Mercruiser 5.0 v8 water pressure sending units and caps

[dlogvine]

Putting together Mercruiser 5.0 v8 1993 engine. Both sides of the block have an opening that a water pressure sending units or a cap can go in. Also there is another opening on the exhaust that has the same diameter. I have a couple sending units that I believe are left from disassembly. The question is do I put sending units into each side of the block and cap the top opening or should I put a sending water pressure unit into each opening? Looked at the manual, it says nothing.
Also there is another wider opening on the starboard side of the exhaust obviously for some sensor but can't figure out which. Will make pictures of them all and post them when the heat goes a little down, it is 118F now.
Thx.

 

[dlogvine]

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[dlogvine]

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Plugs and sending units

 

[Bt Doctur]

the first 2 pics take the plugs, cant tell on the 3rd pic.

 

[dlogvine]

the first 2 pics take the plugs, cant tell on the 3rd pic.

The third pic is of the engine port side, symmetrical to the starboard hole. Oops, i accidentally shot a spark plug gap. The symmetrical hole is covered by the manifold, will try to make a better picture tomorrow. Where does the water pressure sending units goes then?

 

[dlogvine]

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There is a wider hole on the exhaust close to the thermostat housing on the starboard side. None of the senders fit it.

 

[Bt Doctur]

If the 3rd pic is of the head, a plug goes in the hole, the last pic is of the intake manifold and that hole is usually plugged or has a hose barb going to the hot water heater

 

[dlogvine]

So where do the water pressure sending units go?

 

[NHGuy]

Pic 1 gets the allen plug, the square drive one goes in the intake manifold. The sensors probably go in the thermostat housing. The sensors are different, one may be a high temp switch, the other a sender for the gauge. Is the engine carb or EFI? If EFI there will be a cooling water pressure sensor too. I speak carb so I don't know where the water pressure sensors go.
There will be threaded block drains on the lower engine sides. Those get brass fixtures into which thumbscrew plugs are installed.

 

[dlogvine]

Pic 1 gets the allen plug, the square drive one goes in the intake manifold. The sensors probably go in the thermostat housing. The sensors are different, one may be a high temp switch, the other a sender for the gauge. Is the engine carb or EFI? If EFI there will be a cooling water pressure sensor too. I speak carb so I don't know where the water pressure sensors go.
There will be threaded block drains on the lower engine sides. Those get brass fixtures into which thumbscrew plugs are installed.

The engine is carb, the brass seding unit fits in the thermostat housing. The other sending unit does not fit. The drain plugs are already installed.

 

[NHGuy]

So it's a 1993 5.0 carb. I'd expect that year may have the warning beep system for low oil pressure, high engine temp, & low drive fluid. They are connected to the helm with a common brown wire with blue striping.
If you have that system your T-stat housing would use a temp sender and a separate high temp warning switch.
If not there will be only 1 sensor used in the stat housing and it's for the gauge sensor. The temp gauge sensor wire is brown only-no stripe.

Here's a page on just the sensor that should help, stretch out the page and it will be easier to see. You could ohm out the sensor to check it, or look it over for part #'s and find out what you have. The warning sensor is just an on off switch that's not conductive til I think 195 degrees.

 

[NHGuy]

There is a test for the temp switch too. You can find it in the manual. Go to the stickies and get into Manual #17 and go to the instrumentation information.
They recommend putting the sensor in sand and heating it til the switch closes then check the temp....
of course this doesn't solve your question of where it goes. Are there any unused ports in the stat housing?

 

[dlogvine]

Thank you guys, all you said was great. Both senders were going into the thermostat housing, i just had to clean one opening from rust, it was so bad that the sending unit was not fitting in. The bigger opening also needs to be plugged, just with a bigger alen plug. I found a boat in my storage with the same engine and looked at it and made several pics of it. Found the answers to all the questions. All were exactly like you said. Thank you.