454xli Repower

[SanJuanDreamer]

Well, it seems San Juan Dreamer is due for a repower.
She has 1510hrs on both motors and port motor has a serious miss.
Shop says #4 cylinder is not holding compression.
Blue smoke and gas smell is strong.
Oil pressure good on both motors at the lower rpms, but after coming down from plane, oil pressure drops extremely low, like in 5lb area until oil cools, then it’s back to 40lb

Anyone have experienced insight you could offer?
I don’t have time to do it, I’ll be asking a shop to do it…

[tomschauer]

1500 is a good amount of hours, cant complain a whole bunch.
But I believe I would dig in just a bit deeper before you sacrifice a good part of your season and bank account.
Are the crusaders throttle body or multi port injection? If multi port, the gas smell and low oil could be too much fuel in one or more cylinders. If enough over fuel, it would thin your oil, and when the fuel evaporates, wala, oil pressure again. I guess depending on the layout of the intake, this could also happen with a throttle body setup. I would assume then, it would effect four or eight cylinders, not just one or two.

I'm sure Viper will have more insight.

[Viper]

Ya I'm with Tom on this. His thoughts on over fueling is sound and a definite possibility. I'd do some more diagnostics. Did they use a test meter to check oil pressure or are they going by your gauges? Did they do a wet test on number 4 cylinder? That and a leakdown test will determine if the low compression is a lower or upper end issue. If you're lucky, it'll be a top end problem which you can buy some time by simply rebuilding the heads. While they're at it, they should do a vacuum test to see what else may be going on. To the trained eye, it'll tell you a lot.

What grade of oil do you use? Do you get blue smoke ALL the time or just at startup?

The hours are high for a gasser but I always say it's more about the way the engines were run and whether they were properly maintained that dictates whether the high hours are a problem or not. The problem is you don't know what previous owners did unless they all provided meticulous records.

[tomschauer]

Viper, are the crusaders TBI with dual plane intakes? Or MPI?

[Viper]

Pretty sure they're TBI with an adapter plate on a spread boar intake if I remember. I think the MPI would be XLi-MP

[mjk1040]

My 1998 454Xli's call for 40W oil. I know many use 15W40. Guess I'd be researching new power plants with those hours. Engines 20 years newer may be a plus with the exception of the cost of a total repower. Good Luck with your choice!

[bud37]

Only thing I can add would be to have your guys verify by leak down test that #4 is actually dead and why, as has been mentioned.......did the oil issue start with the engine miss?

[SanJuanDreamer]

The oil pressure issue has ben happening for sometime, as the years go by it gets lower...on both.
When the engines are running at 13rpm or less, the oil is ~40lb and steady.
When she gets up on plane 36rpm, after 10-15 minutes, the pressure will start slowly lowering, usually holding at about 20-25lbs
As soon as she comes off plane, they both register just at 5lbs or slightly above.
As the engine cools, the pressure will increase.
Its a progressive slide over the years.

I've had mechs recommed a top end job, but they haven't seen the oil pressure side of the story.
Meaning, If I spend bucks on a top end, to find the bottom is getting bad...then I made the wrong choice...and I get to pay for it again.

[Viper]

I wouldn't do anything with the top end unless proper diagnostics lead to a definite conclusion that the bottom end is okay. If the findings lead to engine replacement, you can probably modify your boating habits to get through the season until a more convenient time of year when you don't boat as much if that's the case in your area.

I'm assuming you're salt water application and closed cooling?

[km1125]

What oil are you running it it now? What is your engine coolant temperature? Does the engine have an oil cooler, and are you sure it's doing it's job?? Do you know what the oil temperature is after running at speed??

Definitely need more diagnosis on the bad cylinder, but I agree, don't do anything to the top end until you figure out what the bottom end is doing.