# Oil Pressure Sending Unit Installation



## Roqetman (Aug 31, 2015)

A few years ago I installed under-dash S-W gauges for my ‘65. I installed the oil pressure sending unit on the oil filter housing where the idiot light switch was. Since then I’ve had intermittent OP readings and now it has completely stopped working... again. I now have the 3rd new sending unit from S-W that is matched to the gauge. I understand that the best place to install the sending unit by the distributor, instead of the oil filter housing. I removed the distributor and have tried to loosen the 5/16 Allen head plug with everything from a 3/8“ racket wrench up to a 1/2” drive torque wrench and so far... it will not budge. See pic. Just to confirm... this is a 5/16 Allen head plug, it is screwed in and it is right-hand threads, lefty loosie? I left it this afternoon soaking in PB Blaster. Any advice on how to break it loose without damage? Thanks!


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## nick rice (Nov 10, 2014)

Keep it soaking and maybe give it a try with the motor hot. Lefty loosie AFAIK.

Sent from my SM-G970U using Tapatalk


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## Old Man Taylor (May 9, 2011)

You could try heating it up and letting candle wax melt around it. Sometimes this will get down into the threads and loosen them up.


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## 1969GPSJ (Feb 26, 2020)

I have used a heat gun (on highest setting) in the past with moderate success,sometimes when you heat it you can try tightening the plug first to see if you get any movement, maybe a soldering iron to pinpoint the heat ,otherwise use a cold chisel to break it loose 
hope you get it loose


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## Jetzster (Jan 18, 2020)

When and if the PB fails , this stuff is the go-to..
Minesa’66 said it’s the Best stuff ever to remove anything & he was right !
Its avail on amaz


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## Roqetman (Aug 31, 2015)

nick rice said:


> Keep it soaking and maybe give it a try with the motor hot. Lefty loosie AFAIK.
> 
> Sent from my SM-G970U using Tapatalk


Thanks but... I’ve already got the distributor out. Maybe a heat gun will work or someone with bigger muscles or both!


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## Roqetman (Aug 31, 2015)

1969GPSJ said:


> I have used a heat gun (on highest setting) in the past with moderate success,sometimes when you heat it you can try tightening the plug first to see if you get any movement, maybe a soldering iron to pinpoint the heat ,otherwise use a cold chisel to break it loose
> hope you get it loose


Thanks! Good ideas. I’ll try the heat gun first.


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## Roqetman (Aug 31, 2015)

Jetzster said:


> When and if the PB fails , this stuff is the go-to..
> Minesa’66 said it’s the Best stuff ever to remove anything & he was right !
> Its avail on amaz
> View attachment 139534


Thanks!


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## Roqetman (Aug 31, 2015)

Old Man Taylor said:


> You could try heating it up and letting candle wax melt around it. Sometimes this will get down into the threads and loosen them up.


Thanks! I‘ve not heard of using candle was before.


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## lust4speed (Jul 5, 2019)

Not as much difference in pressure readings between the two spots as some believe. The top port is about 12" away from the oil filter adapter and is still towards the beginning of the distribution maze. The biggest difference is the GTO angled adapter takes the pressure reading before the filter and the big Pontiac 90° filter adapter takes it after going through the filter. The bypass built into the filter adapter is set to bypass at less than 5 PSI, so the most difference "should" be that much or less.

Pontiac only used 5/16" square insert plugs so someone sometime pulled the original pipe plug out and replaced it with a common 5/16" hex. So it should be less of a battle to remove than the original 50 year old plug. If someone put it in dry it could still be a bear to remove. Removal is easy when block is stripped down on the rebuild because we just drill through the plug and use a hefty easy-out to remove them. Since that's not an option in a running block, you are stuck with trying to muscle it out without rounding off the hex. But like I said, not that much difference anyway between the two spots.


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## Roqetman (Aug 31, 2015)

Thank you for your informative reply and the oiling diagram. After several attempts with PB blaster and a heat gun the 5/16 Allen head plug would not budge and started to wallow out. I tried a ground-down easy-out without any success. So I’m putting the new sender back on the filter housing. If oil is going through the sender before the filter then I suppose it’s possible that some trash could clog the sending unit which would cause faulty pressure readings.


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## BearGFR (Aug 25, 2008)

Make sure you use a tight fitting, good quality hex wrench and you get it fully inserted. The last thing you want is to strip out the socket in that plug. 

Also I'm going to disagree on the assertion that Pontiac always used square headed plugs. I know for certain my car had never been touched when I got it, and it's always had a hex plug in that spot. 
The only place it had square headed plugs was in the coolant drains on the sides of the block. The last time I had it out, I put drain petcocks there with copper tubing extensions on them to make draining the block easy, even with headers.

Bear


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## Roqetman (Aug 31, 2015)

Thanks Bear. Unfortunately the Allen head plug is now wallowed out, see my comments above. I’m going back to the oil filter housing Unless... there is another plug somewhere that would be appropriate On a ‘65 389?


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## BearGFR (Aug 25, 2008)

Ewww... Well, all is not lost. A couple things you might try if you're brave: 

Clean all the paint and grime off the plug (stick a rag into the distributor hole to keep debris out), stick a tight fitting bolt down into the socket and mig weld it to the plug to give you something you can put a wrench on. Use the other suggestions (heat, good penetrating oil, rocking it back and forth, etc) to improve your chances. 

Drill it out. Of course you don't want metal chips from drilling getting into the oil passages. I've heard that keeping the bit liberally coated with heavy grease will catch them when the bit breaks through. Start with a small one to make the initial hole, then go incrementally larger until you get the hole big enough so that you can "knock the sides in" with a hammer and punch. This would be better done with the engine out and on a stand so you could turn it upside down and use gravity to keep debris out of the oil passages, but you could 'get lucky' with it in the car. Make sure you've got a good stand if you pull it, one that won't give up and let it fall on you while you're "underneath" whacking on it with a hammer. 

Bear


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## Old Man Taylor (May 9, 2011)

My 64 had all square plugs throughout the entire engine. I know the car’s history pretty well since I bought it new.


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