Lower Oil Pressure as the season goes on . . .

[tpenfield]

I've been noticing that the oil pressure on my port engine has been looking lower as the boating season goes on . . .

It started out as being 30 psi minimum at idle and maybe 45 psi at cruising speed. . . .

Now it is looking more like 20 psi at idle and 35 psi at speed.

more noticeable when the engine is fully warm/hot from cruising for a while.

I am wondering if it is a sign of oil wear or perhaps something going on with the engine that would contribute to lower oil pressure ? :noidea:
The starboard engine seems to be fine, not showing a noticeable drop in pressure.

The oil is 10W 40 per the engine spec's (engine details in my sig below)

TIA for any thoughts.

 

[alldodge]

If the pressure is actually going down and its not just the gauge/sender then its either wear or oil thinning maybe. Reading of 20 at idle isn't bad after a run, mine use to be lower then that before the rebuild, and I was running straight 40W.

Have a mechanical gauge to put on it?
Isn't the port engine the one you did the de-carbon job on?

 

[Volphin]

I think I read somewhere that 7-10psi is the min. Agree that you should test it with a mechanical gauge.

 

[Bondo]

Hi Ted,.... That's not a Good thing, regardless the reason,....... Are ya into sendin' an oil sample for testin',..??

Changin' the oil, ' inspectin' the filter oughta be step #1 in yer diagnosis,......

Cuttin' apart the filter, may or may not tell ya the story,....

 

[Eric 3.7LX Alpha 1]

I think I read somewhere a rule of thumb is 10-psi per 1,000 RPM's

 

[tpenfield]

Thanks for the comments guys. Actually, it is the starboard engine that is doing the low pressure thing . . . had recalled it incorrectly. But still, one engine good and one engine bad . . .

Anyway, I have always noticed some psi drop as the season goes on with this boat and my previous boat. So, I have figured it to be wear on the oil.

I did de-carbs on both engines last year.

Yesterday, we were out in the boat . . . cruised around, did some tubing, cruised around some more. The psi stayed at or above 30 psi for the whole day. I noted when I first started the engines, the starboard engine was 37 psi and the port engine was 45+ . . . The starboard never went below 30 psi throughout the day, whereas the previous outing it got down to 20 psi.

Maybe I will replace the sender, check the wiring, etc just for good measure.

Oil levels are both full and show no signs of dropping over the past 2 months of weekend usage. Color is good, but it does taste pretty bad

I think I ran 20W-50 oil one year in my prior 454 Merc and the psi showed little/no signs of dropping throughout the season. This year I ran the typical 10W-40.

 

[tpenfield]

Quick update . . .

I checked/cleaned the electrical connections at sender and gauge for both engines, then gave them a test running just at my mooring. No real change.

port engine started - psi went right up to 42

Starboard engine started - psi went up to 27. I revved the engine to 2K and it went to 32 psi and then stayed there even at idle.

Both engines were cold. . . . ran them for about 5 minutes, just to see if the pressure would fluctuate . . . it did not.

It looks like the engines have the aftermarket senders on them and not the VDO brand to match the gauges. So, maybe my next step may be to just replace both senders with VDO brand. I believe the ohm range may be different between the VDO (European) and other brands of sender . . . like 10-180 vs. 240-33 , but not sure. :noidea:

I am wondering if the Starboard sender is getting flaky. More just a process of elimination.

 

[tpenfield]

Also been doing some reading . . . in general, low oil pressure can be caused by engine wear, oil viscosity reduction, pump wear, relief valve issues, oil filter. That seems like a healthy list of possibilities

this engine (starboard) has always run lower in pressure than the port engine (according to the gauges). (maybe I could swap the gauges as well . . . just to see)

 

[alldodge]

I don't think it's the sender. been a lot of time pass and nothing major showing up. Had my VDO gas gauge start hanging a couple years ago and did some looking and found another, it works fine now. Swapping the sender wires using a jumper would be the easiest

 

[tpenfield]

I swapped the gauges, as that was fairly easy to do.

Port side read 38 psi, then went to 50 psi when revved

Starboard went to 32 psi and did not increase when revved.

I'll probably just keep an eye on it for the season and fuss some more with it in the Fall.

 

[alldodge]

Unable to say with certainty but mine had lower pressure and my engine looked great when I pulled it apart. I would suggest stop using the 10Wxxx stuff, and use the 20W or straight 40W stuff. Your in a cooler climate so straight 40W might not be the way to go if you boat in the below 50 degree area

 

[tpenfield]

Yea, I think that I will go with the 20-50 stuff next year. Rarely if ever run the engines when it is below 50 degrees F.

 

[smokeonthewater]

Personally I put new senders on everything BUT it would only take you a few minutes to swap the senders and see if the issue follows.

 

[tpenfield]

Personally I put new senders on everything BUT it would only take you a few minutes to swap the senders and see if the issue follows.

The port engine would be easy . . . the starboard engine would take a long time. Impossible reach as the engines are very close together. That is why I am opting to do the senders over the winter.

 

[alldodge]

My opinion differs but oh well, so nothing new. There is no guarantee the new sender will work any better then the old one. Pretty much proved this within the margin of error that it's not the senders or the gauge during your swap. Only other thing is to put a mechanical gauge on it to see if it to reads the same, then the opinions go away and the reality makes the decision.

 

[HT32BSX115]

Yea, I think that I will go with the 20-50 stuff next year. Rarely if ever run the engines when it is below 50 degrees F.

Ted, If you're not sure of the gages, you might try a direct reading gage to verify for sure.

Not wanting to turn this into an oil thread (it is already isn't it?)..................... Back in the 90's, Consumer Reports did an oil test with several grades.

The biggest point I got out of it was they found that (NON-syn) 10W-40 doesn't stay in grade as well as the single grades or the others (straight 30/40, 15W40/20W-50 etc) did........And subsequently, they recommended NOT using (non-syn) 10W-40 for anything.

Most recreational boats don't really need a multi-grade since they rarely start-up in cold enough ambient temps to need the low-visc to facilitate cold-flow.

Having said all that, I think you'll find the 20W-50 working just like it did before.......


Regards,


Rick

 

[smokeonthewater]

Keep in mind that the mid 90's were 20 years ago.... I wonder if that info is still valid???

 

[HT32BSX115]

Keep in mind that the mid 90's were 20 years ago.... I wonder if that info is still valid???

It may not be at all.........Oil has changed greatly in all these years.

It is interesting that some still recommend against using 10W-40 though.......

From: http://www.aa1car.com/library/oil_viscosity.htm

Note: Motor oils that have a wider range viscosity rating such a 5W-30, 5W-40 and 0W-40 are blended with more base stocks and additives. Because of this, it may be harder for a wider range oil to remain in grade as the miles accumulate (which is why GM does NOT recommend using 10W-40 motor oil.

Maybe the 10W-40 thing is still "current". Mercury certainly doesn't seem to currently recommend using 10W-40 in any of their engines.....

 

[alldodge]

Only reason I'm running 20W50 Castrol now is because that's what the engine builder recommends. Once the year is out "if I actually have a warranty" , I'll probably go back to straight 40W

 

[HT32BSX115]

Only reason I'm running 20W50 Castrol now is because that's what the engine builder recommends. Once the year is out "if I actually have a warranty" , I'll probably go back to straight 40W

And of course..............like we all seem to say: Just about ALL oils have been tried and they all seemed to work .......