Oil Pressure questions, 98 LT1

[keith]

Today was the first use of season and I noticed something different.

Last year, oil pressure was always 40psi or lower, I had the oil changed last week, and the mechanic put in SAE40, (got the boat near the end of last year, no idea what type of oil was in it) and now the oil pressure spikes to about 78-80 psi on acceleration then drops to 65-70 when on plane.

Is this due to the thicker oil?

We could also hear a faint rapping that sounded like a lifter, that was not present last year.

I read some other posts from a few years ago mentioning this, but there were no solid answers, help!

Keith
NH

[tommcat]

cant remember my typical pressures but i know my manual calls for 20W50 oil. i prefer a racing oil due to higher zinc levels

[BrianM]

Manual calls for 20w50 but Indmar now reccomends 15w40. I would use one of those two. I think I would go back to the mechanic and tell them to change it again for you with the proper oil. Hope this was not an MC dealer. Don't know why they would put straight 40w oil in it.

[Datdude]

my 1995 LT-1 does the same thing. The pressure is normal while idling and cruising under 10mph, but as soon as I get up on plane the pressure is usually maxed out on the guage. After a short time it will come down slightly, but is still on the high side. I have talked with a few boat mechanics and they said "high pressure is better than low pressure".

[wtoddburns]

My 01 Predator does the same thing...

[Thrall]

Same as mine. Oil pressure flutuates between about 30psi on the guage at idle (warm) to 60-80psi accleerating.
The noise you might hear is the injectors. I can hear them ticking a little.
I've used 10W40 and 15W50 oil in mine. Without starting an oil debate, as long as the 40W that's in it is up to date API certified oil and is not "non detergent" (some straight weight oils are for older engines) you are fine IMO.

[Maristar210]

Mine bounces around 30 psi until I hit it then it pegs at 80 psi and setlles at 65psi. In this case more is better withing reason. If you were to say you have 15 psi I would be worried as opposed to 80 which I think is relatively normal.

[93ProStar205]

Warm with Mobil 1 10w30 (previous owner's choice) my LT-1 is at 10-15 PSI at idle and 45 PSI underway. I am upping it to Mobil 1 15w50 as I do not like low oil pressure in a high-po engine (particularly in the warm water of NC lakes).

[trickskier]

Warm with Mobil 1 10w30 (previous owner's choice) my LT-1 is at 10-15 PSI at idle and 45 PSI underway. I am upping it to Mobil 1 15w50 as I do not like low oil pressure in a high-po engine (particularly in the warm water of NC lakes).

I talked directly to Indmar several months ago about running a lighter weight oil and the answer was ABSOLUTELY NOT!!!

They said due to the Higher RPM's and the engine operating in an enclosed environment it needed the heavier oil.

Like BrianM said either use 20W-50 or Marine 15W-40.....

The Mobil-1 15W-50 is OK too but you'll still need to change the oil & filter every 50 hours......

[SkiEngr]

Just stumbled upon this thread after a search. I noticed the same problem yesterday. I just had my MC serviced by the dealer and noticed with I "gun it" the oil pressure spikes around 80. Seem strange to me.

[P-hat_in_Cincy]

Mine does the same thing (40 at idle, pegs upon acceleration, falls slighty). I got a manual oil pressure gauge from Harbor Freight for about $10. I'm going to throw that on to make sure the gauge and/or sender is not faulty.

[Chief]

Mine does the same thing (40 at idle, pegs upon acceleration, falls slighty). I got a manual oil pressure gauge from Harbor Freight for about $10. I'm going to throw that on to make sure the gauge and/or sender is not faulty.

Same here.

[JohnnyB]

Same here. My 04 PS 197 has a 5.7 Predator Engine. I know at cruising speeds (34-40) it site in the 70-80psi range.