Oil Pressure Mechanical Gage

Your best bet would be an outlet that sells hydraulic fittings i reckon. Because that is what you will need. We have thousands and thousands of different types of fittings where i work that could help you out. Simply remove your sender unit and take it down there and find a tee-piece so suit your sender unit and the gauge. Too easy

Similar to this pic. Although one end on the fitting(RH side) has a swivel,and its a male tee-piece fitting,not what you want. But rest assured they will have female tee-piece without swivel ends. Hope this has put you in the right direction friend.
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If you know the fitting sized you need, try the folks at http://www.pegasusautoracing.com/

 

Thats why i mentioned earlier to remove the sender unit from your 308 and take it to your local hydraulic fitting retailer and try and match one up. If you have to order by mail cause you cant make it down there,then i understand you wanting to know what size the thread is before you buy. And i cant help you there sorry. But surely there would be somone that makes a tee-piece to suit?? Anyways,good luck brother.

 

FYI, I've found threads elsewhere here on Fchat (searched on "308 thread sender") indicating M18x1.5. I've found an adapter to go to 1/8 NPT (and some for bigger pipe threads as well) so you can hook up your mechanical gauge, but haven't found any female fittings, tees, etc. in that size go hook up the sender, so you'd need to compare under similar conditions. I'm thinking to go this route myself. There was also some reference to some factory senders using an adapter, too, so if your sender is one of these small thread versions, you may be able to find some adapter to get your sender into a tee for simultaneous comparison.
Or you can do like Kermit did and weld one up!
http://www.egauges.com/vdo_acce.asp?Subgroup=Metric_Adapter_Bushings&Cart=

 

I need to fully service this newest 308 and hope to have it road worthy by mid May. I intend to pull the fuel tank and run new vacuum booster and heater hose, and am contemplating putting in a manual guage in the panel. Does anyone know a mechanical guage that would look close to stock in a 77 308? Upon reflection I would be running a aeroquip line to the guage, and plan to install a pressure switch and route the current guage wire to the seat belt light to act as a low pressure warning. We will see how far I get.

 

Fabricating an adaptor may be the only route to go, as you have mentioned, it it a straight thread. I would be suprised to find an elbow that would have the straight thread (male and female) and a side port for the NPT threads. Not a common application at all. A machine shop should be able cut the threded end off of a bolt, and by adding a nut to the end, you will have a female thread for the stock sender. A second nut will be needed to act as a shoulder for the unit to seat against, thus sealing the base. Above the base nut there will be room to ad an 1/8" npt thread.
IME running gauges that are a bit away from the motor will cause a slow gauge response, due to the fluids friction in the tube. An easy fix is to plumb it in a 3/16" diameter (ID) tube, and the gauge will be much more responsive. Slow gauges IMO are worse than idiot lights, as ther can be damage long before the gauge shows a drop in pressure. In stock senders, I have had success in drilling the orifice out to 1/16" or .062. The stock orifice hole (at the bottom of the threaded part) slows the oil down to eliminate too much response. To quick of a response will show a fluttering needle on the dash, as the pressure is not constant.

 

The mechanical aviation guages seem pretty accurate, but doesn't that dodge the issue of **why** the electrical oil pressure sensors are less so in the first place?

Some of the street hot-rodders will plumb in two different oil pressure senders to two different gauges (see pic).

Others report that the electrical sender is very sensitive to where and how it is grounded...with grounds further from the sender causing notoriously less accurate oil pressure readings.
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I think what you have there in the picture is a sender for a gauge and a sender for a light. You can get oil pressure light sending units that come on at different pressures. If the light comes on at too low a pressure, you have what they call a "new engine warning light". I see that my Pegasus catalog shows oil pressure light switches of 20, 30, and 60 psi. When I was working at the race shop, we always installed a great big oil pressure light on the dash to instantly alert the driver of a loss of pressure, without expecting him to see a tiny little light or a drop on the pressure gauge.

 

The large light makes sense!

Btw, I wonder if anything for oil pressure could be reasonably done such as is done for shock absorbers (remote reserve pressure reservoir) that the off-road truck racers use?
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If you have a significant loss of oil pressure, you need to shut off the engine, NOW. In fact, some racing engines are designed so that the ignition is shut off if the oil pressure drops below a certain point. Having a remote reservoir to maintain pressure would only cause further damage if you had a pressure loss due to something like a spun rod bearing. If you had a ruptured oil line, or a blown filter, something like that, a remote reservoir wouldn't be able to keep up with the pressure loss, and you would still be in serious danger of damaging the engine in a very short time.

 

Got it. Thanks.

 

What about plumbing in an Accusump system? Its primary function is more for handling oil surge away from the pickup during cornering in a wet-sump application, but it would give at least a few more seconds to shut down the engine if pressure drops. An added plus is it gives instant pressure on startup.