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Discussion Starter #1
I just went down the street to the store. On the way back on an empty road I was doing 70 with no noticeable power loss, but when I got home and pulled it in the garage I noticed the oil pressure gauge was running dead center and dancing around a little when I give it gas. Before it was always near High and it didn't really move at all.

Could I have blown something in the engine? Could the sending unit/gauge be bad? What trouble shooting steps should I take? The tach is reading the same as it did yesterday when the oil pressure was normal. I checked the oil, its full.

What next?
 

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Check the sending unit wire and all its connections...

I had this problem as a teenager when taking my 67 on its first long trip...scared me to death. You can guess what I found...*G*

Any lifter rattles??
 

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It could be the sending unit or the gauge. There is no good way to test them, really.

You can swap the wires from the temp sending unit and the oil pressure sending unit and see if the temp gauge does the same thing. This will at least test the gauge. If the temp gauge does the same thing then it's likely the sending unit. If not, then keep looking.

If you have access to a mechanical gauge you might use it to verify whether your oil pressure is in fact fluctuating.
 

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Discussion Starter #4
I checked all the wires. I wish I had a mechanical gauge laying around. All probably end buying one just to test it. There are no noticeable noises. Except when I rev the engine real high there's a few pops out the exhaust that I never noticed before. They're not loud, probably nothing. This is while the car is in park.

Good idea kketell, all try that if they can reach. I think maybe it was never working before and all of a sudden it kicked it. The gauge starts at low when I start the car and rises as I give it gas.
 

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Discussion Starter #6
Alright, so I did what kketell suggested. The gauge works fine so it must be the sending unit. Unless there's something else wrong/forums/images/icons/frown.gif.

If I order a new sending unit it wont even ship till Monday and I probably wont get it till later that week. Hmm I need my car before then. I wonder if I bought a mechanical gauge from NAPA, if they would let me take it back after I tested it.
 

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Go to Walmart. I saw a cheap oil pressure guage in the auto section acouple of weeks ago. It was ,like $6or $7.00 for a complete setup. I wouldn't use it in my car.....but, as a test unit, it will work fine, and piece of mind is well worth that.....
luck...
 

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Dollars to donuts it's in the guaging system somewhere...I guess I was lucky that is was just a bad wire connection.

Have you checked locally for a sending unit? I'd recommend doing that Monday before ordering. Perhaps one like this one from Autozone...
 

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The mustang gauges are crap but good enough to warn you when there is something going wrong which is all the gauges is really needed for anyhow. being oil pressure you don't want to mess around. The first thing i would want to do is get a second opinion. Buy a CHEAP aftermarket oil pressure gauge (mechanics or dash mount) and attach it to the engine. See what a new gauge says. If it read like the dash then it is the engine, if it reads fine then it is the dash. Oil should give a pretty steady reading. under 5 your engine is in danger, under 10 it is shacky, above 20 is fine, above 40 is real nice.
 

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Discussion Starter #10
After sweating it for the last couple hours. I got back in the car and started it. When straight to near high like it always has. Took it for a drive, everything is running fine.

I suspect it is just the sending unit. Maybe it was working correctly for a little while and its been bad the hole time. It wasn't running to low I don't think, around mid or slightly above.

This is a big relief. I'm going to replace the sending unit tomorrow and maybe a cheap mechanical gauge just for some more piece of mind.

Thanks for your replies.
 
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Just a note on cheap mechanical gages. Having an instrumentation background, I don't like cheap ones much. They are usually out of calibration sometimes as much as 7-8 pound. However, you are looking for a constant pressure and even if they are out of cal the indication may tell you what you need to know. Just be aware that there may be a (+ or -) 7psi deviation. If your readings are close to specs, then you might get a known good gage before you jump into anything major. I do like checking with a mechanical gage though, as much as I love Mustangs I'll agree with one response above that the factory gages are not very good.

If you find that the pressure is actually low, and you are on a budget, then I would suggest pulling the pan and removing the caps off the mains and rods to inspect the condition of the journals. I have on two occasions found high mileage Mustangs with very little wear on the crank. My convertible had a very smooth crank and the mains and rod bearing were worn to the copper, which was the main reason for a low oil pressure reading that I was receiving. I replaced the bearings in the car with factory standard bearings. I plasti-gaged each one to check clearance and every one was in specs. The rear main was at the very limit but within, the rest of the bearings were well within.

I also replaced the oil pump with a (HV) high volume unit since I figured the cam bearings were worn too and I wasn't going to replace them. As it turned out the HV pump has an overpressure relief at 75psi. I checked the pressure with a good gage and when the engine started the pressure went up to the 75 limit and the excess was dumped as indicated by a constant 75 psi reading. I was pleasantly surprised with 127K on the engine. That was six year ago.
 

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Discussion Starter #12
Here's a questions, since were on the subject. I've been thinking about using Synthetic oil next time I change it. People speak of oil leaks and stuff. All my seals are good externally... oil pan, valve covers, and such; but what about internally? Is this also a risk when changing to Synthetic? My car supposedly has 46,000 original miles. I belive it, the car is in very good shape. Minimal body rust, it's been taken care of very well.
 

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Personal choice....hard to argue effectively for or against...

IMO, it's more cost-effective on modern, tightly sealed (rings, valves, etc) engines vs our older looser engines (even when rebuilt)...

Do a leakdown test and post the results...then I can give you a more informed opinion regarding the switch. Also, note current oil consumption between oil changes (or every 3-4K miles).
 
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Just an FYI to tack on to the end...

Bounding around in my Fastback, I caught my Oil Pressure gauge (after market Autometer mechanical) doing a little dance at the first stop light. Pulled over and checked and saw the oil was about a quart and a half low. Added oil, fired her up, saw the steady gauge and pressed on.

Look into getting a decent set of aftermarket gauges. All sorts of places to mount them - in the original dash panel, in the center console, etc. A reliable and accurate oil pressure and water temp gauge are worth their weight in gold.

Just my two cents...

Matt
 
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