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Old 02-17-2020, 01:41 PM   #1
derek costello
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Default flathead oil pressure?

what is a flathead 1952 mercury oil pressure normally ???
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Old 02-17-2020, 02:58 PM   #2
flathead4rd
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Default Re: flathead oil pressure?

Mine runs about 40 to 50 PSI on startup. I use Castrol 10w-50. After warm up and when it's really hot outside my pressure will drop down to about 10 PSI. With water temperature around 195. Flatheads depend on oil flow not so much on oil pressure. I am running a 286 C.I. flathead.
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Old 02-17-2020, 03:10 PM   #3
derek costello
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Default Re: flathead oil pressure?

So.... At 80psi on the starter with plugs out is excessive ????
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Old 02-17-2020, 03:15 PM   #4
flatheadmurre
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Default Re: flathead oil pressure?

Bypass valve is set at 80psi so i wouldn´t worry until you have a reading over that at operation temp.
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Old 02-17-2020, 05:29 PM   #5
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Default Re: flathead oil pressure?

80 psi is a lot it it stays there for any length of time. Some what akin to blasting the bearing surfaces.
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Old 02-17-2020, 05:48 PM   #6
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Default Re: flathead oil pressure?

80psi on the starter w/plugs out and cold oil isn't necessarily bad. Warmed up fully you may see 50+ at speed and anywhere from 15-40 at idle depending on the bearing clearances,idle speed and oil used. If it has 80 w/hot oil I'd look into it...


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Old 02-17-2020, 06:00 PM   #7
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Default Re: flathead oil pressure?

On my engines, I like to see 25 psi at hot idle and 55 psi at 2500 with the engine at operating temperature. The only time I didn't see it was with a fresh build with a "Speedway" branded pump. I replaced it with a known good used Ford pump and the numbers came back to where I wanted them.
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Old 02-17-2020, 06:14 PM   #8
Merc Cruzer
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Default Re: flathead oil pressure?

Quote:
Originally Posted by derek costello View Post
So.... At 80psi on the starter with plugs out is excessive ????
Location: Niagara Falls Canada....that might have something to do with the readings.

Quote:
Originally Posted by flathead4rd View Post
Mine runs about 40 to 50 PSI on startup. I use Castrol 10w-50. After warm up and when it's really hot outside my pressure will drop down to about 10 PSI. With water temperature around 195. Flatheads depend on oil flow not so much on oil pressure. I am running a 286 C.I. flathead.
Mine runs at 65 PSI at speed and 15 PSI at idle on a warm day. I run Castrol 20/50, with Lucas oil stabilizer, for one of the 5 quarts of oil.

He will be fine when Summer comes and he gets stuck in traffic, on an 80 degree day.

Last edited by Merc Cruzer; 02-17-2020 at 06:24 PM.
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Old 02-17-2020, 06:31 PM   #9
Ol' Ron
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Default Re: flathead oil pressure?

Hi oil pressure can have an erosive affect on the crank and bearings. 10 lbs at idle and 40 in cruise os all you need. Another thing you should know, when running a hi viscosity oil, the opening of the relief valve heats the oil to a very hi temperature, however, as the oil warms up and thins out he valve closes and everything is happy. BUT!!! if your still running 50 [lus pressure the oil will over heat and loose it's effectiveness. The factory when it designed this oiling system rex\comensed 10 at idle and 40 in cruise. At this pressure the all the oil coming from the pump is going through the bearings
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Old 02-17-2020, 08:12 PM   #10
flatjack9
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Default Re: flathead oil pressure?

Most relief valves are set to 60 - 65 lb. 80 seems high.
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Old 02-17-2020, 08:17 PM   #11
Merc Cruzer
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Default Re: flathead oil pressure?

Quote:
Originally Posted by Ol' Ron View Post
Hi oil pressure can have an erosive affect on the crank and bearings. 10 lbs at idle and 40 in cruise os all you need. Another thing you should know, when running a hi viscosity oil, the opening of the relief valve heats the oil to a very hi temperature, however, as the oil warms up and thins out he valve closes and everything is happy. BUT!!! if your still running 50 [lus pressure the oil will over heat and loose it's effectiveness. The factory when it designed this oiling system rex\comensed 10 at idle and 40 in cruise. At this pressure the all the oil coming from the pump is going through the bearings
The caveat to my prior post, is that the gauge and sending unit are probably close to the age of the car - 1953 - and I have not used a direct gauge to check either.
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Old 02-18-2020, 01:49 AM   #12
Graeme / New Zealand
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Default Re: flathead oil pressure?

Quote:
Originally Posted by Ol' Ron View Post
Hi oil pressure can have an erosive affect on the crank and bearings. 10 lbs at idle and 40 in cruise os all you need. Another thing you should know, when running a hi viscosity oil, the opening of the relief valve heats the oil to a very hi temperature, however, as the oil warms up and thins out he valve closes and everything is happy. BUT!!! if your still running 50 [lus pressure the oil will over heat and loose it's effectiveness. The factory when it designed this oiling system rex\comensed 10 at idle and 40 in cruise. At this pressure the all the oil coming from the pump is going through the bearings
Too right Ron, bit like high blood pressure on the old human body.

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Old 02-18-2020, 10:28 AM   #13
Merc Cruzer
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Default Re: flathead oil pressure?

Quote:
Originally Posted by Ol' Ron View Post
Hi oil pressure can have an erosive affect on the crank and bearings. 10 lbs at idle and 40 in cruise os all you need. Another thing you should know, when running a hi viscosity oil, the opening of the relief valve heats the oil to a very hi temperature, however, as the oil warms up and thins out he valve closes and everything is happy. BUT!!! if your still running 50 [lus pressure the oil will over heat and loose it's effectiveness. The factory when it designed this oiling system rex\comensed 10 at idle and 40 in cruise. At this pressure the all the oil coming from the pump is going through the bearings
Ol'Ron,

Would the oil pressure specs have increased for later engines, due to better engineering and materials for bearings, or clearances and tolerances? My manual for 1952 shows them a bit higher. It does show the recommended oil weight as 20W above 32 degrees.
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Last edited by Merc Cruzer; 02-18-2020 at 12:33 PM.
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