Low oil alarm at idle

Beastly1 · **Joined:** Tue Mar 24, 2015 9:50 am **Posts:** 13

1990 Four Winns Vista 245
1990 OMC 5.7 350 chevy with cobra out drive

Bought the boat last week, took it out yesterday for the first test run.
Here is what I have done prior to the test run, and a brief history of the boat,

Changed engine oil, greased splines and gimbals, checked all fluid levels and topped off where necessary, added 20 gallons of fresh premium gas,

Single owner boat since 1990, stored winters and taken care of, engine runs great, but has not been run for 2 years.

Here's the problem, While sitting at idle in both neutral, and drive, the low oil alarm blares (oil is topped off perfectly in the "safe"zone on the dipstick) . As soon as it is given throttle the alarm stops.

The alarm didn't sound until I put brand new oil in, I ran it with the old stuff for about 10 minutes in order to change it.

After pulling out of the water yesterday (first test run!), I did notice that the lower stern drive rubber transom seal exhaust bellows was shot. Old, Crusty, falling to pieces. Have a replacement on the way.

Question.....Could the lack of back pressure from the exhaust not being directed through the lower unit housing cause the low oil alarm to sound?

I'm really hoping this isn't going to be an oil pump issue, do not want to have to pull the whole motor to replace that thing.

Also, Carb (Holley) is a little dirty, will be pulling and cleaning this week as soon as the replacement gasket comes in.

Engine runs great from just above idle, all the way through wide open, and also into long arcing turns at top speed. Alarm only sounds at idle.

Any thoughts or suggestions are much appreciated! LouC? ric? Anyone?

Have a few nights trip planned for may over on lake powell, and want to make sure all is well.

Thanks in advance for any replies!

Winter Sux · **Posted:** Sun Apr 05, 2015 4:01 pm

Didn't do this with the old oil you say. I'd be willing to bet the old owner added STP or another additive to thicken up the oil to cover up this problem. Assuming you used the proper viscosity oil, I'd put in a new oil pressure sending unit. They do get weak over time and will give the exact symptom you are experiencing. They do require a special socket though but if access is good, Channel locks will do the job. Use a little pipe sealer on the threads to prevent any leaks.

deafwish · **Posted:** Sun Apr 05, 2015 5:26 pm

What oil viscosity did you use?

Beastly1 · **Joined:** Tue Mar 24, 2015 9:50 am **Posts:** 13

10 W 30 conventional.

LouC · **Posted:** Sun Apr 05, 2015 7:21 pm

When the alarm sounds what does your oil pressure gauge on the dashboard say?
At idle you should be seeing at least 15-20 psi. If your op reading is normal check the wiring at the sensor for corrosion; excessive resistance can cause erroneous readings.
On my old '88 4.3, the cold idle pressure is 40, hot is about 20 at the lowest . I use Merc 25/40 motor oil but have used straight 30 in the past, worst comes to worst put a manual gauge on it to make sure.

ric · **Posted:** Sun Apr 05, 2015 7:28 pm

10w30 in a small block chevy will not cause a low pressure at idle unless the engine bearings are worn out.

What is the oil pressure at idle? What is the oil pressure at 3000rpms? When warmed up the idle oil pressure should be at least 15-20psi and at cruise RPM should be 40+

Either the sending unit is bad, or like someone else said... the previous owner added a thickening agent to the oil to mask the worn out engine.

How many hours?

deafwish · **Posted:** Mon Apr 06, 2015 2:26 am

Read your manual.
Nowhere will it state to use a 10w30 in a flat tappet, carbureted SBC in a marine application.
Go and buy either a mono 30 truck oil, a 20w50 performance auto oil (one with high zinc/ phosphorous) or ideally a marine 25w40.

ric · **Posted:** Mon Apr 06, 2015 8:59 am

deafwish wrote:

Read your manual.
Nowhere will it state to use a 10w30 in a flat tappet, carbureted SBC in a marine application.
Go and buy either a mono 30 truck oil, a 20w50 performance auto oil (one with high zinc/ phosphorous) or ideally a marine 25w40.

it might not be the recommended oil weight, but that wouldn't cause low oil pressure.

pickledboater · **Posted:** Mon Apr 06, 2015 7:59 pm

My 99 was doing the same thing and here is what all I have done:
I run straight 30 weight oil, and change it mid-season.
I ran a dedicated ground wire from the oil pressure sending unit to the gauge.
I use a k&n oil filter with a check valve in it.
Not sure if one, or all of the above worked, but the alarm doesn't go off at idle anymore.

P.S. Make sure your idle is set correctly and not too low.

www.iFourWinns.com

Low oil alarm at idle

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