[Hitman84]

I am having an issue with my newly built 306. I have installed aftermarket mechanical guages and everything works beautifully. However, after driving for about an hour at a normal cruise speed, my oil pressure drops to 0-5 psi at idle. When I rev up the motor it comes back up to 50 -70 psi and while i have the RPMs up around 1K or more everything is fine. My motor maybe has 600 miles on it, and I installed a brand new Melling High Volume Low pressure mechanical oil pump with a FRPP pump shaft which is connected to a MSD Billet distributor.

When the engine is first cranked up the idle pressure is around 25-35 psi, which should be correct from what I have read. Is it possible that I have an intermittent pump, or would it just be bad from the start to finish and not just at operating temp idle?

Any ideas would be greatly appreciated.

I should also mention that I am running Mobile 1 synthetic 10w-30 with a K&N oil filter. I have a Canton 7 qt. oil pan and matching pick up and dip stick. I have no visible oil leaks.

Thanks!

[Lifted78Chevy]

well something isen't right.....im running a high volume pump and at idle with 20-50 oil it ideals between 50-55 oil psi.........then as i cruise it heats up thins out the oil and pressure at ideal drops to 40ish range, never below that....sounds like it might be your gauge is missed up.......most motors that drop to 0-5 psi range die pretty quickly from no oil to the mains and which lead to a spun bearing.....so your motor is running fine when pressure drops that low, i'd put money its the gauge or something is wrong with the pump/pickup.....change the gauge out, see what happens.

[96greengt]

Originally Posted by Hitman84

I installed a brand new Melling High Volume Low pressure mechanical oil pump

Low pressure ????

You mean HVHP oil pump??

Not a good idea to break an engine in on synthetic IMO. Have you changed it since 600 miles?? On a break in, I normally change the oil after the first start up, gets out all the assembly lube, any dirt or solvents from machine work, etc... Then after the next 500 miles, change it again, then onto the normal 3000 miles.

Pressure readings that low indicate pump problems, bearing clearance issues, or a clogged oil galley.

[racer99]

Why a high volume?They take hp to turn and put all the oil up top,
right where you dont want it.

Sounds like an excessive clearance problem with the mains or rods.
It could be a cam bearing problem but I would tend to think mains or rods.
Cold idle should be 50-70 not 25-35.
Hot idle @ 25-35 would be ok.

[thesource]

I'd guess a clearance issue as well .

[Hitman84]

thanks for the input, the pump is not a high volume pump. when i was building the engine, i checked and rechecked all the main and rod clearances and they were all with in the "Ford Specification" limits.

I ran conventional oil in the motor for the first 2 hours of run time in the drive way and then changed to the synthetic, and plan to change it again this weekend.

The engine runs fine even when the oil pressure drops on the guage, which is what i planned on checking this weekend. this only started happening the last time i got the car out. i put maybe 500-525 miles on it with no problems what so ever. i dont want to burn up my new build, so i parked it until i can figure out the problem. if it is a clogged oil galley, how would i go about taking care of that? and would it be a bad idea to pull the engine back out and check the clearances again after the break in? if so is there a "high performance" specification for the clearances or are the factory specs good?

[87fox2e]

i have the same problem on my stock 302, cant figure out why but motor runs fine and i dont have any other issues, so if you figure it out let me know.

[racer99]

Try a different op gauge before
you get crazy pulling it out.

[RichardM]

Sorry I don't know for sure, but is there a pressure relief vavle in the oiling system to keep the oil pressure from being too high when the oil is cold? If so, it could have stuck open. I have had this valve stick both open and closed on various SAABs.

[Razor81]

Weird. Mines a 308 and was built before I bought it but I have the mechanical auto meter gauges on mine and warm psi at idle is from 30-20 never lower than 20 and never higher that 50-60 at higher rpms. Cold psi is at 50-60 and as I romp on it it gets to where its at 20 at idle and 50-60 at high rpms. Maybe its normal?? Im new to sbf's....

[86LXNXS]

Originally Posted by thesource

I'd guess a clearance issue as well .

+1 or a bad guage

[thunderchicken]

Originally Posted by racer99

Try a different op gauge before
you get crazy pulling it out.

I agree...I had also heard that normal should be 10 PSI per every thousand RPM....At normal operating temp....Thats just what i had heard.....

[racer99]

Originally Posted by thunderchicken

I agree...I had also heard that normal should be 10 PSI per every thousand RPM....At normal operating temp....Thats just what i had heard.....

Thats a general rule of thumb
but I am not comfortable with 10
psi at idle.

[aaronedwards82]

Could it be a weak bypass spring that loses spring pressure when it get warmed up? Allowing oil to be bypassed when the oil gets hot, which would cause the pressure to diminish. Or even a broken spring???
I know i have seen that happen on several engines i have worked on before.
Just a thought and suggestion.

[thunderchicken]

Originally Posted by racer99

Thats a general rule of thumb
but I am not comfortable with 10
psi at idle.

Yea i know what you mean,niether was i when i had first heard that......