Oil pump question

Pete Whitstone

Pete Whitstone

True Classic
Hey all,

This question is about a twin-cam engine but there seems to be plenty of that knowledge here, so here goes.

Twice I have gone to start my Scorpion and the oil pressure never came up. The first time, I shut it down after about 10 seconds, then restarted and everything was fine. Weird but I didn't think too much about it.

The second time was yesterday, and I let it go for maybe 15 seconds. On restart it did not come up again like it did in the first episode, so I shut it down again.

I believe the oil pump is turning, because the needle starts to show movement and responds with little twitches when the RPMs are upped, all of which is "usual", but it always goes away (light goes out and needle starts swinging solidly upward) in a few seconds.

Note that I am still running my summer oil, 20w50, and it has been colder lately (40's at night).

So shooting from the hip here... do oil pumps have some kind of anti-drainback device in them that prevents the pickup tube from draining, and therefore making the next start easy to get the oil circulating again? I'm thinking they do because when you change your oil (and presumably the pickup tube is drained), it takes a whole lot longer for the pressure to come up and that's what it's acting like.

So I guess the question is, am I on the right track here, and if there is an anti-drainback device, what does it look like (I'm guessing spring and check ball?) and is it serviceable or do you just replace the pump?

Thanks,
Pete
 
Probably

Pete,

Your twincam doesn't have a valve to prevent the oil from draining. Most engines don't. However, the oil filter does. I would assume that the problem you have is the anti drainback valve in the filter has failed or is stuck.

Before running the engine again replace the oil filter with a quality unit. I would fear that such a failure may cascade into a loss of oil pressure. Not to mention that dry starting the engine every time will likely result in main bearing failure.

Note: When draining the oil during a typical change, it is the empty oil filter that causes most of the delay in the return of normal oil pressure on startup. This is why it is important to prime the oil filter with fresh oil before installing it.
 
Thanks Steve

I was going to switch to a lighter oil and change the filter before attempting to run it again. Sounds like that will take care of the problem.

Thanks for the info.

Pete
 
Dumb question, but is it an electric gauge? If so, the sending unit or gauge may be at fault and you really do have oil pressure.

Interesting side note: on the early Ford Explorers (I've had 5) the oil pressure gauge will read varying pressures. On "exploration," I found that it really isn't a gauge at all, but an idiot light disguised as a gauge. Over 15 pounds and it reads pressure. Further investigation of gauges makes it appear that electric gauges are not all that accurate.

Ditto on the filter - I'll post a link to an excellent article on oil filters, but that's an easy thing to check, too - before you start look at expensive solutions.

Cheers,
-- Mike
 
It is the factory electric gauge

But I believe it to be accurate.

I was aware of Fords "gauges"... my 2001 F350 diesel has the same thing - oil pressure gauge goes immediately to the middle and stays there. Never reads higher when the oil is cold, never goes up and down with RPM like a real gauge would.

I'll report back after the oil/filter change.

Pete
 
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