Recently installed a mechanical oil pressure gauge in my 71 GS 455. I put 10W-40 Lucas Muscle Car Oil in it when I changed it a couple months ago. My pressure at start up is almost 80 PSI at a high idle speed. With the engine cool, it drops to about 60 at 650 RPM. Once the engine is hot, it will still be about 30 PSI at idle, and runs between 60 and 70 PSI running down the road. To me, this seems a high. Should I drop to 10W-30 and see how it does? The oil pump does have the additional plate on it, so it has had some modifications done. I have no history on what has been done to this car over the years, but think the short block is a later model, and the heads are from 1970, and could be Stage 1 by the casting numbers. Eventually, I will go through the engine, but have higher priority needs now and it runs pretty well.
Run the car down the highway for 20 minutes, then check your hot oil pressure. That will get the oil as hot as it will ever get. You can try 10W/30, it is always best to use the thinnest oil that gives you satisfactory oil pressure, which is 11-12 psi/1000 RPM. BTW, you can't tell Stage1 heads by casting numbers.
Yes try some 10w-30. The oil pressure you have is really good, not too much IMO. However, you should be running the lightest viscosity you can, not to go any lighter than 10w-30, again IMO. I’ve never liked 10w-40 — oil too many viscosity enhancers to get it to behave like that.
My 71 GS 455 does the same thing. High when cold and lower when at idle and warm, although mine gets a little lower than yours. When warm, the oil pressure comes up as the RPM increase. I do run a 10w-30 synthetic oil.
Brand new Autometer gauge, but anything is possible. Factory gauge also runs pinned on high most of the time, and only drops to about midway when the engine is hot and at idle. Thanks
Sounds like you have a problem alot of us would like to have! Perhaps an adjustable regulator for the oil pump? Jim
You mentioned the oil pump has the additional plate on it. While that plate could be a booster plate, it can also be a spacer plate for the longer gears of a Hi volume Hi Pressure oil pump kit. If that is the case, you need to be careful when the oil is cold as the larger pump back loads the front of the motor, and damage to the cam gear, distributor gear, front cam bearing is possible if you wail on it before the oil is up to temperature. In any case, I would use a thinner oil as you have plenty of oil pressure to spare. Hot oil pressure will also depend on main and rod bearing clearances. If the engine was built with tight clearances like specified in the chassis manual, oil pressures will be higher. Lots of unanswered questions if you don't have the records and receipts from the short block rebuild.
