[Dakota773]

Ok Tiara lovers I have a follow-up post with more complete summary of my situation and am looking for input - help!

Need some help and clarity to an oil type & pressure issue I’ve been having with my pair of Crusader 454’s in my 98 Tiara 31.  Early this year the oil pressure in my starboard engine dropped to 0.  I was idling along and proceeded to stop & restart thinking / hoping it was a gauge or electrical issue.  Sure enough the gauge read normal after restarting.  Well, 10 min later it happened again, neither time did the oil pressure alarm sound.  We got home carefully and following the guidance of a great Tiara Owner Forum I dug deeper. I swapped gauges and the problem persisted leading me deeper into the engine as the root cause.  I proceed to change out the oil and filters with manual defined 5W-40 oil (note that the yard had done the preseason oil – filter change), and the problem seemed to go away. Well again the problem showed up a little later, but more as a less abrupt, up – down issue, meaning the pressure on the gauge would fall to 0-10 PSI for a time and then rebound to more normal, only to reoccur occasionally and randomly.   Now, I’ve got the port engine (without any drop out pressure issues) running 50-70 PSI and the starboard engine running 40-50 PSI and occasionally dropping or running down to 0-10 PSI for minutes at a time (variance depending on running RPM’s). The normal PSI spread is a pretty big differential, isn’t it?   What could be causing this? Should I worry? Did the yard gunk me up with bad or the wrong oil?


I’ve checked for leaks and all, and the bilges are clear. Oil levels are ok and the oil & filters have been changes 2x now as well, and last season’s oil analysis was perfect.
Also, my 4 wheel gear head have advised that I use 5W-40 diesel engine oil as it has zinc in it  and is better aligned with the vintage engine blocks of my older 454’s.  Presumably, the zinc takes the place of the lead in the cylinders that has been excluded from the now lead free gas.  Is this true and or does it add any value or do any harm?

[ReelMagic]

My experience w/454's, 1997 31 Tiara open was 15W40 (in owners manual) not 5W40 as mentioned in your post. Was this an error or do you really use 5W40...... I believe 5W40 is to light for engines always running under a load..... M2C

[Dakota773]

OOPS, Sorry all I was/am  using 15w40.  

[Uhehner]

I hope he means 15W-40. He should be running heavy duty oil, not 5W-40.  Also he stated he swapped gauges. What about the oil pressure senders, those 2" round senders that screw into the oil pressure line and have a variable resistance inside that drives the gauge? The oil pressure alarm is turned on by the oil pressure switch, also screwed into the oil pressure line but an entirely separate circuit. I suspect he has a bad oil pressure gauge sender, a common failure point. If it's not the sender, I would look for an intermittent in the wire that goes between the sender and the gauge. It should be a light blue 14 ga. wire and go through the instrumentation connector pin 8. Screw in a new OP sender, about $40 and an easy DIY. Capt. George

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Type "Crusader oil pressure sender" in eBay and look at the brass colored units so you know what to look for on your engine. Then specify single or dual station, depending on whether or not you have a tower with gauges. Capt.  George

[ReelMagic]

I would agree w/Uhehner as it appears, from the description, the oil pressure alarm on the engine is not going off. Had similar problem when I owned the 31 w/454's. Changed the sensor on the engine and problem went away. May sure replacement sensor meets the requirement of the gauge.

[justrollin]

I have a 31ft 1998 with 454,s and I use the straight 40w Rotella for gas and diesel engines with plenty of preasure and no oil issues

[Dakota773]

You guys are the BEST.  Cpt George, especially

I know the crew would step up.  I'll check - replace the sensors this winter, plenty of time and let the crew know.

Thanks all!

[stugiv]

Sounds like a problem I had on a similar vintage Mercuiser 454. Oil pressure was fine at startup & would slowly drop. Turned out it was the oil sender on the engine. They have diaphragms inside & if it has a tiny leak the oil slowly leaks to the side with lower pressure until they equalize. After shutting down, the oil will drain out & it will work again for a little while.

New senders are a pretty cheap & easy fix if that's the problem.