Oil pressure

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I am having some weird oil pressure readings on my newly built 351 Cleveland. At cold start I get 75-80 psi with the fast idle. Then hot idle is 25 and cruising around town around 50 psi. That’s all good as far as I know, but after engine is at operating temp my gauge sometimes starts jumping around some. It goes way down and the back to 50 pretty fast. It never does this at cold or hot idle, only when cruising around.

I have an aftermarket set of gauges that I replaced the original 3 gauges with. They are Classic Instruments and they are made in USA, so I figured they were a good brand to get. The oil pressure gauge is electric, so maybe the sender is going bad already? I have probably only put about 1500 miles on my new engine and I put these in not to long after that. If it’s not the gauge, can my oil pump be messed up? It’s a Melling std. volume and of course brand new with the engine build. 

Thanks in advance for any suggestions!

 

Don C

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My first suspicion would be a loose connection. See if you can see any correlation between hitting bumps and the gauge moving, like driving across a railroad crossing.

Those little nuts that connect the wires to the gauge are difficult to get tighten without over tightening, and often aren't tightened enough. Might be a bad crimped connection, too.

Edit: For peace of mind you might want to temporarily hook up a mechanical gauge to verify that it isn't an oil pressure problem. I've never trusted electrical gauges for troubleshooting. I have a mechanical gauge and length of tubing with fittings in my test instrument drawer.

 
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My first suspicion would be a loose connection. See if you can see any correlation between hitting bumps and the gauge moving, like driving across a railroad crossing.

Those little nuts that connect the wires to the gauge are difficult to get tighten without over tightening, and often aren't tightened enough. Might be a bad crimped connection, too.
It does it on smooth roads too, so I don’t think I have a loose connection. It’s quite erratic when it does this. And it only happens when driving so I could possibly have something loose, but I don’t think I do. And also, it never goes all the way to 0 psi and just stay there. It’s very random, but only after I drive it for awhile.

So if I tightened the wires to the gauge to tight it could do this? I know not to crank down on the gauges when attaching the wires. I’m pretty darn sure all my connections were good but, I’ll have to check. I did check the connection at the sender and that is good. It also seems like it’s getting worse, meaning it’s happening more often.

 
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John, for what it's worth, my engine also has the Melling standard oil pump. I installed aftermarket Bosch mechanical gauges as I think you know. My engine I think is pretty similar to yours. The oil gauge reads 75 psi cold and about 70 hot and never varies. I'll admit on mine, I placed the oil gauge on the right side so it makes it a bit harder to read exactly, but it is steady. 

If you can't find a lose connection, there are two things I'd try; 1, a new sender for the electronic gauge, 2, install a T fitting in the oil sender port and get a small oil gauge as Don suggests, or just put one under the hood to at least see what it's doing at idle or when revved, if that makes sense.

 

Don C

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I'm sure you've checked the oil level. Did you verify that it has the correct dipstick after the first time you filled it with oil?

It's possible you have a drain-back problem in the heads or valley, with oil accumulating.

Yes, if you overtightened the rubber grommets may have gotten misplaced. The thing that worries me about them is the stud can turn when tightening the nuts, and not knowing what it's doing to the connections inside the gauge.

 
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John, for what it's worth, my engine also has the Melling standard oil pump. I installed aftermarket Bosch mechanical gauges as I think you know. My engine I think is pretty similar to yours. The oil gauge reads 75 psi cold and about 70 hot and never varies. I'll admit on mine, I placed the oil gauge on the right side so it makes it a bit harder to read exactly, but it is steady. 

If you can't find a lose connection, there are two things I'd try; 1, a new sender for the electronic gauge, 2, install a T fitting in the oil sender port and get a small oil gauge as Don suggests, or just put one under the hood to at least see what it's doing at idle or when revved, if that makes sense.
70 hot is great! I guess I thought I would have more pressure than 50 hot with a brand new engine. Anyway I’m going to get a mechanical gauge to see what if any difference.

 
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I'm sure you've checked the oil level. Did you verify that it has the correct dipstick after the first time you filled it with oil?

It's possible you have a drain-back problem in the heads or valley, with oil accumulating.

Yes, if you overtightened the rubber grommets may have gotten misplaced. The thing that worries me about them is the stud can turn when tightening the nuts, and not knowing what it's doing to the connections inside the gauge.
I just put 5 qts of break in oil about 200 miles ago. If you happen to remember I had my lifters collapse and I had to install new ones. I did the normal break in and that all went good. I just have some concerns about the oil pump I guess. 

Not sure why I would have a drain back problem. I have 71 quench heads on my Q code block.

Everything in the valley and under the valve covers is spotless. Nothing is blocked.

I am going to get a mechanical gauge and check it against the electric.

 
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I am having some weird oil pressure readings on my newly built 351 Cleveland. At cold start I get 75-80 psi with the fast idle. Then hot idle is 25 and cruising around town around 50 psi. That’s all good as far as I know, but after engine is at operating temp my gauge sometimes starts jumping around some. It goes way down and the back to 50 pretty fast. It never does this at cold or hot idle, only when cruising around.

I have an aftermarket set of gauges that I replaced the original 3 gauges with. They are Classic Instruments and they are made in USA, so I figured they were a good brand to get. The oil pressure gauge is electric, so maybe the sender is going bad already? I have probably only put about 1500 miles on my new engine and I put these in not to long after that. If it’s not the gauge, can my oil pump be messed up? It’s a Melling std. volume and of course brand new with the engine build. 

Thanks in advance for any suggestions!
Hi Jpazzzzzzzz 

I hope I can be helpful as a comparison.

Mine is the same. but without the jumping around.  (need to know more what that means) does it mean gauge or engine?  

I run Edelbrock 1406 with auto choke.. on first cold idle I read 80psi. when warm is 50psi ...ish. ... when I drive long distance .. drops to 25psi when waiting at lights, then back to 50-60 when pulling away.  I'm using VR1 Valvoline with an added  qtr a cup of extra zinc by Edelbrock, FRAM filter, melling standard(not high vol) oil pump.. standard oil capture, std oil pan. 

My Eng 351C is a rebuild on aftermarket gauges also - However I can hear the engine is happy and the output from tail pipes tell a story also. 

To make sure .. I have pulled out oil sensor and plugged in engineers oil pressure gauge to check -- always good to have assurances by means to double check. 



 
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It’s  the gauge is jumping around sometimes. My engine also sounds happy, no knocking, pinging or ticking noises. Seems to be really running good.
 I think putting a mechanical gauge on (somehow)  will tell the story. Problem might be getting one right now with all the closures. Is NPD still open?

 

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I had a bronco II that used to do the same thing, cold it showed great oil pressure on the gauge, hot, would show around around 40 when driving but would drop down when I was sitting at a light. Engine sounded great and never caused issues but ended up selling it before finding out if it was a problem. Post back if you find anything out because I am in the middle of an engine rebuild now and if there is something that I need to change or add to mine to prevent this, it would be good to know now. I will be watching this thread closely. Thanks and good luck brother.

Tom

 
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It’s  the gauge is jumping around sometimes. My engine also sounds happy, no knocking, pinging or ticking noises. Seems to be really running good.
 I think putting a mechanical gauge on (somehow)  will tell the story. Problem might be getting one right now with all the closures. Is NPD still open?
I think its just a wibbly wobbly poor after market gauge - doing typical after market things. So not worried about the engine.

I still think Jpaz's car would look nice on MY drive way  :p

 
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Tom, just a word from me on my bad experience, do NOT think about a high volume oil pump unless the motor is built for it. Ask me how I know! Fortunately I got most of the engine re-rebuilt under warranty as the builder installed it.

 
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It’s  the gauge is jumping around sometimes. My engine also sounds happy, no knocking, pinging or ticking noises. Seems to be really running good.
 I think putting a mechanical gauge on (somehow)  will tell the story. Problem might be getting one right now with all the closures. Is NPD still open?
I already got one. All the auto parts stores are open here till 7-8 pm. I just got a Bosch mechanical to see what is going on.

 
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It’s  the gauge is jumping around sometimes. My engine also sounds happy, no knocking, pinging or ticking noises. Seems to be really running good.
 I think putting a mechanical gauge on (somehow)  will tell the story. Problem might be getting one right now with all the closures. Is NPD still open?
I think its just a wibbly wobbly poor after market gauge - doing typical after market things. So not worried about the engine.

I still think Jpaz's car would look nice on MY drive way  :p
Ya, could be, but Classic Instruments are made in USA. They are actually made in Michigan, the state I live in. Thought they were supposed to be good, but with deal with electrical, who knows.

Sorry, but my car does look better in my driveway!! Lol ?

 

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The gauge may be quality, but is the sending unit also made by Classic or is sourced from a manufacturer that makes them for several companies?

Thinking about the sending unit made me think about the thread sealer you used. I hope it was one that is electrically conductive and not Teflon tape, although if it were the tape I would expect the problem to be less intermittent.

Loctite copper anti-seize works good on pipe thread sending units for brass or iron.

 

mjseakan

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+1 on the sending unit. I had a brand new one go bad after less than a month.

Mike

 
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Looking forward to the results. Bosch mechanical is what I have. I actually chose that brand because they are down sweep so look more like originals more that did they work the best.

 
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