898 Mercruiser - Normal Oil pressure on start up?

[TheBigToy]

Just got a 1978 Glastron Carlson... Original low hour, 898 / pre-Alpha package. Working on numerous small problems that the seller swore did not exist...
Sigh...

On cold start - 900-1000 RPM, the oil pressure is about 25 psi (new gauge, new sender..). Haven't run it long enough to see what it is at higher temps or RPM.

Seem normal?

 

[achris]

Hello TheBigToy and :welcome: to iboats.

That oil pressure seems fine.

Do you have the Merc genuine manuals for the 305 GM engine and MC-1 drive you're working on? (No such thing as a 'pre-Alpha')..

Chris.....

 

[TheBigToy]

Thx, Chris.

I know it's a MC-1...
Haven't downloaded the manuals... yet...

 

[Scott Danforth]

with a small block chevy, 10 psi per 1000 RPM is the rule of thumb for oil pressure.

if you switch to 15W40 or 20W50 oil from the SAE30 weight your oil pressure will be higher.

 

[QBhoy]

For me...no. That’s far too low. But I also know the manual will say it’s ok. My oil pressure will be twice that when cold and never below 40 psi when warm at any rpm.

 

[achris]

For me...no. That’s far too low. But I also know the manual will say it’s ok. My oil pressure will be twice that when cold and never below 40 psi when warm at any rpm.

So, you know better than the engine manufacturer?

I dare say this engine has been tested and trialed more times than you and I have had hot dinners. I'm pretty sure the manufacturer's engineers know a bit more about it than you do.

Spec says Minimum oil pressure at idle (warm) is 4psi. Oil pressure at 2000rpm (warm) to be 30-60 psi.
If the engine fulfills that requirement, it's fine. Nothing wrong.

BTW, if you're reading 40psi at idle on a warm engine, check your gauge, there's something wrong with it!

Chris......

 

[Lou C]

I’m not saying that’s a problem but on my engine after a cold start at 1200 or so Rpm I always have had 45-50 psi oil pressure. The only time it drops below 40 is after coming off plane at a hot slow idle, the lowest I’ve seen is about 22 psi, this is using 30, 40, or 25/40.

 

[QBhoy]

So, you know better than the engine manufacturer?

I dare say this engine has been tested and trialed more times than you and I have had hot dinners. I'm pretty sure the manufacturer's engineers know a bit more about it than you do.

Spec says Minimum oil pressure at idle (warm) is 4psi. Oil pressure at 2000rpm (warm) to be 30-60 psi.
If the engine fulfills that requirement, it's fine. Nothing wrong.

BTW, if you're reading 40psi at idle on a warm engine, check your gauge, there's something wrong with it!

Chris......

Chris. I’ve discussed this before....I know what the manual says...but I don’t know of any engine that runs the oil pressure that the minimum accepted is in the manual. It’s almost ridiculous in what it suggests.
With regards to min oil pressure at idle. 100% verified with the ecu data readout too. Let there be no doubt. Every other mercruiser I’m familiar with in the marina will run 40 psi at idle at the start of the season and fresh oil.
I am not too familiar with the big blocks at all, but the above certainly refers to all 4.3, 5.0 and 5.7 and I’ll even throw in 3.0 too.
the only time my idle oil pressure on any of my engines, ever dropped into the 30’s was at the end of the season and when using the horrendous 25w40 quicksilver standard junk of an oil.

 

[QBhoy]

So, you know better than the engine manufacturer?

I dare say this engine has been tested and trialed more times than you and I have had hot dinners. I'm pretty sure the manufacturer's engineers know a bit more about it than you do.

Spec says Minimum oil pressure at idle (warm) is 4psi. Oil pressure at 2000rpm (warm) to be 30-60 psi.
If the engine fulfills that requirement, it's fine. Nothing wrong.

BTW, if you're reading 40psi at idle on a warm engine, check your gauge, there's something wrong with it!

Chris......

As soon as I’m allowed in the water on the boat Chris, I’ll send you a selection of videos from a 350 mpi, a 4.3 mpi and a 5.0 mpi all reading from smart craft at 38-40 psi at idle and up to temp. The 5.0 mpi in particular I know runs dead on 40 psi at idle and at 151-155 degrees. If I was anything below 30 psi I’d be asking for a tow home because something was far wrong with any of these engines. 100%

 

[Lou C]

I tried to upload a pic but it’s not letting me. Cold start/ fast idle 40-50 psi, running on plane 55-60...then after dropping off plane it drop to about 22-25 at hot slow idle at the lowest. However after idling for about 5-10 min it’s back up to 40 at idle. Always been this way, the short block is original 32 years old with reman cyl heads installed 3 years ago.

BTW not a Chevy but our ‘98 Jeep at 180,000 miles has always been between 30-45 psi. Never lower than 30 at idle, highest in cold weather is about 55 psi.

 

[TheBigToy]

Thx for the replies, although I hoped for a little more consistency...

I did get to run it yesterday for about 40 mins. The pressure came up with RPM as it should, but dropped pretty low idling back to the ramp - less than 20 psi, which concerns me. No idea what oil is in there, but will be changing to 25-40 before trying again. I'm in TX, so more viscosity is warranted.


Separate issue for any willing to help - Ran fine at varying RPMs out on the water, couldn't open it too much due to small boat in chop (18 ft Glastron Carlson). Very slight hesitation off idle but not a stumble. But at the end of the ride, when tied up, idling in neutral, waiting to trailer - it died. Wouldn't re-start without 1000+ RPMs worth of throttle. Temp on gauge was below 180.
When cold, it starts immediately and idles perfect.
As I don't know the history of the boat, my mind goes to corroded exhaust risers causing excessive heating. I got it still winterized from the Northeast, and the water coming out of the freeze plugs on the hose was clean.
Also - maybe a maladjusted electric choke..?
I'm not a fan of pulling the risers just to see if they are bad, but will - if there are no better suggestions / troubleshooting advice.

TIA

 

[QBhoy]

Thx for the replies, although I hoped for a little more consistency...

I did get to run it yesterday for about 40 mins. The pressure came up with RPM as it should, but dropped pretty low idling back to the ramp - less than 20 psi, which concerns me. No idea what oil is in there, but will be changing to 25-40 before trying again. I'm in TX, so more viscosity is warranted.


Separate issue for any willing to help - Ran fine at varying RPMs out on the water, couldn't open it too much due to small boat in chop (18 ft Glastron Carlson). Very slight hesitation off idle but not a stumble. But at the end of the ride, when tied up, idling in neutral, waiting to trailer - it died. Wouldn't re-start without 1000+ RPMs worth of throttle. Temp on gauge was below 180.
When cold, it starts immediately and idles perfect.
As I don't know the history of the boat, my mind goes to corroded exhaust risers causing excessive heating. I got it still winterized from the Northeast, and the water coming out of the freeze plugs on the hose was clean.
Also - maybe a maladjusted electric choke..?
I'm not a fan of pulling the risers just to see if they are bad, but will - if there are no better suggestions / troubleshooting advice.

TIA

Hi

180 degrees would be on the verge of overheating, I’m almost certain. That would explain the low oil pressure, with the oil being very warm and losing its viscosity some.
Maybe a good idea to verify that temperature perhaps. I suspect you might be 10 degrees at best over the highest of the temp tolerance. Just off the top of my head.

 

[TheBigToy]

It never got to 180, but I've read Temp on the gauge doesn't tell the whole story.

I'll be pulling some hoses, and checking inside the elbow and more - over the next several days.

BTW - is there an explanation of the 3 drain, 7 drain, ??? drain differences..?

 

[alldodge]

You have been running for a while so motor is warmed up, the choke should be wide open and have no bearing on idle. If choke is not wide open then it needs adjusting

Check temp with IR temp gun to verify, electric gauges can be off even when new

The motor dying at idle would be carb issue of which needs adjusting or rebuild

If oil pressure is correct (check with mechanical gauge) then your motor may just be a bit tired where over time bearing clearances would be a bit more

 

[QBhoy]

I tried to upload a pic but it’s not letting me. Cold start/ fast idle 40-50 psi, running on plane 55-60...then after dropping off plane it drop to about 22-25 at hot slow idle at the lowest. However after idling for about 5-10 min it’s back up to 40 at idle. Always been this way, the short block is original 32 years old with reman cyl heads installed 3 years ago.

BTW not a Chevy but our ‘98 Jeep at 180,000 miles has always been between 30-45 psi. Never lower than 30 at idle, highest in cold weather is about 55 psi.

Spot on Lou. This would be aligned with my point made earlier. Exactly what I’d expect too.