Mercruiser 7.4 454 CI loss of oil pressure

Thought they were fresh in 2015? What's the issue with the other engine?

I am sure that Mike just wants to enjoy his boat for a while before he has to pull out his wallet for a material set of investments. I know guys who nursed a bum engine for an entire year to save up the money to deal with it. As to the other engine.....it would seem that if the engines were replaced in 2015.....it may call into question the Previous Owner's assurances. I do believe it would be prudent to compression test both engines and take a look at the plugs. Old engine plugs are easy to identify since they usually foul quickly.

In regards to Mike's question about where to find replacements......that is more complicated. The boat is 28 years old....so it will come down to what he finds when pulls that engine and how the other engine tests. Unfortunately...it never is just one thing when you re-power. The best case is no damage was done and the cause of oil pressure loss is repaired.

Anything else will be far more expensive.
 
Post #1. "Engines run great" with no abnormal noise posted later.

So why look for replacements? Spending 3k to change an oil pump and hoping for the best makes no sense to me. Does 3k get the motor out of the boat or lifted high enough to pull the pan ?
 
Well that certainly puts a different spin on it. Spending 3k hoping it's the oil pump is a long shot.
 
Sounds like water probably got in and thus the new heads and risers (double down on that if they are raw water cooled). Hopefully the "new" is true.....then all you need are reconditioned short blocks which are not difficult to find. If it isn't I'm getting depressed.
 
The boat comes out of the water Feb 22nd for a bottom job, and I'm going to replace the oil pump on the port engine at that time. I’ve taken the boat out a few times, and as long as I keep it below 2500 rpm, there is no issue. Port engine stays at 40 psi, but when I try to get it on plane the pressure dropped to below 5 psi.
 
The boatyard pushed me off till the end of April to do the oil pump replacement. I’m stuck at doing 8knots till then.
 
Have you verified:
that the oil is not contaminated with gas
that you checked it with a mechanical gauge
 
I looked over the thread and there is one thing I didn't see checked.
There is one situation other then a pump pickup issue that would cause these symptoms.
You noted high rpm and high angle of attack would cause it to occur.

Since you are delayed anyway have you pulled the valve covers? Clogged or restricted returns in the heads and or the valley will cause the oil to pool there. Then the pan goes low on sucks air. Sludge noticeable in the oil fill?
 
The motor has been flushed and the oil wasn't clumpy or didn't contain any debris. Had an analysis done on the old oil and it came back fine, no metals, water, or fuel in it. The heads are very clean, they were replaced by the Previous owner two years ago. I'm being told that most likely it is the oil pump pressure relief valve spring has gone bad.
 
Update. The motor was pulled yesterday and the oil pan dropped, believe it or not, the pick-up tube fell out of the oil pump. What a junk design by GM.
 
A good race car mechanic will always tack weld the pickup tube to the pump. It is just a press fit a,d could possibly vibrate loose as you found out.
 
A good race car mechanic will always tack weld the pickup tube to the pump. It is just a press fit a,d could possibly vibrate loose as you found out.
Yep. I am having mine tack welded, but now I'm worried that the other engine's tube will fall out. LOL.
 

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