oil alarm / low motor tank

[big tom]

Hey guys looking for some opinions. I have a 31 fountain twin 250 efi's. Last time out I got a low oil alarm, we were only a mile from the ramp so I came in on one engine. To settle my wifes nerves when we were putting the cover on I dumped a gallon down that side. lol. So we need fuel next time out and that's when I usually top off oil tanks. So I top off the side I didn't pour the gallon into and it takes 1 1/2 gallons and the side I had dumped the gallon in only takes 1/2 gallon. So I pop the crowling off and the motor tank is down just enough to set the alarm off, float switch moves free, top it off, no alarm. Going to trace hoses for kinks next. I have read on here about some hull tanks have filters, but not seeing them on merc's parts diagram. I have also read some guys pull there tanks to clean them?. Could there be enough sludge in them to plug the pick up tube?. boat is a 1999 with 850 hours of fresh water use. Talked to a couple mechanics and one said to check caps on tanks for tightness and another said that he has seen this happen once in a while. fill it and run it. I'm a life long boater but these are the first set of O/B's ive had so its a learning curve for me. I was also told these draw oil thru crank case pressure?. Any suggestions would be helpful.. thanks tom.

[vnemous]

there is a valve on the starboard side of the block that the oil line is attached to. This sends air the boat tank and pressurizes it so it can send oil to tank on engine. These often go bad. Common problem and is something to check. JMO

[big tom]

there is a valve on the starboard side of the block that the oil line is attached to. This sends air the boat tank and pressurizes it so it can send oil to tank on engine. These often go bad. Common problem and is something to check. JMO

vnemous, thanks again. I will check the valve out.

[big tom]

The motor tank looks like maybe 2 quarts ?. Not that I would run it just on the motor tank, but what kind of run time can one get out of the motor tank if I needed ?. One guy was telling me like an hour ?.

[big tom]

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Mercury | MERCURY | 250 (3.0L EFI) | 0G760300 THRU 0T408999 | Oil Injection Components


Mercury > MERCURY > 250 (3.0L EFI) > 0G760300 THRU 0T408999 > Oil Injection Components >

Ref	Description	Qty	Price
1	TANK ASSEMBLY, Oil Part No: 830889A1	1	80.67 72.60	Add to Cart
2	TANK ASSEMBLY, Oil Part No: 818456A1	1	74.90 67.41	Add to Cart
3	SPACER Part No: 8260841	1	5.60 5.04	Add to Cart
4	SCREW, (.164-18 x .375) Part No: 58376	1	0.88 0.79	Add to Cart
5	WASHER, (.203 x .562 x .060) Stainless Steel Part No: 72761	1	1.15 1.04	Add to Cart
6	NOT SOLD SEPARATE, Decal-Oil Tank Part No: NSS	1	0.00
7	CAP ASSEMBLY Part No: 814449A3	1	20.40 18.36	Add to Cart
8	GASKET Part No: 42999 42999T	1	10.20 9.18	Add to Cart
9	SWITCH ASSEMBLY Part No: 12886A7	1	19.00 17.10	Add to Cart
10	BUSHING Part No: 19064	3	16.60 14.94	Add to Cart
11	GROMMET Part No: 825380 825380001	3	5.50 4.95	Add to Cart
12	WASHER Part No: 49436	3	0.60 0.54	Add to Cart
13	SCREW, (M8 x 35) Part No: 81893435	3	2.80 2.52	Add to Cart
14	HOSE, (57.00 Inches Bulk) Part No: 830756109 8M0108355	1	45.00 40.50	Add to Cart
14	HOSE, (57.00 Inches Bulk) Part No: 830756109 8M0108355	1	45.00 40.50	Add to Cart
15	FITTING Part No: 424254	1	33.30 29.97	Add to Cart
16	SCREW (M5 X 30) Part No: 82104530	1	1.10 0.99
17	PUMP, Oil Part No: 815536T1	1	347.33 312.60	Add to Cart
18	O-RING Part No: 11379	1	3.40 3.06	Add to Cart
19	O-RING, (.614 x .070) Part No: 48462	1	1.30 1.17	Add to Cart
20	BEARING, Driven Gear Part No: 817631	1	19.50 17.55	Add to Cart
21	GEAR, Driven Part No: 430204	1	56.34 50.71	Add to Cart
22	BEARING, Thrust Part No: 816974	1	12.80 11.52	Add to Cart
23	SCREW, (M5 x 20) (M5 X 20) Part No: 82104520	1	2.20 1.98	Add to Cart
24	TIE STRAP, (8.00 Inches) Part No: 816311T	0	0.44 0.40	Add to Cart
25	TUBING, (25.00 Inches Bulk) (8-3/4 IN.) Part No: 82381455	1	20.10 18.09	Add to Cart
26	TUBING, (15.00 Inches Bulk) (7 IN.) Part No: 82381335	1	7.70 6.93	Add to Cart
27	TANK Part No: 87421	1	61.66 55.49	Add to Cart
28	CAP ASSEMBLY Part No: 43298A2	2	26.40 23.76	Add to Cart
29	NOT SOLD SEPARATE, Insert Part No: NSS	1	0.00
30	O-RING, (2.225 x .210) Part No: 11332	1	3.40 3.06	Add to Cart
31	SENDER ASSEMBLY, Oil Level Part No: 816190A4	1	141.33 127.20	Add to Cart
32	O-RING, (2.225 x .210) Part No: 11332	1	3.40 3.06	Add to Cart
33	TUBE Part No: 99802	1	13.70 12.33	Add to Cart
34	HOSE, (114.00 Inches) Part No: 99439	1	75.70 68.13	Add to Cart
35	BRACKET KIT Part No: 12335A1	1	68.00 61.20	Add to Cart
36	CORD/HOOK KIT Part No: 12323A1	1	14.92 13.43	Add to Cart
37	NOT SOLD SEPARATE, Decal-Caution Remote Tank Part No: NSS	1	0.00
38	HOSE Part No: 858853	1	93.09 83.78	Add to Cart
39	TIE STRAP, (8.00 Inches) Part No: 816311T	2	0.44 0.40	Add to Cart
40	CONNECTOR Part No: 858955	2	2.50 2.25	Add to Cart
41	NOT SOLD SEPARATE, Cap Part No: NSS	2	0.00

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The vavle we are talking about is no# 15

[vnemous]

Thats not the valve I am talking about. follow oil line to starboard side of block. It takes air from crank case.

Hint oil tank is on port side of motor

[vnemous]

part number 8781051 called a check valve part is #7

[big tom]

Wow, my bad. Thanks again. I should have listened more closely. Its raining here and I was trying to find it in the parts listing so I know what I was looking for. Never would have looked in the "Cylinder block and end caps" page. How does one test it?. It should allow air out from crank and not in?.

[vnemous]

if you pull the hose off it while engine running it will "puff puff puff puff" etc Like a baby air compressor Or you can pull hose off on tank in boat and see if it puffs. If I remember the hose with blue line goes to tank on motor.

[big tom]

if you pull the hose off it while engine running it will "puff puff puff puff" etc Like a baby air compressor Or you can pull hose off on tank in boat and see if it puffs. If I remember the hose with blue line goes to tank on motor.

Cool, thanks again. I'll start there and check lines for kinks.

[flabum1017]

Make sure the oil tank caps are on tight. Any leak will cause the tank not to gain the pressure it needs to send the oil to the engine. Soapy water is your friend here, run the engine for about five minutes then start spraying the soapy water on the caps, tank, oil hoses and fittings (with the engine still running)

[big tom]

Make sure the oil tank caps are on tight. Any leak will cause the tank not to gain the pressure it needs to send the oil to the engine. Soapy water is your friend here, run the engine for about five minutes then start spraying the soapy water on the caps, tank, oil hoses and fittings (with the engine still running)

Thanks, I will mix up some soapy water and check everything out when I check valve. Thanks again.

[vnemous]

We serviced one last week where the pressure side hose had disintegrated causing an air leak. Of course it was under the deck and hard to get to. A very simple way to check if making pressure is disconnect the hose from the top of the tank on engine. With it running you should have oil coming out of hose. If not chase it back.