'87 - 5.7 TBI, Separate Temp Sensor & Sending Unit?

[vawildcat]

I've got a really slow coolant leak on the drivers side of the engine, opposite side as all the heater hoses, etc. It looks like there is a fitting at the back of the block beside the distributor (on the drivers side of the dist.) that could be leaking. The fitting looks like it goes with another temp sensor - I'm guessing this one could be the sending unit for the gauge because several months ago I replaced the one that the computer uses for the fuel injection, which is located next to the thermostat housing up front. The oil sending unit is down beside the oil filter. If the fitting doesn't have anything to do with the coolant and it isn't leaking my fear is a head gasket. Being all cast iron, I didn't think head gasket as a first possibility. Any help would be appreciated. Thanks, Will.

 

[Originalthor]

That kinda looks like the oil sending unit for relay for the fuel pump.

Your guage sending unit should be between spark plugs 1 and 3 with a green wire going to it

 

[vawildcat]

After your reply, looked for the part "Oil Pressure Switch" on Autozone site - came up with Duralast Oil Pressure Switch PS215, which looks a lot like it. Also looked in my manual - their numbers look backwards to me (numbers 11 and 30). Thinking you're right. Thanks.

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Not looking good for my antifreeze leak on that side of the engine.

 

[Redfish]

I've got a really slow coolant leak on the drivers side of the engine, opposite side as all the heater hoses, etc. It looks like there is a fitting at the back of the block beside the distributor (on the drivers side of the dist.) that could be leaking. The fitting looks like it goes with another temp sensor - I'm guessing this one could be the sending unit for the gauge because several months ago I replaced the one that the computer uses for the fuel injection, which is located next to the thermostat housing up front. The oil sending unit is down beside the oil filter. If the fitting doesn't have anything to do with the coolant and it isn't leaking my fear is a head gasket. Being all cast iron, I didn't think head gasket as a first possibility. Any help would be appreciated. Thanks, Will.

The one at the back of the manifold just underneath and to the driver's side of the distributor is the Oil Pressure SWITCH which is a part of the fuel relay circuit. The one that is just above your oil filter is for the Oil Pressure Gauge.

I agree with @Originalthor and it is shown in your pic above, the temp gauge sending unit is between the spark plugs at the front of the engine on the driver's side.

This pic (distributor cap is removed) is the Oil Pressure Switch:

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This is the Oil Pressure Sending Unit for the gauge:

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[vawildcat]

Thank you. I wasn't familiar with the switch beside the dist. and that it's part of the fuel circuit. This is very helpful. The photos really help too.

I appreciate the replies!

I think my next step will be to try to clean everything really well and see if I can tell where the antifreeze is coming from. The typical old truck oil leaks make it a little tough to see well.

 

[mibars]

Bumping this old thread,
My oil pressure gauge is always pointing somewhere around 35 PSI, I tested the gauge outside of car and it works OK. So my suspect is an oil pressure sending unit.
I'm looking at oil pressure switch/sending unit in my 1990 350 TBI and it appears that the style is different: I don't have that metal can oil sending unit above oil filter (I can see a small plug that takes a square bit, while the "thing" that I have under the distributor has multiple wires (I think 3?).

I'll be making some order at LMCtruck and they only carry the old style sending unit, that metal can, single wire style. Is it possible to convert to that old style sending unit? Is that 90 degree elbow above oil filter necessary for proper fitment? How about threads?

 

[Bextreme04]

Bumping this old thread,
My oil pressure gauge is always pointing somewhere around 35 PSI, I tested the gauge outside of car and it works OK. So my suspect is an oil pressure sending unit.
I'm looking at oil pressure switch/sending unit in my 1990 350 TBI and it appears that the style is different: I don't have that metal can oil sending unit above oil filter (I can see a small plug that takes a square bit, while the "thing" that I have under the distributor has multiple wires (I think 3?).

I'll be making some order at LMCtruck and they only carry the old style sending unit, that metal can, single wire style. Is it possible to convert to that old style sending unit? Is that 90 degree elbow above oil filter necessary for proper fitment? How about threads?

The later years(GMT-400) they went to a three wire sending unit/switch combo unit instead of two separate units. If the plug on the sending unit on the back of the engine has three wires, it is a combo unit and does both sending unit duty(single wire) and switch duty for the fuel pump(other two wires).