Oil Pressure Gauge swap

dennis112

15 Year Member
May 15, 2005
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Your sending unit started at 10 ohms and started rising? Not possible. Either he meter leads are not making clean contact with the parts or the meter/leads are kaput. Also, DO NOT let your fingers stray onto the metal part of the ohm meter probes as that definitely affects the readings as will the leads NOT making good clean contact with the parts.

You do not have to remove the sending unit from the motor in order to ohm it BUT you should have removed its wire. Simply put one meter lead on the SU stud and the other to its outer case. The reading will be the same on or off the car. The SU measured resistance should definitely be higher than 10 ohms when the motor is off.

The 22 ohm reading in post #19 was also a steady reading on my car. I tried different objects for the ground lead (sending unit case, the aluminum valve covers, even my hood pin studs) and the wire-to-gauge measurement remained at 22 ohms.
 
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gilzuckie

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Nov 3, 2018
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Went out this morning to measure the SU. I left the one SU connected overnight. It was at 17,000 (Ohm setting was 20K) but when I moved it to put on a piece of cardboard to take it picture it started to go slowly go down. I also check the SU that was in the car. I had to change the Ohm setting to get a reading. I changed it to the 2M setting and it read . It also started to 1.000 and slowly started to go down. I took the pic at .964 I had SU wire off. Was getting the same reading when the SU was attached to the motor. Now that I have the SU wire off can I ground that wire with the key on and the gauge peg? It didn't. I also tried 3 different sets of test probes this morning. Something weird is going on.
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gilzuckie

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Just went out and grounded the SU wire. Needle did not move at all. Before I put the IC back in I checked that the gauge would peg if grounded, but I was going straight from the gauge, not using the SU wire. Maybe the SU wire is bad. I guess I will be pulling the IC back out and check the wires. Didn't want to do that. So hard getting the speedo cable back on. I also checked the resistance of the SU wire when not attached the SU. I was getting some weird readings. Most of the it said infinite. But when I moved to different settings on the meter the readings would bounce around but always end up on infinite. So either the gauge is bad or a break in the SU wire.
 

gilzuckie

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Dennis, just a real quick update. Bad SU unit wire. Pulled out the cluster and checked the wire. Infinite. Ran a new wire, grounded it, pegged the gauge. Started it up and right away the needle started to move. Only ran it for about 30 seconds and the needle was almost at the O in Oil. Didn't want to get the motor too hot. That was it. Now I will clean up the wiring and pull out the bad wire. Thanks.
 

gilzuckie

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Thank you Dennis, hope to keep in touch. There's probably so many things I can ask you about. So the wire from the SU went into a molex type wire connector. Nothing coming out from the other side. SU wire from the gauge went to a relay that was part of an alarm system that was installed about 20 yrs ago. I have no idea how the wiring got so messed up. I'm probably going to go under the dash and remove the alarm system. Not working anyway. Thanks.
 

dennis112

15 Year Member
May 15, 2005
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Amish Wonderland of Central PA.
I was looking at my engine's firewall bulkhead connector today and was wondering if that was were your were losing your signal . . . .

We never know what previous owners have done to our cars (and often for those who keep our cars forever) regret the things that we might have done in the past.)

Always happy to help when I can.
 

gilzuckie

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Hi Dennis, I have taken the Mustang out a few times now, on some hot days and been running the a/c. So I noticed that my temp gauge gets up to about 3/4. I like it to be in the middle. I have a few of questions. What is the Max temp I should worry about? Where on the motor would be the best place to place a temp probe or maybe in the fins of the Radiator? Was thinking of putting in a digital temp gauge for a real reading. I dont think I have an available port on my Edlebrock Performer Manifold to but a probe so I was thinking of changing out the water neck with one that has a port. Would that be the best place for a true temp reading. Also, when I returned from a drive I used a infrared digital thermometer to checked all around the motor. The highest it read was 215. I checked the manifold, radiator, hoses, headers, all around. Any thoughts? Is it possible to run the digital gauge to the existing temp probe that is in the manifold or would each gauge need there own probe. probably wouldn't be compatible between 2 different types of gauges. What about cutting the Radiator Hose and connecting an joint with a probe port?
 
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dennis112

15 Year Member
May 15, 2005
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Amish Wonderland of Central PA.
The factory gauge/sending unit really doesn't have an exact calibration and are more to determine differences in temperature. It may be too warm but there is now way to know for sure without an external gauge I know of no such gauge that will work with the factory sensor and especially in tandum with the factory sensor.

Temps can go up to maybe 235* and not be harmful to the motor but of course we would rather have them under 220* if possible. I am not a fan of the radiator probe type sensors but would use one if I had to. Its just not an accurate way to measure temps.

The thermostat housing sensor location wouldn't work for me as there wasn't sufficient clearances in it internally for the sensor probe I tried. I believe I would opt for the hose adapter type sending unit over the radiator fin type and install it in the upper radiator hose which is the output flow of the motor. It is about as close as you will get to being the same as the intake manifold. You might even consider installing the digital gauge in the block and the factory sensor in either the thermostat housing (if it fits) or the upper hose as mentioned above. The digital should react a little faster as the factory stuff have a delay before the gauge moves.

Should your motor get too hot, I am a fan of using aluminum radiators and electric fans. The plus is that a welding shop can install bungs in the tanks for you to run any and all sensors. The bad news is that with AC you might need a high cfm fan or fans (3000cfm min) and certainly a high amp alternator, such as a 95A 3G to keep the battery charged as such fans require lots of amperage. Before considering this route you should make sure your current radiator is clean and flows well. You should also have a shroud (mandatory) and I would opt for a thermal clutch fan (not a flex fan.)
 

gilzuckie

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I have a new Aluminium Radiator with an 2600 CFM 16" Fan as a puller and a 2150 CFM 12" Fan up front as a pusher. The fans are connector to relays. On normal cool days and not running the A/C I only need the 16" Fan to keep the temp needle in the middle. It's on those hot days, 90 degree plus and running the a/c is when it starts to get hot and I turn on the 12" fan. The needle almost gets to 3/4. I like the idea of the Radiator Hose probe and swapping locations with the factory probe. I'll try that. So as long I keep the temp under 220 I should be fine.
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gilzuckie

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Thanks. I try to do everything myself.
Not really. Normally stays in the middle (about what temp is that?) It just starts to creep up a little on those hot days and running the A/C. That's why I am running a 2nd fan. Wanted to put another 16" up front but would not fit. Am I worrying about it to much? Probably because before I switched to the Aluminium Rad I had a lot of over heating issues. Mainly because of that Red Radiator cap in the above pic. I switched over to a standard cap and no over heating issue.
 

dennis112

15 Year Member
May 15, 2005
1,538
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Amish Wonderland of Central PA.
I have never seen a listing as to what the temps are in any location on the factory gauge. Its not intended to be a precision based system as one would normally pay attention to the deviations from what it would normally read.

It might behoove you to add a modern gauge (even temporarily) in order to check actual temps and pay attention to the deviations. The infrared thermometer typically won't give as accurate of a measurement as a true sending unit based system.
 

gilzuckie

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Planning on adding a 2nd Gauge and put the sending unit in the Manifold port. I will keep factory gauge and move that sending unit to a new location. I have a few places to choose from. Cut the top radiator and install a joint and put it there. CJ Pony Parts sells a water neck with a port for a sending unit, but it is after the thermostat. https://www.cjponyparts.com/thermostat-housing-with-threaded-port-260-289-302-351w-1965-1973/p/TH16/ Another option is is to tap into the heater hose fitting. https://www.oreillyauto.com/detail/...hut-off-valve/84704/4522984/1965/ford/mustang Do you think that a digital gauge is better than a needle gauge. I found some that are both. But the reviews have not been that great. Glow Shift has a digital gauge with great reviews. View: https://www.amazon.com/GlowShift-Color-Digital-Transmission-Temperature/dp/B01LZ24K54/ref=sr_1_48?crid=6UNT2N7JHEAK&dchild=1&keywords=digital+temp+gauge+automotive&qid=1596731224&sprefix=digital+temp+gauge%2Caps%2C223&sr=8-48

or Equus has a nice standard gauge. View: https://www.amazon.com/Equus-6262-Electrical-Water-Temperature/dp/B000EVU8YI/ref=sr_1_20?crid=6UNT2N7JHEAK&dchild=1&keywords=digital+temp+gauge+automotive&qid=1596731248&sprefix=digital+temp+gauge%2Caps%2C223&sr=8-20
 

dennis112

15 Year Member
May 15, 2005
1,538
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79
Amish Wonderland of Central PA.
The top tank isn't a good spot as it doesn't necessarily always keep the temp sender in coolant. (I use a side tank horizontal core radiator and that is where I got the idea.) You could put one on the bottom although it would/should read a cooler temp than the actual engine. The radiator does not have to be broken down in order to have a bung welded to it. Cost me $25 total to have 3 installed (I provided the bungs) at a local welding shop. The thermostat housing could work BUT there has to be significant clearance for the probe itself. That is the issue that I had. Not sure what you are planning with the heater hose shutoff . . .

Another place would be to get an inline adapter for the upper radiator hose. They are a little expensive but I didn't shop around for anything but a photo so deals may be out there.


I can't tell you anything about aftermarket gauges and their accuracy, nor whether digital or analog is better.

I don't believe that the radiator combo that you have is overly efficient. The shroud appears to be very close to the fins and the fan appears to be located not very far from them either. That enclosed area interrupts air flow. Also the pusher fan, although it appers helpful, also blocks air flow-pushers are not generally a good solution. You might consider adding the 6 cylinder rubber seal on top of the radiator support to help direct air flow and also find some way to seal the radiator to the radiator support. Both should help direct air better when cruising at speed.
 
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