5.7 Mercruiser Carb Ski inboard Tee on Thermostat housing

[BarneyDTrubble]

I have a Mercruiser 5.7 carb ski inboard serial # 1a091889. On top of the thermostat housing is a tee with the hoses of either end of the tee leading to the exhaust manifolds. inside the tee is a rod with spring loaded balls. what does this do ?

 

[alldodge]

The check balls make sure the manifolds are full of water and keep water from flowing back toward the thermostat housing. Once everything is full of water, they keep most of the flow going from the bottom of the manifolds cooling them first, then out thru the elbows

Without them there the elbows will get more cooling and the manifolds can get to hot

https://www.mercruiserparts.com/bam/subassembly/31422/12843/170

 

[BarneyDTrubble]

Thankyou for replying. Any idea why with those check balls installed there would be more flow out one exhaust than the other ?

 

[Scott Danforth]

Thankyou for replying. Any idea why with those check balls installed there would be more flow out one exhaust than the other ?

your boat is leaning

the side that is higher gets less flow than the side that is lower

especially on muffs on the trailer at idle

 

[BarneyDTrubble]

That is exactly what I thought and thanks for your reply.

 

[BarneyDTrubble]

You may have thought to yourself, why is this guy looking at check balls and asking about waterflow. The motor is like new with only 5-6 20 gallon tanks run through it. We constructed a Glen-L Monaco and put the 5.7 CARB/SKI inboard right from the crate. It has a beep sounding out of the little horn that comes with the wire harness from day one. Running the engine anywhere over 1500 rpm may result in a blast, but it is usually when revving faster the horn sounds more often. Without the check balls in all of this beeping goes away. From the manual, a beep may indication of a water flow problem, The raw water intake is positioned near the stern of the boat as the plans indicate which results in a long 6 foot hose to get from the strainer scoop to the raw water pump. Yes the intake hose is correct with the wire reinforced un-crushable hose. A 90 degree elbow between the scoop/strainer and the intake hose is required to get the hose aiming towards the raw water pump towards the bow. Any suggestions would be very appreciative. I think the intake hose may be too long. Can't remember what the installation instructions with the crate motor said exactly, but I'll have to take another look at them.....Thank-you in advance !

 

[alldodge]

The warning horn sounds for:
Motor over heat
Trans temp over heat
Low oil pressure

Check your oil pressure with a mechanical gauge. If it is in good shape then most often the oil pressure switch is the issue. Not saying this is your issue, but its just what happens most often.

Your motor powers the alarm horn when the key is turned ON. The purple wire from the key switch applies power to the horn along with gauges and the motor. There is a Tan/Blue wire which goes to the 3 switches listed above. The 3 switches are not the same ones that display pressure and temp readings on the gauges

 

[BarneyDTrubble]

Thank-you. It's dark here now but will check tomorrow and report back. thanks again !

 

[BarneyDTrubble]

The oil pressure test resulted in a 41 psi at 750 rpm and 74 psi at 3000 rpm. Lot's of oil pressure. Disconnected the temp sensor dark blue/black wire on the velvet drive and the horn stopped sounding intermittently. The oil hoses leading to the cooler are barely warm after running WOT for a couple of minutes. Oil in the velvet drive is full, light clear pink and odorless. Thinking it could be a faulty sensor on the velvet drive or possibly a short in the factory wiring harness. Either way I will figure out what the problem is as I do not want to continue driving without the velvet drive sensor(although it was nice to drive without that ******* horn going off !). The crate engine installation manual says to make the intake hose as short as possible(No kidding !). Does not state what the maximum hose length could be(Thank-you Mercruiser !). With engine at 3000 rpm there is not much boat left in the water. the intake does not seem to be a problem now anyways. At WOT there is even less. Right now the intake scoop/strainer is port side, out of the path of the propeller and only about 3 feet from the stern. Thanks for the suggestions....really appreciated !

 

[BarneyDTrubble]

Finally eliminated the intermittent beeping horn ! From the very first day of operation, the fluid levels were continuously checked prior to operation. After reading both the engine manual and the installation manual and specifically the details about velvet drive fluid type and level. The velvet drive fluid level always indicated full when checked, however, the installation guide also refers to the velvet drive level having to be adjusted depending on the installation angle. Typical installation angle is approximately 8 degrees, but the installation angle necessary for this boat is 15 degrees. Adding 1/2 quart of transmission fluid increased the level enough to stop the warning horn from sounding intermittently. Sure am glad I reread those manuals before chasing down what I erroneously thought was a possible short in the wiring harness ! Happy Boating everyone !

 

[alldodge]

Typical installation angle is approximately 8 degrees, but the installation angle necessary for this boat is 15 degrees. Adding 1/2 quart of transmission fluid increased the level enough to stop the warning horn from sounding intermittently. Sure am glad I reread those manuals

Great info for others