The Stovebolt Site Forums The Shop Area Engine Shop Oil pressure question

Asking for a friend with limited computer skills.

Don't need to open cans of worms about which oil to use, multi vis vs. straight, synthetic vs. dino, etc

He is located in southeast Texas, so pretty warm in the summer. I don't know how many miles are on the engine, which is a '56 235.

His question is "Oil pressure seems low with 10W30. Will changing to 10W40 increase oil pressure, and is this a good idea?"

He doesn't say how low is low. I've asked for idle PSI and 40 mph PSI and will post here when I get those numbers.

Question to the forum is what PSI should he see at idle and running down the road?

I like Shell Rotella 15w/40 and I add ZDDP (zinc) to help protect the flattop lifters and cam...

Others will be along to address pressures...

Mike B

Just a data point. Doesn’t answer the ~should~ part of your question….

With 15w40 at operating temp, the well-worn 1962 engine in my 1951 truck registers 15 psi at idle and pegs the 30 psi gauge with any sort of throttle input. On a really warm day, if I have the idle turned down to 500ish rpm, pressure might creep closer to 10 psi.

I’ve been told by knowledgeable folks that it’s more than adequate.

I believe the 235 should be about 15psi at idle and 30 while driving.

I also use 15w-40 in most of my vehicles. The AD truck and a couple others get 20w-50 to keep the oil pressure up.

Any oil pressure at all means that the pump is producing more oil than the bearings need. For practical purposes, 10 PSI at idle and 20+ at cruise speed will keep the engine from locking up due to lack of lubrication. More is better, within reason. Don't get caught in the trap of "change the oil pump to get better pressure". Low oil pressure is caused by excessive bearing clearance and/or too-thin oil, not a faulty oil pump. In 65+ years of building engines, I've seen exactly TWO engine failures due to bad oil pumps, and both were caused by debris getting caught in the pressure relief valve.
Jerry

Jerry, does the old rule still stand? 10 psi for every 1000 RPM? is adequate.

It depends on the oil that's being used, and the bearing clearance. Water-thin synthetic oils like 5W-30, etc. have no business being in an engine with oil clearances designed for straight 30 weight.
Jerry

Jerry, I don't think you're understanding the multi-weight designations. 5W-30 oil (whether synthetic or conventional) has the SAME viscosity as straight 30 weight when it really counts, when the engine is HOT. It's only the same as 5 weight oil when temperatures are extremely cold and only assists in starting in really cold winter temps. That being said, 5W-30 is likely a bit too low a winter viscosity for most stovebolt users.

My '52 GMC Maintenance Manual calls for a hot minimum oil pressure of 40 psi at 2750 rpm on a new or rebuilt engine while a "used" engine should have at least 25 psi. At idle (425 rpm) the pressures should be a minimum of 5 psi new/rebuilt and 2 psi used. Are there any such specs in a Chevy manual?

The 48-51 Chevrolet Truck Shop Manual specifies 14 psi oil pressure at 2000 rpm.

But that would be a splash engine, wouldn't it? His is a '56.

Try the standard SAE viscosity test- - - -time the flow of a specific volume of oil through a calibrated orfice with a stopwatch at various temperatures. While multi-viscosity oils lubricate like the heavy stuff at full temp, they don't get physically thicker- - - -at least in every test I've ever done. What have the results been of the tests you've accomplished?
Jerry

By the numbers (kinematic viscosity) Rotella T6 5w40 and the conventional 15w40 have basically identical numbers at 100 degrees C. 14.9 centistokes vs 15 centistokes…..

However, if you’d like to investigate how well the new 5w and 0w multi-grades protect relative to the more traditional ones….

Do some web searching and read a few threads over at the “bobistheoilguy” forums. You will find very sciency studies cited on both sides of the argument, and be totally confused and no closer to a definitive answer.

Now, back to Bill helping his friend with the original question. Did he ever get you some numbers Bill?

Haven't heard from my friend yet about what actual pressures he is seeing. Hopefully I will today. When I do I will post.

In this thread I have received two idle/road speed answers at 15/30 psi and one at 10/20+. Also an answer of 14 psi at 2000 rpm, but that was from a 48-51 shop manual and would be from a different oiling system than my friend's 56 235.

I did find a 55.2 Chevy truck shop manual on line. So far I have found a reference in it that says the pressure relief valve on the pump would limit the oil pressure to approximately 35 psi and in "specifications" at the end of the chapter defines Oil Pump Pressure as 45 psi with no reference to rpm for both 235 and 261 engines.

It’s nice when the official information contradicts itself.

And this from the '56 owner's manual which doesn't specify V8 or 6 cylinder.

I know that there have been improvements in lubrication since 1956, but I'm posting this from that same '56 owner's manual.

Boy, I had no idea you could even get 5w-20 back then, much less that it was a GM recommendation for very cold climates….

I have a 54 235 truck engine in my 53 3100. I use 15w40 travelers oil and when engine is at operating temp and oil is hot, at idle oil pressure is at 15 and when increasing engine speed it pegs the needle on my 30lb guage