The Stovebolt Site Forums The Parking Lot Big Bolts 72 Chevy c50 oil pressure ?s

So my truck has the 350 engine in it and when I first got it, it was leaking oil everywhere. The clutch was roached due to the oil causing slippage. So I took it all apart and changed clutch and since engine was out I got a gasket kit for it and changed the rings on Pistons and all the gaskets but that it, put back together and she has run like a champ since. Until last week I noticed after getting a load of gravel my oil pressure drops at idle but when driving it's fine. And my truck has the original oil pressure gauge so i dnt kno exact psi but it had been running right in the middle for ever and then last week it dropped from the middle to about 1/3 maybe a little higher when stopping at stop signs and red lights but as soon as I started driving it went right back to the middle.

Am I worrying about nothing? Could it be cuz I haven't changed my oil for winter yet? And it did just start getting cold here 2-3 weeks ago. I only change oil in it twice a year, fall and beginning of summer due to limited mileage and plus my odometer doesn't work so.....I use 5w30 in winter and 10w30 in summer. Could It need new main bearings? New oil pump? I know when I had engine out I should have done complete rebuild as I have no clue on the mileage but it is an old grain truck so I guessed it was decently low mileage and I didn't have the funds to do complete overhaul and change clutch so I just did the nessecities.

Thanks Mike

Dosnt sound like any thing is critical yet but when you notice a definite change in something like oil pressure could be first sign of trouble. If it were mine would change the oil first preferably into a really clean pan. This way you can look at the oil as it comes out and afterwards for any metal in it. Also the oil filter i would cut it apart too and look at the filter media for anything traped in it . Check the internet for how to on that . Those two are all right could bethe bypass plunger in the pump sticking a bit. Brand of filter? If you have ever cut many apart and seen how diffrent brands are built change your mind on what ones to buy in a hurry. Frams are cheeply built with a flat tin spring for the filter bypass if it collapses it will just put the filter in bypass not filter the oil.

Metal in the oil or filter be a bad sign, if nothing could be a week pump or pump by pass failing.

I'll for sure do that with the oil when I change it this time. I have a Napa filter, the tall one for school buses as their computer claims. Other wise the small ones are so hard to change cuz of the bell housing clearance for hand spinning isn't there haha. I haven't ever cut a filter open before but I have been informed on the cheap design of cheaper filters so I always just get Napa filters cuz I figure they are better "idk honestly lol".

You might try full synthetic oil, it holds pressure better when it is warmed up. It will allow starts in colder weather that petroleum oils will not, even in the same grade. You could go to a heavier weight in the synthetic too and still be able to start in cold weather.

I would say that you are correct, there is enough wear in the engine to cause the symptoms you describe but it will be everything, not just the pump or just the bearings. The lifters and valve gear as well as the cam bearings are unlikely to be trouble, the main leaks will be at the crank and pump. You can replace all those bearings without pulling the engine, all from below. Of course, the easiest thing to do would be to change the pump and see what you get. I would guess you will need to change the bearings too if the oil change does not help

Since you are working with a “modern” engine I would follow sweepleader’s suggestion and try synthetic oil. I did that a few years back on a 200,000 mile police intercepter motor that was using a quart every 750 miles. After switching to full synthetic we went 2000 miles between changes with no usage and better oil pressure. Just my personal experience.🛠

What type of oil would you suggest? I currently have been using Castrol high mileage in the green jug not sure if it's synthetic or not.

Back then it was Castro SynTech, but they have changed to a different name. 5W-50 if I remember correctly.

High mileage small block Chevy engines have a chronic problem with worn camshaft bearings causing low oil pressure at idle. That's been the case since the late 1950's when the 1955 265's started needing to be overhauled, and things haven't changed since. Our family shop stopped doing "in the frame" ring and rod bearing jobs way back then because too many engines ended up with a flickering oil pressure light at idle.

There are three ways to solve your problem- - - -do a full overhaul including changing the main and cam bearings, which should have been done while you had the engine out, run heavier-weight oil like 15W-40 or straight 30 weight, or install a high volume oil pump to overcome the leakage past the worn cam bearings. I'd go with heavier oil- - - -simple, easy, and no downside unless you're starting in extreme cold weather with cold, thick oil. (Like below zero)

Edit: A Melling M-55HV high volume oil pump costs about $60.00 with free shipping on Ebay. It will make the problem disappear temporarily, sort of like giving a patient a big dose of aspirin for his headache, but it won't cure the cause of the problem, his brain tumor. It just masks the symptoms. NAPA oil filters are made by WIX, with the only difference being one digit on the part number. They are far better than most other filters. Use their "Pro-select" brand filter that big fleet shops use, unless you like paying extra for a little bit of wrinkle paint around the bottom half of the filter and a different color paint on the can.
Jerry