3.0 Mercruiser idling problem when cold

[Chopp]

Hi I have a ‘93 Sea Ray 170 with the 3.0. So when I drop the boat in the lake and start it, I prime and it starts but only with throttle. And I have to continue to do so until it warms up a bit, so I have to sit at the landing and let it warm up enough to idle to shift it in gear to get out of the way. My idle when warm and in gear is roughly 500-700rpms, it depends. I did replace the cap and rotor, wires and plugs. Carb seems to be okay, and the fuel mixture screw I set “properly.” Is this normal? And another thing I notice, it appears to have 20-25psi for oil pressure idling and 35-40psi at WOT. Is this normal? I bought the boat over the winter and haven’t changed the oil as it was changed during winterization. Should probably change it.. which leads to 10w30 oil like it says on the cap, or the 25w40 as Merc recommends?

 

[TunaFish389]

Your idle is normal, while the carb has a slight fast idle cam its not like a cars that is stepped.. Best thing to do is walk boat to non loading side of dock. You oil pressure is good also, 10 psi for every 1000 rpms is a good rule. Oil weight is like asking what football teams the best.. I like 5w30, thinner on the cold and average on the warm side. If they had cheap 0w30 I would run that..

 

[Chopp]

Alright, thank you!

 

[Bondo]

And I have to continue to do so until it warms up a bit, so I have to sit at the landing and let it warm up enough to idle to shift it in gear to get out of the way.

Ayuh,..... Yer choke might be out of adjustment, 'n no boats don't have a hi-idle cam, as the throttle does that,......

I run 15W-50 Rotella motor oil myself,....

 

[alldodge]

Agree, choke needs adjusting

 

[TunaFish389]

(Edit: personal attacks will not be tolerated)Anyways nothing you mentioned even points to choke being off.. The rpm are low due to cold and lack of a meaning full fast idle cam (which it does have). A choke issue would be if you mentioned hard cold starting. You are perfectly normal.

 

[Chopp]

How do you adjust the choke? I noticed when I first got it that it was a little stuck, sprayed some WD-40 on it and it moves more freely. The choke currently leaves a little gap, and runs half choke for awhile then opens up after a good bit

 

[alldodge]

Adjustments

 

[TunaFish389]

https://youtu.be/LN3qJrQS3Sg
this pretty much sums it up.

 

[Chopp]

Thank you guys, I appreciate the help

 

[Bt Doctur]

and the fuel mixture screw I set “properly. By properly you mean you opened the mixture screw until it ran rough. then in until it go smooth then a 1/2 turn out again?

 

[Chopp]

I backed it in, and out 1 1/4 turns. It ran a little rough, so I turned it out another 1/4 until it idled smooth, if I were to go more, Around 2 turns out, it would start to idle rough. So it’s around 1 1/2 turns out

 

[Scott06]

Your oil pressure matches what I saw on mine, I ran everything from straight 30, 10w30, merc 25W40, and 20w50. As it got older the heavier oil kept pressure at higher rpms up at 45-50. Had the same boat as you except it was a 91, tended to drive it pretty hard towing tubes skiers etc. as mentioned above 10 psi per 1000 rpm and it will live a long life

 

[Chopp]

Your oil pressure matches what I saw on mine, I ran everything from straight 30, 10w30, merc 25W40, and 20w50. As it got older the heavier oil kept pressure at higher rpms up at 45-50. Had the same boat as you except it was a 91, tended to drive it pretty hard towing tubes skiers etc. as mentioned above 10 psi per 1000 rpm and it will live a long life

I don’t do a lot of tubing, but I’m glad the pressure is alright. It’s a lot different than my vehicles, my car is around 100psi so it threw me off a bit

 

[Scott Danforth]

the 3.0 is a fairly mild industrial engine with cam in block, not a high-strung high-output OHC engine which requires lots of oil pressure to get top-end lubrication to keep the cam from eating the head. you cant compare it to your typical car. you can compare it to an old tractor or an old pickup truck motor.

the stock oil pressure spring is a 50 psi spring.
you wont get more pressure than that. bearing tolerance is nominal, however the cam and lifters on an in-line are sloppy as can be. the 10psi per 1000 RPM is a good rule of thumb.

if you boat in warm climates, run a higher viscosity oil. if you run in cold climates, run a lower viscosity oil

 

[Chopp]

the 3.0 is a fairly mild industrial engine with cam in block, not a high-strung high-output OHC engine which requires lots of oil pressure to get top-end lubrication to keep the cam from eating the head. you cant compare it to your typical car. you can compare it to an old tractor or an old pickup truck motor.

the stock oil pressure spring is a 50 psi spring.
you wont get more pressure than that. bearing tolerance is nominal, however the cam and lifters on an in-line are sloppy as can be. the 10psi per 1000 RPM is a good rule of thumb.

if you boat in warm climates, run a higher viscosity oil. if you run in cold climates, run a lower viscosity oil

I’m in Wisconsin so it’s warm, sometimes a little chilly. Maybe a 10w40?

 

[Scott Danforth]

I’m in Wisconsin so it’s warm, sometimes a little chilly. Maybe a 10w40?

Wisconsin is not that warm. other than two weeks at 90 degrees in the summer, most of the boating year is between 40 and 80

you would be fine with SAE30 or 10W30 in Wisconsin. I personally would run Rotella T 15W-40