Thread: Engine spraying oil at high RPM

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Hi Everyone,

this is my first post to this site. I have read other threads about SBC spraying oil but so far i havent got the answer for my specific problem.

So what I have is a marine 383 stroker. This was a brand new engine (reman) from the factory. it ran very smooth for the first couple hours of use idling and up to 3500 RPM. once pushed to higher RPMs i got a warning sound that I had low oil pressure. I opened the hatch and the entire engine was covered in oil. Also since this time it no longer sounds smooth. it sounds like i burned up a ring or has piston slap.

the engine only looses oil when at full throttle. I have found oil in the intake.

Any thoughts on what this could be? i have attached the spec sheet for the motor as well

First, welcome to the forum. Glad to have you here.

A couple of questions that may help get you an answer. 1) Did you install the engine "as received", with no modifications like dress up parts? If you made any changes you need to explain them in detail; and 2) What did you do, and how long did you run the engine after getting the audible Low Oil Pressure Alarm?

I did install the engine as received with the exception of replacing all of the freeze plugs. It was supposedly dyno tested before delivery. I doubt the motor was dyno tested because upon delivery i noticed ALL of the brass freeze plugs were cracked.

The motor ran for about 10 seconds with the low oil pressure alarm. I shut it off, put a quart of oil in it and idled back to the dock.

I then took the motor out of the boat and checked the bearings on the crank and they didn't have any damage. I reinstalled the motor thinking maybe it was a one time event. i have idled the motor for about 10 hours of use over the summer but i have not ran it hard with the exception of one time when it did the exact same thing.

Time to check compression and cylinder leakdown on all cylinders------also what fuel and timing are you running---when an cylinder spark knocks, it rattles the rings off the walls and noisy, smokie, etc--------------

And check all of the venting including the venting of the engine bay

Welcome to CHR!

Like a lot of first time posts we get here you’ve got a nasty situation – sorry to hear about your problem but hopefully we can help you get this diagnosed and fixed to get that boat on the water this summer.

It would appear that pressure has built inside the engine to the point that it is literally blowing oil out where ever it can. Fortunately you didn’t get a fire out of this ordeal. Was there any indication of where the oil was coming out of the engine?

If this is a stock Mercruiser, your oil pressure alarm is probably on the same circuit as the engine temperature and transmission oil temperature. The oil pressure is a totally different sender and circuit. What was your oil pressure when you got the alarm?

What was your engine temperature when you got the alarm?

A compression check will tell us quickly if there is a bad cylinder (rings?) that is allowing that piston to be blowing the pressure generated on the compression stoke back into the crankcase. That would definitely be a problem and certainly account for your oil bath.

Did the PCV valve come out of the valve cover in this process? Does your PCV have a hose going into the air cleaner or the base of the carburetor?

Also, when you say the freeze plugs were cracked, did you contact the vendor you bought the engine from and ask why? I would see that as a red flag.

Keep the information coming and we’ll work this through with you.

Regards.
Glenn

I did perform a compression test. Cylinder 6 was low (135) and all others were around 160. I have not performed a leak down test.

I did contact the vendor (Mercury) about the cracked freeze plugs but they didnt even respond as this motor was sent to me free because I found out that the 1st motor I bought from them didn't have the forged pistons as advertised on the pamphlet i show in the original post. Im wondering if they didnt replace freeze plugs whats the chance they didnt do anything with the oil galley plugs as well?

The engine does not have any cooling issues and has always ran around 148-151 degrees. Its typical oil pressure is 45 psi at idle and at full throttle its pegged the gauge at 80 so I do not know how high it actually goes. My other 383 does this as well but has never had an oil spray issue.

when i got the oil pressure alarm it didnt show any oil pressure on the gauge.

The PCV valve did not come out of the valve cover and it does not have a hose going to the air cleaner.

for the life of me i cannot figure out where the oil is coming from when it blows everywhere. there is so much all over then engine bay but non on the engine itself.

Can you post some pictures? It's possible there's a oil galley compromise and a stream of oil is escaping under pressure.

Is it possible to observe the engine when running or is it under a complete cover?

The 80 psi may or may not be a problem. What oil are you using? I'd use 5W-20 until the bearings clearance themselves - probably the first 10-20 hours of run time.

I'd also hook up a temporary mechanical oil pressure gauge - you can "T" off the top/rear of engine behind intake (1/8" pipe thread) or above oil filter there's a 1/4" plug - just to verify the reading on the stock (electric) gauge.

Let's keep after this - others will chime in I'm sure.
Glenn

Originally Posted by axm0z5h

The PCV valve did not come out of the valve cover and it does not have a hose going to the air cleaner.

You say that the PCV didn't blow out of the valve cover, but more important that it does NOT have a hose from the PCV to the air cleaner? What is hooked to the hose connector tube on the top of the PCV? The hose to the air cleaner, or to the base of the carb provides the vacuum pull to evacuate the crankcase, and without a hose that pressure will blow out through the PCV like a demon. That could be the source of your problem.

At 80 plus psi it wouldn't surprise me to hear the oil is spraying past the oil filter seal.

Here are some pics of the engine and around the intake.

The PCV valve is on right rear valve cover with the hose going to front of the intake manifold. The vent hose on left rear valve cover with the hose going to air filter intake.

Too bad you can't put a gopro or similar camera under the compartment lid and go give it a wack or 2 on the water. does your oil fill cap have an o ring on it? Is that a vented cap? I've seen some of those on some BBC boats and they have an orifice drilled through the top edge to the center as a vent. My friend had a massive Baja with 2 502s and it kept blowing oil out after he had the engines replaced. A guy down at the Lake of the Ozarks showed us the fill caps. He swapped a pair from his boat and the problem went away. After that he heard of others having similar issues too. I'm not sure if it was an incorrect shipment from a supplier or what. I'm not sure if that is your problem but it is something to look at.

Ill take a look at that cap. I cant remember what type it is.

I do have a go pro and was thinking of doing that. whats stopped me is having to clean the bilge out again lol.

Originally Posted by axm0z5h

Ill take a look at that cap. I cant remember what type it is.

I do have a go pro and was thinking of doing that. whats stopped me is having to clean the bilge out again lol.

I can understand that. But it would help you see where the oil is coming from. A leak down test would give some good info too. Maybe the rings aren't seated in yet and it's got excessive blow by and it pushes the oil out at higher RPMs. Or maybe for some reason the oil isn't draining down to the lower end fast enough and the oil gets forced out somewhere at the top?

Well I took the boat out yesterday and got on it for a few seconds. I had my friend video the engine. As you can see it was coming from the dipstick and onto the alternator which was why it was flung all over the place.

https://youtu.be/WKNSOOO7E6M

Thanks for coming back and sharing the results of your video. It's good to know what was the problem.

Is that dipstick one of the sealed / locking types? Hard to tell in the video.