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Old 04-26-2017, 12:22 PM
Brandon1975SS Brandon1975SS is offline
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Oil pressure gauge reading 80

My oil pressure gauge reads 80, maxed out with key ignition on and engine not running. When engine starts, gauge goes down and reads 70-75psi. This is an updated white pro star gauge put on my 1980. Engine is a 351w. Also changed oil last night and drained 3 qts and added 3 qts with filter. Dipstick looked like clean oil and was at the full mark. I'm kind of scared to run it if it only has 3qts and pressure gauge isn't reading correctly.
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Old 04-26-2017, 01:15 PM
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ahhudgins ahhudgins is offline
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First thing is to figure out why you only have 3 quarts of oil in pan.

As far as the gauge goes, the simple test is to remove the wire from the sending unit with the ignition ON and the motor not running. It's been a while since I've done it, but it works one of two ways. With the wire removed from the sensor, the gauge will stay at 0. Next, ground the wire to a good ground on the engine block, the gauge will to full scale. It might work the opposite way, sensor wire removed and it goes full scale, and the wire grounded it will go to 0. Either way, you should get a 0 and a full scale reading. If it works, you know that you have a bad sending unit....which is a common problem.

I like that style dash. My first MC was a 79 S&S.
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Old 04-26-2017, 01:38 PM
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Shaun R Shaun R is offline
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You also put gauges designed for a chevy on a ford motor. If could be a sender issue causing it to read high, could be a mismatch between the gauge and sender, could be a gauge problem. Use the old gauge or one that you know works with ford to verify the reading is the same. And 3qts sounds really low for that motor but would have nothing to do with a high pressure reading on the gauge.
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Old 04-26-2017, 01:47 PM
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ahhudgins ahhudgins is offline
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Quote:
Originally Posted by Shaun R View Post
You also put gauges designed for a chevy on a ford motor. If could be a sender issue causing it to read high, could be a mismatch between the gauge and sender, could be a gauge problem. Use the old gauge or one that you know works with ford to verify the reading is the same. And 3qts sounds really low for that motor but would have nothing to do with a high pressure reading on the gauge.
I forgot to ask when the gauges had been installed, and if they had been working correctly until now???
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Old 04-26-2017, 01:51 PM
Brandon1975SS Brandon1975SS is offline
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Just bought the boat and doing its first oil change since purchasing 2 weeks ago. I will try all these things tonight and get back with you guys. Thanks for the input
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Old 04-26-2017, 03:08 PM
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ahhudgins ahhudgins is offline
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Originally Posted by Brandon1975SS View Post
Just bought the boat and doing its first oil change since purchasing 2 weeks ago. I will try all these things tonight and get back with you guys. Thanks for the input
Glade you verified that. Should have 5 quarts in it.
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Old 04-26-2017, 08:09 PM
Brandon1975SS Brandon1975SS is offline
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Alright... so took prong off sensor, and touched ground and the gauge went strait to 80. Took sensor off plugged prong into sensor and touched sensor to ground, went to 80. Replaced sensor with a Chevy sensor to match gauges. Did exactly same thing. Cranked it up, pressure went to 70 on gauge... is this the typical psi they run at cold? Just gonna put a manual gauge were the sending unit mounts to verify. Don't want to risk hurting this classic.. as with the oil. Checked it after I ran it, went down to add. Put maybe one more quart in it and got it to full. That makes 3.5-4 quarts. Read somewhere that in 75 they made a 5.8ltr with a oil capacity of 4. Instead of 5. But I still have distinct unmarked notches in the dipstick were it looks like someone made reference marks. 'My dip stick measures from tip to pull handle, close to 21 inches. If someone has a 351w and their dipstick mounts on the side of the engine under the exhaust manifold, can you give me a measurement and length from tip to full mark. I Think this will help me...
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Old 04-26-2017, 08:32 PM
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Mine will run around 75psi until it warms up, then drops down to 45psi. But I have a Gm motor. Oil pumps have a blow off spring to release pressure if it gets too high. Run it around and get it fully up to temp and see where it sits.
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Old 04-26-2017, 10:24 PM
EricB EricB is offline
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Nothing wrong with 70 psi. When it warms it will drop to 50 or so. Don't worry, 70 psi is a good sign. Make sure there is at least 4 qts in there. Should take 5, but I've had the same experience that the stick reads different than the manual.
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Old 04-26-2017, 11:04 PM
Brandon1975SS Brandon1975SS is offline
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Put a mechanical gauge were the oil sender went. Got good news. 60psi. So the gauge is somewhat correct. Now just got to figure out oil level. Probably will just take your advice and add another 1/2 qrt to make 4 and keep an eye on it underway. Thanks for all the helpful input
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Nothing wrong with 70 psi. When it warms it will drop to 50 or so. Don't worry, 70 psi is a good sign. Make sure there is at least 4 qts in there. Should take 5, but I've had the same experience that the stick reads different than the manual.
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