Oil pressure drops while driving

RVALDEZ

MEMBER
1979 FORD F-100
4.9L
6 CYL
2WD
AUTOMATIC
100,000 MILES

Oil pressure is fine when idling. But it drops all the way down when I drive a block away. Tried putting it in neutral but doesn’t come back up. I was told the oil I might be using 10w-40 might be too lite. I was told to try 20/50. I have also changed the oil sending unit but still have issues. This truck does have oil leaks as well.
At this point I was going to change the oil with 20/50 and move onto the oil pump next. Worse case the bearings or replacing the engine. I would appreciate your help. Thanks in advance.

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Hi,

This is an interesting one. I would think the opposite would happen. When the pressure drops, do you hear any knocking or ticking from the engine that may indicate the pressure is low? If you don't, here is what I suggest.

Go to a local parts store and rent a mechanical oil pressure gauge. Basically, you will remove the electric sensor on the engine and screw in the fitting for the mechanical gauge. Check the pressure using that gauge to confirm the pressure is actually dropping.

Also, the motor oil would have originally been 10w30. Not knowing where you are located, I wouldn't suggest 20w50 unless you are in an area that is somewhat hot on a regular basis.

By chance, could you let me know where the oil leaks are located?

Let me know.

Joe

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Friday, April 22nd, 2022 AT 8:20 PM

RVALDEZ

MEMBER
2 POSTS

Hi Joe, thanks for your time.

It’s been making a light ticking noise for a few years now. And I’ve been having to put it in neutral and give gas to neutralize the pressure until I start moving again for a while now. Sometimes it will be fine for the whole trip. I should have put that in the original post.

I will try the mechanical gauge this weekend and will get back to you.

And I’ll stay away from the 20/50 oil.

The oil leaks seem to be on both sides of the head gasket.

This truck is in very good condition so repairing it is the only option.

Thanks again and I hope to update soon. I’ll add pictures as well.

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Saturday, April 23rd, 2022 AT 7:39 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

Hi,

Sounds good. I will watch for your reply. Also, you may even have the pick-up screen partially clogged which will require oil pan removal.

Let me know.

Take care,

Joe

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Saturday, April 23rd, 2022 AT 8:21 PM