The Stovebolt Site Forums The Shop Area Engine Shop low oil pressure?

Hey guys. 1951 3104 w/216. I went for my longest drive yet in Old Red the other day to take my recyclables to town. I noticed my oil pressure seemed to be lower than normal. It read around 12 psi, and I'm thinking it's typically around 15-16 psi when I'm at 2500-3000 rpm (no tach, just guessing at rpm, but I mean when driving and not coasting or idling).

Couple questions: 1) does 12 psi seem low for this engine? 2) if so, could being 1 quart low account for low pressure? 3) Is it possible this relatively long drive after decades of inactivity busted loose some crud that possibly plugged the oil intake screen or the filter, contributing to low pressure?

BTW, I would think a clogged filter would contribute to high oil pressure, not low oil pressure. Right?

Thanks for any advice.

I alway's figured there was more pressure than that even with an older motor.Shouldn't it be around 40? Or at least 20 with a wore motor.I've had em down to 5 lbs at idle but they were pretty wore out.I'd think that a clogged filter would increase the pressure a tad.Also a quart low could cause less pressure if by chance it was drawing air bubbles?Also mabe a peice of dirt got into the relief valve.I'd change out the oil and filter and see what happen's before overthinking it much more.

I don't think there's anything to really worry much about. Oil will thin out when it gets hot, which will lower the pressure reading. Most likely, judging from what you said about this being the longest trip taken in it, that you haven't really driven very far with your truck. You may have never got it hot enough before to notice the lower pressure for the oil being that hot.
For a bit of explaination on the pre-'54 engines, they tend to run at no more than 16 psi or so when hot. They are low pressure engine, using dip and splash oiling to the rods, pressure to to the cam and rockers only.

Yup what longbox said.Mabe I was overthinking it?

Being in my 70's I drove many a 216 powered car and truck. If I had one that held 16 psi after warmed up I would have bragged about it. Just off zero at idle and 10-12 on the highway was pretty normal and 15 indicated a good tight engine. Driven at 50-55 mph these old dippers would run many a mile.

D.J.,

I agree with with Evan: 10-12 psi when cruising is not dangerously low.

By the way, there was pressure lubrication to both the main bearing and to the camshaft bearings (and then up to the rocker arm assembly) on the pre-54 low pressure truck engines.

What weight of oil are you now running?

Tim

The specs for the 216 in the sedan stated that at 2000 rpm, there should be at least 7 lbs pressure. "It is not dangerous to drive it with slightly less but it should be looked at and repaired". I think some run quite nicely with less pressure, especially on a modern oil like 10W30. The weight of oil has quite am affect on the pressure.

Thanks guys. Your comments are a relief to me.

Tim, I'm running 10W30. It's O'Reilly's store brand for engines with over 75,000 miles. Is this suitable, in your opinion?

This oil has about 40 minutes of run time and maybe 20 miles on it, so I hate to do an oil change so soon, unless it would be advisable since, as Bill says, this may be the first time I've gotten it up to true operating temp, and I'm thinking that may have flushed out some crud and now's a good time for a change???

Anyway, I'll top her off, as she is a quart low, and I'll keep an eye on the pressure.

BTW, the gauge only goes to 30 psi, so if I ever see it register 40, I'll have a real problem.

D.J.,

If you have already switched to a multi-grade detergent oil, at your next oil change you might want to try 20W50 oil. Simply stated, the 20 is the "cold" weight and the second number is the driving temperature weight. The higher driving weight usually increases oil pressure. Some people do not recommend changing from single grade non-detergent oil (10 to 30 weight was commonly used years ago, depending on the time of the year) to detergent oil and/or multi-grade oil, unless the oil pan is cleaned and/or after a rebuild.

Supposedly, the non-detergent oil allows particulates to deposit/settle-out in the pan, while detergent oil holds particulates in suspension (to be more easily filtered).

Tim

I'd also reccomend 20W-50 as the extra physical thickness of the base weight oil will translate into better oil pressure. The oil flows like a 20 weight when cold, and lubricates like a 50 weight when hot. It stays the physical thickness of a 20 the whole time- - - -it does not thicken up as it heats up. Trying to hold oil pressure with what amounts to 10 weight when hot is a losing battle. Originally, these engines were intended to run straight 30 weight in the summer, and 20 or thinner in cold weather for better cold-start lubrication. 15W-40 diesel-rated oil is also another good choice, as there are some zinc compounds in it that help keep the camshaft lobes in good shape.
Jerry