replace it,but its better than the old 2 peice seal,they really are a pain to replace,and you have to pull the pan--you usually dont have to pull the pan on a one peice seal.Might be a good time to install a new oil pump and screen,and check the timing chain if you end up pulling the pan off to change the gasket.I got a new stock melling pump for 12.99 at auto zone,it was less than 50 bucks for the pump,timing chain and gears,oil pump shaft and a steel drive collar for the shaft for my 305--I couldnt justify not changing all that for such a low price,since I had to replace the oilpan due to rust.Hope your leak isnt the rear pain seal(thats what my mechanic friend calls it,after his 4 year old said it--the kid is smart!). /forums/images/graemlins/crazy.gif

 

[k20]

Well the talc powder idea wont work for a few days, its supposed to rain for awhile. I cleaned the oil pan last nite, and this morning, it didnt appear to have any oil on it. (I forgot to look, until I was leaving for school and as the driveway was wet & muddy I didnt really wanna lay on it lol). Anyway, Im back home......oily again. I only have around 8k miles on a rebuild so im going to be PO'd if it is the rear main.

It doesnt appear to have leaked much (according to dipstick). Its just enough that is run down the back of the pan, on the flywheel, on the oil filter, and back on the transfercase skid, because last nite I took the flywheel cover off. After I took it off, I handed it to my dad who washed it, cause it was covered in mud, and he doesnt remember if there was oil in it or not.

I read somewhere else that if there is oil in the flywheel cover, that its rear main, if none in it, its prob oil pan, is this true for bbc's, or is it just some motors?

This post seems long, sorry for that, but Im really bummed, esp cause mobil 1 is 5 bucks a quart, dont really wanna pay for a leak lol. O yeh, it doesnt seem to be leaving spots wherever I park (no rainbows in the water under my truck). Thanks guys. Chris.