just changed my oil and oil filter in my 1961 235 inline six. developed a low oil pressure light in the process. it was suggested that in my old engine i use 20W50. does this sound accurate? now to the main problem. looking into the valve cover with flashlights it doesn't seem to be getting sufficient oil. i assume its the oil pump. i had 10W30 in it. same problem. suggested thicker oil to me so i changed that and same problem. that is when i started looking more into it and found the lack of good oil on the valves. so oil pump is on order. my main concern now as this is my first old work on vehicle is to get it replaced correctly. or rather if there is anything else i could look at before completely changing this part. *what to look for in old pump to ensure it is bad? *what to do with new pump to ensure it goes in and works properly? i tried to find some old posts but it doesn't like the word "oil" too short and common. haven't had much luck with searches as pump brings up nothing but fuel and water pumps. sorry for the long post if i need to include any more info let me know. thanks again for all your time.
In order of importance and ease of fixing, I'd suggest if it did not have the low pressure problem before the oil change, it's likely changing the filter dislodged some crud which got circulated and plugged something up. If the engine is original, it would be a good idea to replace the soft lines from the engine to the filter can. Gas and oil hoses tend to deteriorate from the inside out and can contribute to the problem. Also check for drips or leaks at the hose connections. It doesn't take much of a leak to cause a significant drop in the system pressure. Second, if you're still running the original copper line from the block to the oil pressure gauge, crud could be blocking it. Same thing with the rockers - if the push rods get plugged, soaking them in lacquer thinner and rodding them out with a wire or clearing with compressed air will restore pressure to the top of the engine. If you do this, be sure to keep them in order, so they go back in the same location, and right side up so all the contact surfaces remain matched. These were all common problems years ago before detergent oil and PCV valves came along. If the vehicle was driven at mostly slow speeds, the road draft tube did not generate enough suction to clear the crankcase fumes, which resulted in an incredible amount of sludge inside the engine. If the engine is just old and tired, it could certainly be the oil pump. To confirm a bad pump, pull the cover off the pump and look inside. If it's badly worn the housing, cover, or gears should look worn, pitted, or scored. When replacing a pump it's generally recommended the pick up & tube be welded to the pump housing, although I have never had a problem just using red Loctite. I'm not sure about changing the oil pump in a 235 in a 61 truck, but a 235 in a 54 Chevy car was a nightmare, because the crossmember interfered with removing the oil pan. I'd try everything else before this. In the worst case scenario it could be worn main, rod or cam bearings. Before getting this far however I'd try thicker lubricants. 20w50 should definitely increase the pressure if there is no mechanical blockage. Decades ago i had a severely worn 49 Plymouth engine that turned up about 5 lbs oil pressure. Everything was worn out, bearings, rings, etc. I was unemployed going to school, so I "fixed" it by running 3 qts of 40 wt motor oil, 1 qt of off brand STP additive, and 1 qt of 90 wt transmission lube. For the summer I needed it, the engine pumped up 35 lbs pressure and ran fine. The downside was, when going down a hill it laid down a smoke screen like a destroyer in combat, and wouldn't turn over in cold weather, because the "oil" was too thick for the starter. If you do change the oil pump, it is critical to "prime" the pump before starting the engine. This is done by removing the distributor and spinning the oil pump with a drill motor. You'll need either a special tool for the purpose, or an old cut off screwdriver. The easiest way to make sure it's primed is pull the valve cover, and run the drill on the oil pump until oil is showing in the rocker area. Good luck.
Sounds like you have a case of sluge in the oil pan. It would be wise to change to pump while the pan is off. Replace the pump fill it with oil and run it with engine oil cleaner. Change oil and filter again and you should be good to go.
thanks for the post sounds like i have some work ahead of me what oil would you guys recomend? stick with the heavy 20w50 or back to the light 10w30
Considering you live in Florida, there's no harm in sticking with the 20w50. It might be a problem in regions where the morning temps are sub freezing, or sub zero. Thinner oil flows easier in cold weather. If low oil pressure is a problem, the thicker oil should help keep the pressure up especially after the engine warms up.
anigida09 there was no rebuild. all i did was change oil and filter. everything else you said is accurate i just want the truck to drive around town. as far as location truck was sent to Ohio last week as i am moving. wont drive it much in the winter but summer time it will be out.
