Hi all, this has got me stumped. 1st truck has a 440 and was holding great oil pressure (80 on start up). Last time out in the mud hole my mechanical guage was reading 0 after a few minutes of hard use. Changed oil filter and it went to 20 but dropped back to 0. My brother in laws truck has a 318 and was pulled from a running van with good oil pressure. After the swap that motor did the same thing. The only thing we have in common is the Valvoline racing 50 weight oil. Any ideas? Thanks in advance!

Make sure that you have all the lifters in place.
How much do they rattle. If no rattle you have pressure. The lifters will bleed down almost instantly without pressure.

I would check both guages first. Like the guy said if they aren't making any noises you have pressure, you just can't see it on the guages. 50 wt seems awlful heavy, even for Fl.

Nrw guage on the 318, cold started it just now, 40 lbs at idle dropped to almost 0 when warmed up. Cold started the 440, 40 lbs at idle 60 at 4k, dropped to 0 after it warmed up, holds 20 at 4k. No lifter noise from either motor. My motor has always held good pressure and its weird for it all of the sudden to drop like that. I've been running 50 weight since Marvin Hughes rebuilt it several years ago. Thanks for the suggestions, please keep them coming!

What kind of gauge are you using?

Almost sounds like a stuck relief valve but why on 2 engines at the same time Pull a valve cover and start the engines and see what you have for flow.
Personally have 0 use for that heavy of oil in a engine. Actually get poorer lubrication until that oil is very warm in order for it to flow halfway decently. with that in mind I would definitely check the main bearings.

The 440 has a sunpro guage.

The 440 sees 220 to 240 degrees on a normal mud run which is why I;ve used the 50 weight I have a new guage to try out, my brother in law says he's going to change his oil to 10w-30. How much flow should you see under the valve covers? Thanks!

are you running those "ORANGE" oil filters ?

they are just like the "ORANGE" ignition boxs,,,,, plain junk....

I don't see how the filter has anything to do with it. I've used those orange filters for 30 years in everything from Cat 3406A engines to my pickup sitting outside.

If you had to use or was told to use 50 wt from the beggining, sounds like the clearances were very loose. I'd check the pump on the big block first, easier to get to. Check the relief valve. MAybe the thick oil has it stuck.. It really is something that both have the same thing at the same time. DO you both use the same oil or did you both change brands at the same time. I'm at a loss.

Fram filters are cheap cardboard trash inside and come apart causing an oil flow stoppage that takes out lower ends. I have seen a bunch of them cause low oil pressure ion a perfectly good engine.Installed a new good brand filter on those engines and got good oil pressure back. This is with the frams being on the engine for a short so they weren't dirty and clogged from use.

I don't obviously think they are related. The heavy oil is also not a big deal IMO. If the oil pump shaft hasnt sheared you should be fine. I'd be looking at the pumps themselves... The big block is easy to pull. Remove it and tear it down. Sounds like somethign in the relief valve. If it was me, I'd run one brand consistently because there is such a difference in construction and performance now that mixing them will change your results too. My brand is Wix. I won't run anything else.

A Fram can fail at any time for no reason. just becasue it "worked in the past OK" doesn't mean it won't fail today.

If you are running the engine 220-240 on a regular basis then that right there might be the culprit. You need to put an extra fan and a high flow pump on it, as well as a great radiator. No reason it should ever run that hot.

There will never be a fram filter on this truck ever! The motor before this one failed because of the fram filter. They did help pay for the new motor but didnt come close to what I had in it. As far as cooling goes I have a custom built 6 core rsdiator in it. The problem is there is not alot of air getting through because your not at a high rate of speed compared to the rpms. I tried electric fans but broke the blades going into deep water (forgot to turn off!). Iv'e been looking for a fixed fan blade that will hold up to 6000 rpm.

The 318 had the guage replaced but same results.
Will pull the oil pump and see whats up.