1993 MerCruiser 4.3L V6 RAN OUT OF OIL

[FL370Pilot]

1993 MerCruiser 4.3L V6. TSMOH 4.6hrs

Engine block professionally overhauled under 5 hours ago. I have been running the boat over the past couple of weeks fixing various issues. Today we put it in the water and ran about 2 miles across the lake to play with a new sonar. After idling for a couple of minutes I throttled up and could hear knocking sounds coming from the engine from the intake down. There was oil all over the back of the engine and no oil showing on the dipstick. It was shut down within 30 seconds of the knock starting. After drifting for a couple of hours we were able to put 4 quarts of oil in and get it back to the dock. I have not found the leak yet, but it must be at the rear of the engine up high, like the intake manifold.

After adding oil, we limped back to the ramp and observed the following:

• Oil present in the bilge from the leak
• Oil pressure was normal.
• Temperature was normal.
• Knocking present but strangely not under load (getting up on plane). It got louder at cruise speed at around 2-3000 rpm.

I know the odds of not destroying the engine are not good at this point but I’m looking for suggestions on what to try before sending it off for another $1,500 overhaul. I am going to do an oil change and cut open the filter early next week.

The oil level was perfect when we put into the lake so whatever happened; happened fast.

 

[tank1949]

1993 MerCruiser 4.3L V6. TSMOH 4.6hrs

Engine block professionally overhauled under 5 hours ago. I have been running the boat over the past couple of weeks fixing various issues. Today we put it in the water and ran about 2 miles across the lake to play with a new sonar. After idling for a couple of minutes I throttled up and could hear knocking sounds coming from the engine from the intake down. There was oil all over the back of the engine and no oil showing on the dipstick. It was shut down within 30 seconds of the knock starting. After drifting for a couple of hours we were able to put 4 quarts of oil in and get it back to the dock. I have not found the leak yet, but it must be at the rear of the engine up high, like the intake manifold.

After adding oil, we limped back to the ramp and observed the following:

• Oil present in the bilge from the leak
• Oil pressure was normal.
• Temperature was normal.
• Knocking present but strangely not under load (getting up on plane). It got louder at cruise speed at around 2-3000 rpm.

I know the odds of not destroying the engine are not good at this point but I’m looking for suggestions on what to try before sending it off for another $1,500 overhaul. I am going to do an oil change and cut open the filter early next week.

The oil level was perfect when we put into the lake so whatever happened; happened fast.

perhaps mechanic forgot to tighten oil drain plug or filter. I'd take it to him ASAP. Let him pull it. U start messing with it, he may respond that it is on you. Just saying... Your failure is why I installed audio alarms in addition to gauges. Too may distractions....

 

[Earl Cordova]

Who installed the motor ?
If you did do you feel lucky ?

 

[Scott Danforth]

the oil pressure sensor is on the block up-high

I take it you were not watching the gauges. the oil pressure gauge would have went low about 20 seconds before knocking

knocking is bad. most likely your motor may be coming back out.

 

[FL370Pilot]

perhaps mechanic forgot to tighten oil drain plug or filter. I'd take it to him ASAP. Let him pull it. U start messing with it, he may respond that it is on you. Just saying... Your failure is why I installed audio alarms in addition to gauges. Too may distractions....

I installed the motor and I tightened EVERYTHING to factory recommended specs. The boat SHOULD have that alarm system but it doesn't work.

 

[FL370Pilot]

perhaps mechanic forgot to tighten oil drain plug or filter. I'd take it to him ASAP. Let him pull it. U start messing with it, he may respond that it is on you. Just saying... Your failure is why I installed audio alarms in addition to gauges. Too may distractions....

I was the mechanic. The shop only did the block overhaul.

 

[FL370Pilot]

the oil pressure sensor is on the block up-high

I take it you were not watching the gauges. the oil pressure gauge would have went low about 20 seconds before knocking

knocking is bad. most likely your motor may be coming back out.

Unfortunately no I wasn't watching that. I was playing with the sonar about 5 inches away.

 

[Scott Danforth]

Unfortunately no I wasn't watching that. I was playing with the sonar about 5 inches away.

people wonder why I always watch the gauges. every 5-10 seconds i glance at the gauges

knocking usually means a rod bearing went. if you are lucky and didnt take out the crank, I would invest in coated bearings. the coating will buy you about 30 seconds without oil pressure (long enough for a buzzer to sound)

 

[Lou C]

That does sound like a failure of the oil pressure sensor, I don’t think that much oil would escape even if the rear edge of the intake wasn’t sealed up correctly. Sorry to hear that!
I’m always scanning my gauges!

 

[FL370Pilot]

people wonder why I always watch the gauges. every 5-10 seconds i glance at the gauges

knocking usually means a rod bearing went. if you are lucky and didnt take out the crank, I would invest in coated bearings. the coating will buy you about 30 seconds without oil pressure (long enough for a buzzer to sound)

So if it was a rod bearing how do I know for sure?
I also had a mechanic at the lake say the Cam Shaft might be likely.

 

[Scott Danforth]

Doubt its the camshaft.

Lifters may rattle

A mechanics stethoscope will help

Only way to know for sure.....is pull the engine, flip her over and pull the pan

 

[nola mike]

That does sound like a failure of the oil pressure sensor, I don’t think that much oil would escape even if the rear edge of the intake wasn’t sealed up correctly. Sorry to hear that!
I’m always scanning my gauges!

This happened to me *twice* on my engine. Both times the chinesium pipe nipple I used on the sender sheared at the block. I got lucky, my oil pressure switch saved me by cutting the fuel the first time, second time I noticed the pressure drop before that.

 

[Scott06]

If you lost oil pressure and now with oil have a knock I'd pull it and inspect bearings etc. Even if it was by change a lifter or cam issue as suggested there is still likely metal in the engine that needs to be cleaned out.

 

[tank1949]

if it leaked out, I'd have friend crank motor while I had mirror and light looking for how it leaked. Since, one oil switch or sender (can't remember on mine) is located in the recesses near oil filter (Chevy V8s) and obscured by exhaust manifolds, I suspect that is where the ;leak is located. I feel your pain!

 

[ahicks]

IMHO, if it's knocking after being refilled, it needs to be pulled down, period. There is no point guessing, all you're accomplishing is delaying the inevitable. Energy spent screwing around could be more wisely spent admitting it's broken, and moving toward fixing it. Hard pill to swallow, but it is what it is.

Agree on the metal chip potential - not good. And don't forget to do the cam bearings again....

 

[Scott Danforth]

You can hope its not bad, and maybe run heavy oil for a few hours to mask the knocking

And then when it fails, get towed, and replace the motor

Or you can pull the motor now, repair what needs to be repaired and be boating in a week

 

[FL370Pilot]

UPDATE - Pulled the engine. Found metal in the oil as expected. Also found a crack in the side of the block from the great freeze of 2021 here in Texas. New block is on the way along with a check of all our internals and new bearings. Also got the audio warning system fixed. The leak was the intake manifold gasket at the rear of the engine. It was pretty noticeable once we knew where it was.

 

[Lou C]

Interesting and thanks for the follow up. The front & rear of those manifolds are sealed with a bead of RTV and don’t usually leak but I guess anything is possible....
In fact when I removed mine to replace the heads it was REALLY hard to get off...

 

[FL370Pilot]

Its possible the high oil pressure pushed out the RTV on that manifold. It was not uncommon for that engine to be at 80psi on first start up. Interestingly after we got another overhaul it is now on the low oil pressure side. We had to get a new block so who knows. I started another thread on the subject.

 

[Scott06]

Its possible the high oil pressure pushed out the RTV on that manifold. It was not uncommon for that engine to be at 80psi on first start up. Interestingly after we got another overhaul it is now on the low oil pressure side. We had to get a new block so who knows. I started another thread on the subject.

Not high oil pressure pushing out the rtv but if you had water in the crankcase and it got over full with milk then maybe