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Oil Temp or Oil Pressure



On one of the previous forums, there was a lengthy discussion around two ports on the engine (Oil Pressure and Oil Temperature).

I am working on a 1973 Coupe with a 1984 350cc engine. The whole thing started as a pretty big mess (everything in buckets) but now the engine is running with some minor details left for this forum.

1. Which port should I use for a mechanical Oil Pressure gage?
The one directly over the oil filter or the one under the distributor?
Does it matter?

2. Wouldn’t they both have the same pressure reading?
Wouldn’t they both have the enough flow to get a pressure reading?

Next Question:

3. When installing a new oil pressure line I would assume it necessary to bleed all the air out of the pressure oil line and pressure gage. What is the easiest way to bleed the gage?

Welcome aboard Kritter:
My 71's factory mechanical op gage is plumbed into block at distributor ... uses line that is about 1/8" od. Engine out for rebuild & will replace that line with larger od. I suspect your 73 came plumbed at dist also ... I have no advice regarding plumbing yours into other location(s). Line's probably gonna end up with air pockets in it anyway ... but I may try to "prime" mine with light weight oil ... I'll have larger od/id so may not matter ... requires open line at gage ... I'll try to keep the oil outa the cockpit. FYI, when using fresh plastic op line and external ferrules ... make sure you also use a fresh INTERNAL ferrule at each hose termination. My block fitting had a miniscule integral internal ferrule ... that failed ... blowing the line off ... and the motor!

Thanks for the useful information, I will plug into the block by the distributor. The plug in the hole by the distributor was loose when I started the engine. I couldn't figure out where the oil was coming from. Looking closer I found the culprit. I have to find a new ferrel for the gage. Picked up a fresh pressure line kit for about 5 bucks and it doesn't match the gage.

Thanks again.

73 for me
Line don't match gage

Just a guess here, but is your new line kit have hose w/too BIG OD for your gage? If so, you can get a small adapter at auto parts/plumbing supply house. I plan to do just that on mine because I prefer to use a larger OD hose.
There is no good reason to have to 'bleed' or prime the tube running to a mechanical gauge. Even if air were trapped in the line (there ALWAYS will be some), it will compress to a certain point, depending upon the actual oil pressure and still render an accurate reading.

Where the pressure is taken from, either filter or rear of the block, will not make any difference. However the 'normal' location should be at the back of the block, just behind the intake manifold and slightly to the driver's side of the distributor.

Your second question will take some thought, however I would suspec that you would not be able to see a useful difference in pressure between the two locations . . . both of them should be after the bypass . . .
I appreciate the good information all have provided. I will have to get an adapter for the back of the gage since the pressure line kit doesn't fit, as you mentioned.

Since I just got the engine started last week for the first time, it is important for me to see the oil pressure. Gotsta have oil pressure...

Thanks again.


Most late model C3's that have the Oil Temp optional gauge is plugged in above the filter. rpounds is right, the tap at the filter loc is after the bypass and will give you the same reading. Absolutely gotta have pressure, but I love my Oil Temp Gauge. Been a couple time that I saw the Oil Temp creeping up and backed it off. Oil Temp should also mirror the Coolant temp pretty close too.

........ Nut

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