Low Oil Pressure & None @ the Rockers

[72 Cheyenne K20]

Hey Guys & Gals,

I bought a 1976 GMC K15 with the factory 400, TH350, NP203 about 3 months ago from a guy in Reno. It runs, drives, and stops pretty well. No real issues other than low oil pressure.

Factory gauge reads 30-32 on cold start
after warm up just off of fast idle reads about 25
after warm fully 12-14

It responds when the throttle is pushed but never goes higher than 30 at a steady cruise at 55-60 mph.

I've read posts here and online research and have done the following to diagnose:

New Wix 51061 filter, 15w-40 oil, and a mechanical gauge installed and still same or worse results. at hot idle with these done it had about 5-7 lbs of pressure on the mechanical gauge. (I also notice that it took a really long time for the plastic line to fill with oil to get to the gauge)

So, I bought an oil primer tool and tested it today with valve covers off. I'm getting zero oil to any of the rockers and roughly 35 lbs of pressure on the mechanical gauge on a wide open 3/8" Dewalt drill. Not sure if it matters but I do have the harmonic balancer mark set @ 6am.

It takes a few seconds for the gauge to read any pressure and I'm also hearing a rhythmic kinda whining noise other than the drill turning.

Please send your thoughts on what you think.

Thanks, Scott

[72 Cheyenne K20]

Here's a little more info also

looks like the motor hasn't been worked on too much other than maint. Has a little over 72K original miles.

When I took the valve covers off there was no gunk, crud, or build up anywhere. It looks good, not dry but not soaked either.

No bends or dents in the oil pan that would indicate and lifting or damage.

Thanks, Scott

[Cooter!]

The answer will be different depending on your plans for the truck.

I bought a '70 El Camino (350 Target motor) with barely 20psi at cruise, O at idle hot, with the intention of swapping in a new engine once it expired. No knocks, no ticks and over 7 years of daily driving and hauling bikes around, still runs strong! Heck, it was so bad I removed the gauge so I wouldn't worry about it anymore


So, sure, you know the answer because you're the only one that can choose. Money, time, or trouble? Buy an engine, run thicker oil, buy an oil pump (maybe the bypass is stuck?), or ignore it. All those choices come with their own consequences

[RustyPile]

Little to no oil being delivered to the valve train means the camshaft lobes aren't being properly lubricated.. You'll soon loose the camshaft. That means major spending to bring it back.

For some strange reason, SBCs can survive with low oil pressure, but oil has to reach all the places. Drain the oil and put straight 30W or 40W in it.. This will bring the oil pressure up, but you have to make sure the valve train is getting lubrication. If so, you're home free (almost).. If thicker oil doesn't restore oil to the valve train, replace the oil pump.. And if you feel up to the task, roll in some new rod and main bearings.

[Dead Parrot]

One messy test is to have the valve covers off and then start the engine. Check for oil coming out of all the rockers at idle. You will find out fairly quickly if you are getting oil flow while the motor is running.

Oil flow is more important then oil pressure. If the above test shows good flow, go back to 10w-30 and don't worry about it.

[Getter-Done]

My best story on Low/No oil pressure is.

I once saved a 1974 shortbed K10 from the crusher.

It had a rod knocking and was missing both doors.

I put 2 doors I had from my collection and fed it Lucas Oil Treatment.

I drove that truck for 3 years till someone pulled out in front of me.

This all depends on your situation.

Is this your daily driver or a Project?

[72 Cheyenne K20]

Thanks for the feedback and suggestions. I bought this truck as a possible restoration project down the road and just to drive and play with for now. It’s what I’ve been wanting for quite awhile. Factory orange, original 400, tilt, cruise, dual gas tanks, etc. it checked all the boxes for me and it came with barely any rust issues.

Plus I got it for a steal ! So driving it the way it is without trying to fix this issue and blowing up the engine isn’t going to happen. I’ve had other trucks that I’ve just driven and didn’t do a lot to but this is probably the last one I really enjoy and keep. I’m going to retire in a few years and constant trips to the junkyard for parts is not in my future. I still like it, but not as a steady diet.

I’m going to try and drop the pan today and see what I can find. Hopefully it’s just a pump gone bad and an easy fix.

Thanks Scott

[72 Cheyenne K20]

Here are a few pics

[72 Cheyenne K20]

I was able to get the oil pan off and everything looks pretty good as far as I can see. Certainly no obvious oh sh.. moments. I took the oil pump off and again no obvious damage. I did rotate it by hand and heard / felt a pulsing gurgling noise. I tried it again after lunch and noise is gone. Guessing it was oil that hadn’t drained yet.

[Cooter!]

A new high volume (not high pressure) pump is cheap insurance now that it's in your hand and should bring back the pressure on a worn engine by filling big clearances .

Did you pull off a cap or 2 to see if there's any bad wear down there?

[Getter-Done]

As Cooter said in the post above.

I also suggest a High-Volume oil pump.

Since you are (Probably going to replace the oil pump) in it this far.

If you take the 4 bolts from the bottom plate of the oil pump this will probably tell the story.

If the Plate has excessive wear, there is where the pressure loss is starting to lose it momentum.

[Corts60]

Show us a pic of the oil primer tool. Most likely it doesn't have the casting to complete the top end oil passage and therefore you will never get oil on top end with that priming tool.

I use an old gutted distributor to prime engines so I know oil will get to the top. Also, old school math on enough oil pressure to keep an engine alive: 8psi per 1000 RPM. If you're getting less than that at idle, bearings are worn out.

[RustyPile]

Originally Posted by 72 Cheyenne K20

I was able to get the oil pan off and everything looks pretty good as far as I can see. Certainly no obvious oh sh.. moments. I took the oil pump off and again no obvious damage. I did rotate it by hand and heard / felt a pulsing gurgling noise. I tried it again after lunch and noise is gone. Guessing it was oil that hadn’t drained yet.

That is a Melling high volume oil pump. The engine did not come with that pump from the factory.. It could be worn out, but so could the rest of the engine.. A closer inspection is warranted.

[72 Cheyenne K20]

Thanks again for the input !

I bought a Mahle M55 (stock) oil pump and got everything put back together. Used the primer tool with the same results. Pressure went to around 35 at wide open drill speed.

Then just put everything back together and started the engine. At cold start it had 22 lbs and a dry top end. Only ran it long enough to know it wasn’t good.

I’ll take a pic of the primer tool tomorrow and post. The distributor is factory GM HEI. I’ll take a pic of it also.

Thanks again for the input, it is much appreciated !

[72 Cheyenne K20]

Site won't let me post a pic due to a security token issue. But it is an Amazon 14.99 tool and looks like all the rest you find online.

Would it be of any benefit to take the intake off at this point ? I'm getting oil to the port for the mechanical oil pressure gauge which means I'm getting some oil to the top but obviously none to the lifters/rockers.

Scott

[Corts60]

Originally Posted by 72 Cheyenne K20

Site won't let me post a pic due to a security token issue. But it is an Amazon 14.99 tool and looks like all the rest you find online.

Would it be of any benefit to take the intake off at this point ? I'm getting oil to the port for the mechanical oil pressure gauge which means I'm getting some oil to the top but obviously none to the lifters/rockers.

Scott

No need to post a pic, you had me at 14.99 amazon tool, haha. It for sure doesn't have the casting to complete the oil passage. I'll post a pic shortly of what I mean.

If you only have 22 psi on cold start, then there is bearing wear: cam, crank, rods, any combination therein. No need to pull the intake. If you are not getting rocker arm ticking or lifter tick when you start it, then the top end is getting oil pressure. The rockers would be clattering away with no oil pressure.

[Corts60]

This is the passage that completes the top end oiling circuit. Without this little casting, oil cannot get to the top end.

[Dead Parrot]

If it is this $15 Amazon primer, it looks to have at least made an attempt at the casting:
https://www.amazon.com/DPTOOL-Primer.../dp/B086KR2PY7

This one looks like it might be better: https://www.amazon.com/dp/B078WJM7W6...osi&th=1&psc=1

[72 Cheyenne K20]

Hey Corts thanks for the info and pic & to you also dead parrot. That is in fact the same tool. But mine is green, I got green for good luck lol.

When I started it up last time after getting all put back together I definitely heard top end chattering like I haven’t heard before and it’s been harder, takes longer to start than it did at first. It’s strange, I have put roughly 250 miles on this truck since I’ve had it and this is very new and happening very quickly. Again, I don’t know the history of the is truck but it seem pretty quick to go from where it was to now.

Can bearing go that quickly ? The only real maintenance thing I have done was to pour some Berrymans gas treatment in both tanks to clean the fuel system and to make sure the switch and gauge works with both tanks.

[Corts60]

Oiling issues won't cause runability issues like hard starting.... If it now is running worse, it may be something you touched when you had it apart.

I'm getting the feeling the previous owner had added oil thickener, i.e.: Lucas or STP. And when you changed the oil to regular oil, you now are having pressure and chatter issues. Most likely the previous owner new this.

[72 Cheyenne K20]

Im going to pull the distributor again and check it against the pic you sent and make sure thats not an issue. Then start it one more time with both valve covers off and see what I get. If I’m dry up top at that point I’ll just plan on a rebuild in the spring.

Thanks for all the input and advice!

Scott

[Cooter!]

Unless you are getting LOUD ticking from the hydraulic lifters, you are getting enough oil to them.
Oil goes right up from there, through the pushrods, to the rockers.
Got any pics of under the valve covers? If its dry under there, things get real hot and real blue pretty fast. If its wet inside, you are getting oil there too, without the need to make a huge mess

[72 Cheyenne K20]

Here is a pic of the left head, the right side looks exactly the same

[RustyPile]

Originally Posted by 72 Cheyenne K20

Here is a pic of the left head, the right side looks exactly the same

Things look pretty dry up there.. There should be oily surfaces and small puddles in the "low lying" areas..

While you have the pan off and changing the oil pump, pull 2 - 3 rod caps and main caps. Inspect the bearings and crankshaft journals for excessive wear. I suspect a new oil pump will not fix your low oil pressure issue.

[72 Cheyenne K20]

Hey Rusty, yeah it’s just not happy at all. The new oil pump definitely didn’t fix the issue. I started it one last time after checking a few other things and it’s toast. I let it warm up to almost hot idle and oil pressure dropped to zero and a slight burning smell with some smoke started. I just shut it down and will prepare to pull and rebuild in the spring.

Could be a lot worse, I didn’t blow it up or get stranded in the middle of BF nowhere ! Thank GOD for small victories.