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Discussion Starter · #1 · (Edited)
hi all, i have been restoring my grandfathers 66 mustang 289. i did an oil change a few months ago and have noticed high oil pressure and a slight leak at the front and back of the block. when driving, the gauge will hover around the middle and teeter between there and the line before H. I replaced the filter twice, replaced the screw and gasket and then the oil pressure sending unit and still see the issue. neither the drip or the gauge were abnormal before replacing with high mileage pennzoil 10W-30 (non synthetic). anyone have any ideas? should i be worried? thanks!
 

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Question may be that you have over filled the pan.
Checking the Ford shop manual states that the required amount of oil used should be 5 Quarts with new filter.

Other things to check are the dipstick (if right length) and the PCV valve on the passenger rocker cover for correct operation. The gauge would be worthwhile checking out if all the above mentioned are OK.
 

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Discussion Starter · #4 · (Edited)
engine appears rebuilt (there are autolite 25s there?) but i can’t ask him to know. oil was carefully poured, never overfilled, started with 4.5 quarts. if anything, the stick is showing less than half.
 

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I just noticed that you replaced the oil sending unit.

The original ones are very dependable and work great. New ones - not so much. The mechanism is pretty simple, but all modern ones that I know of are absolute garbage, and do not have a smooth linear response to pressure. The needle will jump all over, and not give any kind of accurate reading. Perhaps your pressure's just fine, but the sender isn't.
 

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engine appears rebuilt (there are autolite 25s there?) but i can’t ask him to know. oil was carefully poured, never overfilled, started with 4.5 quarts. if anything, the stick is showing less than half.
The reason I ask is the timing gear from the original Ford build had plastic teeth. They broke off and jamed the relief valve on my 66 Stang. Oil pressure was high.
 

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Discussion Starter · #7 · (Edited)
Oil pressure was always fine until I changed the oil and filter. The new sending unit is showing the same value as the old sending unit. I did not have any oil leaks until after changing the oil and filter, which is routine so I am at a loss of where to go next.

where can i find the pressure relief valve?
 

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Very doubtful that a leak is coming out of a pressure gallery. More likely it leaks at crankcase through an old cork gasket.

Make sure that your PVC system is working properly. This puts the crankcase under a vacuum and reduces oil leakage.
 

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Discussion Starter · #9 ·
Very doubtful that a leak is coming out of a pressure gallery. More likely it leaks at crankcase through an old cork gasket.

Make sure that your PVC system is working properly. This puts the crankcase under a vacuum and reduces oil leakage.
Can you link me to something or provide more details on how to verify the PCV valve? Is it as simple as removing the valve and seeing if it has suction with a piece of paper or something?
 

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Can you link me to something or provide more details on how to verify the PCV valve? Is it as simple as removing the valve and seeing if it has suction with a piece of paper or something?
The vacuum source is the large (1/2"?) hose at the carburetor spacer. Follow that upstream to one of the valve covers, which vents through a PCV (check) valve. The stem intakes through a filter- sometimes on the opposite valve cover, and sometimes a on the outside of the air cleaner. With the engine idling you should feel a vacuum with your finger(s) over any of these openings.
 

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Discussion Starter · #11 ·
Hi all, I can confirm that removing the check valve from the valve cover, I have suction at the check valve. It seems strong, I put paper there and it sucks it right up. Theres no suction at the valve cover without the hose in place. Image attached.
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Hi all, I can confirm that removing the check valve from the valve cover, I have suction at the check valve. It seems strong, I put paper there and it sucks it right up. Theres no suction at the valve cover without the hose in place. Image attached.
View attachment 782288
Do the same for the filter (circled in red).

If the leak is on the intake manifold you should retorque it. Cork gaskets do require this to be done periodically. These aren't like modern engines which are basically glued together with high tech materials. Use the correct sequence.
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Engine looks neat and relatively clean. (y)
 

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Discussion Starter · #13 · (Edited)
thank you! i just pulled the filter and there is suction, although it is much weaker than at the check valve. it’s pretty dirty too, not sure how much that matters.

if you feel like i should retorque the manifold, do you mind sharing some instructions on how to do that? im definitely more of an expert in interior, electrical and maintenance so i don’t want to mess the engine up. i brought it to a mechanic recently and he said everything was perfect but im always interested in learning new things.
 

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Two things in regard to intake manifold torque:

1) Be gentle. It is incredibly easy for a grown man to snap off an intake manifold bolt, as I have discovered more than once. =)

2) Start in the middle, work your way out to the ends, crossing over side to side. There are lots of diagrams showing a pattern to use. This allows the gaskets to conform and 'squish' to the outside edges instead of being put in a bind and forming waves or bubbles that would leak. ( @Yadkin included a link!)
 
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