| Barney | -- 11-02-2022 @ 5:02 PM |
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Good evening All, I have a 1940 85 HP V-8 with what I believe to be normal oil pressure - but only until the engine's fully warmed. I have the original instrument panel gauge and a bourdon tube type gauge. They agree all the way down to about 12-15 psi. When warm at an idle, the instrument gauge reads about 12 psi; the 'mechanical' gauge reads closer to 2-3 psi. I tend to believe the latter gauge to be more accurate. Should I be concerned? If so, is it as simple as removing the intake manifold and installing a strong oil pressure relief spring or adding a spacer or two to effectively make the spring stronger. When I was a 'kid' I would add washers to my small block Chevy pumps. I thought it was cool to have 80psi displayed on the gauge. Thoughts, comments, reprimands, etc.? Thanks, Barney
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| alanwoodieman | -- 11-02-2022 @ 7:21 PM |
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what weight oil are you using? do you have a filter installed? is the.060 orifice/restrictor installed in one of the oil lines? there is a relief spring in an A/ab engine under the intake and you can change to a stronger spring located there. do you know the mileage of the engine? what is the oil pressure going down the road, engine warm?
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| asimkhan6296 | -- 11-03-2022 @ 3:46 AM |
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I have same question for my ford. https://wheelsrush.com/
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| Barney | -- 11-03-2022 @ 4:30 AM |
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Good morning, Alan, Immediately after I sent my inquiry out I thought I should have included oil weight - good info to know. A bit of history: I bought this car as a basket case - literally. The engine was clean, painted, and had very clean oil in it. After running it a bit, I was hoping it was break-in oil due to the low oil pressure. It starts quickly, runs well, runs strong, doesn't smoke - so I'm optimistic it was rebuilt and has little or no miles until I drove it a few miles. I attempted to find straight 30 wt detergent oil, but failed. I installed 10W-40; it has no filter. I have no idea if it has a .060 restrictor installed. After viewing a manual, it appears as simple as installing a strong relief spring to fix this issue. Fully warmed, running 45-50 mph down the road, it produces about 18-20 psi. I'd like to see at least 30 psi. When cold, it pushes 55 psi, but only for a short time. Thank you for your response, Alan, and from any others that chime in. Regards, Barney
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| 40 Coupe | -- 11-03-2022 @ 5:22 AM |
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It is VERY common for early flat heads to have extremely low oil pressure after getting to running temperature. The engine will run a long time with the low idle oil pressure. Only a full rebuild will correct this. Usually a new oil pressure relief spring or washers will not help!
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| marko39 | -- 11-03-2022 @ 6:05 AM |
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The relief is there to open with excessive pressure and won’t help with low pressure. You should be able to find 20/50 oil which many use on engines with wear. ( myself included). Try it, nothing to loose.
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| JayChicago | -- 11-03-2022 @ 8:25 AM |
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Some of my thoughts, for what it's worth: Your pressure seems fine to me. Around 12 psi on the instrument panel gauge at hot idle is better than what most of us see at hot idle. Your engine doesn't need the oil pressurized any more than is necessary to achieve flow of the oil to all points. As long as there is some residual pressure you are OK. The 2-3 psi you see on the mechanical gauge may or may not be accurate. Even high-quality gauges are not that accurate at the extreme ends of their measurement range. And many after market gauges are very inaccurate. And even if that is accurate, 2-3 psi at hot idle is not uncommon for our flatheads. Fooling with the relief spring will do nothing for low pressure. As said above, that spring is only a hi pressure relief. Don't need to try to find that .060 restrictor. It goes in the feed to an accessory oil filter to restrict flow and drop pressure thru the filter. If you don't have a filter, you don't have the restrictor.
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| 37RAGTOPMAN | -- 11-03-2022 @ 12:14 PM |
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85HP IF you increase the pressure, does that reduce oil volume ? I have a 80 lb pump and never change the sending unit or the pressure relief valve, and have good pressure its been 15 years using the 80 lb pump my 2 cents 37Ragtopman
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| Barney | -- 11-04-2022 @ 4:35 AM |
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Thank you very much to Jay, Alan, Mark, 40Coupe, RagTop and any others who may reply subsequently, Y'all have placed my mind at ease, thank you. It makes sense to me that very little pressure is required - just enough to keep it moving. After all, we're not talking about super high-performance engines here. It's interesting to me that there's a significant difference in pressure from running cold and running warm. That tells me there's probably excessive clearances here and there. Maybe I'll attempt straight 40 or 50 wt oil at the next change - if I can find it. I have had many small block Chevys apart, but never a flathead, so I can't picture the pump in my mind. It seems that a stronger relief spring would help. Isn't the pump a positive displacement type pump, ei. a gear pump? I guess it's very possible the gears in the pump are worn to the point of not being able to produce higher pressure. In any case, I'm taking the attitude, "If it's not broken, don't fix it." The engine sounds great and healthy when running cold or warm. It doesn't 'complain' by making abnormal sounds. The oil does not smell 'burnt'. Thanks again, Barney
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| carcrazy | -- 11-04-2022 @ 7:17 AM |
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Be careful not to run too much oil pressure in a '40 Flathead! I had one rebuilt a few years ago and I let the machinist talk me into running a later, 80 PSI, flathead oil pump in the engine. Big mistake! With straight SAE 20 Detergent oil, this engine had a massive oil leak past the rear main bearing. As long as the engine was running oil would be continuously dripping out of this location. Driving down the highway this car with freshly rebuilt engine used a quart of oil every 200 miles and pegged the oil pressure gauge at the high side at all time while the engine was running, hot idle included.
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| 37RAGTOPMAN | -- 11-04-2022 @ 7:49 AM |
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Barny tip,, try TRACTOR SUPPLY for heavier oil, they do have it for older tractors, hope this helps 37Ragopman,Maine Straight weight oil, non detergent oil has cling factor for start up, was used for years, This message was edited by 37RAGTOPMAN on 11-4-22 @ 2:01 PM
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| JayChicago | -- 11-04-2022 @ 9:01 AM |
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"Maybe I'll attempt straight 40 or 50 wt oil at the next change - if I can find it." Why not use modern multi-viscosity oil? What advantage is there to straight-weight oil? I can only see a possible disadvantage: too heavy for good lubrication on start-up.
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| alanwoodieman | -- 11-04-2022 @ 6:03 PM |
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run 20w50 oil, Kendall, Castrol, many others. do not run a straight wt oil engine does not get proper lube upon starting, especially cold weather--sort of like molasses on a cold morning!
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| GK1918 | -- 11-05-2022 @ 6:34 AM |
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All I can say is for example a 2 stroke Detroit Diesel say a 6-71 the oil pressure only gets what it needs like a shocking 5 lbs at idle and if all is healthy maybe 30 at speed. So my 46 59A pretty close to your 85 hp is 60lbs all day at speed and 35lbs hot idle. because I built it correctly. But the 59A does have 80 lb pump land gauge.
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