FE 390 oil related questions

[KULTULZ]

A quality mechanical oil pressure gauge purpose is for the operator to monitor engine oil pressure irregularities..

If you notice extremely low pressure and/or warning lamp, you are most likely too late.

When I worked on BIG TRUCKS, the starting oil pressure was recorded after every service to monitor any engine problems. That and oil analysis.

A gauge/lamp on a pass car is not an exact reading system.

[KULTULZ]

Entering Into Evidence - https://www.amsoil.com/newsstand/die...my-gas-engine/

The thing is or was, years ago when lubricants wasn't as specific, diesel oil was rated for gasoline engines also. This was mainly for fleet use where mixed vehicles were used (HD gas engines) and the stocking of two different oil types was reduced.

[39deluxecp]

Ha Ha! the guy asks for a oil sender question and it turns into an oil converstation!! Gear heads love to talk about oil!

[JimNNN]

I got my oil pressure warning light and mechanical oil pressure gauge installed and working today, and it was more of a procedure than usual. Spent a fair amount of time wondering where and how to mount them. The mid 60's Thunderbird is unique enough in the dashboard to make aftermarket gauges and stuff less than practical to mount under dash, at least for tall people like me. I decided to mount in dash, and it looks ok, though I'm never thrilled to modify existing dashboards. My dash isn't in great shape, however, so it wasn't that big a deal.



Talk about a different reading from the original factory gauge! I was worried that my pressure was going to be on the marginally low side since the original gauge would show pressure slowly creeping up to it's highest point - about mid range - then just barely hover around what the owner's manual called minimum acceptable range at speed.



The new gauge immediately pegged the needle at 100 plus psi at idle. I was actually alarmed. I did the work in my garage which was close to 60 degrees today, so not real cold. I had changed the oil and filter, so I thought maybe the filter was creating a problem and I changed it, again. Still the same. Because of circumstances I actually had two of these gauges, so I changed the gauge - still 100 + psi.



Then I drove the car around because the pressure always comes down with use and heat. After a good while I was getting 60 - 70 psi on the highway. Hovering around 20 at idle in gear and about 30 with slightly high idle out of gear. Oil pressure warning light working good, glowing brightly at about 16 or 17 psi and below.



I never would've guessed I would get these readings. My original gauge gave the impression I'd be lucky to be at around 55 psi cold start, and 10 or 12 psi at hot idle. This is why I wanted to replace it with something more informative. My impression of these old original Ford gauges is that they can't really be relied upon for accuracy. The sender was old, too, however, so that could've been the culprit. Anyway I'm glad I opted for doing this.

[KULTULZ]

The new gauge immediately pegged the needle at 100 plus psi at idle. I was actually alarmed. I did the work in my garage which was close to 60 degrees today, so not real cold. I had changed the oil and filter, so I thought maybe the filter was creating a problem and I changed it, again. Still the same. Because of circumstances I actually had two of these gauges, so I changed the gauge - still 100 + psi.

Then I drove the car around because the pressure always comes down with use and heat. After a good while I was getting 60 - 70 psi on the highway. Hovering around 20 at idle in gear and about 30 with slightly high idle out of gear. Oil pressure warning light working good, glowing brightly at about 16 or 17 psi and below.

What weight oil (and type) are you using and what brand oil filter?

Has anyone been in the engine lately? You sure you don't have a street 427MR in that BIRD?

[KULTULZ]

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Originally Posted by dmsfrr

A quote...

Modern heavy-duty diesel engine oils have lots of ZDDP additives and will be marked “CI-4 or CI-4 Plus” Diesel oils also have additives that pass all gasoline engine performance tests. Some racing oils also have adequate amount of ZDDP.

from this link... https://www.ctci.org/engine-oil/

If you will notice, the article is describing MOTOR OIL circa 2006.

He should update the write-up on his site.

The ROTELLA-T of that period was not SN.

[JimNNN]

The oil was 15/40 Valvoline. I had put in a bottle of the STP treatment - which is pretty thick - because it has the zinc protection (here we go on the oil again.) Would a high volume oil pump create these cold start readings? Pressure seemed pretty normal after warmup to operating temperature. At normal operating temperature, the psi was about reading about 5 more than the mph (e.g. about 50 psi at 45 mph.) I'll drive the car tomorrow and see what it does.

[KULTULZ]

Originally Posted by JimNNN

The oil was 15/40 Valvoline. I had put in a bottle of the STP treatment - which is pretty thick - because it has the zinc protection (here we go on the oil again.)

Would a high volume oil pump create these cold start readings? Pressure seemed pretty normal after warmup to operating temperature. At normal operating temperature, the psi was about reading about 5 more than the mph (e.g. about 50 psi at 45 mph.) I'll drive the car tomorrow and see what it does.

A HV pump could cause the initial high pressure. Either STD, HP or HV have pressure relief valve(s) to allow the pressure to reduce itself on cold start/Hi-RPM. You may have a inoperative relief valve or somebody shimmed the spring thinking it would make it a race engine. Or there is a defect somewhere in the engine.

The oil pump shaft will get a lot of pressure also.

15W-40 is too heavy of an oil for a street engine (unless it is worn) (IMO). Think 10W-30, maybe 10W-40 for a hot climate.

If the oil is VR-1, no need for a ZDDP booster.

Don't use a WALLY WORLD oil filter unless you know its burst rating.

[JimNNN]

Originally Posted by KULTULZ

15W-40 is too heavy of an oil for a street engine (unless it is worn) (IMO). Think 10W-30, maybe 10W-40 for a hot climate.

If the oil is VR-1, no need for a ZDDP booster.

Thanks for the input, KULTULZ. I think I'll start with changing out the oil to 10w 30 and see what happens. 10w 30 is always what I used in my first cars back in the 1970's, which were all V 8's. That was always my standard until I started getting into "old" cars and motorcycles 17 or 18 years ago. My Ranch Wagon has never had the engine rebuilt, has 66k miles, needs valve seals most likely, and the 15w 40 keeps pretty good pressure in that engine.


I started the T-Bird again this morning, and again at cold start up pegged the needle at 100+ psi. It'll be interesting to see what hot oil pressure readings will be with 10w 30.