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dchatagnon
04-11-2009, 09:57 AM
Hello Team,

I'm trying to fix a mystery oil leak on my Ford 351 Ho (285HP) engine.
Last summer I have rebuilt completely this engine. Put a set off all new gaskets.
Rear main seal + oil pan seal + front seal + valve covers gaskets etc...

Last summer I noticed a small engine oil right under the bell housing. Impossible tio find where it was coming from. I have only found a little bit of oil on the starter plate. I have checked around the oil pan and nothing was leaking. Checked for the valve covers and nothing too.
I have changed the PCV valve to make sure that the engine was not over presurized.
The engine was not overfilled by oil (5 quarts maximum).
Well, I thought it was the rear main seal that was badly installed and I decided to live with the leak until the end of the season.

When I winterized the engine, I have clean completely the oil that was under the bell housing. The boat was kept in the garage for 5 months without running.
Today, when I looked at it the oil was back again at the same place.

So now I'm stuck with that and I would say the leak is coming up from the oil pan.
But I have not found any leak around it.... and before to buy and install a new one, I would like to make sure that it is the oil pan.

What would you thing ? What are the very comon oil leak on a ford 351 ? Is this engine known for leaking oil ?

Thanks for all your ideas !

Jim@BAWS
04-11-2009, 10:10 AM
Hello Team,

I'm trying to fix a mystery oil leak on my Ford 351 Ho (285HP) engine.
Last summer I have rebuilt completely this engine. Put a set off all new gaskets.
Rear main seal + oil pan seal + front seal + valve covers gaskets etc...

Last summer I noticed a small engine oil right under the bell housing. Impossible tio find where it was coming from. I have only found a little bit of oil on the starter plate. I have checked around the oil pan and nothing was leaking. Checked for the valve covers and nothing too.
I have changed the PCV valve to make sure that the engine was not over presurized.
The engine was not overfilled by oil (5 quarts maximum).
Well, I thought it was the rear main seal that was badly installed and I decided to live with the leak until the end of the season.

When I winterized the engine, I have clean completely the oil that was under the bell housing. The boat was kept in the garage for 5 months without running.
Today, when I looked at it the oil was back again at the same place.

So now I'm stuck with that and I would say the leak is coming up from the oil pan.
But I have not found any leak around it.... and before to buy and install a new one, I would like to make sure that it is the oil pan.

What would you thing ? What are the very comon oil leak on a ford 351 ? Is this engine known for leaking oil ?

Thanks for all your ideas !


There are 3 pretty basic places it will leak from.

a) The oil pan is obvious. Some sometimes the screws around the edge get loose. That goes w/o saying that sometimes the QUICK DRAIN LUBE kit hose fitting also gets loose and needs a new teflon seal.

b) Rear main...You need to be careful when changing oil. Let it drain overnight. The next morning replace the oil filter. Then add only 4 quarts of oil. Put the boat in the water run and let it sit for a few minutes. Check oil and add from there. Alot of folks just add 5 quarts WRONG!!!. It only takes about 4.5 quarts thats it. To much oil and you can blow the rear main.

c) On occasion the valve covers get loose and need tightening. They end up dripping down the heads and you smell buring oil

Hope this helps...I have seen em all

Jim@BAWS

CantRepeat
04-11-2009, 10:43 AM
What about at the rear of the intake manifold? But if it were that I would guess you could see it pretty easy with a visual inspection. But I would go with a rear main seal leak from what you have said.

thatsmrmastercraft
04-11-2009, 10:55 AM
I would start wiping around all the areas Jim suggested with a clean paper towl until I found some fresh oil. If your engine is not really clean after the rebuild you may have to do some cleaning before this will work. Starting from the top and working your way down works best.

dchatagnon
04-11-2009, 03:22 PM
Thank you all for your replies.
Jim, I will retight a litlle bit the oilpan screws. What is the torque specs?
The 4 bolts that are on the corner are bigger than the ones on the side.

As it' time to start the season, I will also drain and the change the oil + filter.
I will follow your advise and let it drain overnight. I will start with 4 qts of oil.

I will post some result about the evolution.
Thanks again

Dam

dchatagnon
04-20-2009, 08:57 AM
Well, I have let the oil drain overnight, changed the oil filter and add only 4 qts of oil.
Then took the boat to the lake, run it for 30 minutes not above 3000 rpm and noticed a very thin track of oil in the middle of the bellhousing cover (starter plate).

No oil found at the bottom between the starter plate and the bell housing so I assume the rear main seal is not causing the leak.
Any new idea ? Is it the oil pan that needs to be changed ?

Thanks for your replies.
Cheers

thatsmrmastercraft
04-20-2009, 12:30 PM
Follow that track of oil uphill to its source: intake manifold rear seal, head gasket, valve cover gasket...........those are pretty much your choices.

dchatagnon
04-20-2009, 12:38 PM
Okay, I have checked the following things:

intake manifold=> No leak

rear seal=> How to check ? No oil between the starter plate and the bottom of the bell housing. To be sure, I should remove the transmission, bell housing, dumper plate and flying wheel to have the rear main seal inspected. But this is a long work that I don't wan't to initiate just at the begining of the season !

head gasket=> No leak
valve cover gasket=>No leak: New gasket installed this winter

What else could be checked ?
Thanks for all your help !

CantRepeat
04-20-2009, 12:46 PM
It has to be the rear seal then. If you take all that stuff out your might as well replace the seal anyway.

TMCNo1
04-20-2009, 12:47 PM
Okay, I have checked the following things:

intake manifold=> No leak

rear seal=> How to check ? No oil between the starter plate and the bottom of the bell housing. To be sure, I should remove the transmission, bell housing, dumper plate and flying wheel to have the rear main seal inspected.

head gasket=> No leak
valve cover gasket=>No leak: New gasket installed this winter

What else could be checked ?
Thanks for all your help !


There is a dye that can be added to the engine oil and with the use of a black light, the trail of oil can be tracked to the source. Most any mechanic can help you out with the procedure or it can be performed as a DIY project.

thatsmrmastercraft
04-20-2009, 12:52 PM
I'll second that - it sounds like all that is left is the rear main. And they are well known to end up leaking sooner or later.

Gamble
04-21-2009, 10:34 AM
Yep, rear main is my guess also............my old 83 did it eventually...........I just watched it, and it never did anything else but annoy me and make a mess.

Jim@BAWS
04-21-2009, 02:41 PM
Okay, I have checked the following things:

intake manifold=> No leak

rear seal=> How to check ? No oil between the starter plate and the bottom of the bell housing. To be sure, I should remove the transmission, bell housing, dumper plate and flying wheel to have the rear main seal inspected. But this is a long work that I don't wan't to initiate just at the begining of the season !

head gasket=> No leak
valve cover gasket=>No leak: New gasket installed this winter

What else could be checked ?
Thanks for all your help !

THE REAR MAIN IS BLOWN


You need to jack up the back of the motor and pull the transmission w/ the bell housing
Remove the dampner/Thrust plate. You will then see the seal


THE REAR MAIN IS BLOWN