hi everybody,
so i have a 95 f250 with the big 6 (300). I have a leak from my main rear seal between the engine and tranny that leaks about a quart every 1500 miles. i have only used a lighter synthetic, cant recall right now, but i was wondering if i were to run something like Rotella 15w40 (non synthetic) if it were to not leak as much. i have heard that synthetic will leak more that conventional because of its properties. I cant replace the seal for a while. I know my dads old ford would leak a quart every couple hundred miles and still dint completely blow out. Also, at what point is it necessary to replace the seal?
thanks everybody!

 

you can try it,but your already past the point where the seal should be replaced.whatcha waiting for? complete blow out and engine failure? cus that could happen if she dumps all her oil and you don't get 'er shut down quick enough.
better to be replacing the seal now,rather than an engine latter imho.i know it's cold out and most of us don't have nice heated shops (yet!) but sometimes ya gotta do what ya gotta do.bundle up and get 'er done.easy for me to say as i stroke the fire and sip my coffee right?

 

Well, it could just stay like it is forever and never get worse... or it could be like my Bronco II with the piece of junk 2.9 in it. Driving down the road and she starts cutting out and misfiring. Oil pressure light was NOT on, just running like crap. Pull over in the grass and take a look around... smell hot oil and find it all over underneath the truck. Rear seal just completely took a digger and dumped all the oil. Refilled it and she ran like her usual self again... for about 10 miles til it all leaked out again.

 

I had the same problem with my 460, I was using synthetic 10W-30 for awhile and noticed I was leaking about 1 quart a month from the rear main seal. So I switched back to conventional 10W-30 And it's down to about 1/2 a quart every two months.

So to answer your question. Yes it possibly could help in your situation like it did for me, but there is no guarantee.

 

i would like to do it withing a few months and like you said, i dont have access to a heated garage (northern MN). I was hoping this spring while i was doing the seal, to do the seal for the oil pan also. the seal around the oil pan is pretty warn and definitely needs to be replaced. its a 5 speed so the best way is to just pull the tranny im guessing. is it possible to just do the rear main seal? how long does it take and any tips with the inline 300?
thanks!

also, how accurate is the oil pressure sensor in the dash? ive been told its basically a dummy sensor and ive notice it never changes, which it should specially when im hauling something up a hill.

 

The oil gauge is essentially on or off like a warning light. It can be modified to work like the older models. I did it on my last truck and plan on doing it to this one. All you have to do is get the correct sender and extension and solder a jumper wire across the back of the gauge to bypass the resistor.

Thinner oil will most definitely leak easier. I have know of more than a few situations when switching to a thicker oil helped an older engine with leak problems.

 

Valvoline's MaxLife high mileage oil will often reduce or eliminate leaks. It's become de rigeur on older Jaguars because they leaked even when they were new. Not so much after MaxLife.

 

That high mileage oil is a gimmick. Put in thicker viscosity oil and get the same effect.

OP, you're better off replacing the seal now, even if it's cold. It'll be way easier than replacing an engine in the cold. Thicker conventional oil is a band-aid fix, it will probably slow the leak, but not stop it, and it certainly won't repair the seal.

 

I agree, it may slow it down but at the rate you describe the seal is bad. It is true synthetic sometimes will leak where conventional does not but we are talking small leaks. Rotella is GREAT motor oil and along with a great detergent package it has additives to soften and preserve rubber seals. It is not a miracle product but it may slow it down enough so you can wait for spring. Keep us updated and perhaps a forum member close by could offer a garage and some help if it gets worse.

 

Synthetic will often leak when conventional didn't because it does a much better job cleaning deposits out of the motor, and if debris in the motor is all that's holding the oil in, you already need new seals.

 

Most of the high mileage oils are crap - some of them are even actively harmful to engines - Maxlife is the only one that doesn't seem to be, per many studies. Also, how do you go to a higher weight detergent oil than 20W50? 20W50 is the standard base oil for old XK-engined Jags. You can't run straight 30 or higher weight in them or they get unhappy in street usage. ML was the only oil that slows down or even occasionally stops the leakage - and yes, even new-build overhauled XK engines leak, so you can't even say that the seals should be replaced. :P

 

If you are only losing a quart every 1500 miles I wouldn't even think of replacing the seal atleast until I had to do work on the clutch system. I would try switching back to conventional motor oil. This is not the popular opinion here, just my opinion.

 

i have been told by a few people who say its not worth replacing it tell i have to go into the clutch system. My biggest concern is driving it and it completely blows out. I do have AAA so im not afraid to be stuck on the side of the road, just dont want to have to replace the 300. thanks for the replies!

 

Just wanted to add that my old 302 would leak a quart in less than 1000 miles, depending on how much time it sat idling or driving. Got 6000 miles out of it until I replaced the engine. I just used the cheapest 20w-50 or 10w-40 till I pulled it.

 

i did some reading and a lot of people are saying to make absolutely sure its the rear main before ripping it out. some people suggest getting a fluid die that you put in your oil and check with a black light to see where its coming from. I dicided im going to wait tell early spring to replace the rear main, throwout bearing, oil pan and oil pan seal. the clutch still has good life (just clocked 144k miles) so im just going to replace the throwout bearing. thank for the replies and any info on this job would be great!