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View Full Version : Bad oil leak/crankcase pressure on 91 Prostar? Advice needed


SWGA Boater
06-15-2013, 09:49 AM
So I finally got on the water for the first time since I bought my boat a month ago. Had some electrical and overheating issues that I think have been worked through. After riding for about 20 minutes I stopped to check for any fluid leaks as I replaced several water hoses and all the fuel lines. No issues but now the bilge is filled with oil. I would say probably about a quart.

It appears if the oil is limited to the right side (fuel pump side) of the engine and it looks as if it is mainly coming from high--valve cover area, front and back. I tightened the valve cover gaskets and went back to the landing; nuts were somewhat tight, but needed tightening down. I would not have thought the valve covers would have leaked that much oil in that amount of time.

The oil fill valve cover has a flat plastic push in cover that I replaced as it had no cap when I purchased the boat. Hopefully this is causing my issue. Running the engine in the yard has never shown any evidence of an oil leak. What type of oil fill cap/breather should the valve cover have? Not sure what would be the correct oil fill cap.

I plan on trying to replace the valve cover gaskets and clean the bilge somehow this morning. Any other suggestions as to where the oil could be coming from, block plugs to check, etc.?

Thanks,

Ansley

93ProStar205
06-15-2013, 10:03 AM
Oil leaks suck to find, but given the rate it's leaking this should be an easy one. Clean up the motor/bilge with Simple Green or similar and have someone run it while you look for the source(s) with the motor box up and a good flashlight. Could definitely be the valve cover gaskets, particularly if the crankcase is overfilled. My 93 205 used to pool it in the intake valley between the runners due to a leaky valve cover. Would also check rear main seal area between the motor and trans.

Table Rocker
06-15-2013, 10:08 AM
Do you have a functioning PCV valve on one of the valve covers?

Cloaked
06-15-2013, 10:11 AM
Sometimes, tightening (over tight) can disfigure the valve cover slightly, allowing for more of a leak than less.

Don't overlook the possibility of a main seal (rear is common).

Oil can come out of the filler cap (or absence of one) but nothing to the extent of a massive oil leak per se.... You'd see more of a mess around that area without the cap...

.

SWGA Boater
06-15-2013, 10:23 AM
Do you have a functioning PCV valve on one of the valve covers?

Yes the left cover has a PCV valve. I will check or replace as they are inexpensive.

SWGA Boater
06-15-2013, 10:27 AM
Oil leaks suck to find, but given the rate it's leaking this should be an easy one. Clean up the motor/bilge with Simple Green or similar and have someone run it while you look for the source(s) with the motor box up and a good flashlight. Could definitely be the valve cover gaskets, particularly if the crankcase is overfilled. My 93 205 used to pool it in the intake valley between the runners due to a leaky valve cover. Would also check rear main seal area between the motor and trans.

This is one place I noticed oil pooling which lead me to think valve covers.

I looked at alot of pictures on the web and its seems most Ford engine have a breathable oil fill cap. I will replace the nonbreathable cap with a breathable cap also.

Thanks all for the quick suggestions!

mikeg205
06-15-2013, 10:27 AM
good luck finding the leak - I am voting +1 om the main seal due to the age if motor - or from oil filter top if it did not seat right due to some crud there or something.

j.mccreight@hotmail.com
06-15-2013, 10:29 AM
So I finally got on the water for the first time since I bought my boat a month ago. Had some electrical and overheating issues that I think have been worked through. After riding for about 20 minutes I stopped to check for any fluid leaks as I replaced several water hoses and all the fuel lines. No issues but now the bilge is filled with oil. I would say probably about a quart.

It appears if the oil is limited to the right side (fuel pump side) of the engine and it looks as if it is mainly coming from high--valve cover area, front and back. I tightened the valve cover gaskets and went back to the landing; nuts were somewhat tight, but needed tightening down. I would not have thought the valve covers would have leaked that much oil in that amount of time.

The oil fill valve cover has a flat plastic push in cover that I replaced as it had no cap when I purchased the boat. Hopefully this is causing my issue. Running the engine in the yard has never shown any evidence of an oil leak. What type of oil fill cap/breather should the valve cover have? Not sure what would be the correct oil fill cap.

I plan on trying to replace the valve cover gaskets and clean the bilge somehow this morning. Any other suggestions as to where the oil could be coming from, block plugs to check, etc.?

Thanks,

Ansley

Did you install a solid non vented plug like this pic, If you have a cap like this your motor likely over pressurized and just leaked out because it could not breathe. replace with a breather oil cap and you'll likely be ok.

Do you have the blue finned aluminum "mastercraft power" valve covers?

Cloaked
06-15-2013, 10:30 AM
I looked at alot of pictures on the web and its seems most Ford engine have a breathable oil fill cap. I will replace the nonbreathable cap with a breathable cap also.

Thanks all for the quick suggestions!I have had engines with both caps. Can't say that I know the difference as long as there is one there......works for me....best I recall. my last several have been solid caps....

You can check your PC valve by shaking it. If it rattles, it's (theoretically) good.

.

j.mccreight@hotmail.com
06-15-2013, 10:40 AM
If running a closed or solid cap is has to have a hose run up to the flame arrestor to allow the PCV system to operate properly

A closed cap with a hose or a vented cap without a hose is ok
96841
or
96842

JimN
06-15-2013, 11:16 AM
Yes the left cover has a PCV valve. I will check or replace as they are inexpensive.

Pull the PCV and shake it- if it rattles, don't bother replacing it.

When you changed the oil and filter, did you crank the new filter on like it was a contest? Only tighten it 3/4 to 1 full turn after the rubber gasket makes contact with the block.

What about the hose for draining the oil- is it hanging at the front of the engine, next to the pulleys? I have seen several that wore through because they moved during acceleration and made contact with a pulley.

Remove the starter and use a small diameter flashlight with an inspection mirror to look at the flywheel- if it's covered with oil (it will have a sheen that shouldn't be on it) and looks like it's wet, you may have a bad rear main seal. Not the end of the World, but you don't want to run it this way.

What does the transmission use- Dexron or 20W? Make sure of where the leak exists- did you check the fluid levels after you saw the oil? If not, do it immediately.

SWGA Boater
06-17-2013, 12:01 AM
Replaced valve cover gasket this afternoon, sprayed down the block with brake cleaner, cleaned the bilge and went for a short test run. After a 10 minute run, right front of engine, hoses, etc. is covered in oil. I do not think it is the valve cover gasket, as I can see no leak under the gasket. There seems to be three things that it could be: oil pressure switch piping, oil filter, or dipstick tube. Also made sure oil level was ok. I'm guessing I lost about 1/2 quart as this what it took to bring the level back to the safe zone.

I bought another PVC valve and replaced my solid oil fill cap with a breathable cap also today. I plan on taking the pressure switch plumbing off and checking it and also replacing the oil filter, as well as trying to tighten the dip stick tube.

After I do this I may make a run with the dog box off to see if I can see where the leak is coming from. It is weird that at the dock with the fast idle around 2000 rpms I cannot see a leak.

Hope to get to work on this later in the week. I'll update the thread afterwards.

Thanks for all the suggestions!

john jones
06-17-2013, 12:52 AM
I just chased down a oil leak on my 93 maristar.

SWGA Boater
06-22-2013, 11:02 PM
Made alot of progress today....

Changed the oil and filter (not two seals as I had hoped), took off the oil pressure sender piping as well as dipstick tube, cleaned them and applied tape to the threads and tightened everything back up. Put a little kitty litter in the bilge to help soak up the oil and sprayed everything down with brake cleaner. I then ran the engine on the hose in the yard, for about 20 minutes. Varied the rpms (1000-2500) and did not see any oil leaking. We'll see when the motor is running on the water and under a load. Hopefully the oil leak is repaired.

Now have some issues with my carb (see other thread) not wanting to idle. Secondaries are dripping gas at idle. Hope to make a quick run tomorrow afternoon if I can get the carb issues worked out.

SWGA Boater
06-23-2013, 09:55 PM
Ran the boat with the engine cover off this afternoon. Have isolated the oil leak to blow by out of the dipstick tube. Almost immediately after getting into the throttle dipstck pops up and starts spitting oil out. Had previously installed a new pcv valve and a breather oil fill cap. So much pressure was coming out of the breather cap it literally looked like smoke. Put my nonvented oil fill cap back on which leads to more blow by/oil coming from the dipstick tube. Should have taken a video...

I'll try and pick up or rent a compression gage tomorrow. Piston ring blow by is the only thing I can think of causing this much pressure. Seems to idle fine and no skipping under a load though.

Any other thoughts?

JimN
06-23-2013, 10:38 PM
Ran the boat with the engine cover off this afternoon. Have isolated the oil leak to blow by out of the dipstick tube. Almost immediately after getting into the throttle dipstck pops up and starts spitting oil out. Had previously installed a new pcv valve and a breather oil fill cap. So much pressure was coming out of the breather cap it literally looked like smoke. Put my nonvented oil fill cap back on which leads to more blow by/oil coming from the dipstick tube. Should have taken a video...

I'll try and pick up or rent a compression gage tomorrow. Piston ring blow by is the only thing I can think of causing this much pressure. Seems to idle fine and no skipping under a load though.

Any other thoughts?

Remove the oil filler cap and the breather cap and remove the raw water pump so you can rotate the crank manually. Make sure to disconnect the battery first- don't want any possibility of it starting. Listen for what sounds like gasping coming from the oil filler openings. If you do, it could indicate blow-by.

Rather than do a compression test, do a cylinder leakdown test. It could be rings, but it could be scoring in one or more cylinders, too.

SWGA Boater
06-26-2013, 10:45 PM
Having a hard time coming up with a leak down tester. I was hoping I would not have to buy one....i did run a compression check though just to do it. One cylinder was 135, six were 140, and one was 145.

Jim had mentioned did I have the stock valve covers. I have a pair of chrome covers. They do have a baffle under the holes. Would the aftermarket covers be an issue? They were on the engine when i bought the boat.

Also should the dipstick have some type of rubber, oring, anything that would help seal the tube?

When cranking engine over (coil wire off), dipstick out, thumb over tube, i can feel small puffs of air. Should this be normal?

SWGA Boater
06-26-2013, 11:20 PM
Have been doing a little reading on some Ford forums. I think i understand how the pcv system works now. The breather i installed in the valve cover the other day which was clearly venting pressure should have been sucking air. For it not to be sucking but venting my pcv valve would not seem like it is working. Replaced with new pcv valve though....

With the engine running, and hose off pcv valve, I should have a strong vacuum--correct? Maybe not enough vacuum for the valve to work? I will try and do some more investigating tomorrow night.

Still wondering if the valve covers are the issue. When i checked the new pcv valve tonight there was oil residue in the hose going from the valve to the carb spacer.

j.mccreight@hotmail.com
06-26-2013, 11:48 PM
Valve covers, baffled or not is not your problem. Dipstick are norm slip fit. Can u post picture. Compression is good,

j.mccreight@hotmail.com
06-26-2013, 11:52 PM
Remember the motor is an air pump.

SWGA Boater
06-29-2013, 03:35 PM
Ran engine this morning. Checked to ensure that I had good vacuum on the PCV hose and that the PCV was opening. It was. No oil coming from the dipstick tube. Does not do it in the yard with engine 1500 rpms plus. Forgot to take a picture, but my setup is like this:
http://ajphoto.zenfolio.com/img/s10/v100/p1620033624-2.jpg

Also took a video of the engine running:
http://youtu.be/4NIAoosPuWw

Excessive smoke, running rich or possibly water related? Remember it did run hot earlier. Could a blown head gasket do this and be my crankcase problem? No skips or rough idle or running. Compression seemed good. Look specifically about 20-25 secs and you can see excessive oil in the exhaust water on the concrete.

mikeg205
06-29-2013, 03:56 PM
looks more like steam than smoke based on color.... blown head gasket I believe would give you erratic running. Pull the plugs see if any are oily or black. How are the water passage ways on the port side?

SWGA Boater
07-09-2013, 11:06 PM
Got tired of waiting on the local parts store's warehouse to have a leakdown tester come in. Ordered one from Summit and it came in today. Anxious to see if blow by is the root of my problem. Will report back after running leak down test.

Also, a few replies back someone mentioned an over filled crankcase causing excessive pressure. I filled with oil until it was dead on the full mark on the dipstick (after running). This was about 5.5 quarts with the filter change. I looked in the owner's manual but did not see an oil capacity listed. I would not think this was overfilled and causing my problem, but how many quarts does it take usually for other's oil changes?

Also, replaced the right exhaust manifold gasket (small leak) and valve cover gasket in the meantime....I checked and did not notice any blockage in the manifold though (steam issue Mike referred to).

SWGA Boater
07-18-2013, 10:29 PM
Finally had a chance to run a leak down test. Results as follows:

Regulator set at 100psi

#1---85psi
#2---88
#3---91
#4---93
#5---84
#6---89
#7---91
#8---82


Any thoughts on these numbers? Anything else to try?

Thanks,
Ansley

SWGA Boater
07-20-2013, 04:23 PM
Any thoughts on the leakdown numbers? Was reading where you should expect 10-15% leakdown. I'm in that range except on a few cylinders but there was not a massive drop on any one cylinder.

mikeg205
07-20-2013, 04:28 PM
I agree - Those look pretty good compared to starting point IMO...

SWGA Boater
07-20-2013, 04:52 PM
Thanks Mike. The only thing I can think is when the boat is under a load it is changing the issue. Running in yard idling engine runs like a top, take it on the water for a short run blow by shows up.

mikeg205
07-20-2013, 05:00 PM
isn't there a spec for leak down numbers for your motor? I always thought numbers were above 150psi..?

j.mccreight@hotmail.com
07-20-2013, 05:11 PM
Yes a normal motor will show 10-15% leakage, your numbers are mostly good, cylinder 8 is iffy at best, I would start looking at #8, anything above 15% and you need to start thinking about investigating and possible rebuild. I recently did a leak down test on a 5.6L titan with 135,000 miles none were over 8%. I would clean top end, pistons etc. Mix up some atf/ water mix 50/50, (marvel mystery oil can also be used)remove all spark plugs insert several teaspoons full of mix into each plug, let soak for 10-20 minutes while slowly rotating engine over by hand every few minutes, then spin engine over with starter motor, plugs still out to remove excessive atf mix, install plugs, it will smoke like a chimney until all atf is burned off, run it for a while, let cool down a bit and recheck leak down warm.

j.mccreight@hotmail.com
07-20-2013, 05:13 PM
isn't there a spec for leak down numbers for your motor? I always thought numbers were above 150psi..?

Perhaps you are thinking of compression numbers, you are wrong, minus 7 mcocd points for you. 8p

mikeg205
07-20-2013, 07:03 PM
Perhaps you are thinking of compression numbers, you are wrong, minus 7 mcocd points for you. 8p

Ack.... you are correct... dang tequila... oh well it's 5 o'clock somewhere...

SWGA Boater
07-21-2013, 12:19 AM
Yes a normal motor will show 10-15% leakage, your numbers are mostly good, cylinder 8 is iffy at best, I would start looking at #8, anything above 15% and you need to start thinking about investigating and possible rebuild. I recently did a leak down test on a 5.6L titan with 135,000 miles none were over 8%. I would clean top end, pistons etc. Mix up some atf/ water mix 50/50, (marvel mystery oil can also be used)remove all spark plugs insert several teaspoons full of mix into each plug, let soak for 10-20 minutes while slowly rotating engine over by hand every few minutes, then spin engine over with starter motor, plugs still out to remove excessive atf mix, install plugs, it will smoke like a chimney until all atf is burned off, run it for a while, let cool down and recheck leak down.

Thanks for the suggestion. I talked with a mechanic yesterday and he suggested the same thing, except pouring down carb throat until engine dies and then letting it sit over night. Last resort before going into engine i guess.

Any idea what is the difference betweeen the oil the engine uses and atf for the rings? Why would atf be a better choice?

j.mccreight@hotmail.com
07-21-2013, 12:24 AM
Thanks for the suggestion. I talked with a mechanic yesterday and he suggested the same thing, except pouring down carb throat until engine dies and then letting it sit over night. Last resort before going into engine i guess.

Any idea what is the difference betweeen the oil the engine uses and atf for the rings? Why would atf be a better choice?

Atf will dissolve the carbon build up and free the rings, oil will just sit there. yes pouring down throat is an option I typically don't recommend that method for the fear if not done correctly rods can be bent, fluids typically don't compress well, also you don't know if the mixture actually got into all 8 holes, either way just ensure you get a good soaking to dissolve the carbon.

JimN
07-21-2013, 09:40 AM
Was compression/leakdown tested when the engine was cold, or hot?

SWGA Boater
07-21-2013, 10:13 AM
Atf will dissolve the carbon build up and free the rings, oil will just sit there. yes pouring down throat is an option I typically don't recommend that method for the fear if not done correctly rods can be bent, fluids typically don't compress well, also you don't know if the mixture actually got into all 8 holes, either way just ensure you get a good soaking to dissolve the carbon.

That makes sense...i have a little squirt can so i will go with your recommendation. Will report back afterwards.

SWGA Boater
07-21-2013, 10:14 AM
Was compression/leakdown tested when the engine was cold, or hot?

Leakdown was done when engine was hot.

Thanks

SWGA Boater
07-23-2013, 09:09 PM
No change in my engine situation, but I have found a used engine out a 91 Ski Nautique. The mechanic is telling me it will be a straight swap for the 351 in my boat, in that the Ski Nautique engines are standard rotation (looking from rear engine turns left) same as a MasterCraft. I had always thought SN had a different prop rotation (RH prop). Is the change made in the transmission?

The engine can be had for a reasonable price ($500), but I want to make 100% sure before I tell him that I will take it. Also, the engine is 5 hours from me so its quite a haul.

Will this engine work in my 91? I hope so....

Thanks for any input!

j.mccreight@hotmail.com
07-23-2013, 09:14 PM
No change in my engine situation, but I have found a used engine out a 91 Ski Nautique. The mechanic is telling me it will be a straight swap for the 351 in my boat, in that the Ski Nautique engines are standard rotation (looking from rear engine turns left) same as a MasterCraft. I had always thought SN had a different prop rotation (RH prop). Is the change made in the transmission?

The engine can be had for a reasonable price ($500), but I want to make 100% sure before I tell him that I will take it. Also, the engine is 5 hours from me so its quite a haul.

Will this engine work in my 91? I hope so....

Thanks for any input!

I do remember someone saying nautiques did have a lefty motor and the change was in the transmission causing a RH prop. If the engine is truly a LH you should be all set, as it sounds like it's already a marine motor their is no need to swap freeze plugs, etc.
Perhaps the question should be raised on http://www.correctcraftfan.com/forum/default.asp
Or PM this guy he knows CC http://www.mastercraft.com/teamtalk/member.php?u=4253

SWGA Boater
07-23-2013, 09:23 PM
Thanks for the quick reply! I will also post over on the CC page.

SWGA Boater
07-30-2013, 08:44 PM
Ran the boat this past Saturday with no oil leak issues. My problem may have been a stuck ring, I'm not sure. I filled the cylinders with a few teaspoons of a combination of sea foam and mystery oil. I let it set for about 30 minutes and rotated the engine every 30 minutes for so for about 3 hours. I then ran the engine. Afterwards I added a few teaspoons of ATF into the cylinders and let it set overnight. Ran the engine in the yard and then changed the oil and headed to the lake. Finger crossed it will continue to run fine. Dipstick popped up a few times when I ran wide open, but not when running 2000-2500 rpms as before.

Engine still seems to have excessive steam coming out of the exhaust at times. Engine never ran over 160 degrees though. Any thoughts or run as is?