Thread: Strange combo (Freeway knocking & jumping oil pressure gauge)

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Hey everyone,

I have a 74 Scout II with a '74 Chevy 3970010 350 swapped in. It has been very strong and given me no mechanical problems at all as a daily driver until the last week or so.

It started when I noticed out of the blue the oil pressure gauge started jumping all over the place when sitting at idle. It would jump 20psi seemingly for no reason.

Then when driving on the freeway recently, 70 for me is a sustained 3k rpm, the engine started ticking from the passenger side. I pulled off the freeway and heard that it was definitely coming from under the passenger side valve cover. I waited 5 minutes, then restarted the truck and drove home on surface street and the tick was gone. (Dipstick reads plenty of oil)

90% of my driving is on surface streets, but want to fix this problem before it gets worse. Looking forward to seeing what you guys think it is (lifter? rocker arm?)

Welcome to CHR:

I'd start by draining the oil and looking for anything suspicious, i.e., contaminates or weird coloration. What your describing sounds like something intermittently blocking/clogging your oil delivery passage(s). My guess is that something has clogged the passage between the filter and the top of the block and has limited the flow of oil to the upper reaches of the engine which would account for oil starvation in a lifter which could cause the ticking. It would be especially pronounced at 3,000 RPM (which is, BTW, a pretty good buzz to maintain). How many miles is on this engine? What temperature does your engine typically run?

Look at this page for an excellent primer on SBC oiling systems - hi voluum oil pump installed now no oil pressure? | Grumpys Performance Garage

If you do find crud in your oil you may want to drop your pan and make sure the screen is clear. I'm not a big fan of "engine flushing" but some swear by it. If I were to do a flush, I'd definitely drop the pan afterwords and clean all the glop out of the pan and off the pump screen.

Others will chime in here. Let us know what you find.

Glenn

Thank you! This is great advice, would that explain the gauge acting all strange as well?

I know the 3k rpm is pretty steep for freeway driving I probably should just drive slower in the slow lane. I've got a Chrysler Torqueflite 3 speed auto and a 3.73 rear end with 32" tires so it's as good as it gets without modifying things further.

The engine was supposedly rebuild 20k miles ago when the swap happened, but I can't confirm that and am not sure how to fact check it really. I did just buy a cylinder camera that goes into the spark plug hole to check the pistons, hopefully that will give me some idea. She usually runs at about 190 around town on a belt driven non clutched fan.

Wow - bet your 0-60 time comes right quick!

A clog wold definitely mess with your readings - especially if it's floating up and down, partially blocking the orifice to the pressure sender.

190 is good - so you shouldn't have a lot of varnish and baked on guck. Look at the oil and let us know!

Glenn

First thing I'd suspect is the oil filter. Change it to a Wix or Napa Gold and see if your problems continue.

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Isn't there some kind of spring in the oil pump that can cause that?

Originally Posted by NTFDAY

Isn't there some kind of spring in the oil pump that can cause that?

Are you thinking of the filter bypass? That's a spring loaded route that allows oil to bypass the filter is 10 PSI (or more) resistance is encountered through the filter.

Yes Ken, there is a pressure relief spring in the pump that dumps excessive pressure when the spring is compressed enough to uncover a dump hole. If you want more oil pressure than what the spring is rated for, you can either shim the spring with small flat washers or you can replace the spring with one that has stouter wire diameter. Here's a Melling with a screw-in spring retainer plug, making changes easy.....
http://www.chevydiy.com/wp-content/u...014/01/816.jpg

I personally have never seen an oil pump fail, even on motors with in excess of 200,000 miles on them. What I was thinking when I answered above is that the filter element material is coming apart inside the filter and changing the characteristics of the operation of the filter, ala some Fram filters in the recent past.

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Originally Posted by techinspector1

I personally have never seen an oil pump fail, even on motors with in excess of 200,000 miles on them. What I was thinking when I answered above is that the filter element material is coming apart inside the filter and changing the characteristics of the operation of the filter, ala some Fram filters in the recent past. .

My thoughts exactly in my first post. I have seen little bits of fibrous crud that appears to be part of a filter in the oil. I didn't realize it was Fram specific and I have used the Fram ExtraGuard filters without issues.

This video opens with showing a Fram in which the pleat failed to be captured by the fin, creating a hole that is a direct bypass of the oil without being filtered.....further conversation ensues, with the same individual urinating on a Fram and then using one for target practice.....
https://www.youtube.com/watch?v=XRRgw4B7R-I

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He's a pretty good shot. I haven't used a Fram filter of any kind in some thirty years, Wix or K&N.

how about removing the valve cover and look for oil drainback blockage, broken/bent pushrods/rocker arms, lifter then out of hole causing severe oil pressure loss

OIL GALLEY PLUG AT behind timing gear came out causing low oil pressure

Hey everyone, so I replaced my oil with 5 quarts of Valvoline High Mileage 10w-30 and a Mobil 1 Extended Performance oil filter. The oil pressure gauge is immediately behaving normally again and wonder if there was actually less oil in the engine than my dip stick was showing. I dont have enough experience to be able to eyeball the amount of oil coming out of the pan to know. I did keep the filter, which was a Fram PH5, which I wont be using again hearing about how you guys talk about Fram, and plan to cut it open to see what if any debris is caught in there.

Hopefully that lifter noise will go away now that there is plenty of oil back in the system, time will tell once I take her on the freeway again.

Thanks for all the tips.

Thanks for the follow up - let us know how she sounds at 70 on the free way and what your oil pressure is!

Glenn

Originally Posted by lightyears

wonder if there was actually less oil in the engine than my dip stick was showing. I dont have enough experience to be able to eyeball the amount of oil coming out of the pan to know. there.

With the correct amount oil in your motor, mark your dip stick by filing a slight grove were the oil comes up on the stick.

When I drain my oil, I pour the oil into a gallon jug. Should be close to the top not counting what's in the filter.