oil pressure sender - is this it??

[centuryhouse]

I have a 72 GMC but have been told by two forum members that my engine looks like a crate engine replacement. The seller of the truck told me numerous wrong things, but did say the engine had been rebuilt or replaced in the 80s.

At any rate, the oil pressure gauge doesn't work. I am trying to find the sending unit.

I see a tiny brass (?) tube leading into the firewall near the instrument panel, with a screw in fitting on the end, but it leads nowhere and I don't see anything it might plug in to.

Also, I see a small unit right next to the oil filter, which a wire should clip on to.

Can anyone tell me if it could be that my dash uses a wire connecting instead of tube connection? Or what might need to be done with these two tings (the tube and the wire connection)?

72 GMC 350, automatic, 2wd.

[centuryhouse]

More pics for clarification.

And can anyone tell me what that GMC number means in the last one?

[swamp rat]

Your engine does look like a crate engine or late 70's thru 80's replacement, one way to help id is to note the location of the alternator, if its on the driver side and you have a short water pump its probably period correct pending block number search, if the alt is on the passenger side and you have a long water pump its a late 70's and on block.

On the stock 350 back by the distributor on the driver side, look at the back side of the lifter valley there is a flat machines surface and there will be a pipe plug in the block, that is where the stock gauge would thread into. I don't know if a later 350 casting will also have the same port but cant imagine it won't. The plug could have a squair head or just an allen head.

The pic you show should also be the sending unit so no problem unscrewing it, if oil comes out you have it, No problem leaving it in if you can hook the gauge above. the only other sending unit would be for coolant but it would normally be in a different location, usually on the driver side head or intake manifold, i included a picture of a short water pump, i tried putting the temp sender in it for a short time but it was not too accurate so i moved it to the manifold.

[swamp rat]

Just to be sure you are clear on this, an oil sending unit is for a dash dummy light only, the gauge is strictly mechanical and pressure, the fitting on the end of that copper line will screw into the block, then block pressure will travel to the gauge via the copper tube. If the fitting does not thread in then I'd suspect the later block has a different thread so you would need an adapter.

[beedees]

oil-pressure feeds are 1/8"NPT,whether idiot light or mech.

[centuryhouse]

Originally Posted by swamp rat

Just to be sure you are clear on this, an oil sending unit is for a dash dummy light only, the gauge is strictly mechanical and pressure, the fitting on the end of that copper line will screw into the block, then block pressure will travel to the gauge via the copper tube. If the fitting does not thread in then I'd suspect the later block has a different thread so you would need an adapter.

Thanks for making that clear, I didn't know that.

The only thing I care about is the mechanical gauge then - I want to see the actual pressure and be able to monitor it.

It seems to me that my first picture is showing the correct tubing for the mechanical gauge then. My problem is that I can't seem to find a place to plug it in! I keep reading everyone's descriptions, but since my engine is a replacement, I can't find it!

[centuryhouse]

And should I be looking for a bolt or plug of some sort? Surely oil would be shooting out if there were just a threaded opening waiting for me to screw the tubing into....

[leftybass209]

Your engine does have a provision for it, but it's probably greasy back there, and the hole is going to be plugged, or else you'd get a stream of oil when you start the truck. Grab a small wire brush, and some degreaser or brake cleaner, and scrub the flat plane of the block right behind the intake manifold. There's not much there. Start scrubbing and cleaning, and you'll see the hole, it's the only one back there.

[swamp rat]

Look at the second picture i posted, it shows the port..re read my posts..

[swamp rat]

Another picture, keep in mind with the intake manifold on you will have the rear rail covered up except for that 1/4 circle with the hole/plug in it. This is the rear of the block so grab a flash light and get your head in there.

[Jurassic-1]

Usually the small block is at the rear of the block. The way it was pictured in your photo down at the filter was normally where early big blocks were installed.

[centuryhouse]

Originally Posted by swamp rat

Another picture, keep in mind with the intake manifold on you will have the rear rail covered up except for that 1/4 circle with the hole/plug in it. This is the rear of the block so grab a flash light and get your head in there.

Ok, THAT makes a lot more sense - not having seen one of these torn down before I couldn't make any sense of that previous picture. Thanks for clarifying - I'll get in there and look.