Hey all,

I have just finished swapping a 390FE (from a '65 Galaxie) into my '74 F100 4X4. After countless headaches with my fuel system, I have her running. But now I'm experiencing low oil pressure. I only have the stock gauge, so no concrete PSI numbers, but the needle is below the hash mark at idle. It comes up a little if I rev it. After I noticed this, I changed my oil and filter. The oil was greenish gray, but I didn't feel any particles or grit in it. with the new filter it ran normally until today. Now I have the same problem again, after less than an hour of run time (in five minute chunks). This "new" engine sat in a a shop for several years and I scored it on the cheap. It was stored with oil in it and when I drained it it was black, almost straight crude. Could my pressure problems be coming from the oil flushing the engine and clogging the filter? I have searched the forums, and I'm not finding any one with my exact problem. Any help would be greatly appreciated.

Thanks!

 

First, get a mechanical oil pressure gauge, the factory gauges are notoriously inaccurate.
Was this engine supposed to be a rebuilt?
Generally the main reason for low oil pressure is excess clearance in the bottom end.
Short of tearing it down to check clearances you can "band aide" the problem by switching to a heavier weight oil, straight SAE 40 or 50 and/or replace the oil pump with a high volume unit.
FE's aren't particularly noted for high oil pressure. I ran my 360 for years with the factory gauge just barley off the "L" when it was cold, and that was with straight SAE 50.

 

Thanks for the prompt reply mike; I feel a little bit better now. Will definitely get a good gauge. I tore it down to the block last summer, but left the crank and cam in. New seals and gaskets. My understanding is that it was rebuilt before it was stored. Should I be concerned about the gray oil, or is it just the engine getting cleared out?

 

"AMSOIL" has a prduct called "Engine Flush".
It is a very high detergent oil that cleans up the sludge and oil deposit build up that clogs oil passages.

Low oil pressure will only increase the wear rate on the bearings.
Using full synthetic oil will decrease the wear rate of the bearings.

Increasing SAE oil weight rating will decrease oil consumption, but will not affect oil pressure.

 

I will disagree with that statement. The SAE rating is a measure of oil viscosity. Pressure is a measure of resistance to flow. The more viscous an oil is, the more resistance to flow it will have.
The reason for low oil pressure in a worn engine is because the increased clearances between the bearing and crank/rod/cam will allow oil to flow more easily. The thicker oil will not flow as easily as the lower SAE rated oils increasing pressure.
Granted, this is a band aid/temporary fix, but it does work.

 

Sounds like you changed the black oil before firing, fired her up, experienced low and erratic oil pressure and now the oil is green/grey after short run time. Correct?

I wonder what made the oil turn green/grey? Anti-freeze is often green but if coolant gets in the oil it usually gets foamy. I'd add the aftermarket gauge as others have suggested, change the oil filter and re-test. If the oil changes colors quickly again, something is not happy inside the engine.

Everybody has a preference on oil... that said I like 15w40 diesel engine oil and run it in all my classics. It has enough zinc to take care of the flat tappet cam and cleans things up (gently) if needed.

 

Yes, that's what i did. I took some of the oil down to my mechanic, and it turns out I had gas in the oil due to a flooding carb. I changed it, and now she's running just fine. The oil guage reads very low, but it seems to behave correctly (raises under acceleration, drops at idle, then holds steady), so I think its all good. Way better to drive now than the old 360!