Oil Pressure Troubleshooting

[austinado16]

Could you make a quality (street use) connection between pickup tube and pump using Loctite Green Sleeve Sealing Compound? Pretty serious stuff, and it's used to "glue" bushings into housings.

 

[shortboxchevy77]

Could you make a quality (street use) connection between pickup tube and pump using Loctite Green Sleeve Sealing Compound? Pretty serious stuff, and it's used to "glue" bushings into housings.

In my opinion for street use you should never really have to take steps like this. I would be leery of using any type of liquid compound to permanently fix the tube to the pump. All it would take is a little excess dribble hardening inside and then breaking off to destroy your pump (and engine).

If you are set on doing it I suggest you either do the set screw method or tack weld it for a mechanical lock. You don't have to get crazy with the welder, a small tack will hold it to the end of time.

 

[chengny]

You know what shortboxchevy77, up until I read this thread I would have agreed 110%with your distrust of anything other than somehow mechanically locking the tube into the pump.

But I had to find out more regarding that Loctite/Permatex product mentioned by austinado16. Now I am having second thoughts.

This stuff appears to be a dependable, time-tested sealant/locking compound that performs as advertised. I looked hard - real hard - for any negative revews or tales of bad experiences with Permatex 64000 (AKA Loctite 640 - same product). Nothing!

I was afraid of bond failure due to heat and excessve clearance between the parts but apparently, at least for this application, the stuff is bullet-proof.

As long as the pre-bond gap between the mated parts is less than .007" (that's 7 thousands - not 7 ten thousands!) and the ambient post cure conditions do not exceed 400 F - it does not fail. To break the bond requires the use of a torch or heatgun.

Spec sheet for the Permatex version (64000):

 

[theblindchicken]

If you find that your oil pressure is truly lower now than prior to the recent work, here are a couple of things to think about:

1. How old was the filter you pulled out? See if you can dig it out of the trash and cut it open. To my knowledge Fram oil filters are not fitted with a by-pass valve. And BTW - DO NOT depend on the engine's internal by-pass around the filter:

Consequently, it may have become so fouled over time that one or more of the pleats burst open. This would do a couple of things:

Number one; it would have allowed the oil to pass through it completely unfiltered - bad enough.

But here is another effect of a blown filter (deals with your issue): because the flow of oil from the pump to the system would be unhindered by any pressure drop through the filter - it would actually increase the oil pressure as indicated by the gauge.

Installing a new filter (with intact media) would slow the flow through the filter and result in an apparent drop in pressure.

While you were stuggling with dropping the pan, scraping the old gasket off, re-installing the new gasket and replacing the pan - is it possible that you disturbed the oil pump's pickup tube and the attached screen?

Thanks everyone for their replies and advice. Sorry I didn't get back the past couple days.

The filter hadn't been changed in a while. Probably definitely needed to be done since I know I've changed it, but can't remember when. With both full of oil, the old fram was heavier than the one I replaced it with. So i'm sure it was definitely used up.

The pan came off without any problems and I didn't touch the pickup when taking off the gasket. I used one of the razor blades to remove any paint, putty or glue from a window. Worked like a charm on that cork gasket.

Putting the pan on wasn't too bad. If it hit the pan, then it was just a light tap. Only got stuck on the cross member and the frame because I was putting it in at a bad angle. Pulled it back and put it in no problem.

My father and I have been thinking that the old filter has been the entire pressure issue. And that when the truck sat overnight draining that it may have knocked any residue in the oil lines loose which allowed a lower resistance to the oil flow. Higher volume at lower pressure instead of lower volume and higher pressure.


When I get the time in probably a few weekends, I can pull the pan and get a measurement for the pickup. Do you happen to have a measurement from the lowermost part of the pickup to the lowermost part of the pump?

 

[chengny]

Backtrack on this thread - a lot has gone on since you last visited. There is some discussion about pan floor to pickup screen clearance. Short answer: 3/8" to 1/2".

 

[austinado16]

@chengny: Yep, that's the caliber of the sleeve sealing compound. Once it's cured, you're not getting the 2 items apart without a blow torch. Then red loctite, times a million.

@theblindchicken: I think you should stop betting on scenarios and attach a mechanical gauge. I'm not trying to be a dick about it, just trying to cut to the chase. The oil pickup space-to-pan isn't going to affect your oil pressure with a full capacity of oil in the pan. So you can move on. The scenarios of leaks, oil draining back from where ever-to-where ever, isn't going to affect your oil pressure. Moving from one oil filter (of quality) to the next filter (of quality) isn't going to affect your pressure.

You're engine is either making correct pressure, or it isn't. Find out with a mechanical gauge.

If it isn't making pressure, the pump is either worn out, the check valve for the pressure relief is leaking, or the bearings for the crank, rod, or cam are worn out. That's it.

You can check the crank and rod bearings with the pan removed, and while there, replace the pump. I believe there are high pressure versions available, as well as high volume versions. So in this part of your diagnostics (should the mechanical gauge show low pressure) if the crank/rod bearings are good, and you replace the pump, if you still have low pressure once back together, you can probably assume the cam bearings are bad.

 

[theblindchicken]

@theblindchicken: I think you should stop betting on scenarios and attach a mechanical gauge. The oil pickup space-to-pan isn't going to affect your oil pressure with a full capacity of oil in the pan. Moving from one oil filter (of quality) to the next filter (of quality) isn't going to affect your pressure.

You're engine is either making correct pressure, or it isn't. Find out with a mechanical gauge.

If it isn't making pressure, the pump is either worn out, the check valve for the pressure relief is leaking, or the bearings for the crank, rod, or cam are worn out. That's it.

You can check the crank and rod bearings with the pan removed, and while there, replace the pump. I believe there are high pressure versions available, as well as high volume versions. So in this part of your diagnostics (should the mechanical gauge show low pressure) if the crank/rod bearings are good, and you replace the pump, if you still have low pressure once back together, you can probably assume the cam bearings are bad.

Using the aftermarket mechanical gauge prior to it breaking, it read very similar pressures to the OEM gauge (34psi cold start) while having a small leak at the gauge fitting.

The truck & engine have a total of 80-82k original miles. Approximately 20-30k miles on the engine after a full rebuild even though that was back in the 80's by Joe Reath when his shop was still located on Cherry Avenue in Long Beach, CA.

I feel it is very unlikely that the pressure drop has anything to do with these bearings because the drop only occurred after the following took place:

1. Oil pan was removed
2. Oil pan gasket was removed & replaced
3. Old Fram PH5 was replaced with another Fram PH5
4. Everything was reinstalled

Low pressure was noticed, took everyone's advice and replaced with a quality filter: K&N HP-3002

Prior to the pan removal and parts replacement, the truck idled at a comfortable 45psi cold / 30 psi warm, in gear. The oil pressure responds accordingly when the throttle is increased like it should. Thus, my belief is that the issue is not with the bearings or the oil pump at all, but it was completely with the fact that it was oil and the filter that hadn't been changed in quite a while.

I do not remember the last time the oil filter was changed. The oil was last fully changed at the same time as the filter. I just always made sure the oil was topped off. Thus, if, as Chegny mentioned, the oil filter was damaged due to age and was no longer actually filtering correctly, the pressure may have been higher compared to an oil filter that is actually filtering.

It seems unlikely that the pump is worn out, but parts do sometimes prematurely wear out when compared to their engineered lifespan.

As for the check valve, this is located in the oil pump, correct? Is there a way to test that it is leaking under pressure compared to having oil just being splashed onto it?



Now, I would like to have another mechanical gauge to correctly tell me the current pressures. What aftermarket gauge would any of you recommend that doesn't break the bank? Full sweep would be preferable due to their easier readings.

 

[shortboxchevy77]

You know what shortboxchevy77, up until I read this thread I would have agreed 110%with your distrust of anything other than somehow mechanically locking the tube into the pump.

But I had to find out more regarding that Loctite/Permatex product mentioned by austinado16. Now I am having second thoughts.

This stuff appears to be a dependable, time-tested sealant/locking compound that performs as advertised. I looked hard - real hard - for any negative revews or tales of bad experiences with Permatex 64000 (AKA Loctite 640 - same product). Nothing!

I was afraid of bond failure due to heat and excessve clearance between the parts but apparently, at least for this application, the stuff is bullet-proof.

As long as the pre-bond gap between the mated parts is less than .007" (that's 7 thousands - not 7 ten thousands!) and the ambient post cure conditions do not exceed 400 F - it does not fail. To break the bond requires the use of a torch or heatgun.

Spec sheet for the Permatex version (64000):

Its not the bonding abilities of the product that concerns me. What concerns me is excess epoxy forming a droplet outside of the bonding area when you press the pick up tube onto the oil pump. That little droplet of excess then hardens and runs the risk of breaking off of the little bit of surface its attached to. If it breaks off and goes into your oil pump gears and locks up that pump shearing off a factory pump driveshaft you are done, game over. I'm just terribly leery of using any type of super hardening epoxy like that on the oil pump itself. If you were extra careful you would probably be fine I suppose, its just not a risk I'm willing to take.

 

[chengny]

Oil pressure has dropped down to 15 psi at idle while in gear. Pressure increased to 30psi while going 40mph and no increase while at 70mph.

If everything else appears normal, I would not worry. Drive it and don't over-analyze this issue.

While they usually run over what is shown on the engne spec sheet below, your oil pressure is still well within normal range for a SBC with 80K miles. Oil pressure as indicated by the dash gauge (or warning light) is essentially just intended to alert the driver if there is a severe loss of oil pressure. As reference, the low limit alarm set point of the pressure switch (that activates the warning lamp - or choke light) is 10 psi.