engine oil pressure readings 5.7 Mercruiser

[tarps3]

I have a new-to-me 1997 Mercruiser 5.7 I'm sorting through at the moment.
I hade some widely varying engine oil pressure readings on my dash gauge (they seemed a little high).
At start-up and cold it would read around 60 psi; at 3000 RPM it would climb to around 70psi inching toward 80; at idle when warm it would be closer to 50 psi.

Well to double check everything, I plumbed in a glycerine-filled mechanical gauge and replaced the oil pressure sending unit with a new one. The dash gauge reads the same as before so the unit wasn't a problem.

However the mechanical gauge reads about 10 psi lower than the dash gauge.
So: 50 psi cold idle; 60 psi at 3000 RPM; 40 psi at warm idle.
The mechanical gauge readings are very stable at idle (warm and cold) and doesn't fluctuate at all so thats a good sign.

I'm running 25w-40 oil and I just changed it.

Do those pressures sound about right to you guys or is it a little high?

thanks.

 

[tpenfield]

Re: engine oil pressure readings 5.7 Mercruiser

I would then move onto the gauge as the culprit.

there could be an incompatibility between the gauge and the sender giving you the high readings . . .

 

[alldodge]

Re: engine oil pressure readings 5.7 Mercruiser

However the mechanical gauge reads about 10 psi lower than the dash gauge.
So: 50 psi cold idle; 60 psi at 3000 RPM; 40 psi at warm idle.
The mechanical gauge readings are very stable at idle (warm and cold) and doesn't fluctuate at all so thats a good sign.

I'm running 25w-40 oil and I just changed it.

Do those pressures sound about right to you guys or is it a little high?

thanks.

I don't see a problem with the readings, wish mine were that good. You verified the readings with a good gauge so no issue here. I would guess that if you got it out on plane the pressure would drop and bit after a while with a good gauge. When you slowed back to idle it would probably go a bit below 40, still just guessing.

Once you fix your gauge you will be able to keep a better eye on it.

 

[achris]

Re: engine oil pressure readings 5.7 Mercruiser

Just remember that the dash gauges are not 'precision instruments'. They are there to give the operator an idea of the rough value. If you have a look at the price of dash gauges, then you'd understand what I'm on about. I think an oil pressure gauge is about $40... If you want an exact reading on the values (oil pressure, water temperature, battery volts) you are going to need to spend a lot more than $40 a pop.... Also, electric gauges are rarely spot on... Again, if you desire that kind of accuracy, run mechanical gauges...

Reading 10 psi out is considered acceptable. And now that you know the variation of the gauge, you can mentally compensate...

Chris.......

 

[Scott Danforth]

Re: engine oil pressure readings 5.7 Mercruiser

your pressure is fine. your dash gauges are merely a suggestion

to expand on Chris's post, the OEM's pay much much less (read this as less than $5 per gauge)

to get exact readings, your going to pay for NIST traceable gauges and have then calibrated every year (at $100+ per gauge per calibration). I think the last time I had purchased NIST mechanical gauges from FW Murphy, I paid about $250 per gauge.

 

[tarps3]

Re: engine oil pressure readings 5.7 Mercruiser

thanks for all the good replies.

I'm not terribly concerned with the dash gauge accuracy now that I kow the REAL readings. It may not be spot-on but at least it's consistently wrong by about the same psi.
I'm leaving the mechanical gauge plumbed into the engine in any case. Looks cool and gives me good data.

I was more interested in hearing opinions about whether or not my oil pressure seemed too high for this engine.
Sounds like it's in good shape so i won't worry about it further.

thanks again.

 

[Bondo]

Re: engine oil pressure readings 5.7 Mercruiser

thanks for all the good replies.

I'm not terribly concerned with the dash gauge accuracy now that I kow the REAL readings. It may not be spot-on but at least it's consistently wrong by about the same psi.
I'm leaving the mechanical gauge plumbed into the engine in any case. Looks cool and gives me good data.

I was more interested in hearing opinions about whether or not my oil pressure seemed too high for this engine.
Sounds like it's in good shape so i won't worry about it further.

thanks again.

Ayuh,.... Welcome Aboard,... I'm doin' a set of mechanical gauges at the motor on my latest build too,....

the "Trick" is always findin' a spot the ain't "In the Way",...

 

[Silvertip]

Re: engine oil pressure readings 5.7 Mercruiser

GM oil pressure spec is generally 10psi for every 1000 rpm. That would be minimum numbers. The engines will normally idle with about 20 - 40 psi with the pressure relief valve opening at about 60 PSI or more at the higher rpm. The long and short of this is that if at cruise rpm oil pressure is between 40 and 60 psi you have a healthy engine.

 

[Walt T]

Re: engine oil pressure readings 5.7 Mercruiser

When I build an engine it comes with a mechanical gauge plumbed into the system along with overheat indicator discs on the heads and block. If I install the engine the gauge is installed so it can be seen when raising the cover. Since a lot of my customers are mechanics and just buying long blocks the gauges are supplied in a bag with the block. It's really nice to have that gauge there when spinning up the oil pressure with a drill for pre lube. No question oil pressure is there with those. As for the discs, they say warranty is void if overheated, or removed. 'Nuff said.

 

[tarps3]

Re: engine oil pressure readings 5.7 Mercruiser



here is a diagram of how I added the gauge.
There are nipples you have to buy to join it all together - get a variety so you can more easily adjust where everything is.
I can lift the rear cover up from my engine compartment and easily see the gauge. I bought it at harbor Freight for 11 bucks. The brass fittings ran me another 8 dollars or so.
pretty easy once you figure out where it all fits.